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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



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.



• 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



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



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.



• 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



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



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.



• 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.



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.



• 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.



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)



• 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:


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:


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.



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



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.



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,



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.



• 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.



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.



(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.



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.



(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:



(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



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.



• 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.

1 Engineering Materials - NPKautonpkauto.com/wp-content/uploads/notes/second/3g/mmp/1 Engineering... · 1 ENGINEERING MATERIALS 2015-16 ... • Classification of engineering materials.

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