Despite tremendous growth of synthetic polymers as substitute of wool fibre, the interspecial of national ovine and caprine assets not only holds firm ground on the socio-economic culture of rural products and but makes its presence felt and still, by virtue of its sartorial usefulness, pervades almost all segments and shapes of society. Wool fibre production technology necessitates full understanding of its growth, pristine structure, physical, chemical and functional properties as well as processes involving manufacture of textile fibres. The present book is of its own kind which covers – woollen spinning, knitting, dyeing, bleaching and printing, special wool finishes etc.. This is an important reference book for wool technologists, scientists, new entrepreneurs, research scholars and all others related to this field.
Woollen Spinning
The fundamental
operations for the stocks of fibers from which a woollen yarn is made
are opening, cleaning, mixing, forming a slubbing or roving and finally
thinning the roving to the required yarn number and twisting it to
produce a yarn possessing the requirements for subsequent processing
such as warping, winding, weaving, finishing and dyeing. These demands
vary with the different conditions confronted in manufacturing but
include the following features: strength, elasticity, uniformity in
weight per unit length and even distribution of twist.
In the woollen
yarn-making process, there is only a single spinning operation
following carding, permitting no further cleaning or mixing, its only
functions being as stated above to thin or draft and impart twist in
fact, the thinning actually achieved is only of the order of 50%.
Therefore, the carded roving should be free from impurities,
homogeneous in fiber composition, and as uniform as possible in weight
per unit length. All that can be done in spinning to improve yarn
quality is to improve uniformity and with so little drafting even this
possibility is limited.
Woollen spinning
involves three principal operations, irrespective of whether the mule
or the frameâ€â€or ringâ€â€spinner is used, namely:
   1. Drafting, final drawing out.
   2. Twisting, or insertion of twist.
   3. Winding-on, or packaging.
Drafting or
drawing, concerns the last reduction or attenuation can be toping
itself to that weight or thickness required in the final woollen yarn.
In the mule this is accomplished by a so-called spindle draft
instead of a roller draft, as is done on the
woollen ring spinner.
The drafted
roving is then twisted to give the yarn sufficient strength for it to
be knitted or woven. On the woollen mule this process is partly
combined with drafting, but mainly accomplished by spindle
twisting. On the woollen ring frame the twisting is done by
use of a ring and traveller, and is termed ring twisting.
Winding-on
consists of putting the spun yarn into a form such as cops or
bobbins suitable for succeeding weaving or knitting
operations.
Mule Spinning
The
Self-acting Mule
The evolution of
the spinning mule was dealt with in a recent paper by Catling. The
modern mule on which woollen yarns of all sizes and descriptions can be
spun is often termed the self-acting mule, because of its practically
automatic operation. Most people divide the whole machine into two main
sections, i.e., the head stock and the carriage.
The former receives its power from the main shaft, and in it originate
all the important motions of a mule. This part of the mule is usually
stationary. The carriage, however, is movable and bears the spindles
that draft and spin the roving into yarn, and then wind it on the
bobbins. The carriage extends over the entire width of the machine, and
slowly moves in and out during the spinning procedure (Fig. 1).
The general
spinning procedure as described in Wool Science Review is
as follows:
The delivery
rollers H-A-H of the mule intermittently feed
forward a supply of carded roving from the jack spool M
of measured length to each spindle of the moving carriage. During this
part of the mule cycle the spindles retreat from the rollers at the
speed of delivery, while they are at the same time revolving at
constant speed, and so imparting twist to the roving presented to them.
When the required length has been presented the rollers stop, but the
carriage continues to move away from them, and the spindles continue to
revolve. The roving is thereby attenuated by a stretching action called
spindle drafting. During this operation, an increasing tension is
developed in the drafting thread, and the only factors which control
the response of the fibers to this increasing tension are the
interfiber forces of cohesion, determined by the frictional and elastic
properties of the fibers, and the radial pressure set up in the thread
by the twist.
The required
amount of attenuation having been achieved the carriage is stopped, but
the spindles continue to revolve and perform the last essential
requirement of yarn-makingâ€â€the twisting of the thread to produce a yarn
of adequate strength. This is accomplished by the roving slipping over
the top of the spindle. The spindle S, being placed
at an angle, does not hold the yarn, but simply allows it to slip over
the top as shown in Fig. 1. One turn of twist, therefore, is put into
the roving for every revolution of the spindle. The extra twist thus
added produces a greatly increased tension in the threads, and if it
were not relieved, the majority of them would snap; the carriage is
therefore gradually moved in for a few inches to allow the threads to
contract. This environment is called “jacking-in.â€Â
Twisting having
been completed, the spindles are stopped, rotated for a few turns to
unwind the yarn wrapped round the bare spindle (an action known as
backing-off), the carriage is run in, and the lengths of spun yarn are
wound up in the form of conical packages C on the
spindles themselves. This is accomplished by rotating the spindles
slowly as the carriage runs in. The fallers D and
counter-fallers Di meanwhile come into action to
guide the yarn, and traverse it in such a way as to build a package of
the required shape on each spindle. This package C
is conical in shape, being built as a series of successive,
interpenetrating cones of yarn one on top of he other. As the linear
rate of winding of the yarn is approximately constant (as dictated by a
fairly constant carriage speed), it follows that the spindle speed must
be varied continuously during the run-in, in order to build the yarn
uniformly into a cone. Thus the variety of spindle motions required
during mule spinning is made even more complicated.
The spinning
mule therefore performs an intricate series of mechanical actions, and
it has developed into a cumbersome machine. Its separate functions,
however, are not really complicated since they depend essentially on
the action of just three different components, the carriage, spindles,
and delivery rollers, the motions of which must be coordinated and
correctly tuned, to build up the total spinning cycle of the machine.
None of these motions is very complex in itselfâ€â€their coordination is
the difficulty, and it is the spinner’s art to achieve this
coordination with as few yarn faults as possible.
Just as the
machine consists of three components, so the sequence of operations
which it performs may also be subdivided into three essential actions:
drafting, twisting, and winding-on. Delivery may be regarded as an
essential preliminary to drafting, jacking-in as a necessary
consequence of twisting, and backing-off as a pre-requisite of
winding-on.
The Operations of Mule Spinning
Drafting
During drafting
the thread is stretched in a softly twisted condition; what is the
nature of the response of the fibers? It has been a view held for a
long time by practicing spinners that in this thread, twist gathers
preferentially in the thin places, and consequently the soft, thick
places are drafted preferentially. It is further believed that as this
preferential drafting of thick places proceeds, the twist continually
redistributes itself in such a way that the thinner portions are always
given most support. Thus after a thick place has been drawn down, it
will receive an influx of twist; drafting will stop in this section and
will restart in another section which is now somewhat thicker. If
matters were really as simple as this it can be seen that spindle
drafting would soon reduce the thread to a uniform or level state,
which would be a desirable result. Furthermore, it would seem that,
providing sufficient twist was added during attenuation to maintain the
cohesion of the thread as it became finer, this theory would suggest
that drafting could go on almost indefinitely.
In practice,
however, although it is agreed that a levelling of the thread does take
place in a well-spun yarn, it is known that if the draft used is
excessive the levelness of the final yarn is impaired, and,
furthermore, many ends begin to break down and so impede production.
The spinner’s task during this part of the mule cycle is therefore to
adjust conditions to the optimum, which will allow the maximum draft
consistent with the achievement of as level a yarn, and as few ends
down, as possible. The controllable factors which he has at his
disposal for a given material are the amount of twist he inserts before
drafting, the rate at which twist is inserted during drafting, the
speed at which the operation is carried out, and the amount of draft
applied. His synthesis of these factors to give optimum spinning
conditions is the spinner’s craft, and is not fully understood
scientifically.
Other factors
which are not so readily under his control, but which could be adjusted
to meet his requirements if it were clear how such adjustments would
assist him, are such things as the amount of oil applied to the wool,
the properties of this oil, the degree of cohesion given to the roving
by the rubbers of the condenser, and the physical properties of the
fibers as they are affected by such preparatory processes as scouring
and dyeing. The physical properties referred to are the frictional and
elastic properties of the fibers. The former may affect the relative
motion of fibers during drafting, and the latter will determine the
cohesion of fibers bound together by twist, since stiff fibers will
require more twist than supple fibers to achieve the same degree of
intimate interfiber contact during drafting.
Analysis of
Spindle Drafting. Angus have
investigated the behavior of rovings being drafted on conventional
mules, as well as on a single-spindle apparatus constructed to carry
out the spindle drafting of a single end of yarn under experimental
conditions. McNair has made similar investigations using the electronic
mule designed by Chamberlain as a drafting device which conveniently
allows a wide range of drafting conditions. He has also examined the
reaction of twistless rovings to draft using a Cambridge Extensometer.
Angus
concentrated his attention on two main features of the process: the
tensions generated in the drafting thread and the progressive changes
in thread irregularity which ensued. Changes in tension were
investigated because it was felt that these would give some guidance as
to the behavior, or “activity,†of the fibers in the thread during the
process.
When the
drafting of a partly twisted roving commences, the initial tension is
zero. This induced tension, or drafting force, increases fairly
rapidly, and at an increasing rate, in the early stages of drafting.
Subsequently the rate of increase declines to
zero, so that the force extension curve passes in turn through a point
of inflection and a maximum. Thereafter the force declines, as
extension is further increased, until such time as the thread breaks
and the force again drops to zero. Figure 2 shows a set of curves which
are typical of all the results obtained by Angus. It will be seen that
as the twist content of the drafted thread under investigation was
increased, the induced tension at any given draft became greater, the
maximum tension developed increased, and the breaking extension of the
thread was reduced. Alteration of drafting twist was not accompanied by
any alteration in the form of the curves. There was an indication,
however, that a certain low value of twist content could be discerned
which gave an optimum maximum extension at break, i.e., which allowed
maximum draft.
The percentage
extensions at which the points of inflection and of maximum force occur
vary according to the conditions. Thus, values between 25 and 50% were
obtained depending upon the type of wool used, the twist condition of
the thread while drafting, the angle at which the spindle was inclined
to the axis of the drafting thread, and apparently, the physical
characteristics of the fibers as they had been affected, by previous
wet treatments. All these factors govern the value of the extension at
which maximum force is produced, and also affect the magnitude of the
force generated for a given extension. For example, other things being
equal, a revolving spindle inclined to the axis of the thread will
induce a smaller maximum force than a spindle in the same line as the
thread axis, and at the same time a greater extension will be achieved
before the maximum force is reached. The significance of these
observations is not yet fully understood, but interesting parallels
were found when the concurrent changes in thread irregularity were
investigated.
Two Phases of
Drafting. Angus put
forward the view that fiber activity during drafting could be regarded
as taking place in two phases. The first phase, it was suggested, is a
simple stretching phase in which the curls and convolutions of the
randomly arranged fibers are straightened out. It is not until after
this phase is completed that the second and most usually considered
aspect of draftingâ€â€fiber slippageâ€â€occurs. It was concluded that the
initial rise in tension takes place during the stretching phase, and
that the point of inflection on the forceâ€â€extension curve announces the
onset of fiber slippage. If this is a true picture of fiber activity,
then it would appear that levelling of the thread only occurs while the
fibers are adjusting themselves to the drafting force during the first
phase of the process, whereas slipping of fibers with respect to one
another during the second phase leads to a rapid increase of
irregularity. The assumption that the initial changes are due mainly to
a fiber-straightening process is confirmed by the observation that when
worsted roving is drafted on a mule the point of inflection on the
forceâ€â€extension curve occurs at only about 4-5% extension.
Another
interesting observation was the occurrence, during the drafting of some
samples, of a very irregular decline of the force from the minimum. In
these cases very sharp falls followed by partial recoveries,
reminiscent of stick-slip phenomena, were noted. The interesting
feature was that this phenomenon never occurred in the early stages of
drafting while the force was increasing. This observation seemed to be
consistent with the belief that fiber slippage does not occur until the
force is in the region of the maximum. This unlooked-for occurrence is
interesting in itself in that it does suggest one mechanism whereby
threads may deteriorate, and then suddenly fail, during spinning.
Discussion of
Fiber Movement in Drafting. McNair comments
that although this work “has revealed for the first time the basic
character of the drafting process in woollen rovings a number of points
remain obscure.†He is of the opinion that “the concept of fiber
straightening without fiber slippage during the initial stages of
drafting would seem to err on the side of oversimplification.†In the
roving there will be some fibers less crimped, or less curled, than
others and they will be straightened first. Thereafter these fibers
will have to be stretched, if they are not to move bodily relative to
their still curled neighbours. He points out that if fiber
straightening is all that occurs, the extension should be largely
reversible whereas he found that (for extensions up to 20% or so) only
about half of it is reversible. Although McNair puts forward no
specific alternative explanations, there seems no doubt that his
general contentions are correct.
Perhaps it might
now be suggested that what we can think of as occurring during the
first phase is a straightening of fibers plus a sort of fiber
shuffling, in which contacts between adjacent fibers are released one
by one as the fibers adjust themselves to the induced forces, but that
this type of fiber activity is different from that which arises in the
second phase of mule spinning where fibers, or groups of fibers, move
bodily over one another with the simultaneous
disruption of all fiber contacts between them.
This would produce a kind of flow, rather than an agitation as is
visualized for the first phase.
McNair’s
forceâ€â€extension curves for twisted threads were of the same form, and
showed the same characteristics, as those obtained by Angus and
Martindale.
Other Factors in
Spindle Drafting. McNair showed
that the degree and type of rubbing which a roving undergoes at the
condenser also affects its tensile properties in the early stages of
spindle drafting, although he reported that the differences in tensile
behavior disappeared as extension proceeded. This observation suggests
that fiber movement in the first phase of drafting is sufficient to
destroy the initial dissimilarities in structure. He also showed that
the drafting behavior of rovings from which the oil had been extracted
was different from that of the original rovings, and this, taken with
observations by Angus that wools scoured in different ways and wools
dyed in different ways also give forceâ€â€extension curves with different
maximum drafting forces, and different extensions at which these maxima
occur, provides another problem for future investigationâ€â€the
explanation of the part played by the properties of fibers and fiber
assemblies, and their significance in determining optimum drafting
conditions.
One ought also
to make particular reference to the observation by Angus that a spindle
inclined to the axis of the thread produces a different response from a
spindle which also line this axis, and to which the thread is clamped.
In the first case each revolution of the spindle causes the thread to
be wrapped around the spindle tip for half a turn before being thrown
off. This action produces a
high-speed plucking of the drafting thread, which is consequently
maintained in a state of continual vibration. Such vibrations
apparently have some effect on fiber activity, and presumably promote
conditions favourable to fiber movement. It is therefore interesting to
note that under such conditions the first fiber behavior was prolonged
to greater extensions. It was remarked earlier that the limited part
which the mule plays in the sequence of operations producing a woollen
yarn indicates that it can contribute comparatively little to the final
quality of the yarn, most of the desirable properties already being
inherent in the material present to it. On the other hand it is easy to
impair these inherent qualities by poor adjustment of the mule.
Twisting
Twist Motion. Each revolution
of the spindle S imparts one turn of twist to the yarn, accomplished by
the slipping of the yarn over the smooth and round tip of the metallic
spindle for which purpose the spindle is inclined away from the
vertical toward the feed rolls. The tendency of the yarn already spun
is to rise to the top of the spindle, where it slips over the end,
putting in one turn for every slip.
The twisting
motion goes into action as soon as the draw rolls stop the delivery of
roving. The required twist for the length of drawn roving, i.e., 74â€â€76
in., is now put in by increasing the speed of drum A so
that the required twist has been inserted when the draw is complete.
Since the yarn shortens as it twists, the ends would snap off if there
were not some method of easing-in or backing-off.
Amount of Twist.
The amount of
twist is normally governed by the economic factor, and accordingly most
yarns have the minimum twist inserted in accordance with the least
trouble in subsequent processes. The amount of twist bears a
relationship to the strength and elasticity of a yarn. An increase in
twist will lead to an increase in strength up to a certain amount,
after which further increases lead to a decrease in strength. Also, the
degree of twist affects the bulkiness in the case of knitting yarns and
in the case of weaving yarns the finishing process and the handle of
the cloth. The amount of twist in a yarn is expressed in turns per inch
(tpi), in turns per ten centimeters (tpcm), or turns per meter (tpm).
Worsted Topmaking
During 1967 the
wool topmaking industry had an estimated total in production of tops of
1,290,000,000 lb. Approximately one-third was the output of the six EEC
countries, with a total output of 452,000,000 lb.
The topmaking
industry presently still differentiates between two distinct systems:
   1. The English or Bradford
system developed in England for processing wools whose average staple
length is not less than 2½ in.
   2. The French or Continental
system developed in Alsace-Lorraine for wools whose staple length can
be less than 2½ in.
There is little
fundamental difference between Bradford and French carding except that
the French equipment is usually set up and clothed to handle the
shorter and finer wools. A very small amount of oil or emulsion (less
than ½%) is usually applied to the scoured wool before carding on
either systems to provide surface lubrication for the fibers and to
minimize fly in the card room.
The first
distinct difference between the systems appears in the combing process.
The Heilman or rectilinear comb is used on the French systems, and the
Noble or circular comb on the Bradford system. While the slivers are
backwashed after combing on the French system, they are backwashed
before combing on the Bradford system. The only other significant
difference is that 1-3% of oil is added before combing on the Bradford,
while no additional oil whatever is used on the French system.
While the flow
of material often varies from mill to mill, the flow sheet, Table 1
shows the general comparison between the conventional Bradford and
French systems.
Worsted Carding
After the wool
has been thoroughly washed, dried, lubricated and otherwise prepared,
it is subjected to carding.
The objects of
worsted carding are:
  Â
1. To
straighten, separate and, in general, to make the long wool fibers lie
parallel.
  Â
2. To
clean the fibers, that is to remove as for as possible all vegetable
impurities such as burs, shives, and other extraneous vegetable matter
and dust.
  Â
3. To
blend distribute, and mix the different lengths and qualities
harmoniously into one quality.
  Â
4. To
arrange the fibers into a continuous sliver of definite weight and
thickness.
The carding
action is basically the result of the relative motion of two
interacting rollers, which are densely covered, with specially shaped
hooks of fine steel wire. (Figs. 1 and 2).
The objectives
of worsted carding are accomplished actually by essentially simple
means. Wool, deposited in a fairly thick layer on a slow-moving
cylinder, is transferred to a fast moving roller; this results in an
opening and thinning out of the wool stock. As this operation is
repeated many times over on a carding machine, a small amount of wool
is distributed over a large area in a very thin web. To render this
thin web mechanically manageable for forming into a continuous sliver,
the above-described operation is reversed by transferring the wool
fibers back to a slow-moving cylinder from which it is drawn off and
formed into a sliver of loosely joined fibers.
Whereas the
woollen carder is more concerned with sufficient blending, the worsted
carder is most interested in parallelism of the fibers, the
preservation of the full fiber lengths and the elimination of neps and
pin points. Since worsted yarns are distinguished by strength,
uniformity of spin, and great fineness, with a consequent higher cost,
every precaution must be taken in carding to attain these objectives.
To properly
process the different types and lengths of wool, four types of cards
are in general use:
   1. The single-cylinder
worsted card, with four lickerins for long-staple wools. (Bradford
System). (Fig. 3).
   2. The double-cylinder
Bradford card, with four lickerins and dividers for merino wools
(64/70s quality) (Fig. 4).
   3. The double-cylinder
continental cards, with burr breast-workers, and strippers for shorter
wools (merino type) (Fig. 5).
   4. The all-metallic wire
worsted cards for French and Bradford systems (Fig. 6).
For fine and
crossbred wools, irrespective of the system of drawing or spinning
used, worsted mills prefer the double-cylinder card. For very open
wools, as scoured by the Australian solvent process, a single-swift
card works well.
The preliminary
breastworks, as pointed out above, may consist of four lickerins or a
metallic breast, as the individual carder prefers. No definite
advantages exist for either one of the two methods of opening the wool,
stock, however, great differences of opinion are held regarding them.
The main factor in the choice of a metallic breast or of fillet-covered
lickerings in the worsted card is to avoid fiber breakage and the
shortening of the carded fiber.
Worsted cards
are generally of all-metal construction, rigidly built and relatively
light in weight. Main cylinders are usually cast iron or steel, workers
are aluminum, and strippers are steel tubing. The standard card widths
are 60, 72, 84, and 100 in. Of these the most common in use is still
the 60 in. width and 54 in. diameter of the main cylinder. However, the
tendency is definitely toward the wider cards.
The production
of a worsted card varies with the speed at which it can be safely and
economically operated and the type of wool that is being handled. On a
60-in. card it varies from 60 to 100 lb/hr on long crossbred wools and
from 40 to 60 lb/hr on fine Merino wools, with cylinder speeds of
90-125 rpm. A 60-in. all-metallic wire card with produce up to 120
lb/hr on Merino wools if comparatively free from burs and other
vegetable matter.
The product of a
card is judged to the amount of noils it produces in the comb and by
the number of neps in the sliver; everything else being equal, close
cooperation between carder and comber is necessary for a minimum of
noilage in combing.
A worsted card
generally consists of series of rollers of various diameters, speeds,
and direction of rotation. A card may be divided into three main parts
or sections: (1) the feeding section, (2) the worsted carding machine
proper, and (3) the delivery section.
The Feeding Section of Worsted Card
The costly and
non-uniform hand feeding of former years has been completely eliminated
with the introduction of the automaticÂ
hopper feeders. These units have been perfected to the
extent that uniformity in sliver weight can be accurately effected. The
method of supplying these hopper feeders with wool varies from mill to
mill and can be accomplished in the following manners:
   1. As the scoured wool leaves
the dryer it is dumped into large box-type trucks which are pushed by
hand or by mechanical means to the hopper feeders of the cards for
loading the feeders.
   2. The scoured wool is blown
to large bins or stock rooms for temporary storage. Usually these bins
are located on the floor above the card hopper feeders. An opening in
the floor directly above each card feeder, connected with a chute,
serves to keep the automatic hopper feeders full at all times,
requiring little attention.
   3. In the most advanced
method the dried wool is blown into a large magazine equipped with a
slow-moving lattice apron, which advances the stored wool to an
automatic feeding station from which any desired number of card feeders
can be filled automatically over a system of conveyors.
The automatic
Hopper Feeders. Automatic card
hopper feeders are designed and built by numerous machine manufacturers
here and abroad. Aside from minor variations the basic design and
working principle of modern feeders are as follows:
Large capacity
hoppers with bottom aprons do not require frequent stock replenishment.
A spiked, vertically moving lattice apron carries the wool upward,
passing an oscillating beater comb so adjusted to the lattice apron as
to prevent large lumps of wool from passing this point. The beater
further serves to distribute the quantity of wool uniformly over the
entire width of the apron and the wool then passes over the top of the
hopper where the spikes point downward. At this point the wool is
beaten off by a fast-moving rotary beater into a scale pan extending
the whole width of the card and located directly over one end of a
horizontal feed apron. When sufficient wool is deposited in the scale
pan the movement of the vertical spike apron and the horizontal bottom
apron of the hopper are stopped by either mechanical or electrical
means. The pan bottom opens and the exact amount of wool is deposited
on the slowly moving, horizontal feed apron. There it is dabbed down
uniformly by a dabber and is moved forward by a push board to occupy a
definite space on the feed apron. Thus the amount of wool going into
the card is positively controlled. Adjustments to alter the amount of
wool fed into the card are made at the weigh beam. The feeder is
similar to the one used in woollen carding.
The Worsted Carding Machine
The worsted
carding machine proper generally consists of the following parts: (1)
The breastworks with its feed rollers lickerins, bur cylinder and bur
guards; (2) The main cylinders with their workers, strippers, and
fancies; and (3) the doffers with their dickeys.
The stock as it
is fed into the card is controlled by the slowly turning feed rollers.
The rollers of 2-3 in. in diameter are clothed with inserted sawtooth
wire or they are fitted with brass rings spiked with intersecting steel
pins. Generally, two feed rollers with one stripper clothed with wire
or brush fillet are used. For fine quality wools, four to six feed
rolls and a stripper are preferred to reduce fiber breakage.
The wool as
presented by the feed rolls is picked up by the lickerin. For longer
types of wool, up to five lickerins were formerly thought to be
necessary. This theory has been discarded in favour of all-metal
breastworks and burring attachments for short burry wools. Since many
mills are still equipped with lickerins (three to five, with top and
bottom dividers) it will be appropriate to explain their action. These
cylinders vary in diameter from 20 to 30 in. They are covered with
inserted metallic garnett wire and angular teeth made flat on top to
reduce the spaces or indents with the object of keeping the burs,
shives and other extraneous matter on the surface, so that the bladed
bur-beaters can remove them. Round wire between the metallic wire
serves the same purpose. A common metallic wire is an 18×24
diamond-point wire on the first lickerin. Succeeding lickerins are now
metallic-wire covered, whereas in the older cards coarse filleting of
No. 24, No. 26, and No. 30 wire was used.
Whenever wool
stock has mestiza or spiral burs and other foreign matter in fairly
large quantities, it becomes necessary to use a bur cylinder or
automatic bur cleaner preceding the preparers or lickerins or to
substitute the bur breastworks entirely in place of them. (See Fig. 7,
which shows bur breastwork). Various machinery builders offer devices
for this purpose. In English cards a Morel wire covered roller
approximately 27 in. in diameter is substituted for the third lickerin.
Its purpose is to allow the material, which is well opened by the
previous lickerins, to be pressed down into the spaces between the rows
of wires, leaving the burs and other vegetable matter protruding on top
of the Morel roll. To be knocked off into a tray by a fast-revolving
bur beater. Scraper blades or brushes clean the bur trays at periodic
intervals and deposit the accumulation into a can located on the side
of the card.
The number of
bur cylinders or Morels used depends on the quantities of burs in the
stock and the desired degree of bur removal. It is advisable to remove
as many burs as possible to avoid possible damage to the card clothing.
Much more
difficult than the removal of large burs is the elimination of the
smaller burs which normally pass the bur beaters. To remove these, many
continental carders install a Harmel crusher between the first doffer
and the second cylinder. This unit consists of a smooth 10 in. diameter
steel roller against which two 5 in. diameter fluted steel rolls are
pressed. The web removed from the first roller passes over the plain
roller and through the nips of the fluted rollers. Consequently any
burs passing through these nips will be broken into short pieces and
are ultimately removed in the subsequent carding of the second cylinder.
The commercial
method of assessing the efficiency of bur removal only visual
examination of the individual, or more often, the compounded rejects
obtained from the card for “wooliness†of the rejects. Valuable
information on the relative importance of a deburring point, or the
comparison of the efficiency of one card with another, can be obtained
where the weights of rejects and card throughout are known. The results
give in Table 3 were obtained in this manner from trails carried out by
Bownass Janney, and Lowe, to assess the efficiency of bur removal of
two types of cards, Bradford and Continental using a range of wools of
different fault content.
The Bradford car
was fitted with four bur beaters: First top divider beater third licker
Morel beater second Divider beater, and second or middle Morel beater
(Fig. 4).
The Continental
card was fitted with three bur beaters: First taker-in beater, first
Morel beater, and second or middle Morel beater (Fig. 5).
The rejects from
these beaters were collected and weighed and in addition the shoddy
dust collected by the shoddy tins S1 and S2 was also
weighed. It can be seen that the major part of deburring on the
Bradford card is achieved by the third licker Morel beater, whilst it
is shared by the first Taker in and first Morel beaters on the
Continental card. This was fund to be true for all types of wool
processed. Coupled with visual assessment, the general conclusions were
also drawn that little difference existed in deburring efficiency
between the two cards for clear wools, but for wools containing a high
proportion of spiral bur, the Bradford card was slightly more efficient
and produced a card sliver with far less vegetable matter specks than
did the Continental card. The important rejects contained approximately
75% of actual vegetable matter for the Burry wool No. 2 and only 40%
for the clear wool No. 5.
If an extreme
amount of burs is present in the stock, it should be subjected to
carbonizing for complete elimination of all vegetable matter.
The Main
Cylinders. The stock
having been prepared, sufficiently opened, and freed of large burs, is
then subjected to a thorough carding by the main cylinder, its workers,
and strippers. Typical card constructions are shown in Figs. 3-6.
The Action of
the Worker and Stripper. The action of
these rolls are the main function of the carding operation. The wool
locks or tufts lying on top of the teeth of the cylinder pass under the
stripper and are pushed lightly between the teeth of the cylinder. As
the wool approaches the contact point between the worker and cylinder,
the fibers which are above the teeth of the cylinder are being pushed
against the teeth of the slow-moving worker and become held by the
worker and the cylinder. As the fast-moving cylinder moves forward, the
fibers become tightened and finally slip off the cylinder wires but,
being held by the worker wires, will receive a thorough combing by the
passing wires of the cylinder. However part of the locks and tufts will
remain in the cylinder wires and pass on to the next worker for a
chance to be carded and combed in the same manner. The wool, which has
been collected on the worker, is upon contact with the stripper
returned by it to the cylinder (Fig. 1).
As can be noted
from the diagrams, the number and diameters of workers and strippers
vary from card to card depending on the type of wool being processed as
well as on the amount of carding desired. Newer card constructions
feature a total of up to 13 workers, including the breastworks, instead
of the 5 to 7 found in the antiquated systems of former years. In the
advanced stages of carding a closer setting of workers to cylinders and
the use of finer card clothing becomes necessary. (See Table 4).
The distance
between the cylinder and its workers has to be selected very carefully.
The number of workers offers a fair range of adjustment. The opinions
and practices of technicians often vary widely on this subject.
Starting with the first worker of the first main cylinder, it should be
set approximately at 0.045 in. gauge setting and the distance slowly
reduced until it reaches 0.015 in. gauge setting at the last worker of
the second cylinder.
The opening of
the wool locks and the draft the material has to undergo at each worker
depend greatly on the surface speed of the opposing rolls. Therefore,
the efficiency of a carding machine is directly influenced by the speed
of each individual roll.
The determining
factors of the actual carding action-taking place on a carding machine
are the number of points per square inch, the surface speed of the
opposing rolls and their setting to each other.
Tables 5-7
illustrate common surface speeds found on various types of carding
machines.
Action of Fancy.
After the wool
has been thoroughly carded and returned to the main cylinders, it
becomes fluffy and voluminous. It is the function of the fancy to raise
the carded fibers to the top of the wires of the main cylinders and
allow the doffers to remove them. The location of the fancy is usually
above the doffer, provided with a hood to prevent fly and wind from
up-setting the operation on account of its high speed. See Fig. 2. The
wire of the fancy is long and its surface speed is approximately 30-40%
in excess of that of the main cylinders. Its wire points opposite to
its direction of rotation and is back against back with the cylinder
wire, effecting strictly a raising action. The fancy is 10-12 in. in
diameter and its speed is adjusted to suit the speed of the cylinder
and the kind of wool running in the machine.
Action of Doffer. The doffer
serves the purpose to take the carded and raised stock from the main
cylinder in a uniform web deposit on its wire surface. Working in
connection with the doffer is an oscillating doffer comb, which takes
the fiber web from the doffer to be passed through a funnel to the
drawing-off rolls.
Dickers and
Doffer Dickeys. They are
employed only in worsted cards and are small rolls covered with long,
flexible-toothed card clothing which, working against the doffer, raise
any stock that may have passed the comb, and hence is removed on the
next revolution. Another advantage of a dickey is that it prevents
shives or other foreign material from remaining in the clothing of the
doffer, and keeps the wire sharper and in a much better condition. The
action is about the same as an ordinary fancy.
Worsted Card
Clothing. For card
clothing employed in worsted cards rubber-faced, 5-8 ply filleting is
commonly used. The number of points per square inch varies, depending
on the grade of wool processed. While various authorities are not in
complete agreement on this subject, the clothings given in Table 8 are
commonly found on cards processing 64s wool. The various types of card
wires referring to gauge numbers, counts, and crowns as well as the
different types of metallic wires.
Grinding Worsted
Cards. Flexible
wire-covered worsted cards must be ground at regular intervals to keep
the wire points in optimum working condition. The methods and equipment
for this operation varies considerably. Information regarding grinding,
stripping, and setting details is to be found in the chapter on woollen
carding.
The use of a
special garnett or metal wire on worsted cards has been quite
successful. Figure 6 shows the arrangement of the rolls and other
details of a metal worsted card. It has no lickerin and dividers,
usually considered necessary. The machine also employs smaller rollers
and cylinders, exactly half the size of the card just described. The
builders claim reduced fiber breakage, fewer neps, and less vegetable
matter in the card sliver, almost double the production, and no
stripping or waste made from stripping. Grinding is done away with
completely. Half the floor space is required and less power is
consumed. Metallic card sets have also been installed for the woollen
system on carpet wools and asbestos.
Factors
Responsible for Nep Formation. The factors
responsible for the formation of neps in worsted carding leading to
increased noilage in combing have been investigated by Townsend and
Spiegel. They found that the most important cause of nep formation is
undoubtedly the tangled nature of the scoured wool normally fed to the
card, for when broken tops are carded the sliver is practically free
from neps. It was found that the neppiness of the carded sliver is at a
minimum when the regain of the feed wool lies between 30 and 50%. In
addition, if the amount of residual grease in the wool exceeds 0.5%,
the neppiness is accentuated, just as it is when the amount of added
oil exceeds is 1%. The presence of bur in scoured wool is without
influence on neppiness, except insofar as it necessitates the use of
bur beaters, which promote nep formation.
As regards
mechanical alterations to the machine, the nep content of the carded
sliver decreases with increasing speed of the card as a whole but an
increase in throughput leads to a higher nep content. On the other
hand, a reduction in the relative surface speed between feed rollers
and first lickerin causes a reduction in neppiness. A further factor of
importance is the setting of the workers to the swift; the closer these
rollers are set to each other, the clearer is the sliver. Assuming a
constant worker-swift setting, however, any alteration to the setting
of the licker section is not reflected in the nep content of the sliver.
The action of
the dividers, in reversing the direction of the wool at the
dividerâ€â€licker point of contact, is responsible for a fair proportion
of neps, and the ratio of the surface speeds of fancy and swift is
highly critical. If the fancy runs at a surface speed higher or lower
than the critical value, there is a large increase in the nep content
of the sliver. As would be expected too, grinding has a great influence
on neppiness; a newly ground card reduced the nep content to half the
number present in a sliver produced immediately before grinding.
The Delivery Section
The delivery of
the stock from a worsted card can be accomplished by several means: (1)
Center-drawing balling head, (2) side-drawing balling head, (3)
conveyor balling head, (4) can-coiling head, and (5) direct gilling.
Center-Drawing
Balling Head. The carded
stock leaves the doffer of a worsted card in the form of a web. This is
gathered over a curved brass guide and drawn through a funnel or
trumpet by a pair of calendar or delivery rollers. The formed sliver is
wound onto a bobbin about 20 in. wide, having no flanges which
traverses back and forth giving a cross-wind to the sliver.
Side-Drawing
Balling Head. For low
cross-bred wools, mohair, camel hair etc., which require support,
side-drawing balling heads are preferred or even necessary. This system
collects the stock in a right angle to the doffer. It is equipped with
a revolving sliver tube for inserting a false twist. The formed sliver
is wound in a conventional manner onto a bobbin for further processing.
Conveyor Balling
Head. The so-called
railway-balling head is used extensively on the French system. Slivers
from 5-10 cards are collected on one conveyor belt and delivered to a
balling head at the end of the group. The railway-balling aids in
mixing the stock from the various cards but is only advantageous if a
number of cards can be run on the same stock.
Can-Coiling
Head. The can delivery
method is gaining much favour here and abroad. The wool web as it
leaves the doffer is well condensed by means of a funnel or trumpet and
coiled into fiber cans ranging from 14 to approximately 40 in. in
diameter and up to 48 in. in height. The usual way is to coil the
sliver in circles against the side of the can while the can rotates
simultaneously with the coiler head. The can-coiling method is
preferable over ball winding because the slivers are well protected and
are more easily manipulated in the following process.
Direct Gilling. The most
advanced method is made possible by a high-speed intersecting gillbox
capable of a top speed of 6000 faller drops per minute. As the slivers
are drawn off the cards in the usual manner, they are collected on a
conveyor belt and fed directly into the high-speed gillbox for the
first gilling prior to combing. The gilled sliver is then either coiled
into large cans of up to 40×48 in or the sliver is wound into large
balls. The latest available machines will doff cans and/or balls
automatically.
The object of
the foregoing delivery variations is to wind the sliver into a
practical and convenient form in which it can be efficiently handled in
the processes which follow. The sliver should be uniform in weight
throughout. In order not to damage the sliver and to avoid roughing and
consequent pill and nep formation the spools or balls should be handled
as little as possible hence the preference for can delivery.
The Principle of Weaving
Weaving
constitutes the actual production of cloth or fabric, i.e., to combine
the essentially one-dimensional textile structure thread or yarn in
such a way as to result in an essentially two-dimensional structure of
cloth of certain appearance, hand and strength. The process of weaving
is distinguished from other methods of producing fabrics such as
knitting, braiding, lace-making, or bonded web manufacture. A first
fundamental fact that can be noted from examination of any woven goods
are its length and width. The width of a finished fabric may be from 18
to 35 in.; such fabrics are called narrow goods. If the width varies
from 36 to 130 in., then fabrics are known as broad or wide goods.
Felts, carpets, draperies, etc. are woven in still greater width. The
widest loom built in the world was a loom of 540 in. in width for the
manufacture of paper-maker’s felts. Such fabrics, however, are of extra
and unusual width. The length of a piece or “cut†is usually 50-70 yd
long, and in a few cases, 120-140 yd, known as double cuts. Upon
further examination of a woven cloth one can observe that there are a
series of yarns or threads running lengthwise, spaced equally or
unequally, but generally running parallel to each other. Another system
of yarns runs cross-wise (from selvage to selvage) mostly equally
spaced. These two sets of yarns normally intersect or interlace at
right angles to each other and form a solid, well-bound, and often
thick fabric. Fabrics differ in character, surface, and texture. They
may be thin or thick, single or double, rough or smooth, open or
closely set, and so forth. But, whatever the fabic, the following
simplified definition of weaving applies:
Weaving is the
forming of a textile by the inter-lacing, at right angles to each
other, of two sets of yarns, one running lengthwise in the loom and
termed the “warp†and the other running cross-wise in the loom and
termed the “filling†or “weftâ€Â.
Woven woollen
and worsted fabrics are produced on what is termed a “loomâ€Â; in recent
years the term “weaving machine†is often used instead. According to
German standards this is the official term for mechanical looms. A
“weaving automat†describes a machine in which the replenishment of the
filling pirn is performed automatically. The Chapter on weaving will
describe the basic motions necessary to produce a woven cloth and will
consider the conventional methods as well as new developments that have
been introduced successfully in the field of woollen and worsted fabric
weaving.
The Essential Motions of a Loom
For the
manufacture of woven fabrics on any type of weaving equipment, six
principal mechanical motions or operations are involved and must be
co-ordinated in a certain sequence. They are:
   1. Vertical movement of the warp yarns
to form the shed: Shedding, harness or head motion.
   2. Picking motion (insertion of the
weft).
   3. Beating-up or lay motion (placing
picks into the cloth).
   4. Letting-off motion (warp supply).
   5. Taking-up motion (winding of the
woven cloth).
   6. Automatic stop motions (weft
control, warp thread control and protection mechanism).
These basic
operations are usually supplemented by additional mechanical motions
depending on the type of weaving machinery used:
   7. Box motion in multiple box
looms, for multicolour weaving or weft mixing.
   8. Weft pirn replenishment
motion in automatic looms.
Before
proceeding with the explanation of these mechanical motions, it becomes
necessary to explain the simple principles of mechanical weaving in
general. This will be done on the basis of a simple side elevation of a
weaving machine and its essential parts (Fig. 1). The sheet of the
required number of warp yarns is properly prepared and placed on warp
beam, from which the warp yarns are usually passed in a vertical sheet
upward and over the back rail, which brings the warp yarns into the
horizontal level with the harnesses or shafts. Before the yarns pass
into the heddles of the shafts, they are threaded through two lease
rods, which serve the purpose of separating the warp yarns into two
groups. Now follows the zone of the drop-wires of the automatic warp
stop motion and from here, the yarns are drawn through the heddle eyes
of the heddles placed on the harnesses of which only two are shown in
the diagram. There may be as many as twenty-eight in modern worsted
looms. For a plain weave one end is drawn through one harness, the next
through the other, and so on alternating constantly. The function of
the harnesses is to separate the yarn sheet into two groups, one upper
and one lower forming an opening known as shed. At first, harness 5a
is up and harness 5b is down and on the next
movement or pick, harness 5a is down and harness 5b
is up and so on alternating consecutively with each pick inserted. This
is technically known as the “shedding†operation. In front of the
harnesses is located a lay or batten, which carries the reed and has a
race or race plate. Lay oscillates forward and backward as shown by the
two positions in the diagram. The warp yarns pass through the dents of
reed which spreads the yarn evenly across the desired width and acts as
a backrest to the shuttle, which carries the weft yarn on a pirn. The
shuttle passes through the open shed when the lay is essentially in its
backward position; it travels in front of reed on the race plate and
from one side of the loom to the other.
In recent years,
other weft insertion methods have been developed: Instead of using a
pirn carrying shuttle, a light weight gripper shuttle may be employed,
or the weft is picked by means of rapiers or is carried by an air or
water jet. When the shuttle has passed through the yarn shed and has
introduced one weft thread, or, as it is technically called, a “pickâ€Â
or “shotâ€Â, the lay moves forward and the shed closes, pushing the
inserted filling yarn by means of the reed up to the fell of cloth,
where the last pick is now located. The propulsion of the shuttle is
known as the “picking†motion and the forward motion of the lay with
its stationary reed is known as the “beating-up†motion. The operations
of shedding picking and beating-up take place successively and they
constitute the three principle motions in weaving any cloth. When the
last pick is beaten up, the lay moves backward again and while the
harnesses change, the warp yarns again separate into two groups forming
a new shed, ready to receive the next “pickâ€Â. This operation repeats
itself rapidly at the rate of 120 to 300 times a minute, depending upon
machine weaving type, fabric width and construction.
The cloth begins
to take shape at the fell of cloth and slowly moves on over breast beam
or breast rail down over the sand roll or take-up roll, circling its
circumference almost completely and over a guide roll down to cloth
roll which winds it up at full width. Sand roll is covered with
perforated tin or fine sandpaper and moves the woven cloth very slowly
in direct accord with the number of picks that are to be inserted per
inch of woven cloth. On modern looms, the operation of replacing the
empty pirn in the shuttle by a full one is done automatically without
stopping the machine. The let-off pertains to the constant supply of
warp yarn as needed. The take-up concerns the motions necessary to move
the cloth and warp at such a rate as is required by the number of picks
on the cloth.
The weaving
process requires from the mechanical side utmost precision of timing
and synchronization of all moving parts. The weaving cycle diagram
informs about the relative motions of the crank, warp threads (shed)
and weft yarn during one rotation of the crank shaft. Position 0º
denotes the lay at the beating-up position while at 180º the lay has
moved to the far back. Realizing that the time for one rotation may
take from ½ sec on older looms up to ¼ sec on modern machines, it is
easy to recognize that considerable acceleration and deceleration of
the moving parts take place. The picking only requires approximately
10% of the cycle time (from “1†to “2â€Â); the free shuttle flight,
depending upon weaving width, average shuttle velocity and machine
speed between 25 and 50% (from “2†to “3â€Â).
Details of Principal Components of Weaving Machinery
Shedding
or Harness Motion
The equipment
and mechanism needed to exercise the vertical movement of the warp
yarns, i.e. the shedding motion depends largely upon the design
patterns and their variations, which a particular loom must be able to
produce. If the patterns require relatively few shafts and are not
changed very frequently a cam treading system will suffice, otherwise,
the looms must be equipped with a dobby mechanism. In its simplest
form, the harnesses are actuated by cams inside the loom frame. The
cams are mounted onto the shaft that drives the picking eccentrics,
therefore rotate with half the crank shaft speed, which will result in
an alternating up and down movement of the harnesses. Only the simplest
cloth designs using up to 4 harnesses can be produced by this treading
system. If more shafts must be activated it becomes necessary to
install the drive mechanism outside the machine frame. The so-called
outside treading systems consist of a package of up to 12 grooved cams,
forcing an equal number of shafts positively up and down by means of a
follower roll combined with a lever system.
A limited number
of design patterns can be obtained by the selection of various earn
shapes and drive ratios with respect to the crank shaft. The design
possibilities are increased if the treading system permits to run two
cam groups at different speeds, as is the case on certain new loom
makes. For the production of design patterns requiring a larger number
of shafts, and when pattern changes occur frequently, the loom must be
equipped with a dobby or head motion, which is controlled by punched
cards, roller cards or wood peg cards. It gives the advantage of
flexibility without need for exchanging heavy cams and it can operate,
depending upon the design with up to 24-32 shafts.
The selection of
the two shafts to be lifted is initiated by either “positive†(wooden
pegs or roller chains) or “negative†(punched paper or cardboard) dobby
cards. With positive cards, the dobby mechanism is simpler; however,
such cards have a limited number picks per repeat and long cards are
rather heavy and not very practical for storage. The negative punched
cards, although their use requires a reading-in machine on the dobby,
are much handier. Today they are widely used for high-speed double-lift
motions. A comparison of four types of dobby control cards is given in
Table 1, indicating the great advantages offered by paper cards. The
various dobby systems may be characterized with respect to shed
formation, to shed geometry at the moment of beating-up, to positive or
negative shaft motion and to the speed of the crank shaft.
Shed Formation. In principle
the shafts may be pulled up all the way from a neutral position
(“upper-shed motionâ€Â), or they can be pulled all the way downward
(“lower-shed motionâ€Â), or the shed is formed by lifting, respectively
lowering the shafts by a distance corresponding to half the shed height
(“center-shed motionâ€Â).
Shed Geometry at
Beating-up. When at the
beating-up moment, all warp yarns have returned to the central
position, the dobby is a “closed-shed†motion. On the other hand, if
the warp yarns remain either in the upper or lower shed except for
those which are called to change from upper to lower shed or vice versa
for the next pick, then a so-called “open-shed†motion is used.
Positive or
Negative Shaft Movement. In positive
motions, lifting and lowering of the shafts is performed by mechanical
linkage systems pulling and pushing the shafts up and down. A negative
motion depends for the downward movement of the shafts upon spring
force or gravity.
Relationship
between Dobby and Crankshaft Rotation. In the
single-lift mechanism, dobby and crankshaft have the same rotational
speed, each shaft is controlled by one draw hook only. On the other
hand with a double-lifting motion, two picks are inserted during one
cycle of the dobby. Each shaft is controlled by two draw hooks that are
put into action alternatingly. While one hook is working, the other can
be “prepared†for the next pick.
On conventional
woollen looms, the single-lift, closed-shed motion with positive shaft
movement has been most important. Because rather high forces are
required to lift and lower the warp thread when weaving heavy cloth a
positive acting motion is a necessity. Furthermore, when the warp
consists of relatively weak yarns, a better and more trouble free
operation is generally obtained with the closed-shed motion since
during beating-up phase, the total tension exerted onto the warp sheet
is evenly distributed over all warp threads.
With the ever
increasing loom speeds however, the time available for making the shaft
selection and to drive the shafts in time is becoming critically short.
For this reason the double-lift open-shed motion dobbies gain
importance also in woollen and worsted weaving, particularly since
several makes of double-lift motions combined with positive shaft
movement are now available.
The
“Stäubliâ€Â-dobby, for the “Sulzer†machine can make 20 independent
selections (18 shafts and 2 for colour change) and is able to operate
at 240 rpm on the 85 in. wide machine.
Let-off Motion
Older types of
woollen and worsted looms are equipped with comparatively simple
friction let-off motions. These systems are brake devices and as such
passive working let-off motions. One end of a rope, chain or steel tape
that is wound around a friction drum on both sides of the warp beam is
fixed to the loom frame while the other end is attached to a weighting
lever mechanism. The warp tension is controlled by the weight applied,
and it therefore becomes necessary to reduce weight as the warp
diameter decreases in order to keep the warp tension constant.
On modern looms,
improved warp tension control is provided by automatic let-off motions.
Depending upon their operational characteristics, the mechanism is
called “positive†or “negative†let-off motion. It must be pointed out,
that the definition of these terms is not uniform over the world. Wira
uses the following definition:
Negative Let-off
Motion (is) a motion in which the warp beam is pulled round by the warp
tension whenever the latter reaches a value equal to, or slightly
greater than, that required to overcome the braking force applied to
the beam. Positive Let-off Motion (is) a motion in which the warp beam
is turned at a rate which tends to maintain a constant length of warp
sheet between the fell and the beam, the means of applying the warp
tension being separate from the beam driving mechanism.
The most common
“regulators†belong to the former group consisting of a tension
controlling mechanism and a beam driving mechanism. Tension to the warp
is often exerted by using a pivoted back rail which is pressed against
the warp sheet by a weighted lever or a spring system. As the beam
diameter gradually diminishes, the geometry of the forces acting on the
warp changes, causing a variation in warp tension if no compensation is
provided for. This situation can be cured if an extra rail is placed
between the warp beam and back rail in order to keep the warp angle on
the back rail constant. Another method for maintaining constant tension
is to adjust (increase) the pressure on the back rail as the beam
diameter decreases.
The basic
requirement of the beam drive mechanism on the other hand is that it
should maintain a reasonably constant length of warp sheet in the
weaving zone, i.e. the let-off rate should be the same as the take-up
rate of the warp at the fell. On many motion designs this automatic
control is also tied in with the back rail position, in which cases the
rail serves as an indicator for the length of the warp sheet rather
than a warp tension feeler.
A motion that
deviates from the above described method in that it operates without
employing a moving back rail is shown in Fig. 3.
The warp tension
is governed by the spring, which exerts a counterclockwise torque onto
the worm gear carriage, and herewith onto the warp beam shaft. Thus the
warp tension is caused by the tendency for the spring to turn the beam
in the direction opposite to delivery. As the beam diameter decreases,
the torque must also be reduced to maintain a constant warp tension.
This compensation is achieved by reducing the extension of the spring:
The position of the feeler determines through the teethed segments the
position of the upper end of the spring. The beam drive mechanism is
activated by the fixed oscillating movement of the slide arm, pivoted
at. Let us suppose the condition where the beam rotation is less than
the take-up rate. In this case, the warp beam and the worm gear
carriage would be pulled clockwise (warp becomes shorter) and the peg
would move to a position further away from the pivot shaft. The
rotational angle of the worm gear and herewith of the warp beam will
increase, therefore giving more length to the warp sheet. This in turn
will cause the carriage to make a counterclockwise motion, and thus the
stroke length exerted to peg is reduced again. In continuous operation,
the carriage performs a rocking motion, keeping the warp sheet length
essentially constant.
The Take-up Motion
This motion
serves to take-up the cloth as it is woven and to pass it on to the
cloth roll. Together with the let-off motion, the take-up motion
determines not only the number picks inserted per cloth length but also
the disposition of the weft yarns in the cloth. If the weft yarns are
evenly spaced, i.e. if the take-up beam moves precisely the same amount
each pick, this is called a regular disposition of the weft yarn. On
the other hand, if the amount of take-up is such as to provide a close
pressing up pick after pick, the cloth is woven with an irregular weft
disposition. The difference in cloth structure becomes apparent,
however, only if uneven weft is being woven: In the first case, with
regular disposition, thick and thin places will appear in the cloth,
and it becomes streaky. While with an irregular weft disposition, a
fairly even cloth can be produced.
The take-up
motions (or regulators) suitable for regular weft disposition are
called positive motions, in which, through gear
train and ratched or worm-driven sand roll, the cloth is taken-up
exactly the same length with each pick inserted. Positive take-up
motions work in connection with friction let-off mechanisms or negative
let-off regulators. These combinations are suited for weaving worsted
weft yarns and other materials of good uniformity, especially if
weft-mixing with two or three shuttles takes place. Furthermore a weave
design in which the picks are not closely pressed against each other
can only be obtained by the positive take-up motion.
In the woollen
weaving sector however, the negative take-up motion
is often preferred and required, especially for weaving yarns of highly
irregular thickness. The impulse for driving the sand or cloth beam in
the negative motion is given by a weight or spring force, For obtaining
uniform cover with non-uniform weft yarns, the necessary irregular weft
disposition is made possible only in connection with a negative let-off
motion, furthermore, the drive-force of the take-up motion should be
small so that the actual forward movement of the cloth only takes place
under the influence of the reed-force at the fell of the cloth during
beat-up of the lay.
The basic
principles of positive and negative take-up motions are shown in Fig. 4
where (1) represents the lay, (2) the weight in the case of negative
motion acting over ratchet motion (3) and (4) onto the sand-roll (5).
The cloth roll (6) is pressed from below against the sand roll and is
therefore friction driven. In both cases,Â
a pawl (7) prevents from undesired backwards-rotation of
the roll. On other take-up arrangements, there is no contact between
take-up roll and cloth roll, which requires a clutchdrive for the
latter roll.
The positive
take-up motion in Fig. 4 is an example for the cloth threading method
whereby the weaver will see the backside of the fabric when it appears
on the cloth roll, which on certain weaves may be of advantage in view
of quality control.
Full Width Temples
When weaving
cloths with a close setting of picks, additional work must be done by
the beating-up action, taking the form of a displacement of the cloth
fell by the reed toward the breast rail of the loom. If conventional
temples are used weaving a plain worsted cloth, considerable warp
tension peaks can occur each time the reed beats up.
If it is
possible to shorten the length of the cloth between the fell and the
take-up roller (where tension variations due to the beating-up action
are observed), then the tension peaks can be reduced. The use of the
Wira full width temple offers the possibility of holding the cloth
length in the weaving zone at a minimum. In this way, the high tension
difference between the warp and the cloth, necessary for weaving a
close pick setting, is already reached after a relatively small fell
displacement. This displacement is sufficient to reduce the cloth
tension considerably (becoming practically zero); however, it is small
enough not to increase the warp tension by a great amount.
The working
principle of a full width temple is illistrated in Fig. 5. An L-section
bar (1) winch is longer than the widest cloth to be woven, is secured
by brackets (2) to the breast rail (3). A second bar (4) of similar
length to (1) has an inclined edge to form a sloping face (5) and is
fastened to (1) by screws which pass through slots in (1). This enables
the bar (4) to be moved backward or forward as required relative to the
lip (6). Between the faces of (5) and (6) is positioned rod (7),
underneath which the cloth must pass. When the reed is away from the
fell, the warp tension pulls the rod upwards, therefore the cloth is
gripped firmly and it cannot move through the temple. During the
beating-up, however, the tension on the cloth side of the reed is
reduced, the grip released and the cloth will move forward a distance
of one pick. The rod (7) consists of three to five pieces placed end to
end depending upon cloth width. Furthermore the rods are threaded to
ensure that the cloth is held out to width.
Woollen and Worsted Weaves
The manufacture
of woollen and worsted fabrics of all descriptions requires a knowledge
of textile design. A piece of cloth can be compared to a bridge, the
design of which requires an engineer and draftsman before construction.
In the woollen mill, the designer is the engineer or draftsman. Upon
him rests the construction of a cloth, its composition, or weave
structure, the amalgamation and combination of such weaves, and the
mixing and blending of colours. Hence a textile design may be compared
to a blueprint of a cloth, and represents the specifications of a
fabric. On this design, or pattern, planned ahead of actual production,
depends the success of any line of fabrics and, subsequently, that of
the mill itself.
A study of
weaves involves their application to various kinds of yarns,
constructions, and weights. Each mill keeps its own records of
patterns, designs, drafts, and samples made. The designer is
technically trained in all practical mill operations and is required to
possess a natural sense of colour harmony. The finished plan or design
of a fabric is usually so complete that any boss weaver, finisher, or
any department head knows or can learn from the layout exactly what is
wanted without further questions. He specifies all details concerning
the composition, finished appearance, and weight of a fabric.
Methods of Describing Weaves
Use
of Design Paper
In order to be
able to do this preparatory work intelligently and thoroughly certain
mcans are placed at the designer’s disposal. One of his most important
tools is cross-section paper, also known as “squared†or design paper,
on which he designates the weave or combination of weaves, the
drawing-in draft, and the sequence and arrangement of the harnesses of
a loom. The design paper consists of fine and heavy black or blue
lines, running at equal distances both horizontally and vertically. The
paper comes in large sheets or in pad form, depending on the size
required or most convenient.
The object in
using this paper is to portray the method or system by which the
individual warp and filling yarns will interlace to form the weave of a
fabric. Fig. 1 shows the most common woollen and worsted weaves, and
gives an illustration (somewhat reduced) of the paper used and how the
weaves are designated on it. In order to understand this more clearly,
it should be explained that the spaces between the fine vertical lines
represent the individual warp threads or “endsâ€Â, whereas the spaces
between the fine horizontal lines represent individual filling threads
or picks in a cloth. The occasional heavy lines merely aid in counting
the spaces more readily, being spread eight, ten, or twelve squares
apart in either direction.
Since the wrap
or “ends†run lengthwise in the fabric or loom and the filling picks
are inserted horizontally and at right angles to the warp, there are
only two possibilities of interlacing. Any individual warp thread can
only lay on top or over the filling thread, or under it. To indicate
which it is meant to do on design paper, the square can be left blank
or it can be filled in with a cross or completely filled in with pencil
or ink. If the square is left blank, it meansâ€â€to all designersâ€â€that the
particular warp yarn is to lie below the particular filling pick at
that intersection. If the square is filled in with a cross or
completely filled in, it means that the particular warp yarn is
intended to be raised over, lie on top of the particular filling yarn,
or pick. Hence, all crosses, dots, circles, or other marks in any
square in the design paper represent raised warp threads, unless
otherwise specified by the designer. This system of designation is
universal among textile designers, and technicians, and is used in the
following pages.
Verbal Designation of Weaves
As an
alternative to using design paper, weaves are expressed in other ways
in conversation and in writing. The warp and filling threads are
designated as being “’up’’ or “downâ€Â. Hence, the plain weave could be
stated in a letter, for instance, in the manner 1/1. The word “up†or
the figure above the line, indicates the number of threads raised on
each pick, while the word “down†or the figure below the line.
designates that such threads should be lowered for the filling to pass
over. For instance, in the case of the basket weave, it can be stated
as a 2 by 2 basket, or a 2/2 basket. This method of description applies
very well to the simple weaves but when it comes to twills and satins.
stating just the threads up and down is not sufficient. The class or
kind of weave and, in other cases, the degree of twill and so forth
should be given to clarify what is meant. Nevertheless, this does
constitute another method of indicating the weave of a cloth, aside
from drawing it out on design paper, which, with the elementary weaves,
is not ordinarily necessary.
The Plain Weave
To illustrate
this system by the simplest weave used in woollen and worsted fabrics,
known as the plain, tabby, or cotton weave, reference is made to design
1 in the weave chart. In this weave there are only two single
movements, one thread is up and one thread is down, or all
even-numbered warp threads are up and all odd-numbered warp threads are
down, and vice versa. If this weave is made in contrasting colours, say
white warp and black filling or vice versa, it would look exactly like
the design pictured and resemble a checkerboard. Of course, it must be
borne in mind that the sequence of this method of inter-lacing cannot
be broken or interrupted in any way, without interfering with the
continuity or appearance of the weave throughout the width and length
of the cloth.
The extent to
which the weave is carried out depends generally on its repeat in both
vertical and horizontal directions. The plain weave in the illustration
is extended to 16 by 16 pick, simply to show its appearance in both
directions. It is not necessary to carry it out as far and careful
examination of the first, second, and third end (warpwise or
vertically) will prove that the first two ends act exactly opposite
with respect to the filling: i.e., where one is up (that is, over the
filling or filled out) the adjacent one is down or under the filling.
However, the third warp thread from the left acts exactly the same as
the first thread, the fourth end acts like the second, the fifth like
the third and first, and so on. Therefore, the plain weave really
repeats itself every two ends by two picks. This is the simplest method
of inter-lacing the warp with the filling yarns and requires a minimum
of two harnesses, shafts, or leaves in the loom to weave it. Referring
to design 1, the first pick at the bottom, the warp threads one, three,
five, seven, etc., are down and threads two, four, six, eight, etc. are
raised in that shed. At the next pick, threads one, three, five, seven,
etc. are up and threads two, four, six, eight, etc. are lowered.
This weave is
employed a great deal in woollen and worsted fabrics, from the finest
challis to the coarsest coating or carpet. It gives an exceedingly
strong, firm cloth and a smooth surface, but gives the cloth a harder
feel and less elasticity than fabrics woven with other weaves. This
weave is commonly employed where a flat texture or face is desired. Of
course, the nature of the yarn, the stock, the direction of the twist,
and the closeness or openness of the cloth construction will affect the
surface appearance of the finished fabric. That is true of all weaves.
Derivatives of the Plain Weave
There are three
types of weaves derived from the plain weave, which find much use in
woollen and worsted fabrics. They are the warp rib-weave,
the filling rib-weave, and the basket
weave. The first two as a group are known as “rib†weaves,
because they form ridges in the cloth in either warp or filling
direction. The simplest way to form rib weaves is to weave two or more
threads together as one. For an illustration, refer to design 2 in Fig.
1. This is known as a 3 × 3 warp rib-weave, meaning three warp threads
weave as one with single picks only, and that the rib thus formed would
run in the direction of the warp. They are made with two, three, or
four threads, depending on how much of a rib is desired. The three warp
threads in each group can be drawn on individual heddles on each of two
harnesses, or three ends into one heddle on each harness. The latter
method may cause rolling of the ends over and under each other, which
is objectionable in fine worsteds, for instance. These can alternating
regular, combined, or fancy, and constitute the source of many
interesting rib effects in dress goods and men’s wear.
The next
illustration or design in number 3 in Fig. 1 and consitutes a filling
rib-weave. Here each warp yarn floats over three picks, alternating
over or under and repeating, forming a rib or ridge in the direction of
the filling in the cloth. The one illustrated is a 3 X 3 filling rib
weave. They can be made in all even or uneven combinations such as 2 ×
2, 3 × 3, or 3 × 2, 4 × 1, etc. There is no limit to such combinations.
These rib weaves are valuable in that they alter or break up the
monotony of the plain weave and fine considerable use in striping goods
with or without colour and in combination with other weaves as well.
Design 4
constitutes what is commonly referred to as a basket or hopsack weave.
It is a derivative of a plain weave in which two or more adjacent warp
and filling threads are raised and lowered together as if they were a
single thread. It produces a checkerboard effect more pronounced than
in the plain weave. The basket weave illustrated in design 4 is
designated as a 2 × 2 basket (two warp threads work with two filling
threads). They can be made larger, such as 3 × 3, 4 × 4, 6 × 6, and 8 ×
8 threads. They can also be made unbalanced by using different numbers
of threads, such as 8 × 4, 2 × 1, 4 × 2, etc., giving unlimited
possibilities. Colour can be made to play apart in these checks and
many pleasing effects are obtained. The warp threads working side by
side can be drawn on separate shafts or on the same shaft. Warp ends of
different colours which weave side by side alike on the same harness
motion (split basket) should be drawn in separate dents in the reed to
prevent rolling ends. Because several picks are introduced into the
same shed a binder thread at each selvage must be used to prevent the
filling from being drawn in during weaving. This is also true in the
warp rib-weave.
In order to get
squares of the same width and length, the same number of ends and picks
per inch should be used. If this cannot be done, and the warp is set
closer than the filling a weave having more warp than filling threads
working together is used to prevent the squares from becoming oblong or
unbalanced. Squares of different or alternating sizes can be woven in
the same pattern also, providing unlimited combinations. These weaves
are used extensively in women’s dress goods and coatings as well as
men’s wear. Of course, these derivatives of the plain weave become
looser owing to the larger number of threads that are working in a
group.
The Twill Weave
The twill weave
in its various ramifications is the one most commonly employed in
woollen and worsted dress goods, coatings and men’s wear. In all its
forms the twill weave is distinguished from the plain weave in that it
develops a more or less pronounced diagonal line in the cloth. The
twill weave is characterized by the fact that the float of each filling
thread is advanced one or more warp-thread to the right or left of the
preceding filling thread, assuming, of course, that all the floats are
alike.
The simplest
twill that can be made is a three-harness twill, often called a
prunella or filling-face twill. These names vary according to the
nature the material or the relation of the warp and filling in the
construction of the cloth. This twill is illustrated in design 15.
Close examination of this weave discloses that it is a 45° twill and a
“filling face-twillâ€Â. In written form it is expressed as a ½ 45º twill,
or a 1 up and 2 down 45° twill. It is a 45° twill because it advances
one end to the right with every pick. It is a “filling effect†twill
because two thirds of the filling shows on the face of the cloth and
only one third of the warp, proportionately. No matter from where one
starts to read the weave, it is a one up and two down. The weave
repeats every three ends and three filling picks, but is drawn out to
15 × 15 to show its appearance and effect in a cloth which has the same
number of ends and picks per inch.
It can be noted
that the first warp thread at the lower left corner is filled in,
meaning that it is raised above the first filling pick. The first pick
from the bottom passes under the first warp thread and over the next
two warp threads (to the right) and repeats that way across the width
of the fabric. The second pick directly above (horizontally) passes
over the first warp thread, under the second, and over the third,
fourth, and so on repeating. The third pick passes over warp threads
one and two, and under warp thread three. The next pick is just like
the first, and the fifth and sixth picks just like the second and
third, respectively. Looking at the whole design, the twill is
complete, continuous, and unbroken.
According to the
kind of cloth it is used in, design 15 makes a very line and delicate
diagonal. If the warp ends are made of fine worsted yarns and crowded
together, the twill angle will become steeper without employing a steep
twill weave. If the picks are increased and laid closer together in the
loom the twill line becomes reclining. The twill as it is shown is a
right-hand twill (the usual way of making it), because it runs from the
left to the right. If it is reversed and made to run from right to
left, it becomes a left-hand twill, which is less common in the wool
trade.
To make this
twill a warp twill or “warp effect†twill, its formula 1 up and 2 down,
is reversed to read 2 up and 1 down. The reversal will bring the warp
to predominate on the face, whereas it showed on the back of the cloth
previously.
Such twilled
fabrics are generally softer, and more pliable than fabrics made with a
plain weave. In weaving, twill cloths take the picks much more easily
than the plain woven fabrics, hence they can be set closer in the warp
and reed, making the cloth heavier, everything else being equal. The
three harness warp twill weaves are popular in medium weight worsted,
suitings and in flannels.
Balanced or Even Twills
The most common
will employed in all types of serges, gabardines. over-coatings, etc.
is the cassimere, shalloon, or common twill. This weave is illustrated
in design 5. It is designated as the famous 2 up and 2 down 45° twill,
which makes it a “balanced twill†because one half of the warp and one
half of the filling show on the face. Also, because it is made with an
even number of risers and sinkers in the weave pattern, it is known as
the “even twillâ€Â. It requires a minimum of four harnesses in the loom
and repeats on four ends by four picks. Attention is called to the
angle of the twill, which is 45° with the horizontal. It is continuous
and unbroken.
In designing
this twill or making up other twills, one should always begin in the
lower left-hand corner of the design as is done in design 5. It is
noted that the 2 up and 2 down 45° twill shown commences with the first
warp thread (from the bottom) up on the first two picks, down on the
next two, up for the next two picks, and so forth as far as one wishes
to go. The second warp thread commences with 1 down and 2 up. then 2
down, 2 up, and so forth. In other words, the raised part, which forms
the twill line or diagonal, is always advanced one pick. This is
characteristic of all 45° twills. The third warp thread commences with
2 down, then 2 up and 2 down, showing again that the twill has been
moved up again one pick. The fourth warp thread starts with one end up
for one pick, then down for two picks and up again for two picks and so
forth up the line. The next or the fifth warp thread operates exactly
like the first, the sixth like the second, the seventh like the third,
and the eighth like the fourth end, and so on. Hence, the weave repeats
on four ends and four picks as indicated. This is one of the most
important weaves in the twill family.
Effect of Yarn Twist on Twill
The direction of
the twill and the twist in the warp and filling yarns has a great
influence on the appearance of the twill in the cloth. In order to make
this perfectly plain, it is necessary to come to an understanding about
the direction of twist in single woollen or worsted yarns. Single wool
yarns, which are twisted to the left, are termed S
twist, whereas single twist yarns, which are twisted to the right, are
termed Z twist (A.S.T.M. designations). Two-ply
yarns usually have an opposite twist to the single-ply. S-twisted warp
yarn used running from left to right in a warp twill will make the
twill more prominent. If an indistinct warp twill is wanted, a
Z-twisted warp yarn should be used. In other words, in twill fabrics
the clearness and prominence of a twill line are accentuated if their
direction is opposite to the surface direction of the twist of the
yarn, with the reverse conditions obtaining for distinct twills. The
whole relation of direction of twill to direction of twist in the warp
and filling yarns is summarized in Table 1.
In practical
work, of course, these conditions are greatly modified by the quality
of the wool, the size, character, and turns of twist in the yarn,
whether it is single-or double-ply, closeness of the sley or “set†and
also the finish of the goods. Another circumstance must be considered:
If the twill runs right and left alternately and it is desired to have
them equally distinct, right twist must be used for the warp yarn in
the left twill and left twist in the warp yarn for the right twill.
Steep and Reclining Twills
While this
variety of twill (also known as regular twill) is usually at 45° with
the horizontal and advances one thread to the right or up until a full
repeat has. been obtained, there are other types that depart from this
method and angle of diagonal. They are the “steep†twills in one case
and the “reclining or flat†twills in the other. The steep
twills, as the name would imply, are twills that are steeper
than 45° and run more toward the vertical. These twills are formed when
the warp float or twill line is advanced two or more picks instead of
only one above the float of the preceding thread as is the case in the
common 45° twill and brings the twill line nearer the perpendicular.
Steep twills are exemplified in Fig. 1 by designs 6, 7, 8, and 10.
The diagonal
lines in steep twills are closer together, but frequently, owing to the
filling floats on the back, are more prominent than the regular twills.
They are commonly employed in whipcords, uniform fabrics, tricotines,
gabardines, and other women’s and men’s wear fabrics. These steep
twills are made by advancing the twill float by two, three, or four
picks on each successive end as is clearly demonstrated by the twill
angle diagram (Fig. 2). According to this figure, they are termed 63°,
70°, and 75° steep twills, advancing two, three, and four picks
respectively. The 52° is a combination of one and two advances, but is
not commonly employed. For instance, design 7 is a 5 up and 2 down 63°
warp effect twill. Again, design 10 is a 7 up 1 down, 1 up 2 down, 1 up
2 down, and 1 up 1 down 63° fancy twill. Other 63° twills in Fig. 1 are
designs 6 and 8.
If a regular
twill having an even number of shafts, say ten, twelve, or sixteen, is
selected for the construction of a steep twill, only one half as many
threads are used and hence, only one half as many shafts are needed. On
the other hand, if a regular twill has an uneven number of shafts, the
resulting steep twill will have the same number of threads or shafts in
the pattern. Again, a steep twill with warp floats using three picks at
each succeeding thread requires only one third as many shafts as are
required for the base weave, providing the base weave is divisible by
3. Where the number of shafts of the base weave is not divisible by 3,
then the resulting steep twill will require the same number of shafts
as the base weave.
These weaves can
be made with long- or short-float twill lines, making them more or less
prominent. The twill line, of course, is affected by the “set†or the
sley of the cloth, that is, ends and picks per inch. If the set of the
cloth is balanced the twill will run exactly as planned. If the warp is
closer set than the filling, which is very common, the twill will be
steeper than before. If the yarn sizes differ or are changed, the twill
angle will also change to some extent. Hence, caution is required here,
to prevent radical changes in the character and face of the goods when
changing weaves or yarns.
The reclining
twill is used only occasionally and for special purposes. These twills
decline away from the 45° line and come closer to the horizontal. The
same theory applies as in creating the steep twills, only in the
opposite direction. When two moves or ends are skipped it becomes a 27°
reclining twill; when the twill line is retarded three it becomes a 20°
declining twill; and when a move of four is made it becomes a 15°
reclining twill (see Fig. 2).
Pointed and Herringbone Twills
The term
“herringbone†twill is applied to twills in which a sharp break occurs
when the twill is reversed, especially when it runs for a considerable
length before it is reversed. An illustration of such a twill is shown
in design 9 of Fig. 1. Note in the design that a 2 up and 2 down 45°
twill is employed, which runs one way for eight ends and is reversed
for eight ends. Twills of longer floats than this, all variations and
combinations can be employed here. Such weaves are common in ladies and
men’s suitings and coatings.
The pointed
twill is very similar to the herringbone; in fact many mill men draw no
distinction between the, two in that the twill is reversed without
making a break or that it is reversed after it is allowed to come to a
point. This system forms the basis for damask diamond, zigzag, and
honeycomb weaves, the latter of which is illustrated in design 18 of
Fig. 1, and gives wide opportunities for matching fields, squares, and
checks created by weave only. When colours are applied many interesting
and vivid contrasts can be originated. The pointed herringbone effect
can be created with a twill chain and a pointed drawing-in draft (see
designs). The twill in a herringbone weave can also be arranged to
bring the points at the side of the design. The pointed twill patterns
have the general defect that the float at the apex is nearly double
that of the other floats. When it is important to have them short and
practically uniform, risers are removed or inserted at that point. Of
course, this increases the number of shafts required in the loom.
Broken or Reversed Twills
By breaking the
twill line or practically reversing the direction at intervals in
regular or irregular fashion, many attractive patterns can be created.
The twill can be reversed in either the warp or the filling. For
instance, a 2 up and 2 down twill can be reversed every two warp
threads and while the warp threads still weave two up and two down, the
reversing of the twill causes every alternate pick to inter-lace the
warp in plain weave order. If the twill is reversed in the filling, the
latter becomes more prominent than the warp, which is stitched (bound)
more closely. This applies to the balanced twills only. This weave
shows no twill at all.
Very interesting
designs can be created by rearranging the parts of a twill so that two
groups of threads, with the twill running in the same direction,
alternate with two groups running in the opposite direction and also,
by reversing the twill in accordance with selected motifs. The latter
gives ladder effect and criss-cross twills, commonly employed in fancy
worsteds.
Corkscrew Twills
The peculiar
feature of corkscrew or double twill weaves is the combination of two
or more distinct twill lines, which may be of different colours. They
are also called diagonal ribs and are popular in clear finished fine
men’s wear worsted fabric and many interesting colour effects may be
achieved by using these weaves. They are usually set closely in the
warp and require manifold drawing-in drafts. A typical corkscrew weave
is shown in Fig. 1, design 12.
Corkscrew weaves
can be made by reversing, deflecting, and waving or undulating the
twill line. They may be developed with warp as well as with filling
floats. The twill can be run alternately to the right and left in order
to bring about an undulating effect suitable for stripes in worsted
goods.
Inter-locking and Offset Twills
Inter-locking
twills are used extensively to obtain wide diagonal effects with a
relatively small number of harnesses in the loom. They also permit an
unlimited variety of special designs by inter-locking weaves in the
warp and filling as well as by bringing a ground weave on alternate
picks. They are also used to increase the filling absorbing capacity of
a weave. Any change in position produces a new effect.
Offset twills
are obtained without reversing the twill direction. In balanced twills,
for instance, the risers of the first thread of a group are usually,
but not necessarily, brought opposite the sinkers of the last thread of
the preceding group. An illustration of this type of twill is shown in
the design 11 (Fig. 1). They produce very attractive effects in fine
worsteds and can be enhanced with colour.
Undulating Twills
This class of
twills produces a wavy twill line, which is formed by an irregular
offsetting of the warp and filling floats for instance, by moving the
float three threads at one place and four threads at another, either
vertically or horizontally. The more the twill line is offset the less
distinct it becomes, hence twill with longer floats are used. For
instance, a 3 up and 3 down twill, offset one pick, and a 6 up and 6
down twill, offset two picks, are combined to form an undulating or
waving twill. Very attractive designs for coatings and tree-bark
effects can be made with these, when these waving twill lines are
broken and started again. The same effect can also be created with a
regular twill weave on an irregularly reeded warp, which consists on
groups of fine and coarse yarns, such as five per dent on the fine
yarns and four per dent on the coarse yarns. Many combinations are
possible with undulating twills and they are extensively employed in
the bark-effect coatings.
Diversified, Combination, and Fancy Twills
The twill weaves
are just a few selected types that are commonly employed in woollen and
worsted ladies’ and men’s suitings and coatings. There are other
methods of obtaining twills, such as adding or removing risers, the
spotting of twills, combining basket, rib, and satin weaves to form
twill lines, arranging a twill to form braided effects, etc. In all
such combinations the twill line is usually worked out on design paper
first and other weaves filled in to serve the purpose. Into this
grouping belong the famous tricotine, gabardine, and similar weaves,
shown in Fig. 1 by designs 6 and 8. They are very characteric of fine
worsted ladies, suitings, producing single and double twill lines that
actually rise from the surface and stand erect in fine-yarn worsteds. A
typical fancy twill is shown in Fig. 1 in design 10. These combination
weaves can be carried to such dimensions that Jacquard looms are
required to weave them. In general, all such weaves for practical
purposes are, wherever possible, drafted down to less than twenty
harnesses.
The twills as a
group constitute the most important class of weaves for all types of
woollen and worsted suitings and coatings and offer a great field for
the designer to draw from continually in creating new patterns,
designs, and effects. By the use of these weaves, with the aid of
colour and all types of yarns, there are unlimited possibilities for
application. However, a designer is forced to keep his draft and weaves
in simple and easily followed form, so that matters are not
unnecessarily complicated in the drawing-in department and the weave
room.
The Satin Weave
This is the
third of three main classes of weaves, namely plain, twill, and satin.
The object of the satin weave is to get away from the distinct diagonal
of the twill and to produce a patternless, smooth, lustrous surface in
the fabric. The satin weave is extensively used in venetians,
broadcloths, doeskins, meltons, and kerseys. Satin weaves are usually
constructed from a twill weave, but the inter-weaving of the two sets
of yarns does not follow consecutively but at definite calculated
intervals.
Satin weaves are
classified into two groups: those in which the warp predominates on the
face, called warp flush sateens, and those in which
the fining predominates on the face, known as filling flush
sateens. The word satin originated in
the silk trade, where the satin fabric is made with a satin
weave. The word sateen is more of a cotton term,
employed to designate any fabric in which the filling predominates on
the surface of the goods. In the woollen and worsted trade the words
satin and sateen are used inter-changeably and promiscuously to mean
the weave rather than any particular fabric as is the case in the silk
and cotton trade. The word satinet, however, was
first used to designate a union cloth in which the face shows only
woollen filling, the cotton warp being covered entirely.
The principle
involved in the construction of stain weaves is to determine the order
of progression for the so-called “stitchers†or points of
inter-lacement between warp and filling. To obtain the combination from
which to design a satin is to take any number of harnesses required of
the original twill weave on which it can be woven and divide it into
two parts. These must not be equal, nor must one be the
multiple of the other, nor should they be divisible by a third number.
For instance: the number 5 is divisible into 2 and 3. Beginning with
thread 1 and progressing two warps threads to the right at each pick,
the warp threads are stitched (bound) in the following order: 1, 3, 5,
2, 4. That is, the first warp thread is stitched on the first pick, the
third warp on the second pick, the fifth warp on the third pick, the
second warp on the fourth pick, and fourth warp on the fifth pick.
Hence it can be seen that each warp end is inter-laced with
one pick only and vice versa and that a scattered order of
this inter-lacement is used so that no twill is formed at all, although
a twill weave of 1 up and 4 down is used. This constitutes a filling
flush and by a complete reversal a warp flush satin can be created.
The simplest
satin weave, although not strictly a satin but a broken twill, is that
made on four harnesses. It is shown in filling and warp effect in
designs 13 and 14, respectively, of Fig. 1. The order of inter-lacing
warp with filling is 1, 2, 4, 3. This is generally termed a “crowfootâ€Â
weave and is quite effectively used in stitching of double cloths and
in broadcloths of all types. The twill line is well broken and with the
proper yarn will produce a smooth, lustrous surface.
A more or less
pronounced twill effect will be encountered in many of the satin
weaves, particularly in the even-numbered harnesses such as six, eight,
ten, or twelve harnesses or shafts, where no regular order of
progression is possible. For instance, in a six-harness satin the only
“move†numbers available are 2 and 4 (1 is not used), in the
eight-harness satin 3 and 5 are available, in the ten-harness satin 7
and 3, and in the twelve-harness satin only 7 and 5 are available, and
so on. The uneven-number harness satins produce the best effects,
because a choice in progression exists, one of which will suit very
well, whereas some will show an undesirable twill line. This rule
applies mostly to uneven-number harness satins.
Table 2 gives
the order of stitching satin weaves on various harnesses, which have
been found satisfactory in woollen and worsted work.
This Table
eliminates a lot of experiments and will serve as a guide in selecting
the best progression for any satin weave between five and sixteen
harnesses, which are most commonly in use.
For the “warp
effect†satins a closer set, or, in other words, more warp yarns per
inch are used, whereas the reverse is true in “filling “mush†satins.
If the weave is too loose, the result will be a spongy fabric of poor
appearance, lacking handle and durability. On the other hand, if the
construction of the cloth is too tight it will be difficult to weave
and get the required picks into the cloth and a “ribby†cloth will
generally result. Hence, a happy medium must be found and the filling
shrinkage of the cloth carefully watched.
Another factor
is the use of the satin weave in stripes of all kinds. Here it is
sometimes necessary to crowd the ends in the reed at the stripe to
accomplish desired density of weave formation. Checks can also be made
by using one harness for the crowding of the picks, if necessary. This
is done to some extent in ladies fancy worsted dress goods. The satin
weave can also be employed in coloured yarn goods, where the warp is of
one colour and the filling of another.
One or the other
can be brought to the face independent of the other, and without the
other showing through if the yarn is reeded close enough.
Owing to the
minimum amount of inter-lacing in these weaves, the strength of the
cloth is not as good as with the plain weave, hence precautions must be
taken if strength, slippage, and durability in satin weave fabrics
become factors.
An important use
of satin weave is in double, triple, double-plain, and broche fabrics,
where these weaves are employed in stitching the layers of cloth
together or reversing the back with the face alternately; also in
figured satins, where the warp and filling satins are alternated to
produce patterns, figures and motifs, in regular or irregular order.
There are also irregular satins and double-stitched satins, which,
however, find less use in the woollen and worsted trade. Colour effects
can be worked very well with satin weaves also.
Of course, it
will be realized that satin weaves can also be used in combination with
other elementary weaves to form a variety of stripes, checks,
over-plaids, and colour effects which defy the imagination.
Knitting
The origin of
knitting is unknown. In the Odyssey, there is a
description by Homer of Penelope “weaving a web by day, which she
unweaves at nightâ€Â. This reference possibly means a knitting process,
because the secret delaying deeds of the Queen, opening an already
woven fabric would require as much time as producing it, but a knitted
fabric can be unravelled as fast as the yarn is rolled into a ball.
The earliest
knitted fabrics dating from the third century before Christ were found
in the Egyptian tombs. It can be assumed that the art of knitting
originated around the Mediterranean and from there it spread to Europe
and the rest of the world.
Jesus wore a
seamless coat before his execution on the cross. The references to a
wrought or fashioned garment he wore could have been knitted, because
there is no loom to weave a fabric into shape without a seam.
Dating back to
the fourteenth century, there are several mentions of knitting in
English poetry, descriptions of garments, and acts of Parliament. The
words knot and knitting are derived from the Saxon word of “cnyttanâ€Â,
meaning a fabric produced by hand using threads in the formation of
loops.
Hand knitting,
using two or more pins made of wood, bones or metal became an
occupation of amusement, therapy for the aged and sick, and a
profitable home industry. In the fifteenth century knitted caps and
coarse hosiery were accepted garments in England and fancy knitted hand
embroidered ceremonial clothing and silk stockings were worn by the
nobility in every court of Europe.
In 1589, the
Reverend William Lee invented the hand-knitting machine. Many original
inventions and mechanisms of Lee’s, which he incorporated into his
stocking frame are still used in the modern automatic knitting
machines. Political, economical, and religious prejudices denied Lee
the success he deserved.
Skilled
craftsmen added many improvements and inventions to the art of
knitting. Before the start of the nineteenth century all the
fundamental stitch constructions already were achieved on the original
stocking frame.
The progress of
knitting is best illustrated with the speed of a hand knitter forming
100 stitches per minute, Lee’s hand knitting machine started with 600
stitches per minute, and a modern automatic knitting machine producing
over 4 million stitches per minute. Comparing a fast commercial loom,
weaving a similar cloth as produced on a knitting machine, the knitted
square yardage is 20 times larger than the output of the loom.
The use of
knitted fabrics is constantly growing. A man, woman, and child can be
dressed from the top of their head to the tip of their toe in knitted
apparel. The advantages of the knitted fabric are good fit to the shape
of the body, elastic to conform and move with the motions of the body,
resilient to recover its original shape without wrinkles, needs no
ironing, soft and comfortable to wear, ease of handling as a wash and
wear garment, cheaper to produce than other comparable textile fabrics,
attractive in unlimited colour and texture designs. The disadvantages
of the knitted construction include the lack of perfect stability, and
the need of a finer or costlier yarn to produce a similar weight fabric
as made on the loom.
Knitting is the art and
science of constructing a fabric by inter-lacing loops. The loop
forming elements of the knitting machine draw the yarn into a curved
form called the loop. Two loops, a needle
loop formed around the needle and a sinker loop formed
around the sinker or some other loop forming element, combine into a stitch.
A horizontal row of stitches Knitted across the width of the fabric is
a course, and a vertical row of stitches knitted on
the same needle is a wale (Fig. 1). The stitch is a
basic unit, expressing the fineness of the knitted fabric. Along a
ruler or under a magnifying glass the number of courses per
inch (CPI) and wales per inch (WPI) are
counted and their product give the stitches per square inch
(ST/SQ. INCH), WPI × CPI = ST/SQ. INCH, therefore the increasing number
of stitches in a square inch indicate a finer fabric. There is a wide
range of knitted fabrics from heavy outerwear to fine underwear and
hosiery with a fraction of one stitch to several thousand stitches in a
square inch.
There are two
types of knitting: warp and weft knitting. These terms are also used in
weaving, where the parallel threads following the length of the fabric
are in the warp and those going across the fabric are the weft threads.
In weaving the inter-lacing and inter-secting of the two systems of
threads form a fabric construction, but in knitting one yarn system by
itself is sufficient to inter-lace the stitches. Warp knitted
fabrics are knitted from one or more warps in such a way that
the individual parallel thread is lapped around only one needle in a
course. Then in the following course the thread will form the next
stitch around the same or another needle and knitting progresses in the
length of the fabric. Weft knitted fabrics are
drawing all the stitches of a course from the same yarn. Up to 120
courses can be knitted with each revolution of a circular weft knitting
machine, depending on the diameter of the machine, the circumferential
space restrictions required for the stitch formation, and the angle of
the spiral introduced into the fabric. The volume of weft knitted
fabrics in use is about eight times as large as the warp knitted cloths
due to the versatility of the weft knitting machines.
Principles of Stitch Formation
The parts of the
knitting machine that come into contact with the yarn during the
formation of the stitches are called the loop forming elements. The
most important loop forming element is the needle, made from wire or
sheet metal. Needles are classified in gauges according to their
fineness, listed in Table 1. There are many thousands of differently
shaped needles according to the type of machine, fineness of the
machine, and the special stitch formation technology required. The four
basic types of needles are the straight, spring bearded, latch, and
compound needles. The straight needle is used for hand knitting, where
the thickness of the needle determines the size of the stitch and the
looseness of the fabric. The compound needle is rarely used, because it
has two independently moveable parts. The disadvantage of the spring
bearded needle is the need of a presser, to close the beard during the
stitch formation, whereas the latch needle is self-contained. The
spring bearded needle can be manufactured thinner, demonstrated by the
finest full-fashioned knitting machine with 60 needles per inch,
whereas the finest latch needles are used in 42 needles per inch
seamless hosiery machines. Regardless of how freely the latch of the
needle moves, it requires the yarn to do mechanical work during the
stitch formation, therefore the latch needle needs a stronger yarn than
its spring bearded counterpart, which also can knit a more uniform and
tighter fabric. The latch needle is the more widely used needle,
because its stitch formation is much simpler compared to the spring
bearded needle, as they are illustrated in Figs. 4-10, using different
types of knitting machines.
The other
important loop forming element is the sinker, deriving its name from
the original stocking frame where this thin steel blade sinks the yarn
into a sinker loop between two needle loops.
A weft knitting
machine can form the stitches with loop wheels, loop forming sinkers,
web holding sinkers, holding down sinkers, and the forecut of the
needle bed trickwall between the needles can also function to form the
sinker loop. The web holding sinker in Fig. 5, holds the sinker loop of
the previous stitch in the throat of the sinker (X) while the needle
goes up from the rest position (A) to clearing (B). As the needle
starts to descend to the feeding position (C) the yarn is fed into the
hook or under the beard of the needle, and then the old stitch is cast
off (D), while the sinkerbelly (g) holds the fabric up. The relative
distance between the head of the needle and the top edge of the
sinkerbelly is the primary determining factor to the size of the stitch
and the length of the yarn forming each stitch. The type of yarn,
softness of the yarn package, tension on the yarn, sinker and needle
cam timing, needle spacing, and the takeup weight of the fabric
contribute to the size of the stitch and the ease of the stitch
formation. The increased use of yarn feeding devices incorporated into
the knitting machines are the best method of eliminating some of the
stitch variations and improving the uniformity of the fabric.
Rib machines
have the coordinated movement of two sets of needles during the stitch
formation, illustrated in Figs. 7 and 8. In a circular machine the
horizontal position is taken by the dial needles and the vertical
arrangement by the cylinder needles. In straight rib or V flat rib
machines the front bed needles form plain stitches the same as the
cylinder needles of the circular machine and the back bed needles knit
rib stitches similar to the dial needles. From the rest position (A),
first the dial needles move out to hold the fabric down, then the
cylinder needles move up to the clearing position (B). After the yarn
is fed (C), the dial and cylinder needles draw their loops at the same
time for synchronized timing (D), or one needle forms its loop ahead of
the needle of the opposite needle bed (D1 and D2) for delayed timing.
Synchronized timing is used for strip knitting, because it is easier to
adjust on the machine and it has to be used with broad rib and fancy
design fabrics. Delayed timing is often used on rib yardgoods knitting
machines to knit weak yarns, very tight fabrics, and to reduce the wear
on the needles and on the machine.
Purl machines,
often referred to as links or links-links, have one set of double
headed latch needles, which are staying in their respective needle bed
or they are inter-changing from one of the two needle beds on the same
plane to the other bed during the stitch formation. The needle tricks
(slots, grooves) of the two needle beds are exactly opposite each other
to allow for the free movement of the needles between needle beds and
knit a stitch during the same cycle. The rest position (A) is followed
by clearing (B), then the needle moves to the opposite needle bed or
stays in the same needle bed for the feeding of the yarn (C), and
finally the old stitch is cast off (D).
Weft Knitting Machines
It is important
to get the basic impressions of a knitting machine which will help to
identify its design versatility, manufacturing capacity, and suitable
operating methods with available personnel. All weft knitting machinery
are classified into one of the three major groups illustrated in Table
2, and then each can be subdivided into additional minor groups
according to the specific mechanisms and attachments designed by the
knitting machine manufacturers in the United States and abroad. Many
modifications of knitting inventors have conceived exceptions to the
basic principles illustrated here, but they only prove the versatility
of the knitting technology.
Weft knitting
machines are built with circular needle beds to produce a tubular
fabric and with straight needle beds to knit an open width fabric. The
production limitation of the straight needle bed in weft knitting is
similar to weaving, because only one course can be produced across the
fabric width for each traverse of the yarn. Regardless how fast the
yarn is knitted, it, has to come to a stop and accelerated in the
opposite direction. Whereas circular weft knitting machines maintain a
uniform revolving speed, and the limitations of the number of courses
knitted during each revolution are the mechanical restrictions required
to knit the stitch on the circumferential arc of the needle cylinder
and the diameter of the machine.
Circular rib
machines are manufactured with dog or dogless drive to align the
cylinder needles in the exact center between the dial needles. The dog
drive of older rib machines has the dog-stop on the inside of the
cylinder holding the wing underneath the dial, with the fabric between
them. The pressure of the dog drive frequently causes vertical lines in
the fabric, which is difficult to adjust, and troublesome with cloth
press off. The dogless drive of newly built rib machines hold the
cylinder and the dial in a fixed relative position with gearing or with
sliding pins, which move individually in and out following a cam race
to allow for the yarn passage.
The essential
parts of a machine to produce a weft knitted fabric are the supply of
the yarn on the yarnstand with the tensioning and feeding devices, the
needle bed with the needles, the cams of the cambox to activate the
loop-forming elements, and the fabric takeup. The selection of the
basic machine parts is important in high production, large diameter
circular weft knitting machines, illustrated in Table 3, because the
relative movement of the knitting elements have to suit the product
manufactured.
The fineness of
knitting machines are expressed with one of several systems selected by
the individual machine builders. The fixed needle machines use the
gauge designation, which has no relation to the gauge number of
knitting needles as illustrated in Table 1. The meaning of machine
gauge varies according to the type of knitting machine. because tricot
gauge is needles/1 in., Raschel gauge is needles/2 in., full-fashioned
gauge is needles/1½ in., loopwheel gauge is needles/1½ in., and the
gauge of foreign machines can also be expressed in centimeter, zoll, or
other measurements too. The individually moveable needles require
slotted needle beds expressing the fineness of the machine in cut,
which is the number of tricks per inch. Cut implies the number of
needles per inch only when the needle bed is filled in every trick or
slot with a needle. There can be needle arrangements with empty tricks
where the cut of the machine and the needles per inch are different.
Cut does not accurately express the needle spacing of small diameter
machines, because there are fractional number of needles per inch,
therefore the inside diameter of the cylinder and the number of tricks
in it are given together, such as 3¾ in. D × 474 N.
Plain, Rib and Purl Stitches
The proper way
of holding a knitted fabric for analysis, and to keep it in a record
file, is with the face of the fabric towards the viewer, the edge or
course knitted last is on the top, the edge knitted first is on the
bottom, and then the wales will be running in the length and the
courses across the width of the fabric. To remember the correct
handling of the weft knitted fabric, visualize the appearance of most
circular knitting machines which have the course knitted last still on
the needles or on the top, the fabric coming down vertically roll up
the edge knitted first underneath the machine and the technical or
knitted face of the fabric is on the outside.
It requires some
practice and experience to draw loop diagrams representing a stitch
construction especially with the more intricate designs. Using a
simplified method, most of the weft knitted fabric constructions can be
recorded on graph paper. Each square of the graph paper represents a
stitch, filled in according to a symbol for each type of stitch. A
horizontal row of squares is a course, and a vertical row is a wale.
The design paper has to show one repeat of the stitch construction,
which is the least number of stitches necessary in the width and the
depth of the design, or a multiple of complete repeats.
The stitch is
called a plain stitch, when it appears with its needle loop coming out
from the previous needle loop below it, showing the long parts of the
loop , designated on design paper with     in
the appropriate square representing the stitch. However, the stitch,
which has its needle loop going away through the needle loop below it
is called a rib or purl stitch, showing the semicircular parts of the
loop , designated on design paper with     in
the respective square. In many languages there is only one expression
for this stitch, but in English it is named a purl stitch in a purl
fabric and it is a rib stitch when it appears in a rib fabric.
Taking the most
important fabric from each of the three major types of weft knitting
machines, there is an interesting relationship among their
characteristics and properties, illustrated in Table 4, which help to
identify the general classification of weft knitted fabrics.
The biggest
percentage of the weft knitted fabrics have the plain construction.
This fabric is often referred to as a jersey fabric. “Jersey†is a
misleading word, because it is used both for warp and weft knitted
jersey fabrics, with entirely different characteristics and properties.
The plain fabric has a smoother face than back, because the loops are
coming through the previous loop toward the face and the lengthwise
side alignment of the stitches are predominant. Viewing it on the back
of the fabric all the loops are going way through the previous loop,
providing a rough surface with the semicircular parts of the loops
showing. The uniform quality of a plain knitted fabric is very
important, because any fault of the yarn and setting up procedure will
be noticeable.
The plain
knitted construction is used for hosiery, underwear, outerwear, and
industrial fabrics. The plain knitting machine is built in its simplest
form for high production and limited design versatility that include
the use of diverse fibers, a range of yarn sizes, stitch length
variations, and colour arrangements. The addition of patterning
mechanisms for the primary and secondary knitting elements will create
unlimited colour and surface effects in the plain weft knitted fabric.
The single and multifeed machines are accommodating hand-regulated,
fixed, semiautomatic, or automatic striping controls. Most of the plain
knitting machines have fixed stripers, which require the positioning of
different yarn types or colours in a preselected order according to the
design. Semiautomatic and automatic striper machines have a control
chain attachment which can change one yarn from the active feeding
position to the inactive state or vice versa at the alternate or all
knitting feeds following the design pattern.
The colour
arrangement of a plain fabric shows horizontal stripe designs, commonly
used for polo shirts and dresses. The designer can create new colour
combinations and attractive fabric styles on paper without the actual
process of knitting endless number of samples on the machine in
preparation of the fabric line. It is important to consider the
mechanical limitations of the machine before the selection of the
design, in addition to the stitch density and the size of the colour
pattern repeat, because the type of striper and the number of knitting
feeds determine the courses per design repeat and the finished courses
per inch will set the depth of the colour stripe. The number of courses
per design repeat should divide evenly into, equal to, or be a multiple
of the number of knitting feeds.
Rib fabrics
offer a wide variety of stitch constructions through needle
arrangements, which create vertically spaced lines in the fabrics.
Needle arrangement is the selection of needles out of action without
loops, which has the same effect as removing the needle from the needle
bed. The wide use of rib knitted fabrics stimulated the inception of
several stitch construction designating systems. In addition of
representing the rib fabric on graph paper withÂ
  , for the plain stitches and
   for
the rib stitches, a fraction can be used for one repeat of the design
with the nominator expressing the plain stitches formed next to each
other, and the denominator indicating the rib stitches. One fraction is
used to show a regular rib construction, such as Fig. 11 and two or
more fractions indicate an irregular rib design. such as Fig. 12. One
or both needle beds can hold isolated needles to knit single rib
fabrics, such as 1/1, 2/1,1/4 ribs. and both needle beds are arranged
with needles forming similar stitches next to each other to knit broad
rib fabrics, such as 2/2, 3/2, 4/4, ribs. Some broad and irregular rib
constructions are designed to get pleated effects for skirt and dress
fabrics.
In 1908 Scott
invented a special circular rib machine to knit the fabric construction
called interlock. In the regular rib machine the needles are displaced
between each other, but the interlock machine has two rib machines
built into one with the needles opposite each other. A double raceway
cam or selecting mechanism is used to control the alternate needles in
the dial and cylinder, knitting the individual needles at every other
feed. This way, two 1/1 rib fabrics are knitted together locking each
other at their sinker loops for the interlock construction. Both sides
of the fabric resemble the face of the plain fabric, which explains its
often used name of “double jerseyâ€Â.
The construction
of purl fabrics are represented .on graph paper, using   , for
the plain stitch and     for
the purl stitch. Some of the simplest purl designs, which have the same
type of stitch in the individual courses, can also be designated with
fractions, the number in the nominator showing the plain courses and
the denominator indicating the purl courses. Basket purl designs have
groups of plain and purl stitches alternating in a checkerboard
arrangement.
Tuck and Miss Stitch Fabrics
Colour design
effects and surface texture appearances are knitted on weft knitting
machines with selected needles forming tuck and miss stitches in
combination with plain, rib, and purl stitches.
The tuck stitch
is formed with the needle holding its previously knitted stitch and a
new yarn is also placed under the beard of the spring bearded needle or
into the hook of the latch needle. Tuck stitches can be formed on a
needle for several consecutive courses, depending on the size of the
needle hook, the diameter of the yarn, the strength of the yarn, and
the distortion of the stitches. Tuck stitches can be knitted in a
course on needles next to each other, depending on the fineness of the
machine, the length of the float. and the intended use of the fabric.
The selection of the number of tuck stitches will control the increased
width, thickness, and weight of the fabric. The tuck stitch appears in
fabric as Ù, or Ç,
and it is shown on design paper by placing a dot ( Â Â Â )
into the square representing the stitch.
Latch needle
machines can form tuck stitches, in one of several ways. Tucking in the
hook, illustrated in Fig. 16. is the easiest and most common method.
The needle is raised only far enough to take the new yarn into the
hook. While the old stitch does not move below the latch to the blade
of the needle. Tucking with short and long latches is illustrated in
Fig. 17, which can be arranged in such a way that at the clearing
position B the stitch of the short latch needle will go to the needle
blade to form a plain stitch, while the stitch of the long latch needle
stays on the latch for a tuck stitch in the hook. During the next
course the clearing cam is set high for both the short and long latch
needles to clear their stitches onto the blade of the needle, and both
form plain stitches. Tucking on the latch is illustrated in Fig. 18,
which is necessary in machines without adjustable, moveable, or
inter-changeable clearing cams. The needle follows the movement of
forming a knitted stitch, except at the cast, off D the new needle loop
is not pulled through the previous stitch. This way, the old stitch
stays on the latch, and during the subsequent clearing both the old
stitch and the newly formed tuck stitch move below the latch at B1 to
be cast off by the new yarn fed into the hook of the needle. Tucking
behind the latch is illustrated in Fig. 19. This is commonly used to
feed selected yarns which appear only on one side of the fabric. The
yarn for the tuck stitch is fed behind the latch after the dial needle
clears its old stitch, then the regular yarn is fed in the needle hook
and the old stitch is cast off together with the new tuck stitch by the
new knitted stitch. Tucking with a missing latch is used in purl
machines as it is illustrated in Fig. 20. The needle forms the plain
stitches with its latch the ordinary way, while the latchless hook side
is held by the jack. Then the needle moves to the opposite needle bed
and it cannot cast off the old stitch because the lack of the latch
allows the stitch to return into the hook next to the newly fed yarn.
Finally the needle moves back into its original needle bed and the new
plain stitch casts off the previously formed plain and tuck stitches.
The miss stitch,
also known as welt or float stitch, is formed when the needle holds the
previously knitted stitch and the new yarn misses the needle during
clearing and feeding. Miss stitches can be formed on a needle for
several consecutive courses, and in the same course on needles next to
each other. The miss stitch appears in the fabric as Ú, or È, and it is
shown on design paper by leaving the square blank () representing the
stitch. Comparing tuck and miss stitch fabrics with the same general
face design, the miss stitch is preferred to the tuck stitch in colour
effects, but the tuck stitches make the fabric wider, thicker, and
heavier. Viewing the weft knitted fabrics from their face side, the
position of the tuck and miss stitches are partially hidden behind the
plain stitch, but they are closer to the viewer than the rib and purl
stitches, illustrated in Figs. 21 and 22.
An old fabric
name has reappeared to become a collective description for many rib
fabrics that have a pleasing face and back under the term of double
knit. Actually all rib and purl fabrics, also some plain constructions,
have reversible characteristics to use either side for the outside of a
garment.
The most popular
double knit construction is the Swiss Double Pique. illustrated in Fig.
24. The appearance of the face and back of the fabric will change
according to the ratio of the length of yarn supplied between the
knitting feed where all the cylinder needles knit with every other dial
needle, and the feed knitting the alternate dial needles only. Other
contributing factors to the characteristics of the fabric are the
timing of the dial needles relative to the cylinder needles, the height
of the dial over the cylinder, the tension on the yarn, the width of
the fabric spreader and the tension on the fabric takeup.
There are many
variations of the double pique fabric to produce a double knit type of
construction with rib or needle between needle gaiting, and interlock
or needle opposite needle arrangement. In addition to the Swiss Double
Pique construction, the popular fabrics include the French Double
Pique, Milano Rib, Ottoman Rib, Single Pique, Punta di Roma, and many
others with surface or texture effects and multi-colour design
appearances.
Dyeing, Bleaching and Printing
Dyeing has been
practiced for thousands of years, and among the earliest peoples who
dyed their garments were the Chinese and the American Indians. The dyes
that were available to the ancients were produced naturally by plants
animals. There were two principal colours: blue indigo, which
originated from a plant, red kermas, obtained from the dried bodies of
an insect.
Probably the
most interesting documents on dyeing have been recovered in Egypt, the
‘‘Papyrus Graecus Homkensis’’, preserved at Upsala, Sweden, and the
‘‘Leyden Papyrus’’, preserved at Leyden, Holland. The former contains
seventy recipes dealing with the cleaning, mordanting, and dyeing of
wool, in which the following dyes are mentioned: alkanora (red),
safflower (yellow and red), kermas (red), madder (red), and woad
(blue). The art of dyeing was well developed, following the same
principles that underlie modern dyeing.
The discovery of
America added different dyewoods such as logwood, redwood, and fustic
to the available dyes. The most important of the dyewoods, and the only
one still used on a large scale, is logwood. The dye is extracted from
the blood-red wood of the campeachy, a large tree which grows
abundantly in the West Indies and Central American countries. The dye
is sold today in the form of logwood extract.
In addition to
dyewoods, the Spainards found in Mexico an insect, which produces
cochineal, a beautiful scarlet with a tin mordant which has replaced
the less attractive kermas red. There is every indication that the more
cultured inhabitants among the Indians of Middle America and South
America used these colours to a great extent. Garments and blankets
found is the Inca graves in Peru and Chile, dating from before the
Spanish Conquest, are examples of the various dyes used such as purple
and indigo. The Incas were able to apply these dyes on wool as well as
on cotton.
Modern Dyestuffs
The whole art
and practice of dyeing was completely revolutionized in 1856 by the
discovery of the artificial dye mauve (from the French name of the
violet-coloured mallow flower). The discovery was made accidentally by
a young English chemistry student. William Henry Perkin.
When his
discoveries were published, chemists all over the world began to
manufacture and experiment with the new dye. Factories were started all
over Europe. From the beginning, the manufacture of coal-tar dyes, and
more recently their allied compounds, has become one of the most
important and most profitable of all chemical industries.
Since that time
not a year has passed without several new dyes being put on the market
by some of the great dye concerns. In more recent years whole new
classes of dyes such as fiber reactive, disperse, cationic basic,
neutral dyeing premetalized have been discovered and produced for the
dyeing of the natural and new synthetic, hydrophobic fibers.
The large dye
concerns furnish the trade with excellently madeup sample shade cards
showing actual dyed wool samples in the form of loose wool, yarn, or
pieces and the shades and strengths offered by the company. With the
trends towards pastel shades, several dyestuff manufactures have
improved their shade cards by including swatches, which show the shade
produced by each dye ranging from a pastel through deep shades.
In addition to
shade cards, a number of the large manufactures also supply manuals,
pamphlets and technical bulletins describing improved methods of
application and the fastness of each dye when subjected to a large
variety of tests.
Designation of Dyes
Trade Names
In these sample
cards and manuals, the dyes are grouped according to the class of
application. In each class of dyes they are arranged according to the
colour and their relative shades beginning with yellow, orange, red,
violet, blue, green and black. For proper identification of a dye the
manufacture gives each dye a trade name. The trade name usually bears a
reference to the class, property, and colour of the dye, as ‘‘Acid
Light Red G’’, or to its chemical composition as “Anthraquinone Blue Bâ€Â
or “Alizarine Yellow GGâ€Â. However, in many cases it is simply an
arbitrary and non-descriptive name assigned by the manufacturer or the
jobber.
Letter Designations
The letter or
letters following the name generally refer to the shade, for instance,
B for blue, R for red, Y or G for yellow (German gelb).
Methyl Violet is sold in brands running from 6B to 6Râ€â€that is, from a
shade very close to blue with types becoming increasingly redder to a
bright reddish-violet shade. Sometimes the letter refers to a fastness
property such as Alkali Green 2G to indicate fastness to Alkali or Red
I, where the L, is used to indicate good fastness to light; milling
fast where the word milling is used to indicate good fastness to
fulling or milling.
In other
instances the letter refers to its class such as Wool Green S or Acid
Blue both of which means German Sauer or applied
from an acid bath. Quite frequently letters have no significance and
are used merely to identify a type supplied by a specific manufacturer.
Also, it should
be remembered that letters used for a specific dye can be misleading
since one manufacturer’s Yellow 3G may be redder in shade than a
competitor’s Yellow 2G or G.
Abbreviations and Percentages
In addition to
the letter designations there are such terms as cone and
extra cone., which are abbreviations for the concentration
of the dyes. These terms were further broadened by the addition of a
percentage figure such as 100 per cent or 125 per cent, meaning in this
case that the 125 per cent dye is 25 per cent stronger in its colour
value than the 100 per cent. During World War II most manufacturers
increased their dye concentration in order to conserve packing
material. In buying dyes the concentration factor is one of the most
important things to consider, because the same dye may be sold in
various concentrations and the prices are based accordingly.
In more recent
times concentrations and terminology have changed very greatly so that
a blue called extra conc. may be weaker than one called conc. or one
without any letters to indicate its strength. The true money value of a
dye is dependent upon its strength and performance and not necessarily
by price.
Index Numbers
The Colour Index
originally prepared by Rowe and published in 1924 by the British.
Society of Dyers and Colourists has been revised jointly by the Society
of Dyers and Colourists and the American Association of Textile
Chemists and Colourists. The new revision lists a very large number of
dyes, many discovered and introduced within the past thirty years.
One of the main
functions of the Colour Index is to correlate the different names for
the same dye. For example, colour index number 31 refers to the dye
“Amido Naphthol Red G†which is manufactured by most dye companies.
This same product is sold under many different trade names. By this
numbering system, a dyer is able to find a specific manufacturer’s
trade name for dyes, which are on the market.
The Colour Index
is today the standard reference on dyes used throughout the world and
contains a vast amount of information of value to dyers and textile
chemists.
Theory of Dyeing
The wool fiber
has an affinity for almost all natural and synthetic colouring matters.
This becomes apparent when wool is dipped into an aqueous or solvent
dye solution. The affinity varies with differences in the chemical
constitution of the dye and consequently many methods of application
are used.
The mechanism of
the process of dye adsorption and diffusion into the wool fiber is not
entirely understood by the chemists. A number of different theories
have been advanced to explain the process as already discussed in
Volume 1 of this book, pp. 261-264, but none of the theories proposed
to date completely satisfy all of the known facts about wool dyeing. A
particularly exhaustive study by Delmenico and Peters suggests that the
Donnan theory is the best approach. Others claim the Gilbert-Rideal
treatment is the more attractive.
Wool Dyes
Wool dyeing may
be carried out on loose material, slubbing, yarn and piece. Selection
of dyestuffs and of the dyeing procedure to be employed is largely
decided by the end-use of the finished goods and the state of
manufacture at which dyeing is carried out. The extensive ranges of
dyestuffs available from manufacturers today make it possible to
produce most shades with the fastness properties required, provided
their cost is acceptable to the customer.
A new
classification of dyes, which are applicable to wool, was given in the Ciba
Review by Kehrer, each class representing a virtually
complete range of colours. To the five groups listed by Kehrer a sixth
has been added.
  Â
1. Acid
dyes (applicable from a strongly, moderately, or weakly acid dyebath).
  Â
2. Chrome dyes
(applied by the chrome mordant, afterchroming. and one-bath methods).
  Â
3. Chrome
complex dyes applied from a strongly acid dyebath.
  Â
4. Neutral or
weakly acid dyeing chrome or other metal-complex dyes.
  Â
5. Vat
dyes.
  Â
6. Reactive dyes.
Acid Dyes
The ‘‘acid
dyesâ€Â, mostly sodium salts of sulfonic acids, are dissociated to the
free colour acids in an acid dyebath. In view of the amphoteric nature
of wool, it is a safe assumption that the colour acids combine with the
basic groups of the wool protein to
form saltlike compounds. Besides this relatively simple reciprocal
effect, other, considerably more involved reactions take place owing to
the complex character of the wool fiber.
It is likely,
for instance, that following on the process of salt formation other
reactive groups in the dyestuffs combine with formation other reactive
groups in the dyestuffs combine with certain further groups of atoms in
the wool. The actual dyeing mechanism is no doubt seen in its true
light if one regards the wool surface as a semi-permeable membrane
placed in a liquor. Only certain ions pass through the membrane, i.e.,
dyestuff ions diffuse from the dyebath into the fiber. In all
probability, the size and the shape of the dyestuff molecules exert
some influence on the manner in which diffusion takes place.
According to
Elod, the reactions involved in dyeing wool with acid dyes may be
summarized as follows:
   1. Adsorption of the dyestuff anion
onto the fiber surface.
   2. Diffusion of the anion through the
cortical layer.
   3. Chemical reactions within the wool
fiber (salt formation and other types of combination).
The affinity of
water-soluble acid dyes is a function of the temperature and the pH of
the dye liquor. Dyes, which exhaust onto the fiber slowly are applied
with strong acids such as formic or sulfuric acid; for dyes which have
a high rate of exhaustion the use of acetic acid (which is weaker) is
preferred. Alternatively, an ammonium salt, such as ammonium acetate or
ammonium sulfate, which dissociates at the boil and yields the
corresponding acid may be used. Normally Glauber’s salt is added which
acts as a control for the dye adsorption.
Individual acid
dyes have different affinity for wool. Some exhaust completely from an
acid dyebath and are fast while other dyes exhaust only in part and can
be partly removed from the fiber by the Glauber’s salt contained in the
dyebath. The latter dyes level particularly well as the result of this
two-way process and are sometimes known as “levelling dyestuffs†on
that account.
The acid dyes
which exhaust rapidly and completely onto the fiberÂ
and are stable to Glauber’s salt generally given unlevel
dyeings when applied with strong acids. The general rule holds that
dyestuffs with marked affinity for wool exhibit poor levelling
properties but good fastness to water, while dyes with poor affinity
for wool level well but are not fast to water.
Acid dyes
applied from a strongly acid dyebath in part have good fastness to
light and are used for dyeing dress goods, carpet yarns, certain
upholstery materials and the like, which do not required a high degree
of wet fastness.
The use of dyes
applicable from a moderately acid dyebath is indicated when a
substantial degree of fastness to water and washing is demanded. Shades
produced with such dyes even with-stand very light milling.
The weakly acid
dyeing dyes, also known as milling colours, which have correspondingly
poor levelling property possess good fastness to water, seawater, and
washing, and are fairly stable to moderately severe milling. The field
of application of these dyes includes weaving, machine, and hand
knitting yarns, swimsuits and bunting.
Dip to the
present the normal dye procedure was to wet out the material in bath
with the liquor ratio to the weight of the wool between 20 and 50 to 1.
The starting temperature is set between to 100ºF (20-40°C). The
dissolved dye is added through a filter bath the process started by
running the piece goods or circulating the liquor for 10 min then
adding the salt and acidsâ€â€then opening the steam bringing the bath to
boil within an hour and boil for 1 hour. When the proper shade is
reached the bath is slowly cooled down with fresh water to room
temperature, rinsing off any excess dyes and cooling the material at
the same time. To correct the shade the necessary amount of dye, which
cools well, can be added to the boiling bath and needs an additional 20
min of boiling.
Modern methods
of application call for periodic pH measurements as a means of assuring
better reproducibility from batch to batch. Dyeings should actually be
run by pH control rather than by percentages of acid on the weight of
materials. Such procedures make it possible for the dyer to know before
the lot is started that the acid has been added and the amount is
correct. Thus, differences in alkaline or acid content of the wool,
longer liquor ratios, variations in hardness and other variables are
controlled by adjustment of dye baths to definite pH before the dyeing
is started.
A second pH
reading may be taken when the temperature of the dye bath reaches the
boil. Such controls reduce redyes, speed up dyeing cycles, saving time
and money.
Correcting acid
colour dyeings. For various
reasons, the dyed material may be off-shade, meaning that the dyer has
not properly matched the standard or desired shade. Under these
conditions the lot must be worked longer in the machine, redyed or
stripped and redyed without spoiling the appearance of a fabric or
damaging the wool by prolonged processing.
As a general
rule acid dyes will level readily at the boil under the correct dye
bath conditions. If the lot is uneven due to non-uniform distribution
of the dye, an addition of Glauber’s salt and or acid and longer time
at the boil will produce the desired levelness. Occasionally a feed of
ammonia may be required to cause desorption of the dye. The desorbed
dye can then be exhausted uniformly by careful additions of
well-diluted acid.
When the shade
is too dark and off-shade, it is often good practice to correct the
shade by boiling dyed and undyed materials together in a fresh bath
containing Glauber’s salt and acid. During the boiling period dye will
be removed from the dyed pieces and absorbed by the undyed pieces. Dyes
can be added to this bath to adjust the lot to the desired shade.
If the desired
shade is bright and the shade of the lot is quite dull, there is little
that can be done to produce a brighter shade. The longer such a lot is
boiled the duller the shade becomes. Pastel blues and baby pinks can be
brightened by the addition of an optical bleach in a fresh bath.
If none of these
corrective measures produce the desired result the lot should be dyed
into a darker shade or black.
Correcting
milling colour dyeings. Milling dyes
have much greater affinity for the wool than they have for the dye bath
and therefore once they are absorbed by the wool they are difficult to
remove. Prolonged boiling in the dye bath rarely ever levels an uneven
lot sufficiently to make it satisfactory and therefore whenever
possible, the lot should be dyed black or dark shade immediately. When
this is not possible, a fresh bath containing 1-2% ammonia and 20%
Glauber’s salt may be used. An addition of a good non-ionic
surface-active agent sometimes causes sufficient desorption and
redistribution of the dye to produce a level result.
Stripping with
hydrosulfite or sulfoxylate may destroy sufficient dye and produce a
level bottom so that it is possible to cover by redyeing.
Chrome dyes
As the acid dyes
satisfy medium fastness requirements only, they may have to be fixed
more durably on the fiber. This is accomplished by bringing about
“colour lake formationâ€Â, that is, the dyes are converted into insoluble
metal complexes.
Metal atoms can
be incorporated in an azo dye if the latter exhibits a certain
molecular structure. The metal introduced into the molecule can be made
to combine, through primary or secondary valencies, to form an inner
complex salt, five-and six-membered ring systems resulting in the
process.
In practice, the
goods are dyed and after-chromed, that is, after-treated with potassium
dischromate or sodium dichromate and acid, or the dyebath is set with
so-called Synchromate (Metachrome) mordant, which decomposes during
dyeing and liberates the chromic acid which has the lake-forming
property. This one-bath method calls for dyestuffs which exhaust evenly
from a neutral or weakly acid liquor and do not form an insoluble
colour lake in the dyebath itself. The earliest method by which the
wool was premordanted with potassium dichromate and sulfuric acid is no
longer in favour owing to the prolonged boiling period required by
prechroming and dyeing.
Dyeings produced
by the afterchrome and one-bath methods exhibit fastness properties of
high order. They are distinguished by fastness to water, washing and
milling, even in white styles with coloured effects and possess good to
very good fastness to pressing and decatizing. This makes chrome dyes
specially suited for goods that have to be subjected to milling such as
uniform and coating materials, and hats.
Correcting
mordant colours. Because of the
good fastness properties of these mordant colours, it is extremely
difficult to correct shades that are too dark or streaky. For this
reason it is important to start the dyeing operation at the proper pH
so that the dye will exhaust slowly and be absorbed uniformly.
Microscopical studies have shown that the dye is absorbed first as the
acid or unchromed form in metachrome and bottom-chrome dyeings. This
allows the dye to redistribute itself and level as an acid colour
during the time the temperature is being raised to the boil. When the
boil is reached, chromation of the dye takes place more rapidly and
there is less chance of levelling thereafter. Once the insoluble
chromium complex of the dye is formed, little if any levelling can take
place.
As a general
precaution it is wise to keep the shades on the light side and to use
small amounts of level dyeing acid colours for matching. When the shade
is too light, the dyeing procedure has to be started over again with
chrome colours as with undyed goods.
A rather large
number of chromable dyes can be demetalized, (returned to their
original state) and will then level as though they were acid dyes. When
such fabrics are rechromed the spots do not reappear and the fabrics
are generally level and satisfactory. A method of levelling by the
simultaneous demetalization of the metal dye complex and the removal
and sequestration of metallic impurities has been developed. The method
found to give the best results for the greatest number of chromable
dyes tested was a 2-hour boil in a 40:1 liquor ratio bath containing 8%
oxalic acid, 20% anhydrous sodium sulfate, and 2% of a sequestering
agent (tetrasodium ethylenediamine tetracetic acid) based on the weight
of the material.
Experiments have
shown that desorption and redistribution of dye occurs during this
treatment and thus levelling is promoted in raw stock, slubbing, yarns
and piece goods.
Metal-complex Dyes
Dyestuffs
chemists succeeded in devising a simpler method of dyeing wool by
incorporating the metal required for lake formation in the dyestuff
molecule: they created premetallized azo dyes such as the Neolan and
Palatine Fast dyes. In these chrome-complex dyes the chrome is combined
with a sulfo group to form an internal salt. The chromium atom is not
completely saturated and combines with the amino groups of the wool to
produce permanent fixation of the dye on the fiber. The Neolan dyes are
derived from sulfonated azo dyes, one azo dye molecule containing one
chrome atom. For example, see the chemical formula for C.I. Acid Blue
158.
The introduction
of the chrome-complex colours simplified dying procedures and
eliminated the need for chrome salt, which attacks the wool molecule. A
further advantage is seen in the superior fastness properties of the
chrome-complex dyes as compared with metal-free acid wool dyes.
These dyes
require a strong acid dyebath, 6-8% sulfuric acid, which has an adverse
effect on the physical and chemical properties of the wools. In Table 1
are given the breaking strength, the flex abrasion and the alkali
solubility data of four worsted pieces dyed with 1% Palatin Fast Tan
IWP and 8% sulfuric acid, dyeing time 1½ hr to boil, 2 hr boiling.
These data were obtained during the Princeton Wool Research Project and
reported by Wakelin and Von Bergen.
There is no
significant differences in the properties of the four pieces. The
breaking strength loss is around 20%, whereas there is a decrease of
over 50% in the abrasion resistance. A clear indication of the chemical
damage is the three-fold increase in the alkali solubility. This is
probably the result of a relatively small amount of peptide hydrolysis
produced under these conditions.
Correcting
chrome-complex colour dyeings. This class of
dyes can be levelled rather easily and whenever possible the lot should
be levelled in the original dye bath. If the pieces appear uneven or
skittery it may be due to the presence of insufficient sulfuric acid.
Take a pH reading and if the bath has a higher pH than 20, a further
addition of sulfuric acid should be made. The lot should be boiled 30
min and examined again. If the lot is still uneven add 1-3% of a good
levelling agent and boil 30 min longer.
Redyeing,
however, will reduce the tensile strength and harshen the hand.
Special Wool Finishes
Introduction
The most
important developments that have occurred since 1950 are in the field
of improved serviceability such as Wash-and-Wearâ€â€Durable Creasing and
Permanent Press. The advent of wool and synthetic fiber blends in
fabrics which could be permanently creased and pleated was the stimulus
for the research work on finding methods whereby all wool fabrics could
be given similar properties.
Treatments were
developed for wool such that pleating or other fabric deformation could
be obtained of a stability equal to that of the thermoplastic synthetic
fibers. Similar processes were applied as a flat-setting procedure
yielding fabrics of improved crease resistance.
In all these
treatments, recognition has been given to the important role of fabric
structure on the ultimate performance of the finished garment. In
addition, the treatments have been utilized for special finishes, such
as lustering, embossing, and permanent stretch, which have resulted in
a range of fabrics not only of new design but of higher utility and
beauty.
The further
successful development and application of fiber utilization, fabric
design, and finishing processes to the production of wool garments that
are of improved wearability has become of the vital goal of the wool
industry.
Another area
which has proved fertile for development is that of multi-purpose
treatments. Sironizing is such as process where flat setting is carried
out on shrinkproofed wool fabrics. The incorporation of moth proofing
agents in either aqueous or solvent bath of a shrinkproofing treatment
will convey durable moth resistance to techniques very similar to those
used conventionally for pressing trousers or pleating skirts. A
challenge was thus presented to wool interests to devise, and introduce
on a large scale, methods for producing similar effects in all-wool
garments.
The first
industrial process for producing these effects was the Immacula finish
invented by Speakman and described by Speakman. It is based on the use
of sodium bisulfite, a process of presensitizing the wool fabric by
treatment for 15 min in a cold solution of 2-3% sodium bisulfite and
the permanent creases desired are obtained when the garment is steam
pressed in tailoring.
The Si-Ro-Set
process, an Australian development by Commonwealth Scientific and
Industrial Research Organization CSIRO, was introduced in 1959. The
principle of permanent creasing or pleating is the wool, while held in
the required form, is given a permanent set by the simultaneous
application of heat, water and a chemical reducing agent. In the
Si-Ro-Set process, an aqueous solution of a reducing agent is sprayed
on to the appropriate areas of the finished garment and steaming
carried out immediately while the fabric is still wet. The reducing
agent can be ammonium thioglycollate, sodium bisulfite or
monoethanolamine sulfite (MEAS) and from the technical point of view,
it is immaterial which reagent is used. Pardo suggested the use of MBA (N,
N’ methylene bisacrylamide). In practice, the choice of
chemical depends on the availability of a suitable, stable concentrate,
the price, and the service given by the chemical supplier. Because of
these factors, different reducing agents are used in different
countries, and even in different areas within a particular country.
Other studies
covering the development of methods for durable creases were made by
Davidson. They found that the addition of Urea in concentration of
6-12% increased substantially the crease retentive properties imparted
by the bisulfite, Cednas made a more fundamental study of different
stages in the setting process using concentrated solutions of
urea-bisulfite. After bisulfite or MEAS (low concentration) steam
setting, no careful rinsing is required. By urea-bisulfite or MEAS
(high conc.) setting, rinsing is necessary, and the cloth must be kept
in a flat state.
The Si-Ro-Set
process was first used on a large scale in Australia and, on a
population basis, more permanent creasing and pleating of wool garments
(more than 1 million annually) takes place there than in any other
country. The use of the technique is however increasing continually in
USA, Japan, and Europe.
The details of
the technique as used in the USA by manufacturers of men’s slacks and
suit trousers are given in the WB-4 report of the Wool Bureau Inc. In
the United States in 1967, approximately 5½ million slacks and trousers
have been treated.
An alternative
method to the Si-Ro-Set process is the technique of “presensitizingâ€Â
developed in the USA by the Wool Bureau Inc. The reducing agent is
applied to the fabric in the finishing mill and the permanent creases
or pleats are then produced, after the garment has been made, by adding
water just before steaming. The relative merits of the two procedures
are best compared by considering separately the manufacture of trousers
and skirts.
For trousers,
the Si-Ro-Set technique appears to be a more useful way of producing
permanent creases than the use of presensitized fabrics. Here, the
extra cost of presensitized suit fabrics is wasted for the cloth which
is made into jackets, while the suggested use of damp cloths on the
press as a means of adding the requisite amount of water to the
trousers is very uncertain in practice. In order to obtain the best
results consistently with presensitized fabric, it is necessary to
spray a minimum of 20% water on to the trousers immediately before
pressing. The men’s clothing industry has, therefore, generally
preferred the Si-Ro-Set process.
For permanent
pleating of all-wool skirts presensitized fabrics are preferred. The
required pleating technique is described in WB-5A report of the Wool
Bureau Inc.
The actual
technique of presensitizing is very simple. Generally, the fabric is
impregnated with a 2% solution of sodium bisulphite, then tentered at
the usual temperatures and given a light open decating in the normal
way. Other procedures used involve impregnation with monoethanolamine
sulfite (MEAS) (WB-5 report of the Wool Brueau Inc.), or the treatment
of cloth with either of the reducing agents in a dolly washer or
winch-dyeing machine, then centrifuging or squeezing before drying.
The disadvantage
of these particular creasing and pleating methods is the necessity for
free water to be present during steaming. To overcome this disadvantage
Cook and Delmenico found a dry setting technique based on the use of a
reducing agent urea combination.
Pretreatment
consists in padding the otherwise finished fabric through a solution
containing the reagents and a wetting agent so that the wool retains 5%
urea and 2½-4% diethanolamine as the carbonate. This is followed by
tenter drying and, preferably, hydraulic pressing. At a later stage,
the fabric of normal regain can be creased, pleated or otherwise set
simply by steaming.
Another
technique is the setting of creases or pleats in all wool fabrics by
high pressure steam without the use of reducing chemicals. Davidson
found that durable creases in all wool trousers can be produced by
steaming the neutral fabric for 10 min at 120ºC (248ºF). The loss in
breaking strength is around 4% Kopke developed a method for producing
permanent pleats by steaming the dry fabrics in an autoclave at 132ºC
(270ºF) for 25 min. The degree of setting is influenced only slightly
by variations in cloth construction, finishing routine, pH and moisture
regain. However, cockling in the pleated material is found to be
dependent on the moisture regain of the cloth measured before pleating
and setting. The cockling is caused by hygral expansionâ€â€as higher the
moisture regain, the less cockling. Most fabrics were found to be free
of cockling when conditioned at 65% RH.
The high
temperature setting causes a yellowing of the wool, which may change
the shade of pastel and bright blue colours.
The reduction in
the breaking strength found in eight panels was 11% for the dry
strength, and 25% for the wet strength.
Flat Setting
The principle
used for setting wool fabrics increases or pleats has been applied to
the setting of full pieces of fabrics as a new finishing operation.
This new finish is called “flat-setting†and by now has been given
about a dozen different trade names round the world.
Lipson in recent
papers give the following details on this wool finishing procedure.
Flat-setting of wool fabrics with sodium bisulfite solution results in
an improved wet wrinkle-recovery, which helps to maintain a smooth
surface appearance after wetting and air-drying. Flat-setting combined
with shrink-resist treatments therefore gives a method of producing
washable, minimum-iron fabrics. Flat-setting also gives a luster and
smooth handle to the fabric, and flat-set fabrics are easier to tailor
than normal fabrics. For these last-named reasons, flat-setting is
becoming a common finishing procedure in many countries.
As with all
chemical treatments of wool, flat-setting must be carefully controlled
for satisfactory results, free from undesirable side effects, to be
obtained. The recommended method for flat-setting is that the fabric is
impregnated with a 0.5-1.0% solution of sodium bisulfite and streamed
for 2-5 min. The pH of setting is important. Below pH 4.5, the degree
of setting is usually inadequate, and, above pH 6.0, stiffening of
fabrics and yellowing of the wool can occur. The pH of an aqueous
extract of the fabric should be in the range 4.5-6.0 before
impregnation with bisulfite takes place. This is necessary, even though
the pH of the bisulfite solution is about 4.5, since a simple
impregnation does not necessarily bring the pH of an aqueous extract of
the fabric to this value. For example, the pH of an aqueous extract of
a fabric may be lowered only from 6.8 to 6.2 by flat-setting, whereas a
fabric whose aqueous extract is pH 9.2 can still have an extract of pH
8.0 after setting with sodium bisulfite.
Setting with Monoethanolamine Sulfite Solutions
When
monoethanolamine “sulfite†or “bisulfite†solutions are used
industrially for flat-setting, adjustment of fabric pH prior to
impregnation is particularly important in this case, since the
“sulfite†solutions are prepared with pH values of 6.0-7.0.
If
concentrations of reagents and pH adjustments of fabric and solutions
are accurately controlled, results obtained with monoethanolamine
sulfite-bisulfite solutions and sodium sulfite-bisulfite solutions are
identical.
In practice, the
technique can cause difficulties unless the mill is reorganized to
carry out the process on a reasonable scale, when it can become very
cheap and simple. The only technical problem in industrial application
is the steaming of the wet fabric, since this means that the wrappers
on the blowing machines quickly become wet. Most mills carrying out a
lot of flat-setting have at least two wrappers available for each
machine, scouring and drying them at regular intervals, while some use
specially woven lightweight wrappers made from synthetic fibers.
Flat-setting was
first used industrially as part of the Sironizing processing. In this
case, flat-setting is carried out on shrinkproofed wool fabrics to give
the cloth the ability to retain a smooth appearance during washing and,
in Australia, this is still the main use of flat-setting. Flat-setting
is a very effective way of crabbing and can be used to simplify and
shorten finishing routines. Some European mills now flat-set fabrics
straight from the loom, then scour, tenter and give a light steaming.
This gives fabrics that are quite acceptable for many uses and, when
the necessary reorganization has been carried out, can significantly
lower costs.
Flat-setting is
now a common finishing technique in the U.K. and Europe, being used
mainly because of the luster and improved handle which is given to
worsted fabrics.
Sutcliffe found
that the combination of flat-press characteristics with water
repellency assists the resistance to wrinkling.
The padded
fabric with a 70% pickup was steamed in a semi-decator for 5 min (steam
pressure 80 lb) and vacuum extracted for 7 min and then dried. After
drying the cloth was finished normally ending up with a treatment on
the semi-decator for 3 min steam, 5 min vacuum.
Permanent Press
The ability of a
garment to remain pressed or in other words has a lasting good
appearance is a very desirable attribute. This has become an important
feature. Today’s concept of permanent press in garments involves the
smooth pressed condition, which, together with sharp creases and
pleats, last through repeated washings and tumble dryings so that the
garments may be worn without ironing. Other terms used for this feature
include durable press, press free, washable non-iron, wash-and-wear,
and minimum care.
Permanent
pressed wool fabrics as reported by Farnworth can be produced by
combining any chemical shrinkproofing treatment with a flat setting.
Such fabrics were first introduced in Australia, licensed under the
trade name Sironized. Today such fabrics are produced on an increasing
scale worldwide based on continuous processes as described under
shrinkproofing and flat setting.
Lustering of Wool Fabrics
The demand for
wool fabrics that have a high luster is not new. It is well established
that careful selection of raw materials, such as luster wools and
specially hair fibers such as Mohair and Alpaca still play an important
part in this field. Of the blends the oldest to achieve a permanent
luster are the silk-wool combinations. In many of the modern wool-type
fabrics good luster effects are obtained by the addition of lustrous
man-made fibers.
In recent years
as brought out in the literature, there has been an increasing amount
of attention devoted to the production of lustrous wool fabrics. The
particular emphasis at the present time is placed on the luster
produced during the wool finishing, with the requirement that these
finishes should also be permanent. The latter feature has posed, and
still does, particularly tough problems for the cloth finisher. High
luster finishes on woollens and worsteds have been readily attainable
in a variety of ways, but to make such finishes stable to heat and
steam treatments, such as they have to undergo at the hands of the
spongers and garment manufacturers, has perplexed many wool
manufacturers.
Luster on Pile Fabrics
Luster on pile
fabrics in finishing can be obtained in two ways: Mechanical process
such as teazle raising and laying the surface fibers in one direction
and specific methods to flatten the cloth such as wet decating,
blowing, rotary and hydraulic pressing, previously discussed, are ways
to obtain appreciable luster. Chemical processes in the main, are
related to mechanical processes such as raising, wet decating and
blowing but combined with a pretreatment of the cloth with chemical
setting agents such as sodium sulfide or monoethanolamine bisulfite.
The biggest
change in the finishing of luster pile wool coating fabrics has come
about through the adoption of the method and machinery developed years
ago by the fur industry to convert sheep-skins into the fur known as
mouton, as stated by Frishman. The firm, which pioneered in the
development of the machinery and a new knitted deep pile fabric of man
made fibers, was the Borg Electronics Corporation. The wool finisher
was very slow in adopting this method simply because of the low
permanency of the pile. But today there is hardly any wool finishing
plant without such a machine. The process is known under various names
such as “electrifyingâ€Â, “polishingâ€Â, “ironingâ€Â, electropolishing,
“glossingâ€Â, or “lustering.â€Â
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