Ferrous materials have made a major contribution to the development of modern technology; they span a tremendous range of properties and applications. Reflecting the industrial practices, the information provided here offers easy access to reliable processes involved in the manufacturing of Steel products like Steel Bars, Wires, Tubes, Pipes, Sheets etc that proves to be the backbone of construction and automobile industries booming worldwide.
The work closes the gap in the treatment of steel and cast iron. Each chapter takes into account the gradual transitions between the two types of ferrous materials. It demonstrates that ferrous metal and steel are versatile and customizable materials which will continue to play a key role in the future and also covers the operations performed on ferrous metals for converting them into a commodity.
The book provides a full characterization of steel, including structure, chemical composition, classifications, physical properties, production practices of different steel products, processing of ferrous metals and so on. It will prove to be a layman’s guide for the entrepreneurs who are willing to invest in the ventures related to Iron and Steel Industries, as it contains information related to processing of ferrous metals and production practices followed in Steel products manufacturing units. The text discusses the importance and objectives of processes and material used for the production of disposable products. Many examples have been provided to illustrate the concepts discussed.
The topics covered in the book are: Casting of Ferrous Metals, Heat Treatment of Ferrous Metals, Stamping Process of Ferrous Metals, Forming Process of Ferrous Metals, Machining Process of Ferrous Metals, Joining Process of Ferrous Metals, Production of Stainless Steel Wire, Production and Fabrication of Steel Bars, Steel Tube & Pipe, Stainless Steel Sheet and Different Grades of Stainless Steel.
OF FERROUS METALS
Metal casting process
begins by creating a mold, which is the ‘reverse’ shape of the part we
The mold is made from a refractory material, for example, sand. The
heated in an oven until it melts, and the molten metal is poured into
cavity. The liquid takes the shape of cavity, which is the shape of the
It is cooled until it solidifies.
Sand casting uses
natural or synthetic sand (lake sand) which is mostly refractory
called silica (SiO2). The sand grains must be small enough so that it
packed densely; however, the grains must be large enough to allow
during the metal poured to escape through the pores. Larger sized molds
green sand (mixture of sand, clay and some water).
Expendable-Pattern Casting (Lost foam
The pattern used in
this process is made from polystyrene (this is the light, white
material which is used to pack electronics inside the boxes).
is 95% air bubbles, and the material itself evaporates when the liquid
poured on it.
The pattern itself is
made by molding - the polystyrene beads and pentane are put inside an
mold, and heated; it expands to fill the mold, and takes the shape of
The mold is made by
mixing plaster of paris (CaSO4) with talc and silica flour; this is a
white powder, which, when mixed with water gets a clay-like consistency
be shaped around the pattern (it is the same material used to make
people if they fracture a bone). The plaster cast can be finished to
good surface finish and dimensional accuracy.
One advantage of vacuum
casting is that by releasing the pressure a short time after the mold
filled, we can release the un-solidified metal back into the flask.
us to create hollow castings. Since most of the heat is conducted away
surface between the mold and the metal, therefore the portion of the
closest to the mold surface always solidifies first; the solid front
inwards into the cavity. Thus, if the liquid is drained a very short
the filling, then we get a very thin walled hollow object, etc.
Die casting is a very
commonly used type of permanent mold casting process. It is used for
many components of home appliances (e.g rice cookers, stoves, fans,
drying machines, fridges), motors, toys and hand-tools - since Pearl
delta is a largest manufacturer of such products in the world, this
is used by many HK.-based companies. Surface finish and tolerance of
parts is so good that there is almost no post-processing required. Die
molds are expensive, and require significant lead time to fabricate;
commonly called dies.
Casting Design and Quality
Several factors affect
the quality/performance of cast parts - therefore the design of parts
be produced by casting, as well as the design of casting molds and
account for these. You may think of these as design guidelines, and
scientific basis lies in the analysis - the strength and behaviour of
As the casting cools,
the metal shrinks. For common cast metals, a 1% shrinkage allowance is
in all linear dimensions (namely, the design is scaled p by approx 1%).
the solidification front, i.e. the surface at the boundary of the
and the liquid metals, travels from the surface of the mold to the
regions of the part, the design must ensure that shrinkage does not
TREATMENT OF FERROUS METALS
treatment requires close control over all factors affecting the heating
cooling of a metal. This control is possible only when the proper
available. The furnace must be of the proper size and type and
the temperatures are kept within the prescribed limits for each
the furnace atmosphere affects the condition of the metal being
After a metal has been
soaked, it must be returned to room temperature to complete the
process. To cool the metal, you can place it in direct contact with a
MEDIUM composed of a gas, liquid, solid, or combination of these. The
which the metal is cooled depends on the metal and the properties
The success of a
heat-treating operation depends largely on your judgement and the
which you identify each color with its corresponding temperature. From
of table 2-1, you can see that close observation is necessary. You must
to tell the difference between faint red and blood red and between dark
and medium cherry. To add to the difficulty, your conception of medium
may differ from that of the person who prepared the table. For an
heat-treating operation, you should get a chart showing the actual
steel at various temperatures.
In general, annealing
is the opposite of hardening, You anneal metals to relieve internal
soften them, make them more ductile, and refine their grain structures.
Annealing consists of heating a metal to a specific temperature,
holding it at
that temperature for a set length of time, and then cooling the metal
The purpose of
normalizing is to remove the internal stresses induced by heat
welding, casting, forging, forming, or machining. Stress, if not
leads to metal failure; therefore, before hardening steel, you should
it first to ensure the maximum desired results. Usually, low-carbon
not require normalizing; however, if these steels are normalized, no
Thin pieces cool faster
and are harder after normalizing than thick ones. In annealing (furnace
cooling), the hardness of the two are about the same.
The hardening treatment
for most steels consists of heating the steel to a set temperature and
cooling it rapidly by plunging it into oil, water, or brine. Most
rapid cooling (quenching) for hardening but a few can be air-cooled
same results. Hardening increases the hardness and strength of the
makes it less ductile. Generally, the harder the steel, the more
In plain carbon steel,
the maximum hardness obtained by heat treatment depends almost entirely
carbon content of the steel. As the carbon content increases, the
ability of the steel increases; however, this capability of hardening
increase in carbon content continues only to a certain point. In
percent carbon is required for maximum hardness.
Case hardening produces
a hard, wear-resistant surface or case over a strong, tough core. The
forms of casehardening are carburizing, cyaniding, and nitriding. Only
metals are case-hardened.
Case hardening is ideal
for parts that require a wear-resistant surface and must be tough
internally to withstand heavy loading. The steels best suited for case
are the low-carbon and low-alloy series. When high-carbon steels are
case-hardened, the hardness penetrates the core and causes brittleness.
hardening, you change the surface of the metal chemically by
introducing a high
carbide or nitride content. The core remains chemically unaffected.
heat-treated, the high-carbon surface responds to hardening, and the
Flame hardening is
another procedure that is used to harden the surface of metal parts.
use an oxyacetylene flame, a thin layer at the surface of the part is
heated to its critical temperature and then immediately quenched by a
combination of a water spray and the cold base metal. This process
thin, hardened surface, and at the same time, the internal parts retain
original properties. Whether the process is manual or mechanical, a
must be maintained, since the torches heat the metal rapidly and the
temperatures are usually determined visually.
Flame hardening may be
either manual or automatic. Automatic equipment produces uniform
results and is
more desirable. Most automatic machines have variable travel speeds and
adapted to parts of various sizes and shapes. The size and shape of the
depends on the part.
When the cutting end
has cooled, remove the chisel from the bath and quickly polish the
with a buff stick (emery). Watch the polished surface, as the heat from
opposite end feeds back into the quenched end. As the temperature of
hardened end increases, oxide colors appear. These oxide colors
pale yellow, to a straw color, and end in blue colors. As soon as the
shade of blue appears, quench the entire chisel to prevent further
the cutting edge.
A solution of water and
caustic soda, containing 10 percent caustic soda by weight, has a
cooling rate than water. Caustic soda is used only for those types of
that require extremely rapid cooling and is NEVER used as a quench for
This type of quenching
uses materials other than liquids. Inmost cases, this method is used
slow the rate of cooling to prevent warping or cracking.
Air quenching is used
for cooling some highly alloyed steels. When you use still air, each
part should be placed on a suitable rack so the air can reach all
the piece. Parts cooled with circulated air are placed in the same
arranged for uniform cooling. Compressed air is used to concentrate the
on specific areas of a part. The airlines must be free of moisture to
cracking of the metal.
PROCESS OF FERROUS METALS
A compound die blanks
and perforates a part at the same time in the same station. In most
operation perforates a hole or holes down, while the part blanks up.
allows slugs from those holes to fall through the die. This method
part in the die, requiring some means of part removal.
Compound dies commonly
run as single-hit dies. They can run continuously with a feeder,
can remove the part in a timely manner. Open Back Inclinable (OBI)
presses - in
the inclined position along with an air blow-off - aid in part removal.
A disadvantage of a
compound blank die is its limited space that tends to leave die
and weak. This concentrates the load and shock on punches and matrixes,
resulting in tooling failures.
provide an effective way to convert raw coil stock into a finished
minimal handling. As material feeds from station to station in the die,
progressively works into a completed part.
usually run from right to left. The part material feeds one progression
each press cycle. Early stations typically perforate holes that serve
to locate the stock strip in later stations.
There are many
variations of progressive die designs. The design shown here
common operations and terminology associated with progressive dies.
Fixed strippers have
several drawbacks. They do not hold the stock strip flat and are unable
absorb impact and snap-thru shock. The result is poor part flatness and
premature punch failure.
We generally do not
recommend fixed strippers for high-volume or high-precision jobs. A
clearance under the stripper is 1½ times the material thickness - 1/16"
1/8" is common clearance on the sides of the stock strip.
Clearance under a fixed
stripper is commonly 1½ times the part material. This allows for
part material thickness and for stock strip deformation.
allowance under the punch point results in punch point chipping. That
deformation can also cause lateral movement of both part and punches,
in punch point breakage and poor part quality.
At snap-thru there is a
sudden unloading of pressure on the punches and part material. This
shock, which can lead to punch head breakage.
Note the buckling of
the part material throughout the press cycle, as seen in. This can lead
dimensional and functional problems in the finished part.
The buckling effect
binds the part on the ends of the punches, which increases stripping
and potentially chips the punch face.
Urethane strippers are
inexpensive and simple to use. They slide over the end of a punch with
press fit, which prevents the stripper from falling into the die during
Through use, urethane
strippers fatigue and become loose on the punches. You must continually
them to prevent them from falling into and damaging the die. Some
strippers are molded with a head designed to fit a standard urethane
This greatly enhances urethane stripper life and reliability.
movement of the urethane strippers can move the stock strip or part
creating punch-to-matrix alignment problems.
A urethane stripper
strips the part off the ends of the punches as it returns to its
shape. Due to the urethane’s pliable nature, the part material may
during the perforating and stripping process.
Some urethane strippers
have a steel washer attached to the end to minimize part distortion.
caution when using this type of urethane stripper on shaped punches or
applications where large amounts of pre-load are required. Catastrophic
failure can occur if the punch face catches the steel face prior to
The optimum urethane
stripper should have a combination of two different grades of urethane:
hardness grade of urethane for the face and a medium hardness grade for
body. This helps maintain part flatness without sacrificing durability
Spring strippers offer
Their main advantage is
that as the die closes, they hold the stock strip or part flat and in
during perforating. A spring stripper prevents the part material from
or hanging up on the punches at withdrawal.
throughout the working portion of each press cycle provides superior
performance in tool reliability, part quality and press life.
Over-entry or closing a
die below its recommended shut height can have catastrophic
To calculate tonnage
requirements for perforating, multiply the part material thickness
length of the cut, or perimeter of the hole, times the material shear
Determine the perimeter of a round hole by multiplying pi times the
It is important to
include the stripper pressure when calculating die tonnage
Stripper pressure should be at least 8% of the perforating force. Some
manufacturers require stripper pressure as high as 25% of the
Stagger punch lengths
to minimize impact and snap-thru shock. You can split punch lengths
into two or
three groups, reducing impact and snap-thru shock by half or third.
Common practice is to
stagger the different groups of punches by an amount equaling stock
Although this reduces the initial shock, it does not reduce the total
Each punch, or group of punches, is exposed to both impact and
Making stagger equal to
or slightly less than burnish length in the hole being perforated
reduces impact and snap-thru shock. This amount of stagger allows the
group of punches to contact the material before the first group snaps
The snap-thru energy from the first group of punches is absorbed and
drive the next group of punches through the part material.
Using burnish length
instead of material thickness as the amount of stagger is extremely
in high-speed stamping applications. It reduces punch entry to minimize
wear and slug pulling. Because the punches withdraw from the stock
sooner, you also gain more feed time.
Piercing makes a hole
without removing a slug. A sharp or pointed punch tears open a hole,
ragged edge that has been formed down.
A food grater is a good
example of what pierced holes look like in a finished product.
Perforate and Shave
Shaving achieves a high
percentage of burnish or shear in a hole. Shaving occurs in a
The first station
resembles most perforating operations using optimum engineered die
This optimizes tool life while minimizing work hardening of the part
The second station cuts
the hole to size using tight die clearance.
Determining punch and
matrix sizes starts in the shave station. The shave punch point size
desired finished hole size. The shave station matrix hole has 1% to 1½%
material thickness clearance per side (2% to 3% of the material
clearance). Too much clearance in a shave station results in a shear
rebreaking of the hole.
Once you know the shave
station component dimensions, you can determine the perforating station
component sizes. The perforating matrix equals or is slightly larger
shave station matrix size. Perforating clearance is as much as possible
generating an excessive burr. This clearance is achieved by reducing
Pilots locate the stock
strip or part. The pilot working length extends beyond the perforating
and a fully extended stripper.
The pilot nose picks up
an existing hole and moves the stock strip or part into proper location
the stripper makes contact.
Pilot point diameters
are commonly dimensioned .001" smaller than the punch point diameter
to perforate the locating hole. This prevents the stock strip or part
Proper die clearance
for pilots is subject to debate. Many designers maintain a very tight
of .0005" or less, incorporating the matrix as a guide below the part
material. This offers additional lateral support that results in better
location when forming or working with thick material.
The drawback with tight
clearance around a pilot is when a misfeed causes a pilot to perforate
The extreme stripping force created by the tight clearance galls the
possibly pulling it from the retainer. Ball lock pilots are
vulnerable to pulling due to misfeeds.
employed by designers is to use material thickness as the clearance per
around pilots. The intent is to allow enough room around the pilot for
material to extrude down into the matrix without grabbing the pilot.
problem is that when the material pierces and extrudes down, it tends
back resulting in excessive stripping force.
Coining leaves an
impression in the part surface. You can apply this process to one or
of the part. In many cases coining is used to thin or displace
slug is removed in coining operations.
Embossing deforms a
shape within the part, but without intentional thinning of the part
A punch is used to form
material into a blind hole. The punch bottoms out to produce a flat
the bottom of the form.
PROCESS OF FERROUS METALS
rolling is a metal forming process in which metal stock is passed
pair of rolls. Rolling is classified according to the temperature of
rolled. If the temperature of the metal is above its recrystallization
temperature, then the process is termed as hot rolling. If the
the metal is below its recrystallization temperature, the process is
cold rolling. In terms of usage, hot rolling processes more tonnage
other manufacturing process and cold rolling processes the most tonnage
all cold working processes.
Hot and Cold
In smaller operations
the material starts at room temperature and must be heated. This is
done in a
gas- or oil-fired soaking pit for larger workpieces and for smaller
induction heating is used. As the material is worked the temperature
monitored to make sure it remains above the recrystallization
maintain a safety factor a finishing temperature is defined above the
recrystallization temperature: this is usually 50 to 100°C (122 to
the recrystallization temperature.
If the temperature does
drop below this temperature the material must be re-heated before more
Hot rolled metals
generally have little directionality in their mechanical properties and
deformation induced residual stresses. However, in certain instances
non-metallic inclusions will impart some directionality and workpieces
than 20 mm (0.79 in) thick often have some directional properties.
non-uniformed cooling will induce a lot of residual stresses, which
occurs in shapes that have a non-uniform cross-section, such as l-beams
H-beams. While the finished product is of good quality, the surface is
in mill scale, which is an oxide that forms at high-temperatures. It is
removed via pickling or the smooth clean surface process, which reveals
smooth surface. Dimensional tolerances are usually 2 to 5% of the
Flat rolling is the
most basic form of rolling with the starting and ending material having
rectangular cross-section. The material is fed in between two rollers,
working rolls, that rotate in opposite directions. The gap between the
rolls is less than the thickness of the starting material, which causes
deform. The decrease in material thickness causes the material to
friction at the interface between the material and the rolls causes the
material to be pushed through.
Ring rolling is a
specialized type of hot rolling that increases the diameter of a ring.
starting material is a thick-walled ring. This workpiece is placed on
roll, while another roll, called the driven roll, presses the ring from
outside. As the rolling occurs the wall thickness decreases as the
increases. The rolls may be shaped to form various cross-sectional
resulting grain structure is circumferential, which gives better
properties. Diameters can be as large as 8 m (26 ft) and face heights
as 2 m (79 in). Common applications include rockets, turbines,
pipes, and pressure vessels. Structural shape rolling Cross-sections of
continuously rolled structural shapes, showing the change induced by
The term shape is used
to describe the flatness and the profile of the workpiece. The profile
of the how the thickness of the workpiece varies across the width of
workpiece and can be measured in units of length. The flatness of the
is based on how the fiber elongation varies across the width of the
and it typically measured in I-Units.
Another way to overcome
defection issues is by decreasing the load on the rolls, which can be
applying an longitudinal force: this is essentially drawing. Other
decreasing roll defection include increasing the elastic modulus of the
material and adding back-up supports to the rolls.
A horizontal hydraulic
press for hot aluminum extrusion (loose dies and scrap visible in
In indirect extrusion, also
known as backwards extrusion, the billet and container move together
die is stationary. The die is held in place by a “stem” which has to be
than the container length. The maximum length of the extrusion is
dictated by the column strength of the stem. Because the billet moves
container the frictional forces are eliminated.
drives are more expensive and larger than direct-drive oil presses, and
lose about 10% of their pressure over the stroke, but they are much
to 380 mm/s (15 psi). Because of this they are used when extruding
are also used on materials that must be heated to very hot temperatures
Hydrostatic extrusion presses
usually use castor oil at pressure up to 1400 MPa (200 ksi). Castor oil
because it has good lubricity and high pressure properties.
involves significant capital expenditure for machinery, tooling,
personnel. In the case of hot forging, a high temperature furnace
referred to as the forge) will be required to heat ingots or billets.
the massiveness of large forging hammers and presses and the parts they
produce, as well as the dangers inherent in working with hot metal, a
building is frequently required to house the operation. In the case of
forging operations, provisions must be made to absorb the shock and
generated by the hammer. Most forging operations will require the use
metal-forming dies, which must be precisely machined and carefully heat
to correctly shape the workpiece, as well as to withstand the
We specifically know what kind
of strain can be put on the part, because the compression rate of the
forging operation is controlled. There are a few disadvantages to this
most stemming from the workpiece being in contact with the dies for
extended period of time. The operation is a time consuming process due
amount of steps and how long each of them take. The workpiece will cool
because the dies are in contact with workpiece; the dies facilitate
more heat transfer than the surrounding atmosphere. As the workpiece
becomes stronger and less ductile, which may induce cracking if
continues. Therefore heated dies are usually used to reduce heat loss,
surface flow, and enable the production of finer details and closer
The work piece is then
transferred to the next set of grooves or turned around and reinserted
same grooves. This continues until the desired shape and size is
advantage of this process is there is no flash and it imparts a
structure into the workpiece.
In bottoming, the sheet is
forced against the V opening in the bottom tool. U-shaped openings
used. Space is left between the sheet and the bottom of the V opening.
optimum width of the V opening is 6 T (T stands for material thickness)
sheets about 3 mm thick, up to about 12 T for 12 mm thick sheets. The
radius must be at least 0.8 T to 2 T for sheet steel. Larger bend
require about the same force as larger radii in air bending, however,
radii require greater force—up to five times as much—than air bending.
Advantages of bottoming include greater accuracy and less springback. A
disadvantage is that a different tool set is needed for each bend
thickness, and material. In general, air bending is the preferred
PROCESS OF FERROUS METALS
We will be working with
a piece of 3/4" diameter 6061 aluminum about 2 inches long. A workpiece
such as this which is relatively short compared to its diameter is
that we can safely turn it in the three jaw chuck without supporting
end of the work.
For longer workpieces
we would need to face and center drill the free end and use a dead or
center in the tailstock to support it. Without such support, the force
tool on the workpiece would cause it to bend away from the tool,
strangely shaped result. There is also the potential that the work
forced to loosen in the chuck jaws and fly out as a dangerous
Turning with Power
One of the great
features of the 7x10 is that it has a power lead screw driven by an
gear train. The leadscrew can be engaged to move the carriage under
turning and threading operations. Turning with power feed will produce
smoother and more even finish than is generally achievable by hand
Power feed is also a lot more convenient than hand cranking when you
multiple passes along a relatively long workpiece.
The power feed is
engaged by the knurled tumbler gear lever on the back of the headstock.
change the lever setting you must pull back on the knurled sleeve with
considerable force. With the sleeve pulled back you can move the lever
down to engage its locking pin in one of three positions. In the center
position the lead screw is not engaged and does not turn. In the upper
the lead screw rotates to move the carriage towards the headstock and
lower position the lead screw moves the carriage away from the
turning, you will generally want to cut towards the headstock, so move
lever to the upper position and release the sleeve to engage the
Grinding is a subset of
cutting, as grinding is a true metal-cutting process. Each grain of
functions as a microscopic single-point cutting edge (although of high
rake angle), and shears a tiny chip that is analogous to what would
conventionally be called a “cut” chip (turning, milling, drilling,
(also called center-type grinding) is used in the removing the
surfaces and shoulders of the workpiece. The workpiece is mounted and
by a workpiece holder, also known as a grinding dog or center driver.
will change due to stresses put on the part during finishing. High
temperatures may cause a thin martensitic layer to form on the part,
lead to reduced material strength from microcracks.
Threading is the
process of creating a screw thread. More screw threads are produced
than any other machine element.
also colloquially called single-pointing (or just thread cutting when
context is implicit), is an operation that uses a single-point tool to
a thread form on a cylinder or cone. The tool moves linearly while the
rotation of the workpiece determines the lead of the thread.
The cutter geometry
reflects the thread pitch but not its lead; the lead (thread helix
determined by the tool path. Tapered threads can be cut either with a
multiple-form cutter that completes the thread in one revolution using
or with a straight or tapered cutter (of single- or multiple-form)
path is one or more revolutions but cannot use helical interpolation
use CAD/CAM software to generate a contour-like simulation of helical
Then the blank is
slowly rotated through approximately 1.5 turns while axially advancing
one pitch per revolution. Finally, the centerless thread grinding
used to make head-less set screws in a similar method as centerless
The blanks are hopper-fed to the grinding wheels, where the thread is
formed. Common centerless thread grinding production rates are 60 to 70
per minute for a 0.5 in (13 mm) long set screw.
Many, perhaps most,
threaded parts have potential to be generated via additive
which there are many variants, including fused deposition modeling,
metal laser sintering, 3D printing, solid free form fabrication,
manufacturing, and stereolithography. Most additive technologies are
the laboratory end of their historical development, but further
commercialization is picking up speed.
For instance, a 15-inch
drilling machine can center-drill a 30-inch-diameter piece of stock.
to determine the size of the drill press are by the largest hole that
drilled, the distance between the spindle and column, and the vertical
between the worktable and spindle
of Drilling Machines
Lubrication is important
because of the heat and friction generated by the moving parts. Follow
manufacturer’s manual for proper lubrication methods. Clean each
use. Clean T-slots, grooves, and dirt from belts and pulleys. Remove
avoid damage to moving parts. Wipe all spindles and sleeves free of
avoid damaging the precision fit. Put a light coat of oil on all
surfaces to prevent rust. Operate all machines with care to avoid
the electric motor.
The power-feed drilling
machines are usually larger and heavier than the hand-feed. They are
with the ability to feed the cutting tool into the work automatically,
preset depth of cut per revolution of the spindle, usually in
thousandths of an
inch per revolution.
Common twist drill
sizes range from 0.0135 (wire gage size No. 80) to 3.500 inches in
Larger holes are cut by special drills that are not considered as twist
The standard sizes used in the United States are the wire gage numbered
letter drills, fractional drills, and metric drills. Twist drills can
classified by the diameter and length of the shank and by the length of
fluted portion of the twist drill.
The margin is the
narrow surface along the flutes that determines the size of the drill
the drill aligned.
The portion of the
drill body that is relieved behind the margin is known as the body
The diameter of this part is less than that of the margin and provides
clearance so that all of the body does not rub against the side of the
cause friction. The body clearance also permits passage of lubricants
When grinding the lip
angle, use the drill point gage and grind one lip perfectly straight
and at the
required angle (usually 590). Then flip the drill over and grind the
Once the angle is established, then the lip clearance angle and lip
be ground. If both lips are not straight and of the same angle, then
edge will not be established. It is it important to have a sharp and
chisel edge or the drill will not rotate exactly on its center and the
will be oversized. If the drill point is too flat, it will not center
on the workpiece.
Drill drifts are flat,
tapered keys with one rounded edge that are designed to fit into a
chuck’s slot to force a tapered shank drill loose. The rounded top of
end of the drill drift is designed to face upward while inserting the
into the slot. There are two types of drill drifts, the standard type
safety type. The standard drift must be inserted into the chuck’s slot
struck with a soft hammer to jar the taper shank drill loose. The drill
fall quickly if not held by the hand and could break or cause injury.
safety drill drift has a sliding hammer weight on the drift itself to
a free hand to stay constantly on the drill as it comes loose.
Table or Base
When a workpiece is
table or base mounted, the strap clamps must be as parallel to the
base as possible. All bolts and strap clamps should be as short as
rigidity and to provide for drilling clearance.
Parallel bars should be
set close together to keep from bending the work. Washers and nuts
should be in
excellent condition. The slots and ways of the table, base, or vise
free of all dirt and chips. All work holding devices should be free of
and wiped clean of oil and grease. Work holding devices should be the
size for the job. Devices that are too big or too small for the job are
dangerous and must be avoided.
When drilling shafts,
rods, pipes, dowels, or other round stock, it is important to have the
punch mark aligned with the drill point. Use V-blocks to hold the round
for center punching and drilling. Align the center of the round stock
square or by lining the workpiece up with the twist drill point.
to drill round stock is to use a V-block drill jig that automatically
the work for drilling.
PROCESS OF FERROUS METALS
recently, structural steel connections were either welded or riveted.
High-strength bolts have completely replaced structural steel rivets.
the latest steel construction specifications published by AISC (the
Edition) no longer covers their installation. The reason for the change
primarily due to the expense of skilled workers required to install
Strength structural steel rivets. Whereas two relatively unskilled
install and tighten high strength bolts, it took a minimum of four
skilled riveters to install rivets in one joint at a time.
Blind rivets, also
known as pop rivets, are tubular and are supplied with a mandrel
center. The rivet assembly is inserted into a hole drilled through the
be joined and a specially designed tool is used to draw the mandrel
rivet. This expands the blind end of the rivet and then the mandrel
These types of blind rivets have non-locking mandrels and are avoided
critical structural joints because the mandrels may fall out, due to
or other reasons, leaving a hollow rivet that will have a significantly
load carrying capability than solid rivets. Furthermore, because of the
they are more prone to failure from corrosion and vibration. Unlike
rivets, blind rivets can be inserted and fully installed in a joint
one side of a part or structure, “blind” to the opposite side.
The stress and shear in
a rivet is analyzed like a bolted joint. However, it is not wise to
rivets with bolts and screws in the same joint. Rivets fill the hole
are installed to establish a very tight fit (often called interference
is difficult or impossible to obtain such a tight fit with other
result is that rivets in the same joint with loose fasteners will carry
the load—they are effectively more stiff. The rivet can then fail
before it can
redistribute load to the other loose fit fasteners like bolts and
The welding processes
covered in this chapter are gas welding, arc welding which includes
metal arc welding (MMA), tungsten inert gas shielded arc welding (TIG),
metal arc welding (MIG, MIG/CO2), submerged arc welding is (SAW), etc.
energy density processes like electron beam welding, laser beam
welding are also dealt with. Pressure welding and some special welding
techniques like electro-slag welding etc. are also discussed in detail.
broad classification of the welding processes.
Submerged arc welding
is a method in which the heat required to fuse the metal is generated
electric current passing through between the welding wire and the work
The tip of the welding wire, the arc and the weld area are covered by a
of granular flux. A hopper and a feeding mechanism are used to provide
of flux over the joint being welded.
MIG welding (gas
metal arc welding)
Gas metal arc welding
is a gas shielded process that can be effectively used in all
shielding gas can be both inert gas like argon and active gases like
argon-oxygen mixture and argon-carbon-di-oxide which are chemically
It can be used on nearly all metals including carbon steel, stainless
alloy steel and aluminium. Arc travel speed is typically 30-38 cm
minute and weld
metal deposition rate varies from 1.25 kg/hr when welding out of
5.5 kg/hr in flat position.
Since too powerful a
jet would cause a turbulence in the molten puddle, the jet effect on
piece is softened by limiting gas flow rates through the nozzle. Since
flow alone may not be adequate to protect the molten puddle from
contamination, auxiliary shielding gas is provided through an outer gas
The molten metal
flowing around the keyhole forms a reinforced weld bead. Square butt
upto 6 mm thick can be welded in a single pass by this method.
For heavier plates
which require multi-pass welding partial beveling is done and the root
the largest size is deposited with the key hole technique without using
wire. The rest of the passes are then carried out with normal melt-in
with filler wire addition. PAW process is limited to around 25 mm thick
STAINLESS STEEL WIRE
The involved process of
manufacturing precision stainless steel wire begins at the melt shop.
initial melt is composed of controlled scrap, processed ores and virgin
metallic elements. When charged into a furnace, melting is accomplished
high-power electric arcs transferred from graphite electrodes. Once
entire batch or heat is given a unique alphanumeric identity and tapped
waiting preheated ladle for transfer to a secondary refining operation.
Once cooled into a
straight billet, each length of the billet is identified to maintain
trace-ability from melt all the way through to finished wire. Each
often times visually inspected for surface consistency to ensure that
abnormal surface irregularities were formed during the
process. Depending on the condition found, billets may be spot surface
to blend or remove irregularities that could otherwise contribute to
A majority of spring
wire products begins with hot-rolled and solution-annealed wire rod
been de-scaled and acid cleaned. The resultant consistent white pickled
is now ready for conversion into high-quality drawn wire.
Spring manufacturing is
also a demanding process. It requires a wire starting stock that is
manufactured with the utmost consistency in size, and mechanical and
properties, as specified as part of an order or specification.
By keeping variations
to a minimum, the springmaker can realize a much greater degree of
in the coil winding operation, where free length and coil OD are held
Spring wire can be
produced in a wide variety of specialty alloys. Applications for these
grades may include springs for high heat resistance, corrosion
other high-performance attributes needed in the automotive, aerospace,
and process industries.
In addition to common
stainless steel types 302/304, 316 and 17-7PH, other exotic stainless
can bring added benefits. Duplex stainless steel UNS S32205 or 2205
alloy is a
grade that combines the properties of austenitic and ferritic stainless
Drawing is usually
performed at room temperature, thus classified as a cold working
it may be performed at elevated temperatures for large wires to reduce
More recently drawing has been used with molten glass to produce high
The American wire gauge
scale is based on this. This can be done on a small scale with a draw
on a large commercial scale using automated machinery. The process of
drawing improves material properties due to cold working.
The areal reduction of
small wires is 15-25% and larger wires are 20-45%. Very fine wires are
drawn in bundles. In a bundle, the wires are separated by a metal with
properties, but with lower chemical resistance so that it can be
drawing. If the reduction in diameter is greater than 50%, the process
require annealing between the process of drawing the wire through the
Commercial wire drawing usually starts with a coil of hot rolled 9 mm
diameter wire. The surface is first treated to remove scales. It is
into either a single block or continuous wire drawing machine.
The block is also
tapered, so that the coil of wire may be easily slipped off upwards
Before the wire can be attached to the block, a sufficient length of it
pulled through the die; this is effected by a pair of gripping pincers
end of a chain which is wound around a revolving drum, so drawing the
until enough can be coiled two or three times on the block, where the
secured by a small screw clamp or vice. When the wire is on the block,
set in motion and the wire is drawn steadily through the die; it is
important that the block rotates evenly and that it runs true and pulls
wire at a constant velocity, otherwise “snatching” occurs which will
even break the wire. The speeds at which wire is drawn vary greatly,
to the material and the amount of reduction.
Often intermediate anneals
are required to counter the effects of cold working, and to allow
drawing. A final anneal may also be used on the finished product to
ductility and electrical conductivity.
An example of product
produced in a continuous wire drawing machine is telephone wire. It is
to 30 times from hot rolled rod stock.
cross-sections dominate most drawing processes, non-circular
drawn. They are usually drawn when the cross-section is small and
are too low to justify rolling. In these processes, a block or
machine are used.
Lubrication in the
drawing process is essential for maintaining good surface finish and
effect of wire drawing can be substantial. The highest gruel strengths
available on any steel have been recorded on small-diameter cold-drawn
austenitic stainless wire. Tensile strength can be as high as 400 ksi
Drawing dies are typically made of
tool steel, tungsten carbide, or diamond, with tungsten carbide and
manufactured diamond being the most common. For drawing very fine wire
crystal diamond die is used. For hot drawing, cast-steel dies are used.
steel wire drawing, a tungsten carbide die is used. The dies are placed
steel casing, which backs the die and allow for easy die changes. Die
usually range from 6-15º and each die has at least 2 different angles:
entering angle and approach angle. Wire dies usually are used with
power as to
pull the wire through them. There are coils of wire on either end of
which pull and roll up the wire with a reduced diamet.
Steel is a metal alloy
containing iron, carbon and other metals. Steel bars, which are used to
reinforce concrete work, come in different shapes, strengths and sizes.
are built through different methods. Steel is non-combustible, but it
lose strength when temperatures reach 750 degrees Fahrenheit. Common
steel bars include hot rolled bars, cold twisted deformed bars and TMT
Hot rolled bars are
round, have a smooth surface and are made by a method called hot
consists of transforming a piece of steel into a cylindrical bar by
when still hot. Hot rolled bars can also have ribbed surfaces, which
the bond strength of the pieces.
Twisted Deformed Bars
These bars are first
hot rolled with three or more parallel ribs or indentations. When
bars are twisted, thus straining the steel’s elastic limit this helps
the bar stronger. However, cold twisted deformed bars corrode much more
than other bars because of the hot-cold method by which they are
As deformed bars are
rods of steels provided with lugs, ribs or deformation on the surface
these bars minimize slippage in concrete and increases the bond between
materials. Deformed bars have more tensile stresses than that of mild
plain bars. These bars can be used without end hooks. The deformation
spaced along the bar at substantially uniform distances.
To limit cracks that
may develop in reinforced concrete around mild steel bars due to
bars and some lose of bond under load it is common to use deformed bars
have projecting ribs or are twisted to improve the bond with concrete.
bars are produced in sections from 6 mm to 50 mm dia. In addition the
of bonds of deformed bars calculated should be 40 to 80% higher than
plain round bars of same nominal size. And it has more tensile stress
of plain round bars of same nominal size. Cold twisted deformed (Ribbed
Steel Bars) bars are recommended as best quality steel bars for
work by structural Engineer.
Various Grades of
Mild Steel Bars
Some of manufacturers
stamped MS bars grade with their make/name and also give certification
and grade. On the basis of the above information you can store mild
grade-wise at the site of work.
Steel Bars for RCC
All finished steel bars
for reinforced work should be neatly rolled to the dimension and
specified. They should be sound, free from cracks, surface flaws,
rough, jagged and imperfect edges and other defects. It should be
finished in a
work manlike manner.
Weight of Different
When we want to
purchase Mild steel members from the market, the shopkeeper quotes the
steel members in weight. When any type of steel members for use in
construction is required, we calculate the length of steel member in
meter but we are ignorant about the weight of steel.
Here are details of
weight per meter for various types of steel members :
Types of Cold
Cold drawn bars are
widely used in mass production of parts due to their excellent
dimensional properties, with machining characteristics in excess of the
rolled bar condition. Round, hexagonal and square bars can be produced
Turned and polished
round bars have similar mechanical properties to those of equivalent
bar, but exhibit a smooth, bright surface finish and improved
accuracy. They are widely used where a surface free of decarburisation
required, for example in induction hardening and when the surface must
from surface defects, such as for use in cold forming.
To meet the diversified
end-use requirements, cold-rolled coil is designed to provide specific
attributes such as high formability, deep drawability and good
How those good attributes come will be explained by the following steps.
The cold reduction
operation induces very high strains into the sheet, thus, the sheet not
becomes thinner, but also becomes much harder, less ductile. However,
cold-reduced product is annealed, it becomes very soft and formable. In
the combination of cold reduction and annealing lead to a refinement of
steel that provides very desirable and unique forming properties for
use by the customers.
The pickling operation
must be well-controlled to assure that all the oxides formed during hot
are removed. The thickness of the hot-rolled strip is important in that
properties of the final cold rolled and annealed product is influenced
cold reduction. This means that the thickness of each hot-rolled coil
carefully controlled to provide the mill with a specific thickness to
the proper cold reduction. Among other things, cold reduction affects
forming behavior of the product after annealing.
After the steel is
batch annealed, the specific properties of the steel sheet depends on
chemistry, the temperatures used during hot rolling, the amount of cold
reduction, and the annealing cycle.
In the method of
annealing, the steel is maintained under a protective (non-oxidizing)
atmosphere using hydrogen and nitrogen to prevent oxidizing the steel
is at high temperature. In addition to preventing oxidation, the
atmosphere is designed to clean the steel breaking down the oils that
present after cold rolling and entraining the oil vapors in the
hydrogen/nitrogen gases that are passed through the furnace.
After annealed, the
steel coil is most often processed by passing it through a set of rolls
appear similar to the rolls used during cold rolling, in fact, skin
impart a small amount of cold reduction, typically between 0.25 and 1.0
After those processes are finished, the
will involve packing steel coils after being done in skin pass mill.
coils are moved into the warehouse waiting for loading.
STEEL TUBE AND PIPE
In the case of seamless
tube and also in the case of the Fretz-Moon welding process, the
stage invariably involves a heating operation, in which case the
also be referred to as hot-formed tube or pipe. Downstream facilities
for hot drawing
or hot expanding occur relatively rarely; on the other hand, hot-formed
are extensively used as starting products for a downstream cold forming
process. The latter is used in order to extend the product mix of a
toward smaller diameters and wall thicknesses (DIN 2391), to reduce
thickness and diameter tolerances, and to achieve special surface
mechanical/thermo-mechanical properties in the tube.
As the requirements
imposed on tubular products continued to increase, not only were the
manufacturing processes constantly improved, but also appropriate
effective production control and quality assurance were introduced.
tube and pipe manufacturers of renown all have a system in place
production process from the steelworks to the finished tube to be
monitored and documented for total traceability, and effectively
the basis of quality criteria. The mechanical and nondestructive tests
stipulated in the relevant technical specifications are carried out by
personnel operating independently from the production control
department so as
to guarantee product of a constantly high quality.
Another possibility for
the production of seamless tube was invented by H. Ehrhardt. By
solid square ingot in a round die, he was able to produce a
shell with a closed bottom. This shell was subsequently stretched on a
bar through tandem-arranged ring dies to produce the final tube
so-called push bench process in its modified form has remained viable
Pierce and Pilger
The pierce and pilger
method for the production of seamless pipe is also referred to as the
Mannesmann process after its inventors, the Mannesmann brothers. Pipe
above the rolling range indicated can also be produced by expansion. To
end, the largest rolled pipes are reheated and then expanded either by
through a plug - a process often performed in several passes to
increase the outside diameter - or by rolling on a becking mill.
the two processes is employed, the wall thickness is, of course, also
With small pilger mills
for manufacturing the lower size range, the two-stage rolling process
employed today. The starting material takes the form of round rolled
blooms, although round ingots are still frequently used. Round
billets measuring between 100 to approx. 300 mm in diameter are also
The piercing mill
features two specially contoured work rolls which are driven in the
direction of rotation. Their axes are inclined by approx. 3 to 6° in
to the horizontal stock plane. Generally, the roll gap is closed by a
support roll at the top and a support shoe at the bottom. Located at
of the roll gap is a piercing point which functions as an internal tool
held in position by an external thrust block via a mandrel.
Push Bench Process
This process is also
known as the rotary forge process, and - in Germany - after the name of
inventor, as the Ehrhardt process. It is employed for the manufacture
in the diameter range from approx. 50 to 170 mm with wall thicknesses
from 3 to
18 mm and lengths up to 18 m. Modern push bench plants usually only
(large) hollow bloom size, leaving a downstream stretch-reducing mill
convert this into all the usual tube dimensions down to a smallest
diameter of approx. 20 mm.
Arranged in the foundation
bed of the push bench are up to 15 roll stands. The roll stands usually
comprise three (sometimes four) circumferentially distributed,
grooved rollers. The gradually decreasing cross sections of the roller
produce reductions which, in the main work passes, can amount to up to
During this process, between 6 and 7 roll stands are simultaneously in
operation at any one time. The push force is applied to the mandrel bar
rack-and-pinion arrangement, and operating speeds can be up to 6 m/s.
Pierce and Draw
This process, also
developed by H. Ehrhardt, is similar to the push bench variant but,
technologies described so far, is not suitable for mass production.
Consequently, therefore, the number of plants employing this process is
small. These, however, are specially designed for the manufacture of
hollow components combining large diameters with large wall thicknesses.
The production range of
such facilities lies between approx. 200 and 1450 mm in outside
wall thicknesses ranging from approx. 20 to 270 mm. This therefore
effective complement to the product mix available in large pilger
mills. With a
maximum length of around 10 m, tube blanks and hollow sections can be
manufactured (in all steel grades), by this process for items such as
plant components, hydraulic cylinders, high-pressure gas cylinders and
vessels, as can products such as thick-walled square section tubes.
Assel mills are used
nowadays to produce stainless tube with outside diameters ranging from
250 mm and lengths of up to 12 m. The ratio of outside diameter to wall
thickness tends to lie in the region 4 to 15. The smallest inside
the tubes is approx. 40 mm. The tubes manufactured by this method are
characterized by their excellent concentricity and are extensively
the production of turned components (shafts, axles) and also for
steel roller bearing production (general product name: mechanical tube).
The starting material
predominantly takes the form of round steel blooms of the appropriate
which are heated to forming temperature in a rotary hearth furnace.
descaling and end face centering, the bloom is formed into a hollow
the cross roll piercing mill and then fed into the Assel mill.
Although Diescher mills
have not enjoyed wide market penetration as elongating or
facilities, modern cross roll piercing mills are nowadays being
and more with Diescher discs (see continuous mandrel process and plug
steel tube has been standardized in DIN 2391 for the diameter range
from 4 to
120 mm and wall thicknesses from 0.5 to 10 mm. In addition, however,
non-standardized intermediate sizes, and tube up to 380 mm outside
with wall thicknesses up to 35 mm, can also be manufactured by cold
take the form of draw benches equipped with a continuous chain; or draw
with reversible finite drawing and return chains attached to the
carriage. Other designs include rope-type draw benches, rack and pinion
benches and also draw benches with a hydraulic drive system.
Large tube lengths are
generally drawn using a floating plug on continuous-type straight-line
in which two reciprocating sledges alternate in the performance of the
operation. Tube of small diameter is usually cold-drawn by the bull
process in which the stock is taken from a coil and the drawing power
applied by a capstan.
The pass design of the
two rolls consists of a circular recess, corresponding to the cross
the hollow blank, which tapers over a certain portion of the roll
to provide an ideal, continuous transition to the finished tube
Consequently, as the rolls move forward and backward, the hollow blank
formed in the desired manner. An essential aspect of the process lies
fact that elongation of the hollow blank to produce the finished tube
performed by simultaneous reduction of the diameter and the wall
This is aided by the shape of the mandrel which tapers from the hollow
inside diameter to the finished tube inside diameter. Following a
backward rolling cycle, the rolls release the blank which is then
advanced by a
certain, infinitely variable feed value. The corresponding material
then elongated with the subsequent forward and backward rolling cycle
by the stand.
Aside from this hot
pressure welding technique, in which the strip is heated in a furnace
welding temperature, several other processes were devised by the
Thomson between the years 1886 and 1890 enabling metals to be
The basis for this was the property discovered by James P. Joule
passing an electric current through a conductor causes it to heat up
due to its
The starting material
can be formed into its tubular shape in either the hot or cold
distinction is made in this respect between continuous tube forming and
single tube forming process.
In continuous tube
forming, uncoiled strip material is taken from an accumulator, with the
end and trailing end of the consecutive coils being welded together.
In single pipe
production, the tube forming and welding process is not performed over
lengths, but rather (as the name suggests) in single pipe lengths.
The main methods used
for the production of welded tube and pipe are the Fretz-Moon,
induction, submerged-arc and combination gas-shielded submerged-arc
plus the various gas-shielded welding methods for the production of
steel tube and pipe.
In this process, named
after its inventors, steel strip in the form of a continuous skelp is
welding temperature in a forming and welding line. The stock is
formed by rollers into an open-seam tube and then the mating edges are
together and welded by a process related to the forge-welding technique
The hot-rolled steel
strip coils used as the starting material are uncoiled at high speed
in loop accumulators. These serve as a buffer during the continuous
process, enabling the trailing end to be butt-welded to the leading end
strip provided by the next coil. This continuous strip or “skelp” is
through a tunnel furnace where it is heated to a high temperature.
burners increase the temperature at the skelp edges to a welding heat
100 to 150°C higher than the temperature prevailing at the skelp
In this process,
welding is performed with alternating current frequencies from 50 to
400 Hz. An
electrode comprising two insulated discs of a copper alloy serves not
the power supply but also as the forming tool and the element which
the necessary welding pressure.
constitute the critical components of the plant, because not only must
provided with a groove which matches the diameter of the tube being
manufactured, but also this radius has to be constantly monitored for
during production operations.
The material extruded
during the pressure welding process forms an inner and outer flash
weld zone which has to be removed inline just downstream of the welding
by internal and external trimmers.
The welding current can
be introduced into the open-seam tube both by conductive means using
contacts and by inductive means using single or multi-wind coils.
a distinction is made in the nomenclature between high-frequency
(HFI) welding and high-frequency conduction welding. The strip or skelp
in a roll forming mill or in an adjustable roll stand (natural function
forming) into the open-seam tube for the manufacture of a wide range of
products. These include line pipe and structural tube in the size range
approx. 20 to 609 mm OD and 0.5 to approx. 16 mm wall thickness, and
blanks as the feedstock for a downstream stretch-reducing mill. The
stock is provided in the form of coiled steel strip or hot-rolled wide
Depending on the tube dimensions and application, and particularly in
manufacture of precision tube, the steel strip may either undergo an
pickling operation, or cold-rolled strip is used. The individual coils
welded together and, at high uncoiling speeds, the strip first passes
loop accumulator. The tube welding machine operates continuously at a
ranging from 10 to 120 m/min by drawing the strip from the loop
The roll forming mill
is used for tube diameters up to max. 609 mm, and generally consists of
8 to 10
largely driven roll forming stands in which the strip is gradually
the open-seam tube-as indicated in stages 1 to 7 in Fig. 29. The three
stands - 8, 9 and 10 - guide the open-seam tube toward the welding
forming rolls have to be precisely matched to the final tube diameter.
manufacture of large-diameter pipe, the natural function forming
also be applied. Fig. 30 shows the principles of this forming process
a series of roll stands (roller cages).
The main features of
the roller cage is that a number of non-driven internal and external
rollers, adjustable within a wide product diameter range, are
configured in a
funnel-shaped forming line which gradually bends the strip into the
shape. Only the breakdown stand at the inlet and the fin pass stands at
exit end are actually driven. The cross-sectional details A-B, C-D and
Fig. 30 indicate the degree of deformation and the arrangement of the
rollers at various sections along the line.
Before the strip enters
the forming section, it is straightened and cut to a constant width by
longitudinal edge trimmer. The cut edges may be additionally bevelled
welding preparation. The strip is then formed into an open-seam tube as
described above, and with the gap still relatively wide, fed via three
fin pass stands to the welding table. The overhead fin rolls, the width
which is tapered toward the welding point, determine the gap entry
control its central position in the welding table. There the converging
edges are pushed against each other by shaped squeeze rolls and then
means of the high-frequency electric resistance process.
The HF pressure weld
can either be left in its as-welded condition or subsequently
the normalizing range, depending on the application. Partial inductive
annealing of the weld may also be performed on the continuous tube, or
individual tubes may be subjected to a separate heat treatment
cutting to length, depending on the material flow conditions within the
In the subsequent tube
finishing department, the tubes are further processed on straightening
machines. The straightening operation may be preceded by a heat
on the tube dimensions and application. Nondestructive examination
and the performance of a visual inspection serve to monitor the
process. Once completed, the tubes are subjected to the relevant,
acceptance procedures irrespective of the in-process tests and
performed on them.
Induction Welding Process
In the high-frequency
induction welding process (HFI or Induweld process), welding speeds of
120 m/min may be attained, depending on wall thickness and application.
The open-seam tube 1 to
be welded is introduced in the direction of the arrow to the welding
where it is engaged by the squeeze rolls 5. These initially press
incoming open seam edges approaching at angle 2. The high-frequency
supplied by the welding generator 4 forms an electro-magnetic field
induction coil 3 which induces an AC voltage in the open-seam tube
corresponding to a current travelling around the tube circumference.
Any increase in the
rate of deposition beyond this limit requires the employment of several
electrodes. This then allows a higher overall current to be applied for
welding work without the danger of the current carrying capacity of the
being exceeded at any of the individual wire electrodes. In practical
operations, increased performance is obtained by employing a multi-wire
configuration with 2, 3 or 4 electrodes.
The MAG process is
being increasingly used for tack-welding in the manufacture of spiral
longitudinally welded large-diameter pipe. The tack weld also serves as
weld pool backing for the subsequent submerged-arc welding process. The
prerequisites for an optimum weld are a precise edge preparation
joint with wide root faces) and a good, continuous tack weld. In
pipe production, the welding speeds for the tack weld range from
approx. 5 to
The Production of
Longitudinally Welded Pipe (U-ing/O-ing process)
The plates employed for
longitudinally welded pipe are formed on presses featuring open dies
U-ing and closed dies for the O-ing operation. The process is also
referred to as the UOE process (U-ing, O-ing, Expanding) and is applied
manufacture of longitudinally welded large-diameter pipe in individual
up to 18 m. Depending on the material and diameter, the wall
from 6 to 40 mm. The starting material invariably takes the form of
as indicated above.
Production with Separate Forming and SAW Welding Lines
A special roller table
rotates the pipe in precise accordance with its spiral joint, so
SAW welding heads to perform first the inside and then the outside
Precise weld centerline alignment control of the inside and outside
heads is required in this operation in order to minimize weld offset.
The two- or three-wire
method is employed for the inside and outside pass welding operations.
Aside from a few
modifications, the subsequent production stages such as pipe end
hydrostatic testing and also the nondestructive examinations and
tests, are in principle the same as those applied in the conventional
pipe manufacturing process.
Here again, a high
standard of quality is achieved by in-process quality control
are performed after every stage of production. The results of these
inspections are immediately fed back to the individual production stage
concerned in order to ensure continuous product quality optimization.
OF STAINLESS STEEL SHEET
The manufacturing of
stainless steel sheet involved a series of processes. First the raw
melted in a electric furnace. This step usually involves 8 to 12 hours
intense heat. Next the mixture is cast into slabs. Next the slabs goes
forming operations, beginning with hot rolling, in which steel is
passed through huge rolls.
After the stainless
steel is formed, most types must go through an annealing steps.
Annealing is a
heat treatments in which is steel is heated and cooled under controlled
conditions to relive internal soften the metal. Some steels are heat
for higher strength. Lower aging temperatures produce high strength
fracture toughness, while higher-temperature aging produces a lower
Nibbling is a process
of cutting by blanking out a series of overlapping holes and is ideally
for irregular shapes.
Stainless steel can
also be cut using flame cutting, which involves a flame-fired torch
oxygen and propane in conjunction with iron powder. This method is
fast. Another cutting method is known as plasma jet cutting, in which
ionized gas column in conjunction with an electric arc through a small
makes the cut. The gas produces extremely high temperatures to melt the
A bright finish is
obtained by first hot rolling and then cold rolling on polished rolls.
reflective finish is produced by cold rolling in combination with
a controlled atmosphere furnace, by grinding with abrasives, or by
finely ground surface. A mirror finish is produced by polishing with
progressively finer abrasives, followed by extensive buffing. For
polishing, grinding wheels or abrasive belts are normally used. Buffing
cloth wheels in combination with cutting compounds containing very fine
abrasive particles in bar or stick forms. Other finishing methods
tumbling, which forces movement of a tumbling material against surfaces
parts, dry etching (sandblasting), wet etching using acid solutions,
surface dulling. The latter uses sandblasting, wire brushing, or
Manufacturing at the
Fabricator or End User
After the stainless
steel in its various forms are packed and shipped to the fabricator or
user, a variety of other processes are needed. Further shaping is
using a variety of methods, such as roll forming, press forming,
drawing, and extrusion.
are a variety of methods for joining
stainless steel, with welding being the most common. Fusion and
welding are the two basic methods generally used with many variations
In fusion welding, heat is provided by an electric arc struck between
electrode and the metal to be welded.
Process of Steel Sheet
The Air Bending
The upper tool (or
punch) is pressing down on the sheet metal at the center of the bend
lower tool (or vee die) is pressing up on the sheet metal.
In general, the tooling
only touches the sheet metal along these 3 lines. Thus the process is
In general, sheet metal
stretches when it is bent. For example, if you were to take a piece of
that measured exactly 2.000" in the flat and then bent it down the
at 90°, when you measure the length of the 2 bends (from the outside of
bend), the sum of the leg lengths would be greater than 2.000" (in the
case of 16 GA (.059) cold roll steel, it would be likely to add up to
Brief Overview of Stainless Steel
This development was
the start of a family of alloys which has enabled the advancement and
chemical processing and power generating systems upon which our
society is based.
important sub-categories of stainless steels have been developed. The
sub-categories are austenitic, martensitic, ferritic, duplex,
hardening and super alloys.
Austenitic grades are
those alloys which are commonly in use for stainless applications. The
austenitic grades are not magnetic. The most common austenitic alloys
iron-chromium-nickel steels and are widely known as the 300 series. The
austenitic stainless steels, because of their high chromium and nickel
are the most corrosion resistant of the stainless group providing
fine mechanical properties. They cannot be hardened by heat treatment,
be hardened significantly by cold-working.
The “L” grades are used
to provide extra corrosion resistance after welding. The letter “L”
stainless steel type indicates low carbon (as in 304L). The carbon is
.03% or under to avoid carbide precipitation. Carbon in steel when
temperatures in what is called the critical range (800 degrees F to
degrees F) precipitates out, combines with the chromium and gathers on
The “H” grades contain
a minimum of .04% carbon and a maximum of 10% carbon and are designated
letter “H” after the alloy. People ask for “H” grades primarily when
material will be used at extreme temperatures as the higher carbon
material retain strength at extreme temperatures.
Ferritic grades have
been developed to provide a group of stainless steel to resist
oxidation, while being highly resistant to stress corrosion cracking.
Duplex grades are the
newest of the stainless steels. This material is a combination of
and ferritic material. This material has higher strength and superior
resistance to stress corrosion cracking. An example of this material is
2205. It is available on order from the mills.