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1 ENGINEERING MATERIALS 2015-16
Rohan Desai, Auto. Engg. Dept.NPK. Page 1
Chapter Name of the Topic Marks
01
1 ENGINEERING MATERIALS:
1.1 Introduction:
• Classification of engineering materials.
• Ferrous metal and their alloys:
• Cast iron: types, composition and applications
• Plain carbon steel: types, composition and applications
• Effects of alloying elements like- Nickel, chromium, silicon,
molybdenum and tungsten on the properties of steel
• Alloy steels like stainless steel, Tool steels, their composition
and applications
1.2 Non-ferrous metals and their alloys:
• Aluminium and its alloys: duralumin, ’Y’ alloy, their
composition, properties and applications
• Copper and its alloys: brass, bronze, gun metal, Babbitt metal
their composition, properties and applications
1.3 Other materials:
• Polymeric materials- properties and applications-
Thermoplastics- Nylons and Polypropylene.
Thermosetting Plastics-Epoxy resins and Polyesters,
Rubber – Natural and synthetic
• Ceramic materials: Properties and application in automotive
industry.
20
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1.1 INTRODUCTION
Materials are probably more deep-seated in our culture than most of us
realize. Transportation, housing, clothing, communication, recreation, and
food production virtually every segment of our everyday lives is influenced to
one degree or another by materials. In fact, early civilizations have been
designated by the level of their materials development (Stone Age, Bronze
Age, and Iron Age).
The earliest humans had access to only a very limited number of
materials, those that occur naturally: stone, wood, clay, skins, and so on.
With time they discovered techniques for producing materials that had
properties superior to those of the natural ones; these new materials included
pottery and various metals. Furthermore, it was discovered that the
properties of a material could be altered by heat treatments and by the
addition of other substances. At this point, materials utilization was totally a
selection process that involved deciding from a given, rather limited set of
materials the one best suited for an application by virtue of its characteristics.
It was not until relatively recent times that scientists came to understand the
relationships between the structural elements of materials and their
properties. This knowledge, acquired over approximately the past 100 years,
has empowered them to fashion, to a large degree, the characteristics of
materials. Thus, tens of thousands of different materials have evolved with
rather specialized characteristics that meet the needs of our modern and
complex society; these include metals, plastics, glasses, and fibers.
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• CLASSIFICATION OF ENGINEERING MATERIALS
• PROPERTIES OF MATERIALS
All important properties of solid materials may be grouped into six
different categories: Mechanical, Electrical, Thermal, Magnetic, Optical, and
Deteriorative. For each there is a characteristic type of stimulus capable of
provoking different responses.
Category Stimulus Example
Mechanical Force Strength, ductility
Electrical Electric field Electrical conductivity
Thermal Heat Thermal conductivity
Magnetic Magnetic field Magnetic flux
Optical Radiation Index of refraction
Deteriorative Chemical reaction Corrosion resistance
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MECHANICAL PROPERTIES:
The mechanical properties of materials define the behaviour of
materials under the action of external forces, called loads. Mechanical
properties have great importance in the machine design.
STRENGTH
It is the ability to withstand the force to which it is subjected. It is
termed as shear strength, tensile strength, and compressive strength. Unit of
strength is N/mm2
Typical tensile strength values of some important materials are given below:
Structural Steel 400 N/mm2
Grey Cast Iron 170 N/mm2
Aluminium 110 N/mm2
Titanium 900 N/mm2
ELASTICITY
Elasticity is that property of a material which enables it to regain its
original shape and size after load is removed.
PLASTICITY
The plasticity of a material is its ability to be permanently deformed
without rupture or failure. Plastic deformation will take place only after the
elastic range has been exceeded.
DUCTILITY
Ductility is that property of a material which enables it to draw out into
thin wire. Mild steel is a ductile material.
MALLEABILITY
Malleability of a material is its ability to be flattened into thin sheets
without cracking by hot or cold working. Aluminium, copper, tin, lead, steel,
etc. are malleable metals.
TOUGHNESS
Toughness is a measure of the amount of energy a material can
absorb before actual fracture or failure takes place. For example, if a load is
suddenly applied to a piece of mild steel and then to a piece of glass, the mild
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steel will absorb much more energy before failure occurs. Thus mild steel is
much tougher than a glass.
HARDNESS
Hardness is defined as the ability of a material to resist to scratching,
abrasion, cutting, indentation, or penetration. Many methods are now in use
for determining the hardness of a material. They are Brinell, Rockwell and
Vickers.
BRITTLENESS
The brittleness of a material is the property of breaking without much
permanent distortion. There are many materials which break or fail before
much deformation takes place. Such materials are brittle, e.g. glass, cast iron.
Therefore a non-ductile material is said to be brittle material.
RESILIENCE
Resilience is the capacity of a material to absorb energy elastically. On
removal of the load, the energy stored is given off exactly as in spring when
the load is removed.
CREEP
Creep can be defined as the slow and progressive deformation of a
material with time under a constant stress at temperatures approximately
above 0.4 Tm (where Tm is the melting point of the metal or alloy in degrees
Kelvin).
FATIGUE
When subjected to fluctuating (repeated) loads, the material tends to
develop a characteristic behavior which is different than that under steady
load. This behavior is called as fatigue.
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• FERROUS METAL AND THEIR ALLOYS
The principal ferrous metals and alloys used in the engineering are
classified under the following groups:
1. Pig iron
2. Wrought iron
3. Cast iron
4. Carbon Steel
5. Alloy Steel
PIG IRON
All iron and steel products are derived originally from pig iron. This is
the raw material obtained from the chemical reduction of iron ore in a blast
furnace. The main raw materials required for pig iron are: (1) iron ore, (2) coke
and (3) flux.
Iron ores are generally carbonates, hydrates or oxides of the metal, the
latter being the best.
The coke used in the blast furnace should be a very high class hard
coke. Flux combines with the ashes of the fuel and the ore to form fusible
products which separate from the metal as slag. The most commonly used
blast furnace flux is limestone.
WROUGHT IRON
It is produced by remelting pig iron in a puddling furnace. It is the purest
form of pig iron. The chemical analysis of the metal shows as much as 99%
of iron. It is ductile when cold. It is good corrosion resistant than mild steel.
CAST IRON
Cast irons are basically the alloys of iron and carbon in which the
carbon content varies between 2 to 6.67%. Commercial cast irons are
complex in composition and contain carbon in the range of 2.3 to 3.75 % with
other elements such as silicon, phosphorous, sulphur and manganese in
substantial amount. Because of their poor ductility and malleability, they can
not be forged, rolled, drawn, or pressed into desired shape, but are formed
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by melting and casting to the required final shape and size and so the name
‘Cast irons’.
Cast irons have following characteristics:
1. They are the cheapest amongst the commercial alloys.
2. They are easier to melt due to their lower melting temperature
(1150-1250 0C) as compared to steels (1350-1500 0C).
3. They can be easily cast due to high fluidity of melt and low
shrinkage during solidification.
4. Their corrosion resistance is fairly good.
5. In general, they are brittle and their mechanical properties are
inferior to steels.
CLASSIFICATION OF CAST IRONS:
Cast irons are classified according to various criteria as below:
(a) On the basis of furnace used in their manufacture:
(1) Cupola cast irons
(2) Air furnace cast irons
(3) Electric furnace cast irons
(4) Duplex cast irons
(b) On the basis of composition and purity:
(1) Low carbon, low silicon cast irons
(2) High carbon, low sulphur cast irons
(3) Nickel alloy cast irons
(c) On the basis of microstructure and appearance of fracture:
(1) Grey cast irons
(2) White cast irons
(3) Malleable cast irons
(4) Nodular cast irons
(5) Mottled cast irons
(6) Chilled cast irons
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Table showing typical composition of irons & Cast Irons
Material Carbon Silicon Manganese Sulphur Phosphorous
Pig Iron 3.0 to 4.0 0.5 to 3.0 0.1 to 1.0
0.02 to
0.1 0.03 to 2.0
Wrought iron
0.02 to
0.08 0.1 to 0.2 0.02 to 0.1
0.02 to
0.04 0.05 to 0.2
Grey cast iron
2.50-3.75 1.00-2.50 0.40-1.00 0.06-0.12 0.10-1.00
White cast iron
1.75-2.30 0.85-1.20 0.10-0.40 0.12-0.35 0.05-0.20
Malleable cast iron
2.20-3.60 0.40-1.10 0.10-0.40 0.03-0.30 0.10-0.20
• GREY CAST IRON
Process:
Grey cast iron is obtained by melting pig iron, coke and scrap in a
cupola furnace and allowing it to cool and solidify slowly. While solidifying, the
iron contains carbon in the form of graphite flakes. It has a dull grey
crystalline or granular structure and a strong light will give a glistering effect
due to reflection of the free graphite flakes. In tension, the ultimate tensile
strength is 120-300 N/mm2 while in compression it is 600-750 N/mm2.
Characteristics:
(a) They have excellent damping capacity
(b) Cheaply available
(c) Low melting temperature (between 1150 to 1200 0C)
(d) Good machinability
(e) Graphite on the surface acts as lubricant
Applications: Grey cast irons are widely used for machine bases, engine
frames, drainage pipes, and elevator counter weights, pump housings,
cylinders and pistons of I.C. engines, fly wheels, etc.
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• WHITE CAST IRON
Process:
White cast iron is obtained by melting pig iron, coke and steel scrap in a
cupola furnace and allowing it to cool and solidify rapidly. While solidifying,
the iron contains carbon in the form of iron carbide. (Cementite- Fe3C
compound)
Characteristics:
(a) White cast iron is very hard, brittle and wear resistant.
(b) Its fractured surface appears white because of absence of graphite and
hence the name white cast iron.
(c) It has poor machinability and mechanical properties.
Application: wearing plates, road roller surface, grinding balls, dies and
extrusion nozzles. White cast irons are widely used for making malleable cast
iron.
• MALLEABLE CAST IRON
Process:
These are produced from white cast irons by malleabilizing heat treatment.
The heat treatment consists heating the white cast iron slowly to a temp. at
around 9000c and holding at this temp. for long time followed by cooling to
room temperature.
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Fig: Malleablizing heat treatment cycle
Upto 1= heating
1-2 = holding period= cementite converted into graphite in rosset form
2-3= moderate cooling= gets pearlitic malleable cast iron
2-3’= slow cooling= gets ferritic malleable cast iron
Properties:
• Good mechanical properties like ductility and malleability
Applications: connecting rods, transmission gears, differential cases,
flanges, pipe fittings, valve parts, marine services.
• NODULAR CAST IRONS
Process:
These cast irons contain graphite in the form of nodules or spheroids. These
are produced from grey cast iron by addition of small quantity of magnesium
or cerium just before pouring. Due to this addition, instead of graphite flakes,
spheroids are formed.
Properties:
• Good mechanical properties like ductility and malleability
Applications: Valves, pump bodies, crankshafts, gears, and other
automotive and machine components.
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• MOTTLED CAST IRON
These cast irons show free cementite as well as graphite flakes in their
microstructure. For certain compositions, particularly in terms of carbon and
silicon content, such structures are observed under the existing conditions of
cooling. For a given composition, faster cooling gives white structure and slow
cooling results in gray structure. For intermediate cooling rates, mottled
structure is observed. Hence, mottled structure is also observed in certain
region between the surface and centre of a chilled casting. Mottled structures
do not have good properties and should be avoided.
• CHILLED CAST IRON
Process:
This type of cast iron shows white structure at surface and gray structure in
the centre. The composition of melt is adjusted in such a manner that rapid
cooling gives white structure and usual cooling gives gray structure.
Properties: hardness, wear resistance, machinability, damping capacity and
low notch sensitivity
Applications: railway-freight-car wheels, crushing roll, grinding balls, road
rollers, hammers and dies.
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MICROSTRUCTURES OF VARIOUS CAST IRONS
Fig (a): Grey cast iron (the dark graphite flakes are embedded in α ferrite matrix)
Fig (b): Nodular cast iron (the dark graphite nodules are surrounded by α ferrite matrix)
Fig (c): White cast iron (the light cementite regions are surrounded by pearlite)
Fig (d): Malleable cast iron (dark graphite rosettes in α ferrite matrix)
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• PLAIN CARBON STEEL
Plain carbon steels are classified into three groups depending on the
carbon content. These are:
(A) Low carbon steels (0.008 - 0.30%C)
(B) Medium carbon steels (0.30 - 0.60%C)
(C) High carbon steels (0.60 - 2.00%C)
(A) Low Carbon Steels:
Composition: 0.008% to 0.30% Carbon and remaining iron with impurities.
Properties:
They are soft, ductile, malleable, tough, machinable, weldable and non-
hardenable by heat treatment.
Applications:
Steel with 0.008% to 0.15% carbon are used for fabrication work. For
example wires, nails, rivets and screws. Steels with 0.15% to 0.30% carbon
are widely used as structural steels (mild steel) and finds applications as
building bars, grills, beams, angles, channels, etc.
(B) Medium Carbon Steels:
Composition: 0.30% to 0.60% Carbon and remaining iron with impurities.
Properties:
They are medium hard, not so ductile and malleable, medium tough, slightly
difficult to machine, weld and harden. They are also called as Machinery
Steels.
Applications:
They are used for bolts, axles, lock washers, large forging dies, springs, wires,
wheel spokes, hammers, rods, turbine rotors, crank pins, cylinder liners,
railway rails and railway tyres.
(C) High Carbon Steels:
Composition: 0.60% to 2.0% Carbon and remaining iron with impurities.
Properties:
They are hard, wear resistant, brittle, difficult to machine, difficult to weld and
can be hardened by heat treatment. The hardness produced after hardening
is high. They are also called as Tool steels.
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Applications: They are used for forging dies, punches, hammers, chisels,
vice jaws, shear blades, drills, knives, razor blades, balls and races for ball
bearings, mandrels, cutters, files, wire drawing dies, reamers, and metal
cutting saws.
• EFFECT OF ALLOYING ELEMENTS ON PROPERTIES OF STEEL
Molybdenum promotes hardenability, increases tensile and creep strength at
high temperature.
Chromium improves corrosion resistance, toughness and hardenability.
Nickel provides toughness, corrosion resistance, and deep hardening.
Silicon increases strength without decreasing ductility and resists high
temperature oxidation.
Tungsten increases hardenability, wear and abrasion resistance. It reduces
the tendency of decarburization.
Manganese deoxidizes, contributes to strength and hardness, and decreases
the critical cooling rate.
Vanadium deoxidizes and promotes fine-grained structure.
• ALLOY STEELS
Alloy steel may be defined as steel to which elements other than
carbon are added in sufficient amount to produce an improvement in
properties. The chief alloying elements used in steel are nickel, chromium,
molybdenum, cobalt, vanadium, manganese, silicon, tungsten.
Alloying elements are added in steel for the following purpose:
1. To improve elasticity.
2. To improve corrosion and fatigue resistance.
3. To improve hardness, toughness and tensile strength.
Alloy steels: Stainless steel, tool steels, heat resistance & shock resistance
steel
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STAINLESS STEEL
Composition Range of Stainless Steel
Class C% Cr% Ni% Uses
Ferritic 0.1 to 0.25 16 to 30 — Dairy components,
kitchen- ware, automobile
fittings
Martensitic 0.1 to 0.7
10 to 25 — Turbine blades, ball
bearings table cutlery.
Austenitic 0.08 to
0.25
15 to 25 5 to 25 Tableware, cutlery,
chemical plants,
ornamental goods.
Properties:
i. High ductility and formability
ii. Good mechanical properties at low and high temperatures
iii. High resistance to scaling and oxidation at elevated temperatures
iv. Good weldability
v. Good machinability
vi. Good creep resistance
vii. Excellent surface finish and appearance
TOOL STEELS
The selection of proper tool depends upon many factors like the
operation to be performed, characteristics of material to be cut, machine tool
to be used and rate of cutting. The society of automotive engineers has
classified tool steels into the following six major groups.
1. Water hardening tool steels
2. Shock resistant tool steels
3. Cold working tool steels
4. Hot working tool steels
5. Special purpose tool steels.
Water hardening tool steels contain 0.7 to 1.5% carbon and 0.4 to 0.5
% manganese. These are used for files, twist drills, chisels, hammers, etc.
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Shock resistant tool steel contains one or more alloying elements like
manganese, chromium, tungsten, silicon and molybdenum. Commonly used
shock resistant tool steel contains 0.5% carbon, 2% chromium and 0.5%
tungsten. These steels are used for coal cutter picks, cold chisels, pneumatic
chisels and punches.
Cold working tool steels contain manganese, tungsten and chromium
as the main alloying elements. These are used in master tools, gauges, twist
drills, taps, milling cutters, drawing dies and boring tools.
Hot working steels contain 0.3% carbon, 10% tungsten, 3%
chromium, 0.3% molybdenum and 0.3% vanadium. It is used for hot
drawing, hot forging and extrusion dies for aluminium, brass, zinc, and their
alloys.
Special purpose tool steels contain a variety of alloying elements like
nickel, tungsten, molybdenum, chromium and vanadium. These steels are
used for special purposes like stainless and heat resisting components.
HEAT RESISTING STEELS
Composition:
23 to 30% chromium, carbon less than 0.35% and remaining steel.
Heat resisting steels are those which are particularly suitable for working at
high temperatures. This steel provides a useful combination of nonscaling and
strength-retaining properties together with resistance to acid corrosion
comparable with that of stainless steels.
Applications:
Furnace parts, annealing boxes and other equipments requiring
resistance to high temperatures are often made of these steels.
SHOCK RESISTING STEELS
Shock resisting steels are those which resist shock and severe fatigue
stresses. One grade of steel for this purpose contains 0.5% carbon, 2.25%
tungsten, 1.5% chromium and 0.25% vanadium. Another grade of shock
resisting steel, known as silicon manganese steels, contains 0.55% carbon,
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2% silicon, 0.8% manganese, and 0.3% molybdenum. This kind of steel is
mainly used for leaf and coil springs.
• NON-FERROUS METALS AND THEIR ALLOYS
Nonferrous metals are used for the following reasons:
1. Resistance to corrosion.
2. Special electrical and magnetic properties.
3. Softness and facility of cold working.
4. Low density.
5. Attractive colour.
• ALUMINIUM AND ITS ALLOYS
Aluminium
Aluminium is a white metal produced by electrical processes from its
oxide (Alumina) which is prepared from a mineral called Bauxite. In India, it is
chiefly available in Bihar, Madhya Pradesh, Karnataka, Maharashtra and
Tamilnadu.
Properties:
(i). It is light in weight (Specific gravity 2.7)
(ii). It has very good thermal and electrical conductivity. On weight to
weight basis, it carries more electricity than copper.
(iii). It has excellent corrosion and oxidation resistance. This is due to
formation of Al2O3 film on the metal surface.
(iv). It is non magnetic.
Applications:
Aluminium is used for cooking utensils, electrical conductors, food
containers, ashtrays, etc. it is also used in transportation industry in the
manufacture of bicycles, motorcycles, trucks and buses, aeroplanes and
marine vessels.
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• ALUMINIUM ALLOYS: Duralumin & Y alloy
Aluminium finds its widest uses when alloyed with small amounts of
other metals. The addition of small quantities of other alloying elements
converts this soft, weak metal into a hard and strong metal, while still
retaining its light weight.
(1)Duralumin
Composition:
This is composed of 3.5 to 4.5% copper, 0.4 to 0.7% manganese, 0.4 to 0.7
% magnesium and aluminium the remainder.
Properties:
High tensile strength, high electric conductivity, very hard and can be easily
forged.
Application:
It is widely used in wrought condition for forging, stampings, bars, sheets,
tubes and rivets.
(2)Y-alloy
Composition:
Y-alloy contains 4% copper, 2% nickel and 1.5% magnesium.
Properties:
This alloy has the characteristic of retaining good strength at high
temperatures.
Application:
Piston and other components of aero engines. It is also largely used in the
form of sheets and strips
• COPPER AND ITS ALLOYS:
Copper has the following notable properties:
1. It has good ductility and malleability.
2. It has high electrical and thermal conductivity.
3. It is non magnetic and has a pleasing reddish colour.
4. It has fairly good corrosion resistance to general atmospheric
conditions.
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Applications: Electrical conductors, bus bars, automobile radiators, roofing,
pressure vessels, kettles, utensils and other similar applications.
• COPPER ALLOYS
1. Brasses:
Brasses are the alloys of copper and zinc. Brasses are classified either
on the basis of structure i.e. α-brasses and α-β brasses or colour i.e. red
brasses and yellow brasses.
α- brasses contain zinc less than 30% and α - β brasses contain zinc
between 30 to 44%. Below 20% zinc, the colour of brasses is red and above
20% zinc, the colour is yellow.
(1) α-Brasses:
They are soft, ductile, and malleable and have fairly good corrosion
resistance in annealed condition. All the a-brasses are suitable for cold rolling,
wire drawing, press work, and such other operations. Some of the important
brasses from this group are as below:
(i) Cap copper:
It contains zinc between 2 to 5%. Zinc is used as a deoxidizer for the
deoxidation of copper. If zinc is not added, copper oxide present in the
structure reduces ductility and malleability. Cap copper is very ductile and is
used for caps of detonators in ammunition factories.
(ii) Gilding metals:
They contain zinc from 5 to 15% and have different shades of colour
from reddish to yellowish according to the zinc content. They are used for
bullet envelopes, drawn containers, condenser tubes, coins, needles,
emblems and dress jewellery because of colour like gold.
(iii) Cartridge brass: (70-30 Brass)
It contains about 30% zinc and has maximum ductility and malleability
amongst all the brasses, and is used for forming by deep drawing, stretching,
trimming, spinning and press work operations. It is also known as 70-30
brass. It is used for cartridge cases, radiator fins, lamp fixtures, rivets and
springs.
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(2) α - β Brasses :
Commercial α - β brasses contain zinc between 32 to 40%. They are
hard and strong as compared to α - Brasses and are fabricated by hot
working processes. Some of the important brasses from this group are given
below:
(i) Muntz metal:
It contains about 40% zinc with balance copper. Hot worked 60-40
brass (i.e. Muntz metal) shows a tensile strength of 35 to 40 kg/mm2 and a
hardness of 100 to 120 VPN. It is used for utensils, shafts, nuts and bolts,
pump parts, condenser tubes and similar applications where corrosion is not
too severe.
(ii) Naval brass:
Addition of about 1% tin to Muntz metal increases corrosion resistance
to marine environments and the brass is called as Naval brass or Tobin
bronze. Brass with 39% zinc and 1% tin is used for marine hardware,
propeller shafts, piston rods, nuts and bolts, and welding rods.
(3) Brazing brass:
Brass with 50-50 composition is used for brazing purpose. The 50%
zinc brass melts at lower temperature (~ 870°C) and can be used for joining
commercial brasses. Since the alloy is brittle, it has no other engineering
application than for brazing purpose.
2. Bronzes:
Bronzes are the alloys of copper containing elements other than zinc.
In these alloys zinc may be present in small amount. Commercially important
bronzes are discussed below:
(i) Aluminium Bronze:
Composition: 4 to 11% aluminium and remaining copper. Other
elements such as Fe, Ni, Mn and Si are also added to improve certain
properties.
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Properties:
(a) Good strength, ductility and toughness
(b) Good bearing properties
(c) Good corrosion resistance
(d) Good fatigue resistance
Applications:
These are used in jewellery, heat exchangers, heavy duty parts,
marine equipments, gear bearings and bushes.
(ii) Tin Bronze:
Composition: 88% Cu, 10% Sn and 2% Zn.
Properties: They have good ductility and malleability. They also have good
corrosion resistance.
Applications: They are used in coins, pumps, gears, heavy load bearings
and marine fittings.
(iii) Gun metal:
Composition: It consists of 2 to 5% of zinc, 5 to 10% of tin and remainder
is copper.
Properties: (a) Corrosion resistant
(b) High tensile strength
(c) Zinc acts as deoxidizer and also improves fluidity of melt.
Applications: (a) Used for gun barrels and ordnance parts
(b) Marine castings, gears, bearings and steam pipe fittings.
(iv)Phosphor Bronze:
Phosphor bronzes can be divided into two main groups
(a) Cast phosphor bronze
(b) Wrought phosphor bronze
(a) Cast phosphor bronze: It contains 5 to 13% phosphorus and
remainder as copper. It is used in bearings, gear wheels, slide valves and
gudgeon pins. A12% tin, 0.3% phosphorus bronze has a hardness of 100
BHN. It possesses good tensile strength with 5% elongation.
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(b) Wrought phosphor bronze: It contains 2.5 to 8.5% tin, 0.1 to 0.35%
phosphorus and remainder as copper. It possesses high strength, good
corrosion resistance and is mainly used as a spring.
BEARING MATERIALS:
These are used in construction of machines, engines or parts of equipment
which requires rotary or reciprocating motions. A good lubricating material
should posses following properties,
i. It should have high compressive strength.
ii. It should have sufficient hardness & high wear resistant.
iii. It should have low coefficient of friction.
Types of bearing materials: White metal alloy, Copper lead alloy & Tin
bronzes.
White metal alloys (Babbitt):
It is a tin-base white metal and it contains 88% tin, 8% antimony and 4%
copper. It is a soft material with a low coefficient of friction and has a little
strength.
Babbitt metal makes a fine and heavy duty bearing and does not affect the
shaft very easily when the lubricant fails.
• POLYMERIC MATERIALS
Polymeric materials include the familiar plastic and rubber materials.
Many of them are organic compounds that are chemically based on carbon,
hydrogen, and other nonmetallic elements; furthermore, they have very large
molecular structures.
Plastics are superior to metals in the following respects.
1. They have good insulating properties.
2. Many plastics are transparent.
3. They possess good colouring properties.
4. They possess good surface finish.
5. Easy formation in different shapes is possible.
6. They possess good corrosion resistance.
Classification of Polymers:
Polymers are broadly classified in to two major groups as below:
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(i) Thermoplastic polymers (ii) Thermosetting polymers
(i) Thermoplastic Polymers:
Some polymers soften on heating and can be converted into any shape. The
polymers which can be remelted to manufacture fresh new products are
called as thermoplastics.
Examples: Acrylics, Polypropylene, Nylons, Polycarbonates, Polystyrene &
ABS.
Sr. No. Thermoplastic material Properties Uses
1 Polypropylene Light,hard,resists shocks Drinking straws, Car
bumpers,Dash board
2 Nylons (Polyamides)
Good tensile strength,
abrasion resistance &
toughness
Gears and bearings
(ii) Thermosetting Polymers:
Polymers which can be melted once and cannot be remelted again are known
as thermosetting plastics.
Examples: Alkyd, Epoxies, Phenolics, Polyester and formaldehydes.
Sr. No. Thermosetting material Properties Uses
1 Epoxy Flexible & resistant to
chemicals
Adhesives, tanks and
laminating tooling
2 Polyester Tough and resists most
solvents, acids and salts
In cloths and paper
luggage
Rubbers
1. Natural rubber
2. Synthetic rubber,
Natural rubber: It is generally found in countries which are lying up to 12
degrees on either side of the equator, e.g. South Africa, Malaysia, Singapore,
Mexico, Peru and Sir Lanka. It is found in the juice of many plants, like shrub
quayule, Russian dandelion, milkweed and many other shrubs, vines and
trees. The chief source of rubber is Heveabrassiliencis tree that produces the
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best rubber latex. The latex is coagulated by acids or by a smoking operation,
and the resulting spongy mixture is passed through rollers to form a sheet.
This rubber is known as smoked rubber or crude rubber. The crude rubber is
further treated by filters, plasticizers or softeners to produce commercial
rubber.
Synthetic rubber: Synthetic rubber is obtained by suitable combinations of
selected monomers. These rubbers are based on models of natural rubber.
Actually these are synthetic elastomers. Different types of synthetic rubbers
are:
1. Styrene-butadiene rubber (SBR)
2. Butyl rubber
3. Nitrile rubber.
• CERAMICS
Ceramics are inorganic, nonmetallic materials. Most of the ceramic materials
are silicates, aluminates, oxides, carbides, borides and nitrides. Ceramics are
generally classified as
• Clay products
• Refractories
• Glasses
Depending upon their industrial application and structural criteria, ceramics
can be classified in two ways,
• Functional classification
• Structural classification
Properties: Tensile strength is low but high compressive & shear strength.
They do not have electrical & thermal conductivity. They have high hardness
and high resistance to heat.
Applications: Tiles, sanitary ware, insulators, semiconductors, fuel elements
in nuclear power plant, cutting tools, concrete and variety of glasses.
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• COMPOSITES
The materials produced by combining two or more materials are known
as composites. The various types of composites used in industry are
1. Glass fibres or resins were first used in aeroplanes in World War II.
Glass fibres possess good strength while the polymers have good
toughness. The fibres are woven together and pressed into mats to
form the composite. High temperature polyamide resin with pure silica
fibres are used at high temperatures and possess good wear and
fatigue resistance.
2. Carbon fibre reinforced plastics are produced from synthetic textile
fibres, treated in such a manner that the side groups are totally
removed. These composites possess properties similar to glass fibre
reinforced resins. They possess lesser density, good strength and
fatigue resistance.
3. Reinforced cement concrete combines the properties of tensile and
compressive strength acting on structures. Steel possesses good
tensile strength and concrete possesses good compressive strength.