Construction industry is the largest consumer of material resources, of both the natural ones (like stone, sand, clay, lime) and the processed and synthetic ones. Each material which is used in the construction, in one form or the other is known as construction material (engineering material). No material, existing in the universe is useless; every material has its own field of application. Stone, bricks, timber, steel, lime, cement, metals etc. are some commonly used materials by civil engineers. Selection of building material, to be used in a particular construction, is done on the basis of strength, durability, appearance and permeability. The stone which is used in the construction works, in one form or another is always obtained from the rocks. The rocks may be classified in four ways; geological classification, physical classification, chemical classification and classification based on hardness of the stone. Various king of rocks come under these classification for example; igneous rocks, plutonic rocks, sedimentary rocks, silicious rocks, stratified rocks etc. brick is the most commonly used building material which is light, easily available, uniform in shape and size and relatively cheaper except in hilly areas. Bricks are easily moulded from plastic clays, also known as brick clays or brick earth. Bricks can be moulded by any of the three methods; soft mud process, stiff mud process and semi dry process. There are various kinds of bricks; specially shaped bricks, burnt clay bricks, heavy duty bricks, sand lime bricks, sewer bricks, refractory bricks, acid resistant bricks etc. lime is an important building material, it has been used since ancient times. Lime is used as a binding material in mortar and concretes, for plastering, for manufacturing glass, for preparing lime sand bricks, soil stabilization etc. Concrete is a construction material obtained by mixing a binder (such as cement, lime, mud etc.), aggregate (sand and gravel or shingle or crushed aggregate), and water in certain proportions. Based on the binding materials, the common concretes can be classified as; mud concrete, lime concrete, cement concrete and polymer concrete. World demand for cement and concrete additives is projected to increase 8.3 percent annually in next few years.
This book basically deals with rock and stone, formation of rocks, classification of rocks, geological classification, metamorphism physical classification of rocks, chemical classification,
classification based upon hardness of the stone composition of stone (rock forming minerals), igneous rock forming minerals, sedimentary rock forming minerals, texture of the rocks, types of fractures of rock, uses of stone, natural bed of stone, aluminium and magnesium alloys, mechanical properties of a partially cured resin, DMA characterization, chemical advancement of a partially cured resin, differential scanning calorimeter characterization, chemical mechanical relations, moisture content as a variable, wetability and water repellency of wood, fungal and termite resistance of wood etc.
The book provide wide coverage of building materials such as stone, bricks, lime, mortars, concrete, asbestos, gray iron, cast iron, steel castings, aluminium, wood, architectural paints and so many others with their applications in building construction. The book is resourceful for all professionals related to construction field, technocrats, students and libraries.
Rock and Stone
Formation of Rocks
Classification of Rocks
Physical classification of rocks
Classification based upon hardness of the stone
Composition of Stone (Rock-forming Minerals)
Igneous rock forming minerals
Sedimentary Rock Forming Minerals
Texture of the Rocks
Types of Fractures of Rock
Uses of Stone
Natural bed of Stone
Seasoning of Stones
Characteristics or Qualities of Stones
Characteristics of principle Building Stones
Decay or Deterioration of Stones
Preservation of Stone
Important point to be Considered before Starting Quarrying
Methods of quarrying Stone
Various Operations of Blasting
Precautions in Blasting
Making of Primer Cartridge
Storing of explosives
Handling of misfires
Dressing of Stone
Machines Required for Quarrying Stone
2. BRICKS AND OTHER CLAY PRODUCTS
Brick Earth and its Constituents
Sources of Brick Earth
Qualities of Brick Earth
Chemical composition of Brick Earth
Functions of the constituents of Brick Earth
Pebbles of Stones and Gravel
Limestone and Kankar
Vegetation and Organic Matter
Manufacture of Clay Bricks
Selection of site
Preparation of Clay
Moulding of bricks
Soft mud process
Stiff Mud Process
Semi Dry Process
Drying of Bricks
Burning of Bricks
Classification of Burnt Clay Bricks
Properties of Burnt Clay Bricks
General Quality of Bricks
Dimensions and Tolerances
Water Absorption of Bricks
Strength of Bricks
Testing of Bricks
Test for Compressive Strength
Test for Water Absorption
Test for efflorescence
Test for warpage
Specially shaped Bricks
Burnt Clay Facing Bricks
Heavy Duty Bricks
Perforated building bricks
Sand lime Bricks
Acid Resistant Bricks
Process for Manufacturing Roofing Tiles
Process for Manufacturing Flooring and Wall Tiles
Specifications for Building Tiles
Glazed Earthenware Tiles
Properties of Lime
Uses of Lime
Source of Lime
Some Important Terms and their Definitions
Varieties of lime
Classification of Lime
Uses of fat lime
Classification of Lime According to I.S. 712-1984
Indian Standard Specification for Lime
Description of Each Stage of Operation
Field Control Test for Assessing Quality of Lime
Manufacture of Fat Lime
Advantages of continuous kiln
Manufacture of Natural Hydraulic Lime
Manufacture of Artificial Hydraulic Lime
Storage of Lime
Field Slaking of Lime and Preparation of Putty
Objective of Slaking
Determining the Slaking Nature of Lime
Slaking Procedure for Quick Slaking Lime
Methods of Slaking Lime
General Precautions in Slaking
Slaking Procedure for Medium and Slow-slaking Limes
Making Coarse Stuff and Putty from Hydrated Lime or Powder
Storage after slaking
Testing of Lime
Classification of binding materials
Precautions to be taken in handling lime
Properties of Lime
Classification Based on Fineness
Bulking of Sand
Desirable Properties of Sand
Function of Sand in Mortars
Fineness Modulus of Sand
Tests for Sand
Selection of Sand for Use
Substitutes for Sand
Types of Mortars
Properties of Good Mortar
Test for Mortars
Precautions in using Mortar
Preparation of lime Concrete
Laying of Lime Concrete
Properties of Lime Concrete
Use and Precautions
Grading of Aggregate
Proportioning of Fine Aggregate to Coarse Aggregate
Maximum Size of the Aggregate
Measurement of Cement Concrete Ingredients
Significance of Bulking of Sand
Water Cement Ratio (W/C Ratio)
Proportioning of Concrete Mixes
Cube strength of Concrete
Properties of Cement Concrete
Factors Affecting Proportions of Concrete
Strength of Concrete
Mixing of Concrete
Transporting the Concrete
Placing of Concrete
Consolidation or Compaction of Concrete
Curing of Concrete
Removal of Form Work
Joints in Concrete
Some other Types of Cement Concretes
Asbestos Sheets and Boards
Asbestos Cement Pipes
7. ASPHALT, BITUMEN AND TAR
Other Allied Terms
Bitumen Felt/Tar Felt
Specifications and use
Other Bituminous Materials
Tests for Bitumen
8. GRAY IRON
The Metastable Iron-Iron Carbide System
Solidification of an Fe-C-Si Alloy
Chemical Composition Effects
Silicon Content and Graphitization
Sulfur and Manganese
Heat-treatment of Gray Iron
Effect on Microstructure
Aluminum and Titanium
Effect on Properties
9. CAST IRON
Composition and Graphitization
Properties of Cast Irons
10. STEEL CASTINGS
Molding Processes And Sands
High permeability and Low Moisture Content
Organic and Other Additions
Green-sand-molding Casing Defects
Dry-sand Molds and Skin-dried Molds
Other Types of Molds
Core and Mold Washes
11. ALUMINIUM AND MAGNESIUM ALLOYS
ALuminum Alloying Principles
Heat-treatment of Cu-Al Alloys
Magnesium and silicon
12. DUCTILE IRON
Solidification Of Ductile Iron
Development of Graphite Spheroids
Role of Magnesium
Control of the Common Elements
Acid Cupola Melting
Basic Cupola Melting
13. MALLEABLE IRON
Pearlitic Malleable Irons
Other Malleable Irons
14. RESIN CHARACTERIZATION
Mechanical Properties of a Partially Cured Resin â€” DMA Characterization
Chemical Advancement of a Partially Cured Resinâ€”Differential Scanning Calorimeter Characterization
Moisture Content as a Variable
Measurement of Pressing Environments
15. THERMO-GRAVIMETRY OF WOOD REACTED WITH FLAME RETARDANTS
Results and Discussion
Phosphorus And Nitrogen
16. WETTABILITY AND WATER REPELLENCY OF WOOD
Automated surface tension analyzer
Computer program: wood wettability study
Contact angle from attractive force
Contact angle from work of adhesion
Surface free energy estimation
Interaction parameter calculation
Results and Discussion
Surface free energy estimates
Interaction parameter calculation
17. FLAME RETARDANT TREATMENT OF
Materials and Methods
Preparation of specimens
Treatment of specimens
Dimensional stability tests
Results and Discussion
Treatment of specimens
18. FUNGAL AND TERMITE RESISTANCE OF WOOD
Materials and Methods
Reaction time and chemical analysis
Results and Discussion
19. WEATHERING OF WOOD
The Weathering Process
Weathering of Wood-Based Materials
Protection Against Weathering
20. ARCHITECTURAL PAINTS
Exterior Paints for Wood
Characteristics of Wood Siding
Binders for Exterior House Paints
Pigments for Colored Paints
Microorganisms in Paints and Coatings
Formulating Exterior Paints for Wood
Interior Paints for Plaster and Wallboard
Exterior Emulsion Paints for Masonry
Exterior Solution Type Paints for Masonry
Interior and Exterior Enamels
Enamels for Wood and Concrete Floors
21. BUILDING CONSTRUCTION ADHESIVES
Advantage of Using Adhesives in Construction
Gap-Filling Phenol Resorcinol Adhesives
Resorcinol Resin Adhesives
Polyvinyl Acetate Resin Emulsion
Phenolic Resin Adhesives
Melamine-Urea Resin Adhesives
Urea Resin Adhesives
Epoxy Resin Adhesives
Types Of Epoxy Flooring
Future Developments In Epoxy Floors
Adhesion And Grouting
Concrete Crack Repair
Bonding Concrete to Concrete
Epoxy Bonding in New Structures
Bulk Mechanical Properties
Miscellaneous Bonding Applications
24. GROUTS FOR LEVELLING: MISC.
Epoxy laminates for concrete moulds
Manufacture and Processing
Cement Paste Structure and Concrete Properties
Special Purpose and Blended Cements
Economic Aspects, Production, and Shipment
Specifications and Types
27. INSULATING MATERIALS
Terminology Related to Thermal Insulation
Requirements of Thermal Insulating Materials
Types of Insulating Materials
Expanded Blast Furnace Slag
Units of Sound
Velocity of Sound
Requirement of Sound Insulating Materials
Types of Acoustical Materials
Unifil Acoustical Plaster
Prefabricated Boards or Tiles
the engineering structures
are made from some materials. Each material which is used in the
one form or the other is known as engineering material. Engineering
are also sometimes termed as building materials or materials of
Every engineer has to come across various materials in carrying out
engineering works and projects and as such he is supposed to be fully
conversant with their properties and behaviour.
in the universe is useless. Every material has its own field of
engineer has to be conversant with the properties of most of them.
timber steel lime cement metals etc. are some commonly used materials
Civil Engineer. Even engineers in branches of Mechanical Electrical
etc. are required to know the properties of these materials. Selection
building material to be used in a particular construction is done on
of strength durability appearance and permeability. In order to carry
constructions some standards for the materials to be used are fixed.
standards are fixed by Indian Standards Institutions (ISI). These
continuously reviewed and modified from time to time to suit to the
conditions. All the commonly used Engineering Materials have been
this book in regard to their properties place of occurrence manufacture
uses. In the first chapter stone has been discussed.
that our country may face shortage of common building materials like
bricks aggregates plywood plastics etc. It is therefore an urgent need
handle the situation by manufacturing cheap building materials and also
developing new building materials. Shortage of building materials and
costs are likely to hamper many projects and developmental programmes.
therefore imperative to lay greater emphasis on the growth of such
which use local raw material resources for producing less costly
Rock and Stone
is the term
used to name a solid portion of the earth s crust. It has no definite
chemical composition. It is generally very big in size. The rocks have
more than one minerals. Rocks having only one mineral are known as mono
mineralic rock and those having several minerals as Poly mineralic
Quartz sand pure gypsum magnesite are examples of mono mineralic rocks
granite basalt etc. those of poly mineralic rocks. The rocks are named
the predominant mineral present in it.
calcium carbonate mineral as predominant mineral is termed as
Similarly rock predominant in clay is called argillaceous rock. Quartz
mica augite dolomite are some of the common rock forming minerals.
always obtained from rock. The rock quarried from quarries is called
Quarried stone may be in form of stone blocks stone aggregate stone
lintels stone flags etc. Stone has to be properly dressed and shaped
is used at the place of its use.
Formation of Rocks
consists of sun as the centre and all other planets revolve around it.
earth is one which originally was in form of mass of incandescent
mass of gases after cooling first converted into molten mass and then
further cooling the surface of the molten mass converted into solid
process of cooling of earth is still continuing and thus process of
solidification of molten matter is also continuing. Existence of molten
under earth s crust is reflected by eruption of volcanos from time to
molten matter of which the earth and other planets were originally made
up and existence
of which is confirmed by the volcanic eruptions is known as Lava or
Classification of Rocks
is used in the construction works in one form or the other is always
from the rocks. The rocks may be classified in following four ways.
based on hardness
of the stone.
to this classification
rocks may be divided into following three categories.
Sedimentary rocks and
Igneous rocks. As already
explained in article
1.3 formation of rocks the
portion of the earths surface is very hot and it can cause fusion even
ordinary pressures. The molten lava or magma occasionally tries to come
the earth s surface through cracks or other weak spots. This magma when
exposed to the outside cooling effect solidifies in the form of a rock
igneous rock. Hence igneous rocks are formed as a result of
molten lava lying below or above the earth surface due to cooling
Depending upon the cooling effect following different types of igneous
igneous rocks. This type
of igneous rock is formed when molten lava or magma gets exposed to
the surface of the earth. In this case cooling of magma is very rapid
structures of these rocks are extremely fine grained. This rock may
some quantity of glass which is non crystalline. Example of Volcanic
rock is Basalt.
byssal rocks. This rock is
formed when magma is allowed to cool at comparatively slower rate. Such
conditions of cooling generally prevail at relatively shallow depth
crust. Since rate of cooling is not as fast as in case of volcanic
structure of resulting rocks is fine grained and crystalline but not as
in case of volcanic rocks. The best example of hypa byssal rock is
rocks. These rocks are
formed when cooling of magma takes places at a very slow rate. Such
of cooling generally exist at a considerable depth from the surface of
earth. The structure of these rocks is coarse grained and crystalline.
from Plutonic rock is most commonly used in building industry. The best
of plutonic igneous rock is granite.
the igneous rocks contain
minerals like Augite Felspar Horn blende mica quartz etc. Before
all these minerals are in molten state along with some gases forming
rocks. The rocks are
formed by the deposition of broken up materials like sand clay
1. Sedimentary Rock
rocks dead sea organisms etc. with the aid of water wind frost etc. on
existing rocks. Earth s crust when subjected to weathering cause
which results in the formation of clay sand and pebbles. The
is carried by rain water streams wind etc. and settles as and when
become favourable to it. The process of deposition of new disintegrated
continues in regular layers. With age this deposited mass becomes a
as Sedimentary rock. Since the sediments get consolidated in horizontal
nearly horizontal layers these rocks show different layers distinctly.
layers of this rock may have same or different composition colour and
as all the layers have deposited under varying conditions. The
these rocks is shown in Fig 1. These rocks can be easily split along
bedding plane. Sand stone limestone slate and shale are some common
rocks. These rocks
are formed when igneous as well as sedimentary rocks are subjected to a
large heat and pressure. The process of change due to heat and pressure
known as metamorphism. The rocks change their character due to
the resulting mass of rock change into hard and durable foliated
quartzite and slate are common examples of metamorphic rocks.
igneous and sedimentary origin represent a mass of mineral composition.
mass remains in equilibrium under the general atmospheric conditions.
either temperature or pressure or even both are increased the
the mass gets disturbed and its minerals realign themselves to re
equilibrium. Re alignment of minerals change the texture of the rock.
process is known as metamorphism. It should be remembered that
action and sedimentation action are not included in metamorphism.
chemically active fluids are the three agents which bring about the
supplied by the general rise of temperature inside the earth or by hot
and pressure may be caused due to heavy overlay rocks or due to
movement of the
earth during earthquakes. Chemical liquids do not take any active part
process of metamorphism. Following four types of metamorphisms occur.
metamorphic change takes place at large depths under the earth. Uniform
pressure and high temperature are responsible for this change. This is
the fact that rocks become plastic mass at certain depths and plastic
be in equilibrium only under uniform pressure.
metamorphism. The changes
brought about in this metamorphism are predominantly due to high
metamorphism or change is brought about by directed pressure only and
temperature uniform pressure do not play any role in it. This change
place at the surface of the earth.
have used two terms above
uniform pressure and directed pressure. Directed pressure can be
solids only. Directed pressure when applied to liquids is converted
uniform pressure. Uniform pressure can be applied to liquids and solids
Temperature increases with depth inside the earth. The changes brought
the rock by combination of heat and directed pressure are known as
Thermal metamorphism. This change takes place not at very large depths
a result of
metamorphosis limestone and marl become marble Basalt and trap are
schist and laterite and granite becomes Gneiss.
Physical classification of rocks
to general structure the
rocks may be classified into following three categories.
or laminated rocks.
rocks. These are such
rocks which possess planes of stratification or cleavage. These rocks
easily split along these planes. An experiences supervisor at the
quarry site can
easily locate these planes. All the sedimentary rocks have distinct
stratification and thus are stratified rocks.
rocks. The structure
of these rocks is compact granular. They do not show any layers of
stratification or cleavage. All the igneous rocks of volcanic origin
examples of unstratified rocks.
or laminated rocks.
These rocks comprise of thin laminations. They can be split in definite
direction and size. Metamorphic rocks come under the category of
upon chemical composition the
rocks can be classified into following three categories
or clayey rocks
rocks. These rocks
consist of silica as their predominant constituent. These rocks are
and durable and are not easily affected by weathering agencies.
trap basalt sandstone etc. are the examples of silicious rocks.
weaker materials may cause their disintegration.
constituent of these rocks is clay. The principle constituent alumina
nothing but clay remains mixed up in varying proportion with siliceous
and carboneous matter. These rocks are hard durable dense and brittle
nature. Laterite slate porphyry are the best example of argillaceous
rocks. The predominant
constituent of these rocks is calcium carbonate. The durability of
is greatly dependent upon the constituents of surrounding atmosphere.
stone marble dolomite kankar etc. are the examples of this type of
based upon hardness of the stone
classification stone may be classified as soft medium hard and very
Granite trap taconite are the very hard varieties of rocks. Hard rocks.
basalt trap gravel quartzite are the hard varieties of rocks. Medium
Dolomite and lime stone are the medium varieties.
gypsum sand stone slate etc. are the soft varieties of stones.
hardness of various minerals starting from hardest to softest have been
(Hardest) Corundum Topaz
quartz Felspar Apatite Flouspar Calcite rocks salt Talc (softest).
of Stone (Rock
rocks are composed of mineral earths alkalies oxides or iron and
Silica (SiO2) alumina (Al2O3) lime (CaO) and magnesia (MgO) are the
earths which are usually found is rocks in one form or the other. Soda
and Potash (K2O) are the usual alkalies present in the rocks. Presence
alkalies in the rocks is not preferred as it causes stone to
exposed to weather. Generally stones comprise of more than one mineral
BRICKS AND OTHER CLAY PRODUCTS
deals with construction materials such as bricks tiles refractory
and stonewares. All these materials are made from clay and are also
clay products. Burning of moulded clay products makes them sufficiently
for use as construction materials. Though tiles refractory bricks
and stonewares serve different construction purposes brick is the most
used building material. It is light easily available uniform in shape
and size and
relatively cheaper except in hilly areas. Bricks are easily moulded
plastic clays also known as brick clay or brick earth.
BRICK EARTH AND ITS CONSTITUENTS
Sources of Brick Earth
derived by the disintegration of igneous rocks. Potash feldspars
microcline (K2O Al2O36SiO2) is mainly responsible for yielding clay
the earth. This mineral decomposes to yield kaolinite a silicate of
which on hydration gives a clay deposit Al2 O3 2H2O known as Kaolin.
of Brick Earth
earth should be such a mixture of pure clay and sand that when prepared
water it can be easily moulded and dried without cracking or warping.
contain a small quantity of lime which causes the grains of sand to
helps bind the particles of brick clay together. It should also contain
amount of oxide of iron which acts in the same way as lime and moreover
the brick its peculiar red colour.
composition of Brick Earth
to IS 2117
1975 the clay or mixture of clay selected should preferably conform to
following mechanical composition
20 30% by weight
20 35% by weight
35 50% by weight
content of clay and silt may preferably be not less than 50% by weight.
total lime (CaO) and magnesia (MgO) in the case of alluvial soil should
more than one per cent and in other cases should not be preferably more
15%. The lime should be in finely divided form. Also the total water
material should not be more than one per cent by weight.
of the constituents of
in brick earth prevents shrinkage cracking and warping of bricks but
of sand will make the bricks brittle. Clay or alumina makes brick earth
and lends the brick its hardness but unless mixed with sand it will
and warp in the process of drying and burning. Lime and oxides of iron
as fluxes helping the grains of sand to melt and bind the particles of
together. Oxides of iron also impart a red colour to the brick but
excess of it
makes the brick dark blue. Magnesia present in clay with oxide of iron
materials if present in brick earth have an adverse effect on the
brick and should be removed or treated before undertaking the
Pebbles of Stones and Gravel
do not allow the clay to be
mixed uniformly and thoroughly and result in weak and porous brick.
containing grits are likely to crack and cannot be readily cut or
present act as hygroscopic substances. They absorb moisture from the
in due course of time and create damp conditions. The moisture on
behind a greyish white deposit known as efflorescence on account of
appearance of the building is spoiled. Common salts generally present
are sulphates of calcium sodium and potassium. The presence of Reh or
consisting of sodium sulphate with more or less of sodium carbonate and
chloride renders the clay utterly unsuitable for brick making. Presence
or Kallar can be easily detected by the efflorescence on the sides of
excavation if the soil is moist but it would be appropriate in all
moisten the soil with water and subject it to evaporation and check for
Limestone and Kankar
large quantity of lime and limestone in lumps is detrimental to brick
lumps of limestone if burnt in a brick slake afterwards and split the
Thus limestone should be present in very finely divided state.
and Organic Matter
Matter if present in
brick earth will produce porous bricks. This is due to the evolution of
during the burning of the carbonaceous matter resulting in the
MANUFACTURE OF CLAY BRICKS
by treating suitable brick earth or clay moulding it to shape and size
(allowing for shrinkage) drying it and then baking burning or firing it
temperatures in order to fuse the constituents to a hard homogeneous
process of manufacture can be described under the following heads.
Selection of Site
selected for the manufacture of bricks must have suitable soil
sufficient quantity otherwise unnecessary labour and cost of digging
transportation of the soil would be involved.
making soil suitable for brick making certain materials are required to
mixed with the soil. Therefore the availability of such materials near
of brick making is of great importance. It is also necessary that water
fuel like coal and wood are easily available in sufficient quantities.
to IS 2117
1975 the site should be selected after giving due consideration to the
of soil and location of the water table. Select a site such that the
table during burning session is at least 1 metre below the kiln floor.
Preparation of Clay
to IS 2117 1975 brick
clay should be prepared in two stages
The soil is
in heaps and exposed to weather for at least one month in cases where
weathering is considered necessary for soil. The soil is turned at
and it is ensured that the entire soil is wet throughout the period of
weathering. The purpose of weathering is to disintegrate big boulders
under the action of atmospheric agencies to make it a uniform mass and
eliminate the impurities which get oxidized.
the required quantity of water should be mixed with the soil to obtain
right consistency for moulding. Addition of sand and other materials if
necessary may be made at this stage to modify the composition of the
water to be added may range from ¼ to 1/3 of the weight of soil sandy
requiring less water and clayey soils more water. But the nature and
wetness of the soil at this stage should also be duly considered.
soil is kneaded with spades or other manual or mechanical equipment
plastic mass. After the addition of water and kneading the soil may be
in a pug mill of suitable size corresponding to quantity of bricks to
manufactured. The pug mill may be mechanically operated or hand
shown in fig. 1a and 1b.
Moulding of Bricks
may be moulded by any one
of the following methods
mud process (Hand moulding)
mud process (Machine
dry process (Machine
Soft Mud Process
by using 25 to 30% of water is pressed into the mould by hand. Some
moulds of timber or metal are shown in fig. 2.
1 (a) Manually operated pug
mill (b) Mechanically operated pug mill.
either of wood or of thin steel plates. Seasoned wood should be used to
changes in the dimensions of the mould. The edges are protected with
brass or steel. Steel moulds made of plates 6 mm thick are used if the
are to be manufactured on large scale. Normally shrinkage allowance
from 10% to 12% is provided. Thus the size of the mould is such that it
give the finished brick its required size.
per IS 2117 1975 the mould
should be constructed preferably of metal. The thickness of the sides
mould shall not be less than 3 mm if made of metal and not less than 10
made of wood.
moulding bricks with the help of moulds is also called hand moulding.
to IS 2117 1975 handmade bricks may be either ground moulded or table
In case it is ground moulded a level firm surface should be used.
specifications for accessories used in table moulding are given below
The moulding table is 1.2 to 1.8 m long and 0.6 to 1.0 m wide and is
wood or iron. It is smoothly finished at the top and supported
a height of 1m to 1.2 m. Also there are holes to accommodate accurately
bottom pins of the stock board.
is a wooden board with iron lining around the upper edge and with such
dimensions as to fit accurately but loosely the interior of the mould
3.4.). The stock board is provided with four pins one at each corner of
bottom side which when fitted into the corresponding holes on the
table hold the board tightly in position during moulding. The stock
should also have a projection at the top so as to form the frog of the
These are rectangular pieces of wood of size 30 cm x 15 cm x 10 mm
thick with a
smooth surface on one side. Pellet boards are used for conveying
to the drying yard.
inside of the mould is cleaned and then sprinkled with sand or ash. If
moulding is adopted then the mould is dipped in water and cleaned. The
then set firmly on the level surface.
clay slightly more than the volume of the mould is taken and rolled in
is then shaped suitably into a single lump and dashed firmly into the
with a force that is to be judged by the moulder by experience so that
completely occupies the mould without air pockets and with minimum
removal. The surplus soil is scrapped off with a sharp straight edge
known as a
style or a stretched wire and the top surface is leveled.
assembly of the mould is then lifted given a slight jerk and inverted
release the moulded brick on a pellet board in the case of table
moulding or on
a dry level surface of the ground in the case of ground moulding.
ground may be advantageously sprinkled with sand before releasing the
over it so that bricks do not stick to the ground. When a frog is not
bottomless mould may be adopted in which case inversion to release the
bricks from the mould will not be necessary. It may be added that each
can make on an average about 500 to 1000 bricks per day.
Stiff Mud Process
clay after proportioning of the ingredients is mixed with water up to
to 18% and is thus initially prepared for being put in the machine.
two stages in machine moulding
final mixing when kneading and tempering is done in the pug mill.
the second stage bricks are formed by extruding stiff clay through a
orifice in the extruding machine.
the extruding machine may be combined in one unit as shown in Fig. 5.
cylinder or barrel of the machine known as the pug mill is kept filled
prepared clay which is mixed well and pressed down against the coarse
of a horizontal spiral screw. The pressing screw is fixed near the top
horizontal axle called `auger. At one end of the auger power is applied
driving the machine and at the other end is fixed a metal die through
clay extrudes with the desired section. The extruding clay is a
and is received on a conveyor to be further cut into pieces of the
sizes of bricks.
cut either by a single wire or by a number of wires fixed on a frame as
in Fig. 6. The bricks obtained by this method have a smooth rectangular
Semi Dry Process
only 7 to 10% of water is added so that it forms just a damp powder. It
pressed under a pressure of 1000 to 1200 kg/cm2 with the aid of a
machine to form the bricks. At the first plunger machine the material
automatically measured off fed into a steel mould and pressed by
(heated to prevent sticking) on two opposite sides. It is then expelled
the mould and transferred to another plunger machine where it is again
of the beds receiving the frog at this stage. Pressed bricks do not
drying and could be put into the kiln directly for burning. They are
strong and compact and on account of the latter quality they are more
than bricks moulded by the stiff mud process.
can also be employed for the soft mud process to press pugged clay into
with the aid of the plunger. It is possible to mould 4 to 8 bricks at a
against one by hand moulding.
construction material obtained by mixing a binder (such as cement lime
etc.) aggregate (sand and gravel or shingle or crushed aggregate) and
certain proportions. The mix is placed properly in moulds or forms to
a suitable environment. When the various ingredients are mixed these
plastic mass which can be moulded into the desired shape and size. The
mass when allowed to cure in suitable environment hardens to become a
mass capable of maintaining its shape and size and sustaining certain
Hardening in concrete is a result of the chemical/physical combination
binding material water and air in a given environment. The hardened
obtained serves different purposes depending on the type of binding
used quality and grade of concrete location and size of such concrete
The type of
concrete is basically known by its
binding material. It is the binding material which plays the main role
behaviour and characteristics of the resulting concrete. Based on the
materials the common concretes can be classified as
are used to serve certain requirements of various concrete elements
different situations. Behaviour of these concretes can further be
the use of certain admixtures special treatments or combination of
materials. Properties of some of these concretes can further be
through certain special techniques of construction (such as
made by using suitable mud as the binding material. Mud is prepared
quality clay and water by kneading. The mud is mixed with coarse
shingle to obtain mud concrete. The mud concrete is laid in suitable
compacted by ramming or tamping. The mud concrete properties are mainly
interlocking of aggregate particles and filling of voids by mud. Mud
can easily be affected by moisture and has poor impermeability
strength characteristics. This type of concrete is generally used for
temporary type of constructions in foundation bases non load bearing
water proofing treatment on external faces etc.
popular binding material in Civil Engineering constructions. Properly
lime slurry or putty is used as binding material in lime mortar and
concrete. Lime concrete is prepared by mixing lime mortar with
(shingle or gravel). Lime concrete is laid in layers and compacted
ramming. Lime concrete is commonly used for foundation base layers
layers roof insulation layers over stone patties (slabs) etc. Lime
exhibits fairly good properties of durability impermeability and
specially suitable for base courses. It has been used in many important
monumental buildings which have stood the test of time. The details of
preparation properties and used shall be dealt in a subsequent section.
advent of cement as binding material in the 19th century revolutionized
construction activities. Cement concrete obtained by mixing cement sand
or shingle or crushed aggregate and water is a versatile and popular
construction material. Cement concrete is used in almost all modern
due to its superior qualities and appropriate quality controls possible
and after construction. Cement concrete is used in various forms and
different purposes in construction works. Certain weak points in cement
concretes for specific purposes can easily be overcome by adopting
techniques such as steel reinforcing prestressing fibre reinforcing
cement and polymer impregnation techniques etc. The properties of
concrete can also modified by the use of certain admixtures during its
preparation. The details of preparation properties and uses shall be
certain polymers and epoxy resins have been developed which exhibit
binding qualities. These polymers are now being used for preparation of
polymer concretes. Polymers concrete is obtained by mixing epoxy resins
polymers with plastic aggregates. Polymer concrete exhibits very high
Cost of polymers and other epoxy resins used as binding material is
and hence the cost of polymer concrete is also high. Due to the high
small production of epoxy resins the use of polymer concrete is
India use of such polymer concrete is yet to pick up. The future
the manufacture and use of polymer concrete for construction of highly
sophisticated structures is very good.
Mud concrete. This concrete
does not carry any importance. It is prepared by mixing brick bats in
mortar. Brick bats may be made from kuchha or pucca bricks. Sometimes
crushed stone may be mixed with mud mortar to form mud concrete.
used for preparing hard base. Over which lime concrete may be laid and
flooring may be spread. During construction of ground floor of
of earth is first of all consolidated by sprinkling sufficient amount
During consolidation process broken brick bats or crushed stone pebbles
waste at the site are also spread and rammed into the fillings by
Earth filling added with water and broken brick or stone bats forms mud
concrete which on setting develops a hard surface over which permanent
of any form may be laid. The same processes of consolidation with mud
may be carried out during preparation of foundation bases.
aggregate used in mud concrete is usually of broken bricks of size 4 cm
brick ballast is mixed with 40 m3 of prepared mud mortar.
Preparation of Lime Concrete
ingredient of this concrete is slaked lime as the binding material. The
lime is obtained in various forms as hydrated lime powder lime putty or
lime slurry prepared by grinding in suitable grinding mill (ghani
lime is first mixed with sand to prepare lime mortar which is further
with coarse aggregate (shingle gravel crushed stone or brick aggregate)
suitable proportions. Preparation of hydrated lime and lime putty has
been discussed in the chapter on lime and may be referred to for
of lime concrete a hard impervious level base is prepared by stone or
pitching. Appropriate quantity of sand is spread as a horizontal stack
(generally taking lime sand 1 1 to 1 3 by volume). Measured quantity of
putty or slaked lime is spread over the sand stack and the whole mass
thoroughly by cutting and turning the mass with shovels and
sprinkling enough quantity of water to make the mass plastic. The
mortar is allowed to mature for 1 to 3 days during which it is not
dry. Another method of mixing is by using a small water tight trough
or tank made from stone slabs or brick masonry. Enough quantity of
measured quantities of lime are added to the prepared trough and lime
stirred well in water.
desired proportions the measured quantity of sand is added and then
upside down a number of times till the whole mass become uniform (Fig.
and (b)). This mortar is left for one to three days for maturing in wet
conditions if the slaked lime is not already matured earlier.
aggregate of the desired type and quantity is laid in stacks on the
hard impervious level surface and a measured quantity of lime mortar is
uniformly over the coarse aggregate stack. Sufficient water is
the stack and it is cut into layers and turned upside down with the
spades or shovel till the whole mass becomes uniform.
Laying of Lime Concrete
lime concrete is to be laid is prepared by cleaning leveling wetting
compacting by ramming properly. The material is laid on prepared
bases or flooring bases in layers and rammed manually with steel
During the ramming process some water may be sprinkled if the concrete
and stiff. After ramming the lime concrete thoroughly it is moist cured
sprinkling water for 7 to 14 days.
can also be laid in roof terraces for providing an insulating and water
proofing layer over stone slabs. Generally kankar lime is preferred for
purpose. Kankar lime is slaked and laid on the roof slab and mixed with
weight coarse aggregate (preferably brick aggregate). In case of kankar
concrete for terracing (Dhar) no fines are used and lime is also used
higher proportion (Lime coarse aggregate 1 1 to 1 2). After thoroughly
the lime and coarse aggregate some angular aggregate of 10 mm size is
the surface of the wet plastic lime concrete. The lime concrete terrace
compacted by light weight rammers (stone thapies of about 2 to 3 kg
covering the whole surface a number of times till the concrete mass
dense stiff and solid. While the lime concrete is wet and plastic
admixtures such as jaggery (sugar or gur solution) powdered fenugreek
(methi) hemp (or jute) fibres etc. are sprinkled near the surface
ramming is started. Ramming continues for 2 3 days during which the
kept wet by sprinkling gur water. During this process lime cream comes
surface and forms a thin film which helps in obtaining a smooth
fibrous material increases the surface resistance to shrinkage or other
methi powder fills the pores and makes the surface more water proof.
solution helps in better maturing and curing of lime concrete specially
ASPHALT, BITUMEN AND TAR
these materials can be traced back to ancient times. Their importance
realized by early civilizations who employed them for a variety of
ranging from mummification to building temples palaces and vast
systems and enduring highways. A ritual pool dating back to 3000 B.C.
discovered in Mohenjodaro in the valley of the Indus was water proofed
layer of bitumen on the walls. After an apparently extinct phase
middle ages and renaissance period bitumen was re discovered in the
deposits of impregnated limestone in France Switzerland and Germany in
eighteenth century. Put to use for side walls and pavings in different
the continent it proved to be satisfactory. The utility of the material
grown ever since and today its versatility as a construction material
well judged from its use and application for roofing road surfacing
varnishes acid resistant paints and cold moulded products.
introduction asphalt bitumen and tar are referred to as Bituminous
which are essentially hydrocarbon materials frequently accompanied by
metallic derivatives. They may be gaseous liquid semi solid or solid in
and are completely soluble in carbon di sulphide (CS2.). They possess
common properties as follows
Thermo viscosity i.e. variance of
viscosity (which is roughly the opposite of fluidity) with temperature.
Adhesion to solid surfaces.
Water proofing characteristics under
above desirable properties of bituminous materials render them very
useful as a
protective agent an adhesive and a sealant.
for native asphalt was asphaltos and the Latin word bitumen. The latter
comes from the original Sanskrit word Gwitumen applied to native
fuels. Fundamental differences still persist between the two terms
used viz. bitumen and asphalt. In India as in most countries (except
refinery product is officially termed bitumen and the mixture of
inert mineral matter (natural mixture) is known as asphalt. Asphalts
bitumens) are dark brown or black solids or semi solids which are found
natural state and are also obtained by refining crude petroleum. The
crude oil is heated in a distillation plant operating at atmospheric
the volatile components such as gasoline kerosene and light gas oil are
by distillation and fractional condensation. The residue is processed
higher temperature and in vacuum to remove the lesser volatile products
highly viscous material obtained is called straight run bitumen
range of grades from very soft to very hard consistency can be produced
varying the temperature and rate of flow during processing. The softer
are designated by the penetration limits e.g. 80/100 whereas the harder
are identified by their softening point e.g. 80/90.
the straight run bitumens has to be reduced before they can be used.
three main groups of bitumen (asphalt) products produced from the
Hot bitumens or asphalts those
whose viscosity is reduced by heating.
Cutback bitumens or asphalts those
whose viscosity is reduced by dissolving in mineral solvents.
Emulsion bitumens or asphalts those
whose viscosity is reduced by dispersion or suspension in a water base.
Other Allied Terms
It is an
liquefied with petroleum distillates used for cementing down floor
and for water proofing walls. Protective coatings based on asphalt
economical paints for protection against salts alkalies and non
at temperatures up to 55°C.
types of cutbacks are used depending on the type of distillate. When
(petrol) is used as the solvent a rapid curing asphalt is the result
produces a medium curing asphalt heavier fuel oils produce a slow
is an asphalt
emulsion in water solution used for floor surfacing painting pipes and
proofing concrete walls. The addition of water decreases the viscosity
renders the emulsion easy to handle and apply. Drying involves
loss of water by evaporation. They have good bonding qualities even on
divided into three groups depending upon the type of emulsifier (a)
soap type in
which soap is used as the emulsifier (b) clay modified soap type with a
combination of clay and soap as emulsifier and (c) clay base type with
mineral matter usually clay as the emulsifier.
combined with a rosin ester to increase the penetration tack and
known as modified asphalt. It is used for laminating paper and for
flooring felts. Asphalts for paints and coatings may also be modified
properties of which have been modified by the passage of air under
an elevated temperature is known as blown bitumen or oxidized bitumen.
bitumen is of a rubbery consistency and has a higher softening point
greater resistance to flow than straight run bitumen of the same
mastic asphalt. It is a preparation made by using natural asphalt
sand. It is water proof fire proof and elastic to some extent. It is
used as a D. P. C. water proofing layer over flat roofs and for making
It is not used much for road construction as roads paved with this
in summer and slippery in winter.
is used to saturate felt paper and to
coat craft paper to render it water proof. These saturated felts are
built up roofing.
As per I.S.
1951 bitumen is defined as a no crystalline solid or viscous material
adhesive properties derived from petroleum either by natural or
process. It is substantially soluble in carbon disulphide.
proportion of bitumen is obtained from crude petroleum. It is obtained
fractional distillation process in which the simpler components of the
petroleum such as white spirit kerosene fuel oil light medium and heavy
lubricating oils which have lower boiling points are evaporated leaving
the bitumen. It is black or brown in colour. Bitumen may be extracted
distillation process or cracking process. Mostly distillation process
Straight run bitumen. The
bitumen which has been distilled to a definite viscosity or penetration
further treatment is known as straight run bitumen. During processing
regulating rate of flow and temperature bitumen from very soft to a
consistency grade can be produced. Before this bitumen can be used it
has to be
processed to reduce its viscosity either by heating addition of cut or
emulsifying agent. This bitumen is mostly used for road construction.
Air blown bitumen. Special
properties can be developed in semi solid bitumen by blowing air
residue still in hot condition. This bitumen is sometimes called
bitumen also. This bitumen is not used in paving mixes but is a useful
for roofing battery boxes water proofing etc. It is widely used as
joint filler material for concrete pavements.
Cut back bitumen. Cut back is
defined as a bitumen whose viscosity has been reduced by the addition
volatile diluent. Volatile diluents are gasoline kerosene and high
point light oils. Cut back is used when it is essential to have a fluid
can be readily poured or sprayed at relatively low temperature. The
features of a cut back are its viscosity at the temperature of its use
the rate at which it sets. The rate of setting is the rate at which
evaporates from cut back.
backs are commercially manufactured in three groups namely rapid curing
curing (M.C.) and slow curing (S.C.). R.C. cut backs contain naphtha or
gasoline M.C. cut backs contain kerosene and S.C. cut backs contain
as the fluxing agents. Each group of cut backs is further divided into
categories varying from 0 to 5. The six different viscosities are named
numbers from 0 to 5 in the increasing order of viscosity. Zero grade
lowest viscosity and grade 5 the highest.
Emulsions. It is a combination
of water bitumen and an emulsifying agent. Bitumen does not dissolve in
But when heated bitumen and water are mixed together and agitated. The
disperses in water inform of spherical globules of about 2 micron
prevent bitumen spheres from coalescing an emulsifying agent is added
emulsion which remains dissolved in water. Soap is used mostly as an
emulsifying agent. Depending upon the stability of the protective
emulsifying agent the emulsion may be classified as Rapid setting
setting (M.S.) and slow setting (S.S.) Emulsions are always stored in
drums. It is used mostly for the construction of roads. It is not
be heated before use and as such are very useful for the places where
of the bitumen has to be avoided. Emulsion is mixed with road metal and
applied. When emulsion changes its colour from brown to black it is
emulsion has started breaking. As the emulsion starts breaking it start
the aggregate. Emulsion can be used for soil stabilization patch repair
of bituminous roads etc. Its main feature is that it can be used in wet
gray iron denotes a certain type of cast iron
yet the chemical composition structure and properties of gray iron may
over broad limits. The range of alloy compositions and properties
gray irons may be better understood by consideration of some of the
of gray iron metallurgy. The metallurgy of cast irons depends in large
upon the nature of the iron carbon equilibrium system.
THE METASTABLE IRON CARBIDE SYSTEM
system iron carbide carbon in the alloys occurs as the metastable
carbide (Fe3C). During solidification or melting and in thermal
the solid state the iron carbide functions according to normal
phase relationships as expected from the equilibrium diagram. For
of a hypoeutectic alloy less than 4.30 per cent carbon will begin with
formation of austenite dendrites and be completed by solidification of
eutectic austenite iron carbide. After solidification cooling in the
state results in transformation of the austenite to pearlite.
SOLIDIFICATION OF AN Fe C Si ALLOY
silicon in the alloy is the most important single composition factor
graphitization in gray cast irons. The effect of silicon may be
the aid of vertical sections of the ternary alloy system Fe C Si.
freezing processes for an Fe C Si alloy with 2% Si and about 3.50% C.
equilibrium freezing conditions primary austenite dendrites are formed
temperature range from the liquids curve to the curve indicating the
of eutectic freezing about 2300 to 2060 F. Simultaneous solidification
eutectic austenite plus graphite completes the freezing process. The
freezing occurs in a temperature range of about 2060 to about 2010 F.
solidification is complete in the alloy under consideration the
consists of about 20 per cent primary austenite dendrites and 80 per
austenite graphite eutectic. At the solidus temperature austenite is
with carbon. Further decrease in temperature is accompanied by
carbon from the austenite as graphite and its precipitation on the
flakes in the eutectic. Carbon precipitation continues until the
temperature range is reached (about 1475 to 1400F with 2 per cent
silicon). At the
eutectoid temperature the 2.0% Si austenite contains about 0.60%
Equilibrium cooling through the range results in the transformation of
austenite to ferrite and precipitation of the remaining carbon on the
flakes. The final microstructure then consists of isolated areas of
originating in the primary austenite dendrites and other areas of mixed
and flake graphite having their origin in the austenite graphite
demonstrated the freezing processes under consideration in Fe C Si
commercial cast iron alloys. The microstructural changes described
those occurring in a ternary alloy of Fe C Si. Similar processes in
cast irons are much more complex since many other elements are present
number of other factors are introduced. However the simple alloy
does point out the three important stages of graphitization
Graphitization during solidification
Graphitization by carbon precipitation from austenite
Graphitization during the eutectoid transformation (solid
Graphitization also occurs below the transformation range down to about
1000 F although
this is of lesser importance unless the time spent at that temperature
graphitization and their effects on microstructure and properties will
referred to again.
CHEMICAL COMPOSITION EFFECTS
normally present in gray iron exert some influence on the
microstructure of the
iron. Carbon and silicon of course are fundamental in their effect on
irons and may be considered first.
iron is present from about 2.5 to 4.5 per cent by weight. Two phases
carbon in the form of graphite and combined carbon as Fe3C. The
reported ordinarily is the total carbon percentage in the iron. Since
forms may be determined separately by chemical analysis the degree of
graphitization may be assessed by the following relationship % total
graphitic carbon + % combined carbon.
graphitization is complete the percentage of total carbon and the
graphitic carbon are equal. If no graphitization has occurred the
graphitic carbon is zero. If about 0.5 to 0.80 per cent combined carbon
in a gray iron it generally indicates that the microstructure is
pearlitic since pearlite in gray iron having about 2 per cent silicon
from the austenite eutectoid containing about 0.60 per cent carbon.
Thus the relationship
above offers a chemical criterion of the degree of graphitization in a
iron. For sufficient graphitization to develop during solidification of
gray iron a certain minimum total carbon content is necessary which is
about 2.20 per cent but this value depends on silicon percentage in the
equivalent of a particular iron is calculated to be 4.3 then that iron
corresponds approximately to a eutectic alloy (even though it is not a
eutectic in the sense of the ternary phase diagram). If the carbon
of an iron is less than 4.30 the alloy is a hypoeutectic alloy. The
equivalent is a useful expression because many properties of gray iron
been found related to it. If the combination of carbon and silicon
according to the carbon equivalent equation the iron is a hypereutectic
this case the freezing process begins with the formation of graphite.
graphite precipitates first during solidification the melt is said to
kish. Because of its buoyancy kish pops out of the melt into the air
and can be
observed as sparkly graphite flakes floating on the surface of the iron
the air above the iron.
Not only is
eutectic point shifted by silicon in cast irons but it also shifts the
eutectoid point and the solubility limits of carbon in austenite to the
equivalent points in the Fe C system. For this reason pearlite in a
gray iron may contain only about 0.60% carbon rather than the 0.76% C
the Fe C diagram
structurally silicon occurs dissolved in the ferrite of gray iron. As
hardens and strengthens the ferrite as pointed out in Chap. 18. Ferrite
iron will measure 80 to 90 Bhn whereas 2.0 per cent silicon in a
ferritic iron raises
the hardness to about 120 to 130 Bhn.
Silicon Content and Graphitization
graphitization. Low percentages are not sufficient to cause
during solidification but will cause nucleation and graphitization in
state at high temperature as for example during malleableizing heat
Certain silicon percentages will cause limited graphitization during
solidification and a mottled iron partly white and partly gray results.
minimum silicon (and carbon) concentration is necessary for
proceed sufficiently during solidification to develop a satisfactory
More accurate diagrams have as their purpose a limiting description of
silicon and carbon percentages which will cause an iron to freeze gray
section sizes of commercial castings poured into green sand molds.
these diagrams are useful as a guide successful metallurgical
the type of castings made in particular foundries remains the ultimate
for the carbon and silicon content. Hence foundries producing certain
castings and types of gray irons will ultimately develop silicon and
combinations suitable to their work.
Sulfur and Manganese
be present up to about 0.25 per cent is one of the important modifying
present in gray irons. A low sulfur iron silicon carbon alloy under
0.010% S will
graphitize most completely. Boyles has shown that higher sulfur
favor the retention of a completely pearlitic microstructure in a gray
The latter effect causes sulfur to be known as an element restricting
graphitization (carbide stabilizing). Above about 0.25 per cent sulfur
considered to contribute undesirable hardness and decreased
because of its retardation of graphitization.
sulfur needs to be considered relative to its reaction with the
the iron. Alone sulfur will form FeS in cast irons. The latter compound
segregates into grain boundaries during freezing and precipitates
final stages of freezing. When manganese is present MnS or complex
iron sulfides are found depending on the manganese content. The
sulfides begin to precipitate early and continue to do so during the
freezing process and are therefore usually randomly distributed. As MnS
effect of sulfur in causing a pearlitic microstructure to be retained
to a major extent. The effect of Mn alone as an alloying element is to
resistance to graphitization. Therefore manganese above that necessary
with the sulfur will assist in retaining the pearlitic microstructure.
phosphorus may result in lowering of the temperature of final
about 1800 F. The percentage of steadite present in the final structure
amount to ten times the percentage of phosphorus in the iron. Because
segregation the steadite usually adopts a cellular pattern
the eutectic cell size developed during solidification. In certain
of melting and chilling iron carbide is associated with the phosphide
ternary iron iron phosphide iron carbide eutectic. Then an amount of
constituent considerably in excess of ten times the per cent phosphorus
formed. If the ternary eutectic is accompanied by graphitization of its
during solidification expansion of the liquid occurs and beads of
exude from the iron. These are often found at the surface of sprues and
a eutectic as it segregates phosphorus is often looked upon as
tendency for a particular iron composition to be a eutectic type alloy.
iron is hard and brittle as is the carbide. Increasing phosphorus
the iron causes a proportional increase of the hard constituent and
increasing hardness and brittleness of the iron especially above about
To a limited degree improved fluidity of the molten iron is a desirable
property contributed by phosphorus through its influence on carbon
Gray Iron Specifications
iron is used in so many different engineering applications numerous
specifications covering its use in special fields have been developed.
irons are the tonnage product of the foundry
industry. Cast iron foundries produce over a million tons of castings
thus supply more than twice as much casting weight as all other
combined. Iron foundries are found everywhere that manufacturing
occurs. Of the
5674 foundries in India 2068 produce gray iron 350 nodular iron and 116
malleable iron castings. These foundries send a steady stream of iron
into every conceivable industry. The demand for iron castings is based
nature of cast irons as engineering materials and their economic cost
advantages. Cast irons offer a tremendous range of the metallic
strength hardness machinability wear resistance abrasion resistance and
corrosion resistance and other properties. Furthermore the foundry
of cast irons in terms of yield fluidity shrinkage casting soundness
production and others make the material highly desirable for casting
From all standpoints the cast iron family offers a variety of
properties which ensure its continued and widespread use. Since many
of different properties are employed it is desirable that a student
obtain an over all picture of the entire field. This chapter offers
picture and presents some of the simpler and more fundamental
between members of the cast iron family.
iron is a generic one referring to a family of materials differing
their properties. It general a cast iron is an alloy of iron carbon (up
about 4.0 per cent) and silicon (up to about 3.50 per cent) which
not usefully malleable as cast. Definitions of specific types of cast
An iron having a chemical composition such that after solidification a
portion of its carbon is distributed throughout the casting as free or
carbon in flake form. Gray cast iron always presents a gray sooty
An iron having a composition such that after solidification its carbon
present in a chemically combined form as cementite (iron carbide).
presents a white crystalline surface when fractured.
iron of intermediate composition which freezes partly as a white iron
partly as a gray iron under prevailing cooling conditions.
iron. An iron of such composition that it would normally freeze as a
but which is caused to freeze white in some locations by rapid cooling
solidification i.e. chilling. Fractured surfaces of chilled irons show
white iron where freezing was rapid and other areas of gray iron where
cooling rate was normal.
An iron with ductility or malleability produced by heat treating
a white iron casting of suitable chemical composition. The carbon in
iron is present as nodular shaped aggregates of graphite.
iron (also known as ductile cast iron or spheroidal graphite cast
specially prepared iron treated in the molten condition with a small
of magnesium cerium or other agent that will cause a large proportion
carbon to occur as spheroids of graphite rather than as flakes.
obtained in the iron as a result of the spheroidal type of graphite
This type of cast iron presents a bright steely surface when fractured.
given above suggest certain factors of major importance controlling the
of cast irons. These are chemical composition solidification process
rate and microstructure. A number of other factors are involved but the
aforementioned ones are of prime importance.
of chemical composition of some cast irons are given in Table 1. The
shows that even the terms gray iron and white iron are general ones in
they refer to a number of alloys falling within broad composition
Within the broad limits occur a number of irons with narrower
limits and different properties. Typical Chemical compositions
uses of a few commercial cast irons are given in Table 2.
Composition and Graphitization
chemical composition on the properties and uses of cast irons is
related to the two alloying elements carbon and silicon and their
the process of graphitization. Both elements promote the formation of
as their percentage increases in the iron. Carbon may occur in cast
iron carbide (cementite) and is then referred to as combined carbon. It
also occur in free form as graphite. Graphitization is the process
carbon is precipitated in the iron or chemically combined carbon Fe3C
changed to free carbon (or graphite). Increasing the percentage of
carbon in an
iron especially above 2.00% C increases the likelihood of
Furthermore the presence of certain other elements in the iron such as
iron carbide to become less stable and thus promotes the formation of
are said to be graphitising elements. Probably the simplest picture of
combined effects of carbon and silicon on graphitization is that
the diagrams in Fig. 2a and b. In Fig. 2 it can be seen that if carbon
silicon are both below certain percentages a white iron is formed
solidification. If either carbon or silicon is held at a constant
and the other is increased the iron changes from white to mottled to
Carbon and silicon thus may be varied to produce a white or gray iron
desired. It must be recognized that the diagrams of Fig. 2 do not
variable of cooling rate or section size in castings. This is another
affecting graphitization. Slower cooling rates (heavy casting sections)
the lines on the diagram to the left and rapid cooling (thin casting
shifts them to the right. Thus in practical situations gray iron piston
are high in carbon and silicon percentages whereas heavy machine tool
gray irons are low in carbon and silicon percentages. White irons for
malleable castings are even lower in carbon and silicon content so that
carbon will be in combined form as cast. The carbides in this white
cast iron however
are still sufficiently unstable so that they can be graphitized slowly
solid state by a malleableizing heat treatment.
silicon are not the only elements which influence graphitization and
structure of the iron. At this point however it is obvious that
composition is a prime factor in causing the differences in the various
of cast irons.
between gray mottled and chilled irons are largely established during
freezing process. The fundamentals of the freezing process are related
nature of the iron carbide silicon ternary equilibrium system (Fig. 2).
a simplified schematic diagram presenting the essential ideas is given
3. With reference to the diagram the freezing and cooling of an iron
A may be described by the following steps
Liquid melt cools until
freezing begins at point 1. At this point solid austenite dendrites
form and grow until the temperature at point 2 is reached. This step is
when the composition is eutectic at B on the diagram.
Eutectic (a liquid saturated
with respect to two solids) freezing begins as the area at point 2 is
with decreasing temperature. The eutectic solids which form may be a
austenite and carbide or of austenite and graphite. If the former
iron is freezing as white iron. If the latter occurs the iron is
freezing as a
gray or a nodular iron. Graphite will prevail if graphitizing factors
high silicon content and slow cooling rate are operative. Low silicon
and rapid cooling will cause the eutectic to freeze as a mixture of
austenite (white). When the temperature has dropped to point 3 freezing
completed. Thus an iron freezes as white gray or nodular iron. Actually
solidification of nodular cast iron is somewhat more complex than this.
iron freezes as gray or nodular the nature of the graphite is
during freezing mottled irons are borderline cases where both graphite
carbide have formed.
At the end of freezing the
structure consists of the solids developed during steps A and B. In
nodular irons these are austenite and graphite and in white irons
Further cooling between points
3 and 4 results in the precipitation of carbon from the austenite
the austenite may contain as much as 2.0% C at the end of freezing but
about 0.60 to 0.80% as the temperature decreases to point 4. The excess
carbon in the austenite is precipitated as carbide in white irons and
in gray and nodular irons.
Between points 4 and 5 the
final change occurs in the solid state during cooling. Austenite
over the temperature range of points 4 to 5. Because this change is
complex only a few generalizations are offered. With the most
graphitizing conditions only ferrite is formed in gray and nodular
less severe graphitizing conditions ferrite and pearlite or only
formed. In nodular cast iron mixed structures of ferrite and pearlite
form as bull
s eyes of ferrite around the graphite spheroid (Fig. 1). In white irons
pearlite is formed. The final microstructure of white iron such as is
produce malleable castings.
Cooling below point 5 to room
temperature produces little change in the iron.
foregoing it can be seen that the type of iron whether white mottled
gray is largely established during the freezing process. Furthermore
temperature microstructure reflects the entire freezing and cooling
the iron. Thus the properties of cast irons are greatly influenced by
thermal and chemical changes occurring during its entire history from
melt to cooled casting.
Many of the
advantages that make wrought steel such an outstanding material of
can also be assigned to steel castings. In addition the casting process
special advantages not obtainable otherwise and by the same token is
accountable for certain disadvantages.
tensile strengths ranging from 60 000 to about 280 000 psi. Steel is
ductile and the combination of strength and ductility adds up to give
great toughness and resistance to shock. The properties of steel can be
controlled within rather wide limits by controlling its composition
its carbon content. Steel is essentially an alloy of iron and carbon
remarkable properties and the ability to control its properties stem
presence of carbon. For example when carbon is absent iron is quite
weak. If carbon is added in as little as 0.2 to 0.3 per cent the
raised appreciably and the ductility although reduced is still
result is that steel exhibits a versatility found in no other metal.
shows this effect of carbon on the tensile strength and percentage
area of plain carbon cast steel. Curves for yield strength and
elongation showing similar trends are also available.
with this means of controlling properties steel is further favored by
control of its properties namely heat treatment. Iron and steel undergo
change in their crystal lattice structure (i.e. the arrangement of the
the solid state) that makes it possible to control properties by
the cooling rate from an elevated temperature (1500 to 1650 F). Further
is also obtained by reheating (tempering or drawing) after rapid
(quenching). See Fig. 1b.
attribute or steel castings in comparison with wrought products is the
that steel castings have a uniformity of properties regardless of the
in which they are tested. This so called isotropic behaviour is absent
that has been worked down into structural shapes from ingots or billets
the working operation introduces a directionality in properties. Thus
worked is tough and strong when tested in the direction of greatest
but is weaker and more brittle if tested in a transverse direction.
does not possess this directionality and is therefore better suited to
applications where this effect might prove harmful.
advantage of steel castings not readily realizable in other ferrous
products is case of welding. The fact that steel can be readily welded
serious loss of properties means that this valuable tool can be used in
fabrication and in the repair and salvage of castings. Of perhaps
potential importance is the opportunity to combine by welding steel
with shapes fabricated by other means to produce a composite structure
partly of castings and partly of wrought steel parts.
ironically one of the major advantages of steel namely its strength and
ductility becomes a definite handicap in the foundry. Steel castings
(as do certain other castings and alloys) extensive risering to
a rather large shrinkage that occurs during freezing. After casting
these sometimes quite massive gates and risers presents a definite
since the ductility and strength of the metal preclude their being
hammered off as in the case of brittle alloys like cast iron. Saws
cutoff wheels torches etc. are required for this purpose leading to
finishing costs in many cases.
combination of properties found in steel has already been mentioned.
foundry practice standpoint however it taxes the ingenuity of the
metallurgist because of its casting properties and the close limits of
composition. The high pouring temperature of steel also demands that
attention be given to refractories ladles molding sands metal transfer
shop filling the mold with no misruns and related problems. The high
solidification shrinkage of steel also introduces design and molding
seldom exceeded in other alloys. In the melting of this alloy there are
special problems more or less unique to steel. The nature of the alloy
reactivity with oxygen and other impurities require that a rather
procedure of melting and refining be established to ensure the
good quality metal.
MOLDING PROCESSES AND SANDS
steel castings is no different from that for other casting alloys.
of certain characteristics of steel certain methods cannot be used and
are not used to the extent that they are employed in other metals.
cast into molds made by any of the sand molding processes. Dry sand
sand molds skin dried molds and cement bonded molds are used to a
extent in steel foundries than for most of the other casting alloys.
for this is the severe conditions imposed by steel. The problems
with various molding methods should become more apparent as these
to molding methods other than those using sand the high pouring
required for steel prevents its being made by the permanent mold
in certain special cases or by die casting or plaster molding. Steel
poured in investment molds because the investment materials are
refractory. Graphite molds can be used for steel if precautions are
avoid carbon pickup. Ceramic molds can be and are being used.
Green sand Molding
castings are made using green sand molds. The general practice is no
from that for other alloys. However steel foundry sands differ from
chiefly in the following characteristics.
contact with steel may be heated to an excessively high temperature the
sand must be of sufficient purity so that it will not fuse together or
deteriorate. Figure 15.6 illustrates that the sand at a metal mold
may reach high temperatures but a short distance away the sand does not
hot nor does it heat up so rapidly as at the interface. As a
consequence of the
demand for high thermal stability most green sand molding for steel is
with compounded sand mixtures the bond is usually bentonite. Associated
refractoriness of the sand is the problem of durability. The high
exposure to which the sand is subjected alters the sand and its bond
physically and chemically leading to a gradual change in its properties
it is amply replenished with new sand. Unfortunately there is no simple
indicate the occurrence of these gradual changes. In one investigation
observed that the rate of deterioration of the sand could be linked
development of relatively high hot strength and sensitivity to thermal
progressive build up of cokey coatings on the sand grains.
High Permeability and Low Moisture Content
requirements are linked together because they are inter related. When
heated part of the moisture in the sand is changed to steam. The air in
mold is heated and increases in volume and organic additions may
gaseous products. These gases must be vented away from the mold cavity.
heats the mold to higher temperatures than do other alloys hence a
volume may develop and more venting is needed. The necessary conditions
achieved for steel by increasing the permeability above that required
alloys and restricting the moisture content to a relatively low value
per cent). Much of the gas can escape through risers and other openings
Organic and Other Additions
The use of
synthetic sands with a relatively low binder content for steel is
by a tendency toward certain casting defects such as scabs buckling and
rattails that result from the expansion of the sand as it is heated.
addition of certain materials to the sand may reduce the tendency to
of these special conditions imposed by steel on green sand properties
in establishing a range of properties that differ rather markedly from
for molding sand mixtures used for other alloys. These differences are
demonstrated by the data in Table 5.9 which lists typical sand
properties for various alloys including steel.
work is done with a facing sand which is especially compounded to
desired properties and a backing sand which being essentially reused
is also controlled as to properties and grain size. This practice
adds to the complexity of molding since it involves delivery of both
backing sand to the molder has the advantage of cutting down the
sand that must be treated with additives and ensures sand properties at
metal mold interface that are always under close control.
Green sand molding Casing Defects
such defects as rattails buckles scabs hot tears etc. which are
elsewhere in this book and also treated thoroughly in reference
defect that can develop is pinhole porosity.
characterized by small smooth walled holes elongated in a direction
perpendicular to the mold wall and occurring immediately below the
skin. The exact cause of the defect is still a matter of debate but it
generally agreed that the formation of either CO or H2O or both by a
at the metal surface or slightly below is responsible. The fact that
occurs more frequently in green sand molds suggests that it is at least
aggravated by certain conditions existing at the metal sand interface
the only major difference between green sand and dry sand molds would
moisture content the formation of H2O by reaction between hydrogen and
in the steel is strongly suspected as at least a contributing factor.
in the sand could aggravate the condition by being dissociated to
could then diffuse into the steel and react with dissolved oxygen. This
explain why pinhole porosity can be prevented by deoxidizing the steel
aluminum before pouring since the oxygen would react with the aluminum
of the hydrogen.
Dry sand Molds and Skin dried Molds
molding is preferable to other methods of molding because it is more
and gives maximum production rates. There are times however when
because of the
need to increase the strength of the mold or to avoid pinholes or for
reasons drying of the mold before pouring is desirable. Superficial
be accomplished by heating the surface with torches infrared lamps or
hot air or
the molds can be dried in large car type ovens at temperatures up to
content of the green sand used for skin dried or dry sand molds may be
higher than for ordinary green sand work for greater moldability and
because a higher moisture content leads to greater dry strength.
Other Types of Molds
have used cement as a sand binder but the practice has not been very
investment molding has proved effective is in the castings of the
alloys and shapes used for gas turbine blades and other parts subject
temperature service that cannot be readily formed by other methods.
been used with some success but there is a tendency to form surface
These can be eliminated by use of hill type shell molds. Ceramic molds
feasible. These permit pouring thinner sections than with conventional
molds. A special process combining graphite molds and air pressure
been used to produce steel car wheels and other shapes.
methods of molding such as hand ramming jolt ramming squeezing and sand
ramming are used on steel sands no difference exists in the ramming
used for steel in comparison with other casting alloys.
ALUMINIUM AND MAGNISIUM ALLOYS
and magnesium being relatively poor casting materials aluminium and
castings are actually produced from alloys. The casting alloys used are
having properties peculiarly suited to casting purposes. Since a large
of aluminum and magnesium base casting alloys are available it is
quite widely different properties may be obtained from the various
all these alloys two types of properties should be considered the
properties those characteristics of the alloy which determine the ease
difficulty of producing acceptable castings and the engineering
properties which are of interest to the designer or user of the
two sets of properties can be used as a basis for studying the
differences of the large number of aluminium and magnesium casting
ALUMINUM ALLOYING PRINCIPLES
base alloys may in general be characterized as eutectic systems
intermetallic compounds or elements as the excess phases. Because of
relatively low solubilities of most of the alloying elements in
the complexity of the alloys that are produced any one aluminium base
contain several metallic phases which sometimes are quite complex in
composition. These phases usually are appreciably more soluble near the
eutectic temperatures than at room temperature making it possible to
some of the alloys by solution and aging heat treatments. Specific
the application of these heat treatments are given in subsequent
of interest are of course influenced by the effects of the various
with which aluminium is alloyed. The principal alloying elements in
base casting alloys are copper silicon magnesium zinc chromium
manganese tin and
titanium. Iron is an element normally present and usually considered as
impurity. Some of the simpler effects of alloying can be considered.
shows solubility of copper in aluminium increasing in the solid state
than 0.50 per cent at room temperature to 5.65 per cent at 1018 F.
the solubility limit at any temperature appears micro structurally as
The latter phase has a composition approximating the formula CuAl2
053.5% Cu) and is a hard brittle constituent. By comparison the solid
phase is relatively soft and ductile. Structurally then increasing
content in Cu Al base alloys result in an increasing percentage of the
The mechanical properties of hardness and strength can then be expected
increase as copper content increases while the ductility decreases. A
percentage of copper thus has a beneficial effect of strengthening and
hardening in Cu Al base alloys. Furthermore ductility is reduced to a
level and brittleness results in alloys of high copper content.
copper percentages do not exceed 12 per cent in most aluminium casting
Actually the copper percentages in aluminium casting alloys are
that the lower contents 2 to 5 per cent are used in alloys required to
optimum ductility (or toughness) whereas the higher percentages are
greater hardness and strength are desired.
Heat treatment of Cu Al Alloys
property curves of Cu Al alloys are shown to be markedly shifted by
heat treatment and age hardening. In fact the degree of strengthening
obtainable by heat treatment is greater than that gained by alloying
few elements namely Cu Mg Zn and combinations of Mg and Si confer heat
potentialities to Al base alloys in which they are present. These are
to as heat treatable grades of aluminium alloys and they greatly extend
range of properties available in aluminium castings.
treatment. Solution heat treatment of aluminium casting alloys consists
thermal cycle of heating a suitable period of holding the metal at some
elevated temperature and then rapid cooling of the castings usually by
quenching in water. The temperature and time of holding are exceedingly
factors in the treatment. The temperature must be high enough to cause
substantially large amount of the alloying elements (usually present as
intermetallic compound phases) to dissolve in the aluminium rich solid
casting and slow cooling to room temperature this alloy consists micro
structurally of the aluminium rich phase k and the hard phase copper
concentrated mainly in the latter phase. Reheating the alloy to a
of about 900 to 950 F causes the phase to disappear from the
the higher temperature permits all the copper in the alloy to be
the aluminium hence the name solution heat treating. Of course adequate
for dissolving of the phase into the K phase must be allowed. Thus
placed on the time at temperature of the solution heat treatment. A
holding period at the solution heat treating temperature is one which
in the aluminium rich phase having reached a uniformly high percentage
alloying elements. When this condition exists rapid cooling from the
temperature will retain the enriched solid solution phase 4% Cu 96% Al
present case down to room temperature. The end microstructure after
heat treating then is a supersaturated Al rich solid solution phase. In
case the k phase contains 4 per cent dissolved copper rather than the
amount of less than 0.50 per cent for the slow or equilibrium cooled
Since solution heat treating results in a more uniform distribution of
alloying elements it also assists in minimizing the harmful effects of
segregation developed during solidification.
microstructural effects of solution heat treatment are improvements in
mechanical properties. A marked increase in tensile and yield strengths
improvement in ductility are revealed in Fig. 3 as a consequence of
treatment. Most important is the fact that solution heat treatment is
necessary step in preparing the alloys for age or precipitation
which further benefits may be obtained.
treatment by chill casting. Rapid cooling from any elevated temperature
above 700 to 800 F will cause retention of a supersaturated A1 rich
to room temperature. Hence casting processes such as permanent mold or
casting which are inherently rapid in their cooling effect have this
possibility. Sand casting by contrast is a slow cooling process.
Therefore if a
given alloy Cu A1 for example is cast in a metal mold it will usually
higher hardness strength and ductility than if the same alloy is cast
in a sand
mold. This point will be considered again later.
hardening or precipitation
hardening. Natural age hardening is a gradual increase in hardness (and
strength) which occurs with the lapse of time at atmospheric
increased hardness may reach a maximum value in a few days but may
several years in some alloys. More rapid aging can be caused to occur
elevated temperatures 300 to 400 F. Heat treating to cause aging is
artificial age hardening or precipitation hardening. Aging effects by
method are obtained only from alloys which have been previously
treated. Or the alloy can be aged if it has been processed so that
similar to solution heat treatment are retained as for example by chill
casting. The metallurgical changes associated with aging are
complex so that only the more simple details are considered here.
precipitation hardening temperatures are such as to promote
the supersaturated solid solution remaining from solution heat
the case of the 4% Cu 96% A1 alloy considered earlier the direction of
microstructural changes during aging is toward reprecipitation of the
from the supersaturated k phase developed by solution heat treatment.
most beneficial aging effects are obtained before microstructural
precipitation is revealed. In fact when the precipitating phase is
metallographically visible overaging has occurred. Overaging results in
substantial decrease in hardness strength and other properties.
time of aging are exceedingly important factors determining the end
aging. High temperatures are to cause rapid aging or overaging at
times. Low temperatures can prevent aging. Thus it is evident that a
temperature and time interval will produce the most desirable
treatments for specific alloys will be considered later.
requires foundry operations which are similar to those for other cast
Process control is critical however and the conventional foundry
be adapted to the requirements of ductile iron. Since the development
graphite as spheroids is of principal concern in this material factors
affecting this part to the structure are considered first.
SOLIDIFICATION OF DUCTILE IRON
base chemistry of gray and ductile iron is essentially the same (with
exception of sulfur and magnesium) these alloys solidify according to
different modes. These dissimilarities are especially pronounced in the
solidification of the eutectic and are responsible for many of the
variations experienced in gray and ductile iron production.
Development of Graphite Spheroids
eutectic solidifies in a
more or less conventional manner with both the austenite and the
contact with the eutectic liquid. Solidification proceeds by the growth
cells of austenite and flake graphite at the expense of the liquid.
iron is essentially an Fe C Si alloy the eutectic solidifies over a
range usually about 60 F. Further cooling of the completely solidified
results in the rejection of carbon from the solid austenite and the
precipitation of graphite on the preexisting graphite flakes. This
continues until the eutectoid temperature range is attained. Cooling
the eutectoid range will result in a variety of matrix structures from
ferrite to all pearlite depending on the rate of cooling and /or the
of alloying elements.
of the spheroidal graphite eutectic in ductile iron starts at
above those of the flake graphite eutectic for similar carbon
this case the graphite spheroid is enveloped by a shell of austenite so
only one phase austenite is in contact with the eutectic liquid.
of this type has been termed neoeutectic. Each unit of a graphite
austenite shell may be considered a cell where carbon must diffuse
shell of austenite in order for the spheroid to grow. The result is
process is slower than that of gray iron eutectic solidification and
neoeutectic freezing range is extended to about 120 F. Liquid metal is
present over a wider temperature range and to lower temperatures for
iron than for gray iron.
spheroidal graphite occurs once growth of the neoeutectic starts. The
graphite spheroids is therefore determined at an early stage of
Subsequent cooling of the solidified ductile iron is accompanied by
precipitation on the existing spheroids at temperatures down to the
range. As with gray cast iron the cooling rate through the eutectoid
and/or alloying treatment determines the matrix structure.
of an adequate number of spheroids in obtaining fully spheroidal
structures must be stressed. When the number of spheroids is low there
inadequate number of sites to which the carbon of the liquid may
Depending on the composition and processing variables either flake
iron carbide will form from the liquid during further cooling. Both
alternatives result in properties inferior to fully spheroidal graphite
Role of Magnesium
earlier a magnesium addition is the most commonly accepted method of
spheroidal graphite in either hypo or hypereutectic analyses. Other
have been suggested but all these have proved inadequate. Among them
calcium and yttrium. The mechanism by which magnesium causes graphite
to occur is unknown however the function of magnesium additions is well
First magnesium serves as a deoxidizer and desulfurizer of the molten
the oxygen and/or sulfur content of the melt is too high a substantial
of magnesium will be consumed in the formation of magnesium oxides and
Second magnesium promotes the development of graphite as spheroids by a
mechanism not yet defined. Finally magnesium prevents the nucleation of
graphite during the solidification process and thereby promotes the
graphite spheroids. Generally only 0.05 per cent residual magnesium is
necessary to achieve spheroid formation in most ductile irons. Methods
magnesium addition are discussed in a later section.
of the Common Elements
carbon content for commercial ductile iron is from 3.0 to 4.0 per cent
much narrower limits are usually desired. Nodule counts are directly
by the carbon content greater numbers of spheroids formed at the higher
contents. Increasing the carbon content also increases castability by
fluidity and feeding.
equivalents greatly in excess of 4.3 promote the development and growth
graphite spheroids. Since graphite is far less dense than molten iron
spheroids may become buoyant and float toward the cope surface of a
in gross carbon segregation. Flotation as this phenomenon is called is
prevalent in analyses having carbon equivalents greater than 4.60 and
section sizes greater than 1 in.
for silicon in ductile irons is 1.80 to 2.80 per cent. Since silicon
the carbon equivalent value it also affects the number of spheroids and
occurrence of flotation. Silicon increases the amount of ferrite formed
the eutectoid transformation and also strengthens the iron by
ferrite. Additions of silicon are more influential in spheroidal
control when the additions are made late (inoculation). This operation
described in a later section.
important effect of sulfur in ductile iron is to increase the amount of
magnesium required to achieve spheroidal graphite. The level of sulfur
iron prior to magnesium treatment is a function of the melting practice
Sulfur content after treatment is usually 0.015 per cent.
forms the very brittle
structure known as steadite in ductile iron as well as in gray cast
phosphorus adversely affects toughness and ductility a maximum of 0.05
is usually specified.
the elements carbon silicon sulfur and phosphorus discussed above a
other elements may be present in ductile iron. Most alloying of ductile
makes use of manganese nickel molybdenum and copper. Alloys involving
elements may be designed for higher strengths greater toughness or
high temperature or corrosion resistant properties. Other elements
in trace amounts may be avoided because of their deleterious effect on
development of the ductile iron structure. Lead titanium aluminium
zirconium for instance have been cited as promoting the development of
graphite. On the other hand arsenic boron chromium tin and vanadium are
to promote the formation of pearlite and/or iron carbide. Accordingly
control over the quantities of these elements is usually exercised.
of melting practice to the type and amount of spheroidizing alloy used
important to casting quality and physical properties. Considerable
the amount of spheroidizing alloy and the percentage of defective or
castings can be realized by paying close attention to charge materials
methods and control and iron composition. Ductile iron producers have
found it necessary to improve normal melting practices and to exercise
greater degree of control than that used for gray iron.
is the most common method of melting for ductile iron however electric
induction furnaces are in use in a number of foundries. About 75 per
the ductile iron producers employ the acid cupola. In nearly all these
instances the cupola is used for both gray and ductile iron production.
those foundries which have provided separate melting facilities for
iron the basic cupola is preferred. Approximately 70 to 85 per cent of
tonnage of ductile iron produced is melted in basic cupolas.
Acid Cupola Melting
ductile iron producers also produce gray iron and are generally limited
a common cupola for melting both materials the acid cupola has been
Acid melting is much less costly than basic melting. Estimates of the
differential in lining and maintenance of refractories for the basic
have been as high as four to five times as much as for acid
acid cupolas necessitates close control over charge materials and coke
the acid slags produced are not capable of reducing the sulfur content
iron. This results in sulfur contents of 0.06 to 0.12 per cent which if
lowered necessitates the use of increased amounts of spheroidizing
cupola melting however is capable of controlling the more readily
elements in the charge such as chromium and manganese since it is a
oxidizing process than basic cupola operation. Because of the moderate
pickup in acid cupola melting and the desired base iron chemistry the
pig iron in the charge is required and the use of returns is somewhat
Close composition control and high metal temperatures however can be
without the need of a hot blast.
If the high
sulfur content of acid cupola iron is not reduced prior to treatment
spheroidizing agent an appreciable amount of the high cost magnesium
be consumed before graphite spheroidization can occur. A reduction of
cent sulfur requires approximately 0.01 per cent magnesium by this
It is therefore desirable to desulfurize the iron by one of a number of
from 0.12 to 0.02 per cent has been reported from the injection of
carbide into the melt. These injections are commonly made either in the
forehearth or in the ladle and have an efficiency of approximately 15
The fine calcium carbide is injected through a refractory tube using
nitrogen gas as the carrying agent. The calcium sulfide formed floats
surface of the melt as a readily removable dross.
additions are also used to reduce the sulfur level of the melt and can
desulfurization from 0.14 to about 0.06 per cent. A second treatment
ash may lower the sulfur to between 0.030 and 0.025 per cent.
with lime is also used by some producers either alone or in conjunction
innovation of desulfurization has been the development of the shaking
this process desulfurization occurs by the reaction of lime with the
the melt. Shaking the ladle increases the contact of the iron with the
in sulfur levels as low as 0.02 per cent at a 70 to 75 per cent
Basic Cupola Melting
melting is characterized by the definite advantage of sulfur control.
sulfur content of the basic melt before spheroidizing ranges from 0.025
0.035 per cent. This decreased sulfur level in the melt is obtained at
expense of higher operating costs higher silicon losses during melting
effective temperature and composition control and a greater carbon
during melting. Attempts to reduce the refractory cost and to provide
operating control have resulted in the widespread use of water cooled
and the incorporation of hot blast equipment. When operated on a steady
continuous basis however basic cupolas are capable of producing a high
low sulfur content melt at a lower cost than acid cupola melting.
Induction Furnace Melting
used induction furnaces for ductile iron production are the low
cycle type of unit. These furnaces can be operated either for cold
for duplexing i.e. using the induction furnace to superheat an existing
Very close control must be exercised over raw materials in these
the rust on scrap and other slag forming ingredients rapidly attacks
linings. Extremely close control of composition and of metal
possible in these furnaces so that quality ductile iron can be
trends in the ductile iron industry indicate that an increased use of
frequency induction furnaces is to be expected.
melting units other than those mentioned for ductile iron production is
widespread because of either their cost of operation lack of
versatility or the
degree of control which can be exercised over metal composition and
malleable iron occupies the unusual position of being truly a product
the American foundry man s inventiveness. The first blackheart
malleable iron castings
were developed by Seth Boyden at Newark N.J. starting in 1826. Boyden s
eventually resulted in the growth of the American or blackheart
industry until it has become the third largest tonnage producer in the
is an important engineering material largely because its properties
certain special advantages among the family of cast irons. Desirable
include case of machinability toughness and ductility corrosion
certain applications strength adequate for wide usage magnetic
uniformity resulting from 100 per cent heat treatment of all castings
Applications of malleable castings usually reflect a need for one or
the foregoing properties. Principal users of the castings are the
and truck industries construction machinery producers and agricultural
of malleable iron are mainly related to its metallographic structure.
iron may be defined micro structurally as a ferrous alloy composed of
carbon in a matrix of ferrite containing dissolved silicon. The
the result of heat treatment applied to white iron castings. The
composition of the common grades of white iron which may be heat
malleable iron is given in Table 1.
converts the massive carbides and pearlite of the white iron to ferrite
temper carbon. Chemically heat treatment causes a change from combined
to graphite or temper carbon the combined carbon generally being less
per cent by weight after heat treatment. The ferrite structure with
interspersed graphite gives malleable iron mechanical properties in the
of those specified in Table 2 under standard malleable iron. The
properties and Bhn are characteristic of ferrite alloyed with 1 per
annealing or malleableizing the manufacture of malleable iron castings
the same basic foundry processes used with other alloys. Molding core
melting pouring etc. are adapted to the special casting properties of
iron which are primarily related to its metallurgical nature. This area
therefore be considered first.
malleable casting is generally performed in the air furnace the cupola
or direct are electric furnaces or a combination of these furnaces when
duplexing is employed.
Batch melting Process
air furnace shown in Fig. 3 is used for batch melting. The air furnace
reverberatory type furnace fired with pulverized coal or oil. Common
capacities range from 15 to 40 tons. The furnace hearth is rectangular
provides a molten bath depth of generally less than 12.0 in. Tapholes
provided on the side of the furnace. The side walls are made of
supported by steel and the bottom is either silica sand or firebrick.
furnace top consists of a series of removable firebrick arches known as
removing some of the bungs the furnace may be charged with cold metal
the top. A typical furnace charge is given below
charge materials are usually placed on the bottom of the furnace. Both
listed above contain about 50 per cent sprue because this is the usual
percentage of remelt in a malleable foundry. The balance of the air
charge is selected so that the iron will melt down at about 2.65 to
2.85 C phosphorus
and sulfur percentages below the maximum permitted and silicon and
within or slightly below the desired analysis range. Less than 0.07 per
preferably less than 0.03 per cent chromium should be in the charge
element interferes with annealing. Melting down is performed with a
mixture which will produce flame temperatures of about 3080 to 3150 F
oxidation of the metal to a minimum. A slag forms during melting down
metal oxidation products and refractory attrition. During melting down
the bath reaches a temperature of about 2600 F the slag is skimmed. The
temperature is then raised to the desired pouring temperature usually
2900 F. Losses of silicon and manganese occur during melting down and
metal has reached a temperature of about 2700 F. At higher temperatures
losses can occur rapidly under oxidizing atmospheres but there may be a
pickup from the refractories and slag. The iron gains about 0.05 to
cent silicon per hour at 2800 to 2900 F from reduction of silica by
the iron. Typical composition changes during a heat are given in Table
are counteracted by melting with a higher fuel to air ratio (reducing)
adding graphite petroleum coke or proprietary recarburizer or by
powdered coal on the metal surface from the burners.
changes occurring in the course of an air furnace heat are accompanied
structural changes in the solidified iron. Early in the heat iron cast
bar about 1¾ to 2 in. in diameter and 8 to 10 in. long will freeze gray
mottled. Mottling results from the formation of flake graphite during
iron then not being a completely white iron. As the temperature
2600 F and the carbon percentage in the iron drops mottling gradually
disappears. Finally before tapping the test bar will cast white and
will have a
completely white fracture as illustrated in Fig. 5. Generally the
quality malleable iron melting is to produce a completely white iron
free flake graphite in the castings since flake graphite lowers the
of malleable iron. Melting may be conducted to favor white iron by
temperatures oxidizing conditions low carbon and silicon percentage in
additional steel in the charge moisture in the air and a number of
When the iron has reached the necessary composition limits and is known
freeze white it is tapped from the furnace. Furnace addition of
and ferro manganese may be employed if it is necessary to adjust the
of the iron. Tapping is usually done at 2800 to 2900 F and pouring
2600 to 2800 F depending on casting section thickness. Tapping in air
heat may require from 30 min to over an hour depending on the furnace
malleable iron combined with its ductility makes it suitable for many
applications. Probably its greatest engineering value rests in the
of its mechanical properties service life cost and suitability to many
fabricating and processing operations. Among these advantages are
Machinability. Malleable iron
is among the most machinable of ferrous alloys. Especially desirable is
fact that a high degree of uniformity of machinability in large numbers
castings can be maintained because every casting has been heat treated.
Ductility in processing. Many
processing operations such as coining crimping press fits punching and
straightening can utilize or require ductility.
Ductility or toughness in
service. Many applications are best served when the casting is capable
deforming rather than fracturing when overstressed. Clamps pipe fitting
chain links tractor bolster posts and many other cases may be cited.
Surface coatings. Corrosion
resistance of malleable iron may be greatly increased by coatings of
aluminium and lead. Hot dip galvanizing may be applied to clean
castings to provide good corrosion resistance to exposure in a wide
outdoor conditions which may be encountered by electrical conduct boxes
fittings fence fixtures playground equipment castings and numerous
Wear resistance. Malleable
iron with a ferritic structure does not have inherent wear resistance
than that normal to soft ferrous alloys. It may be hardened however. If
metal is heated to the austenitic temperature range carbon goes back
solution and permits a hard martensitic structure to be obtained by
Caster wheels cams rollers and other items may be flame or induction
to give wears resistance.
conditions for curing thermosetting resins used in particleboard and
composite wood products differ between manufacturing sites and quite
change in any one operation due to planned or unplanned alterations of
process variables. Composite manufacturers rely almost entirely on
suppliers to provide them with the most appropriate resin to bind their
product. Necessary changes in resin formulation or synthesis
based on empirical experience and often require extensive laboratory
trials. Although the performance of a resin depends on its reaction
numerous variable environmental conditions adhesive characterization is
presently restricted to physical and chemical features such as
content pH and molecular distribution and reaction in simple gel tests.
purpose of the research outlined in this paper was to develop a means
characterize a resin based on its response to the common process
time temperature and moisture.
A number of
methods have been used to quantify the extent of reaction in an
adhesive as it
ages or cures. Gel permeation chromatography (GPC) is useful in the
of cure while the resin is still in a liquid stage. Fourier transform
(FTIR) spectroscopy can characterize the reactions into the solid
represents major difficulties in making quantitative determinations.
magnetic resonance (NMR) spectroscopy has been used to characterize
structural changes in phenolics as curing progresses. Differential
calorimetry (DSC) measures the cure of resins by sensing the exothermic
output of a small sample during controlled heating. However FTIR NMR
and DSC do
not differentiate chain extension from cross linking reactions and the
not directly informative about mechanical property buildup.
objective of the research was to characterize resin response to changes
environmental conditions during the pressing process a method was
measuring degree of cure in samples that had been exposed previously to
different combinations of those variables. Prior research showed that
dynamic mechanical analyzer (DMA) had good potential for meeting these
The DMA is sensitive to changes in the mechanical stiffness of a curing
sample and therefore gives a direct indication of the molecular cross
that occurs in the late stages of resin cure.
motivated in part by problems associated with steam injection pressing
phenolic resin bonded composites. During this newly developed process
steam was injected into the mat to enhance transfer of heat to the
core. Use of
phenolics with this pressing system has produced sporadic results. Good
was obtained with Douglas fir ring flakes. However bonding was poor
disk flakes were used in conjunction with phenolic resins to make
has been attributed to various factors including precure moisture
glue lines caused by excess penetration and type of wood particle. The
injection system was appropriate to this study in that environmental
are severe and can be finely controlled in the pressing operation.
developed to characterize the curing and bonding of phenolic resins
steam injection pressing are also applicable to conventional pressing
operations and can be expanded to include other resin types.
MECHANICAL PROPERTIES OF A PARTIALLY CURED RESIN
A Du Pont 983
DMA was used for all mechanical measurements of resin samples. In tests
this DMA the sample a special 0.2 by 12.5 by 35 mm nonwoven glass
impregnated with resin is clamped horizontally between the ends of two
arms (Figure 2). One arm and the sample are driven to oscillation at a
prescribed amplitude by an electromagnetic drive. Energy dissipation by
sample causes the actual sample strain to be out of phase with the
signal. The instrument detects this time shift as a phase angle and
calculations are made to determine the storage modulus E a measure of
material s stiffness and the loss modulus E a measure of the material s
viscosity. The ratio of these two properties E /E is designated tan
is useful in determining the extent of resin mechanical cure.
resin impregnated glass cloth sample is first conditioned at room
in a humidity chamber (for the rest of the paper called precure
The sample is then precured for a period of time in an atmosphere of
temperature and humidity. After reconditioning (for the rest of the
called pre DMA conditioning) at 91% relative humidity (RH) over a
chloride solution the sample is tested in the DMA to determine initial
stiffness and its reaction to further heating while in the DMA.
numerous difficulties encountered in developing the testing technique.
Substrate selection resin application resin shrinkage clamping mode
torque oscillation amplitude fixed and resonant frequency modes of DMA
operation and isothermal and isochronal heating have been discussed in
elsewhere. The precure conditioning is necessary to prevent sudden
expansion or shrinkage with resultant crazing when the sample is
exposed for a
short time to the desired environmental conditions. For a dry exposure
sample is conditioned over phosphorous pentoxide to bring it close to
moisture content. The pre DMA conditioning at 91% RH plasticizes the
the response of the partially cured resin to DMA conditions and
differences caused by precure treatments.
E curves for two samples precured for two minutes at two temperatures
in Figure 3. Typically a sample precured at the higher temperature
showed a higher initial modulus. However after exposure to further heat
DMA in this case at a constant temperature of 150°C the sample cured at
lower temperature (130°C) attained a higher ultimate modulus. It was
hypothesized that this phenomenon was caused partially by the
molecular chains in the precure exposure which reduced their mobility
subsequent ability to cross link during the final curing process in the
softening counteracted by a loss of moisture determined the shape of
storage modulus curve prior to the point where the glass transition and
modulus rise due to rapid molecular cross linking. Previously the
effects of heat softening and moisture loss have hindered the expansion
techniques to solvent based adhesives. Considerable progress in
cure has been made due to the refinement of specific procedural
as substrate selection and pre DMA conditioning at high RH.
Additionally in the
pursuit of data interpretation the focus has been shifted from the
modulus E to tan delta.
the tan delta curve is related to the development of mechanical
delta curves for a resin exposed to 115°C for three precure times are
Figure 4. The areas under the curves indicate the extent to Fig. 3
modulus Resin A precured at two temperatures temperature in the dynamic
mechanical analyzer was 150°C.
tan delta area has been plotted as a function of precure time at 115°C
different phenolic resins. Compared with resin A resin B had a higher
weight and contained less free formaldehyde and more NaOH at 115°C
reacted at a much lower rate than did resin A. However after precuring
both resins developed mechanical properties at relatively fast rates
by a rapid decrease in the tan delta areas (Figure 6).
Advancement of a Partially Cured Resin Differential Scanning
To determine how resins differ in their chemical response to
conditions a Perkin Elmer DSC 2 differential scanning calorimeter (DSC)
used to test a partially cured sample trimmed from the DMA specimen
following precure exposure and reconditioned to 91% RH. A 10 mg sample
placed in a stainless steel capsule that had been fitted with an O ring
prevent release of volatile components. The partially cured sample was
to an empty control capsule. The difference in energy supplied to
constant temperature rise of 10°C/min in each capsule was a measure of
exothermic reaction remaining in the partially cured resin and thus the
chemical response of the resin to heat. The weight corrected area under
exothermic heat curve decreased with precure exposure time.
responses of two resins precured at 115°C and 140°C are shown
Figures 7 and 8. Unlike their mechanical responses (Figure 5 and 6) the
chemical responses of these two resins maintained the same general
at both temperatures.
FLAME RETARDANT TREATMENT OF WOOD
inherently good properties which make it a preferred building material
applications. However the flammability of wood can be a problem when
used to build permanent structures. The tendency to burn can be greatly
by adding fire retardant chemicals to wood. However in many instances
chemicals introduce other problems including increased hygroscopicity
corrosivity and reduced adhesive bonding. These problems occur
inorganic salts are used as fire retardants.
great deal of
research has been done to develop treatments that make wood flame
free of the problems associated with leachable inorganic salts. One
treatment is the amino resin system which uses chemicals such as
urea formaldehyde and phosphoric acid. The amino resin fire retardants
reduce or eliminate hygroscopicity corrosivity chemical blooming and
Leach resistance is attributable to polymerization of the components
wood and possibly to some reaction with the cellulose in wood. Despite
reported leach resistance of the amino resin treatment Juneja reports
water leaching can remove as much as 91% of the phosphorus from
treated with dicyandiamide phosphoric acid formaldehyde and 71% of the
phosphorus from shingles treated with melamine dicyandiamide phosphoric
foams are commonly made
flame retardant by reaction of a phosphorus polyol with an isocyanate.
prepared flame retardant compounds by reacting chemicals having free
groups with cross linking agents such as isocyanates. Von Bonin propose
proofing absorbent substrates used in roofing and packaging with a
mixture of a
polyisocyanate and a condensate that contains phosphorus and has two or
hydroxyl groups. Isocyanates have been reacted with wood to increase
dimensional stability and decay resistance.
contain phosphorus change the thermal degradation processes in wood.
effective as flame retardants because they reduce the temperature at
pyrolysis occurs and increase the amount of residual char. Phosphorus
are acid precursors during combustion or pyrolysis and the acids formed
selective decomposition of the carbohydrate materials. Dehydration and
formation are enhanced and combustible volatile formation is suppressed.
our research were to develop new fire retardant treatments for wood
leach resistant and at the same time not hygroscopic or corrosive. To
accomplish these objectives an aliphatic diisocyanate and an oligomer
phosphonate were mixed in an appropriate solvent impregnated into the
cured with heat. Reaction of the diisocyanate with the oligomer
the wood should enhance leach resistance.
MATERIALS AND METHODS
diisocyanate was selected for this study because it is less reactive
aromatic diisocyanates which allows the reaction to be controlled.
does not occur at room temperature in most cases but can be initiated
increasing the temperature. Aliphatic diisocyanates are less likely to
than aromatic diisocyanates when exposed to sunlight. Isophorone
(IPDI) was used in this study. It has a relatively high molecular
and a low vapor pressure which make its use and handling relatively
51 used in
this study is an oligomer phosphonate containing 20.5% phosphorus and
hydroxyl groups that will react with an isocyanate. Fyrol 51 is soluble
water methanol ethanol. 2 propanol chloroform and dichlorome thane.
alcohols are not appropriate as reaction solvents for isocyanates and
the solvents known to swell wood dissolve both Fyrol 51 and IPDI.
and dichloromethane were selected as the most appropriate solvents for
solutions of Fyrol 51 and IPDI. The ration of the fyrol diisocyanate
solutions was 1 2 20 (by volume). The amount of solvent was increased
decreased to control chemical weight gains in the reacted wood.
Preparation of Specimens
ponderosa pine and southern pine were cut into 25 by 25 by 6 mm (radial
tangential by longitudinal) pieces for dimensional stability tests.
140 by 7 by 3 mm were cut for leaching thermogravimetric analysis and
analysis. All specimens were oven dried at 105 C before weighings and
Treatment of Specimens
placed in a container inside a desiccator and a vacuum was drawn for 1
a water aspirator. Specimens were then covered with solution and the
returned to atmospheric. After a 1 h soak the solution was drained and
drawn for 10 min to remove excess chemicals and solvent. The specimens
then cured overnight at 105 C reweighed and the weight percent gain
calculated based on the original oven dry weight. Ten specimens of each
were treated at each level of treatment.
methods of leaching were used. The method used depended on what was to
later with the specimens. Method 1 was used with specimens milled to
pass a 40
mesh screen. One half of the milled specimens were soaked 24 h in
water followed by several rinses with distilled water. Next these
were rinsed with several 50 ml portions of acetone then oven dried at
Each half of the milled specimens was subjected to thermogravimetric
and nitrogen analysis and unleached and leached portions were compared.
Method 2 a
combination of water and solvent leachings was done using solid
by 7 by 3 mm). Leaching data represent the average of four specimens in
group. The specimens were (1) leached 4 days in running water (2)
h with toluene ethanol (2 1 v v) in a Soxhlet extractor (3) extracted
18 h with
acetone in a Soxhlet extractor and (4) leached 4 days with running
Before and after each cycle of leaching or extraction the specimens
dried and weighed and the WPG was calculated based on the original
consisted of 4 day cycles of leaching in running water. Solid specimens
7 by 3 mm) were subjected to three cycles of leaching with oven drying
weighing before and after each cycle. The WPG based on the original
weight was calculated after each cycle. Data reported are the average
specimens per group.
Dimensional Stability Tests
stability was determined using a flat bed micrometer by measuring the
in volume (swelling) of treated and untreated specimens. Specimen
determined oven dry and after specimens were soaked in water. The
measured after each hour for the first 5 h then after 24 h. The
swelling was calculated from the wet volume of the specimen compared to
treated oven dry volume.
analysis (TGAs) was done using a Perkin Elmer TGS 2 system. Specimens
pyrolyzed in a flow of nitrogen (40 ml/min). Pyrolysis temperatures
programmed from 30 to 600 C at 20 C per minute. The specimen weight
at 600 C was used to calculate the percentage of residual char. The
at maximum rate of pyrolysis was recorded.
FUNGAL AND TERMITE RESISTANCE OF WOOD
against attack by fungi and termites by methods based on modification
cell wall polymers has been investigated at the Forest Products
several years. Most of this research has dealt with the bonding of
organic monomers to the hydroxyl groups on lignin hemicelluloses and
More recently we have investigated chemicals that form stable complexes
cell wall hydroxyl groups and are resistant to water leaching.
that form stable complexes with wood are periodic acid and sodium
Periodic acid is known to react with diols in carbohydrates with
oxidation taking place between the two diols. This method has been used
many years to determine carbohydrate structure. Even though these
have been reacted with isolated carbohydrate polymers and monomers
reactions with whole wood have not been reported.
investigations we found that both periodic acid and sodium periodate
with wood to form leach resistant complexes. Little oxidation of the
polymers took place as evidenced by infrared spectroscopy.
this research was (1) to determine the resistance of reacted wood to
white rot fungi and subterranean termites in standard laboratory tests
to study the reactions of periodic acid and sodium periodate with wood.
MATERIALS AND METHODS
sweet gum sapwood blocks 1.9 X 1.9 X 1.9 cm (radial X tangential X
longitudinal) in size were selected according to the American Society
Testing and Materials (ASTM 1976) standards with three to four annual
centimeter. Blocks were reacted with aqueous solutions of either
or sodium periodate at six concentration levels 1% 0.5% 0.25% 0.1%
0.05% and 0.01.
each test wood
blocks were placed in a vacuum chamber for 1 h at 16 to 22 mm Hg. They
then impregnated with one of the six aqueous solutions. Blocks treated
periodic acid were soaked for 2 h those treated with sodium periodate
for 4 h.
After soaking seven blocks per treatment were dried under a hood for 1
then conditioned at 27 C and 30% relative humidity (RH) for 3 weeks.
seven blocks per treatment were leached in 350 ml of distilled water
2 weeks. After leaching the leached blocks were also conditioned at 27
30% RH for 3 weeks.
fungal decay tests were run according to the ASTM standard.
trabeum a brown rot fungus was used with loblolly pine blocks and
versicolor a white rot fungus was used with sweetgum blocks. Five
blocks from each treatment and five control blocks were tested for
resistance over a period of 12 weeks. The extent of fungal attack was
determined by weight loss. Solution retention concentration that
weight loss by decay of less than 2% was generally considered as the
sapwood blocks 0.4 x 2.5 x 2.5 cm (tangential x radial x longitudinal)
were selected according to the ASTM standards with four to six annual
Blocks were reacted with aqueous solutions of either periodic acid or
periodate at five concentration levels 5% 1% 0.5% 0.25% and 0.1% (w/w)
addition 10% concentration was included for the periodic acid solution.
blocks were placed in a vacuum chamber for 20 min at 16 to 20 mm Hg.
then impregnated with one of the six aqueous periodic acid or five
periodate solutions and soaked in the treating solution for 24 h. After
four blocks per treatment were dried under a hood for 1 day and then
conditioned at 27 C and 30% RH for 3 weeks. Another four blocks per
were leached in 200 ml of distilled water daily for 2 weeks. After
leached blocks were also conditioned at 27 C and 30% RH for 3 weeks.
flavipes for this study were freshly collected at Janesville WI. Each
and control block was exposed to 1.0 g of termites (natural caste
averaging 270 undifferentiated functional workers 1 soldier and 0.3
Termite resistance of the treated wood was evaluated for a period of 4
The extent of termite attack and mortality were determined by weight
the blocks and final live weight of the termites. Threshold retentions
weight loss and termite mortality were determined.
Reaction Time and Chemical Analysis
loblolly pine blocks (1.9 X 1.9 X 19 cm) were placed in a vacuum
chamber for 1
h at 16 to 22 mm Hg. They were then impregnated with 0.1% periodic acid
solution and soaked at room temperature for 2 8 and 24 h. After soaking
blocks per treatment were dried under a hood for 1 day and then
27 C and 30% RH for 3 weeks. Another seven blocks per treatment were
350 ml of distilled water daily for 2 weeks. After leaching the leached
were also conditioned at 27 C and 30% RH for 3 weeks. Five replicate
from each treatment and five control blocks were tested for fungal
resistance by G. trabeum over a period of 12 weeks. The extent of
was determined by weight loss.
WEATHERING OF WOOD
Wood is an
extremely durable material even under adverse conditions but the
depends upon the environment (Fig. 1). Buried deep under ground fully
to the weather submerged under water or hidden in an ancient tomb it
for tens of centuries. There are many examples of structures ships and
wooden objects which have survived centuries of use. The same type of
exposed to an unfavourable environment however may vanish almost
trace within a year or two. In the tropics a wooden house may under
conditions disintegrate in a few years.
biological materials wood consists of organic substances primarily
polysaccharides and polyphenolics cellulose hemicelluloses and lignin.
Extractives are also present in relatively small quantities and their
concentration determines color odor and other properties of a wood
of wood by any biological or physical agent modifies some of its
molecules. The cause of the change may for example be an enzyme a
electromagnetic radiation but invariably the net result is a change in
molecular structure through some chemical reaction. Stalker
divided the environmental agencies that bring about wood degradation
categories. Physical forms of energy were used to describe all factors
than fungi insects or animals. In Table 1 the importance of the various
agents on wood can best be considered by comparing two situations
outside wood structures. The most serious risk to wood indoors comes
intense heat of an accidental fire. Outdoors the factor most deserving
attention is weathering a complex combination of chemical mechanical
1 Old Fairbanks house at
Dedham Massachusetts. Built in 1637 most of the white pine clapboard
replaced in 1903 and has stood 75 years without paint.
to be confused with decay which results from the presence of excess
for an extended period of time. The condition of decay can lead to
deterioration of the wood and result in a phenomenon far different than
observed for natural outdoor weathering.
(1827) was the first to comment on the changes in wood caused by
(Browne 1957). Studies in considerable detail were made by Wiesner
(1906a 1906b) Wislicenus (1910) Browne (1925) and Frey Wyssling (1950).
(1957) concluded that there was not a sufficiently through going
weathered wood to establish conclusively the changes that take place in
proportions and composition of the lignin and of the cellulose as
changes to weathered wood. An excellent annotated bibliography was
the California Redwood Association which provides a source of
pertain to wood weathering and applied surface treatments and/or
well as to wood substrate and/or extractive modification materials and
CRA bibliography covers references to significant published material
pertinent unpublished material as well.
THE WEATHERING PROCESS
weathering of smooth wood original surfaces become rough as grain
the wood checks and the checks grow into large cracks grain may loosen
boards cup and warp and pull away from fasteners. The roughened surface
color gathers dirt and mildew and may become unsightly the wood loses
surface coherence and becomes friable splinters and fragments can come
these effects brought about by a combination of light water and heats
comprehended in one word weathering.
The principal cause of weathering is frequent exposure of the wood
rapid changes in moisture content. The action of water on wood has been
thoroughly described. Rain or dew falling upon unprotected wood is
absorbed by capillary action in the surface layer of the wood then
within wood cell walls. Water vapor is taken up directly by adsorption
increased relative humidities. Adsorbed water has been shown to
its volume to that of the cell walls resulting in swelling. Stresses
are set up
in the wood as it swells and shrinks as a result of moisture gradients
the surface and the interior. These induced stresses are greater the
the moisture gradient and are usually concentrated near the surface of
wood. When unbalanced they may result in warping cupping and face
Grain raising results from differential swelling and shrinking of
2 White oak log cabin near
Middleton Wisconsin constructed about 1845 and never painted or
3 Close up view of weathered
white oak logs in Fig. 2.
The photochemical degradation of wood or wood related materials has
reviewed in several publications. It was recognized quite early that
initial color change of wood exposed to sunlight was a yellowing or
The graying of wood occurs after browning and was thought to be related
salts. Sunlight particularly the ultraviolet (UV) end of the spectrum
the organic materials in wood lignin decomposes preferentially to a
shallow depth of 0.05 0.5 mm. Photo degradation by UV light induces
chemical composition particularly in the lignin.
that infrared light penetrated deeper than visible light while the
of UV light was negligible. Stout using reflectance curves showed that
absorption of UV light is primarily due to lignin and lignin like
Pine cellulose exhibited a high reflectance whereas the reflectance
lignin substances closely approximated that for wood. Sandermann and
made a comprehensive study of color changes of numerous wood species.
another study decomposition by UV light as indicated by the coloring
wood during the first several hours of exposure appeared to be
ambient atmosphere exposed wood samples darkened with or without oxygen
environment. Desai described the photo degradation process for
to note here that the two most significant elements of weathering light
irradiation and water tend to operate at different times. Exposed wood
irradiated after having been wet by rain or when surface moisture
high from overnight high humidity or from dew. Time of wetness
therefore is an
important parameter in relating climatic conditions to exterior
The action of the combined elements can follow different degradation
irradiation accelerating the effect of water or the converse.
The role of temperature in the natural weathering process is generally
be of less importance than those of light and water.
changes. Over a century ago Wiesner reported that intercellular
wood had been lost because of weathering and concluded that the
layer consists of cells that leached by atmospheric precipitation have
robbed entirely or in large part of their infiltrated products so much
remaining membranes consist of chemically pure or nearly chemically
reported by Kalnins compiled some analytical data on white pine wood
been weathered outdoors for 20 years. Results showed that weathering
and solubilized lignin. Cellulose appeared to be affected considerably
for the top surface layer of the wood. Similar results were obtained
various kinds of wood exposed on a test fence for 30 years. The top
consistently exhibited very low lignin content. The brown layer
under the outer gray layer had a lignin content varying from 40% to 60%
normally found for fresh unexposed wood. The interior wood layers only
millimetres under the outer gray surface had a wood composition similar
of normal unweathered wood. Analysis of wood sugars from hydrolysis of
extract of the weathered wood showed that xylan and araban were
more rapidly than was glucosan. It was also observed that glucose did
predominate in the hydrolysed water extract during analysis although
units do predominate in unaltered wood polysaccharides.
degradation process is initiated by the formation of free radicals and
presumably with oxidation of phenolic hydroxyl groups. This results in
decrease in methoxyl and lignin content and an increase in acidity and
concentration of wood substance. These photochemical changes are
by moisture than by heat. The products of decomposition of weathered
addition to gases and water are mainly organic acids vanillin
higher molecular weight compounds which are all leachable. Cellulose is
some degree attacked photochemically by UV irradiation and is bleached
is weathered less rapidly than other wood components.
It can be
concluded from all the work on chemical changes of weathered wood that
absorption of UV light by lignin on the wood surface results in
lignin degradation. In the graying of wood most of the solubilized
degradation products are washed out by rain. Fibers high in cellulose
and whitish to gray in color remain on the wood surface and are
resistant to UV
The color of wood exposed outdoors is affected very rapidly (Fig.4).
woods change toward a yellow to brown color which is due to the
lignin and extractives. This yellowing or browning occurs after only
months of exposure in sunny warm climates. Woods rich in extractives
redwood and cedar may first become bleached before the browning becomes
observable. In the absence of microorganisms wood weathers to a soft
gray as a result of the leaching of decomposition products of wood
4 Artist s rendition of the
changes (including surface character and color) that occur during the
weathering process of a typical softwood.
color reveal chemical changes in wood during weathering as described in
preceding section. Only those parts of the wood close to the exposed
are affected. Initial browning penetrates only 0.01 2 mm into the wood.
leaches the brown decomposition products of lignin a silver gray layer
mm thick consisting of a disorderly arrangement of loosely matted
develops over the brown layer. The gray layer as indicated previously
composed chiefly of the most leach resistant parts of the wood
surface color change to gray is observed when the wood is exposed to
radiation of the sun in cooler climates with little rain. This would
on structures with large roof overhang which protects the wood
rain and sun. However another mechanism of graying of weathered wood
predominates particularly in the presence of moisture.