Non Metallic Materials Used for Machine Elements

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NON METALLIC MATERIALS

Contents1) Types of materials.

2) Selection of materials and its criteria.

3) Non-metallic Materialsdefinition.4) Various types of non metalic materials.

1) ceramics

2) polymers

3) composites

5) conclusion.


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TYPES OF MATERIALS


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SELECTION OF MATERIALS

Selection of material for the machine component is one of the mostimportant steps in the process of machine design.

The following factor should be considered while selecting the material

Availability- The material should be readily available in the market ,inlarge enough quantity to meet the requirement

Cost- For every application, there is limiting cost beyond which thedesigner cannot go. It is likely that the cost of material might be low, butthe processing may involve costly machine operation.

Mechanical properties- The important mechanical properties of materialsfrom the considerations of design are Strength, rigidity, toughness,resilience, frictional properties , wear resistance, creep characteristics,corrosion resistance, hardness etc.


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Strength (static load) Ultimate tensile strength or tensile yield strength

Strength (fluctuatingload)

Endurance strength

Rigidity Modulus of elasticity

ductility Percentage of elongation

Hardness Brinell or rockwell hardness number

toughness Charpy or Izod impact valueFrictional properties Coefficient of friction

These properties are measured in terms of following quantities


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NON METALLIC MATERIAL

Non-metallic Materials- Materials that do not have theproperties of, or do not contain, metal and that are able to combine

with hydrogen to form stable compounds, acids, acidic oxides, andanions.

Non-metal

Ceramics Organic polymers Composite


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Ceramics-

The word ceramic is described from Greek, Keramos through thegroup of materials now so described includes glass, products, cements,and plasters, some abrasive and cutting tool materials, buildingmaterials such as bricks, tiles and drain pipes, various electricalinsulation materials etc.

The term ceramics is applied to a range of inorganic materials ofwidely varying uses. generally these materials these materials are nonmetallic and in most cases have been treated at a high temperature atsome stage during manufacture.

Ceramics materials can be classified conveniently into four main

groups-1) Amorphous ceramics.

2) crystalline ceramics.

3) Bonded ceramics .

4) cements.


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Types of ceramics

Amorphous Ceramics-

These are substances referred to generally as glasses . They includethose such as obsidian which occurs naturally and glasses used for themanufacturing of bottles, windows, and lenses.

Crystalline Ceramics-

These may be single phase materials like magnesium oxide oraluminium oxide or various mixtures of materials such as these. Inaddition some carbides and nitrides belongs to this groups.

Bonded Ceramics-

Materials in which individual crystals are bonded together by a glassy

matrix as in large number of products derived from day.

Cements-

cements a number of these arte crystalline but some may containboth crystalline and amorphous.


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Properties of ceramic materials

1) Opticalproperties- many types of glasses have been used for theproduction of windows and optical lenses. A number of specialglasses have also been employed for selective transmission orabsorption of particular wavelength such as infrared and ultraviolet.

2) Thermal properties- ceramics posses favourable properties at hightemperature and under oxidation conditions.

3) Electrical conductivity-Although many ceramics are insulators of themof course conduct electricity quite well at room temperature and

constitute a very special class of semi-conductors.

e.g.)porcelain, steatite, forsterite, and alumina etc.

4) Mechanical properties-

a) Non-ductile stress concentration has little or no effect on

compressive strength.


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b) The compressive strength several times more than the tensile strength.

c) Temp rigidity is high.d) The ceramic materials posses ionic and covalent bonds which impact

high modulus of elasticity etc.

e) Below recrystallisation temperature, non-crystalline ceramics are fullybrittle.

f) In case of alloy consisting of two or metal, each phase many haveappreciable difference of coefficient of thermal expansion whichgenerate stress. This stress may then cause the metal to fail.

Application of ceramic materials-1) Ceramic materials are used in electrical and electronics industrybecause of their high electrical resistivity , dielectrical strength andmagnetic properties suitable for applications such as magnets forspeakers.


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2) The capability of ceramics to maintain their strength and stiffness atelevated temperatures makes them very attractive for high temperatureapplications.

3) High resistance to wear makes them suitable for applications such ascylinder liners, bushings, seals, and bearing.

4) Internal combustion engines are only about 30% efficient, but withthe use of ceramic components their operating performance can beimproved by at least 30%

5) Ceramic materials have been used successfully especially in gasolineand diesel engine components and as rotors, are silicon nitride,silicon carbide, and partially stabilised zircon.

6) High speed components for machine tools.

7) Ceramics are also used to coat metal which may be done to reducewear, prevent corrosion and a thermal barrier.

8) Silicon-nitride ceramics are also used as ball bearing and rollers.because of their strength and inertness.


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Polymers

Polymers means many units (poly=many, mer=units) is composed of alarge number of repetitive called monomers or simple molecules.

Thus a polymers is made up of thousands of monomers joinedchemically together to form a large molecules.

It has been observed that each molecule of polymer is either a longchain or a network of repetitive units or monomers.

Classification of polymers

1) Thermoplastic polymers.

2) Thermosetting polymers.


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B) Thermosetting polymers-1) Thermosetting polymers are the polymers which are the opposite of

thermoplastics. They become hard and rigid when heating.

2) Common thermo-setting polymers which is subdivided into twocategories, thermosetting and elastomers. In this case, thermosetsrefers to materials that share with the engineering polymers.

3) Significant strength and stiffness so as to be common Metalsubstitutes. However , thermosets have the disadvantages of notbeing recyclable and in general, having less variable techniques.

4) In addition to the many applications found. Such as films foams andcoatings. The adhesive serves to join the surfaces of two solids by

secondary faces similar to those between molecular chain inthermoplastics.


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mechanical properties of polymers

Materials Specific gravity Tensile strength Compressivestrength

polyamide 1.04-1.14 70 50-90Low densitypolythene

0.92-0.94 7-20 -

acetal 1.41-1.42 55-70 -

polyurethane 1.21-1.26 35-60 25-80

Teflon 2.14-2.20 10-25 10-12


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C) Synthetic Rubbers

Synthetic rubbers or elastomers are manufactured from raw materials such ascoke, limestone, petroleum, natural gas, salt, alcohol, ammonia, coal tar etc.

We can say that the processing of synthetic rubbers involved approximatelythe same steps as that of natural rubber. moreover, some of the properties of

the synthetic rubbers are better than those of natural rubbers.

Example, some synthetic rubbers are more resistant to sunlight than thenatural rubbers. Similarly , some synthetic rubbers have greater solventresistance and other have greater elasticity than that of natural rubber.

Some important synthetic rubbers are-

1)silicon rubbers 2)polyurethane rubbers 3)nitrite rubbers

4)butadiene rubbers 5)butyl rubbers 6)polychloroprenes etc.


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Properties of engineering polymers

The following are the properties of engineering polymers-

1) Polymers have good corrosion resistance.

2) Low density

3) Low co-efficient of friction.

4) Temperature resistance.5) Poor tensile strength.

6) Good mouldability.

7) Modulus of elasticity.

8) Light weight.9) Polymers are good thermal and electrical insulators.

10) Good resistance to chemicals.

11) High coefficient of thermal expansion.


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Application of polymers

1) Several inorganic materials have structure composed of buildingblocks connected in chain and network configurations.

2) The rear quarter panel on this sports car was a pioneering application

of an engineering polymers in a traditional structural metalapplication.

3) In automotive industry engineering polymers are used.

4) Consumer and industrial products made of polymers include foodand beverage containers, packing, housewares, textiles, medicaldevices foam, paints, safety, shields and toys.

5) Relative humidity is a design consideration for the use of nylons.


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Composite materials

Composite materials comprising two or more different materialsbonded together having combined properties of constituents are calledas composites.

In its simplest form composites consists of two independent anddissimilar materials.

The common example of composites used in everyday life are plywood,vehicle tyres etc. plywood is the composites of thin sheets of wood with

grains of alternate sheets perpendicular to each other and bondedtogether by a polymer in between them.


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Classification of composite materials


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Properties of composite materials

1) The properties such as strength resistance to heat or some otherproperties of composite materials are better than the properties ofthe individual materials from which they are made.

2) The specific strength is sometimes referred to as the strength to

weight ratio.

3) Composite materials have stiffness, toughness, creep resistance.

4) Properties like density and heat capacity depend on the amount of

each phase and are independent of microstructure.

5) Properties like elastic modulus, thermal and electrical conductivitiesdepends upon geometry of the constituents as well as to their volumefraction.


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Application of composite materials

Carbon-carbon fiber, alternatively graphite fiber. Carbon fiber is a materialconsisting of fibers about 5-10m in diameter and composed mostly ofcarbon atom.

Glass-

fiber glass also called glass reinforce plastic. Glass fiber Reinforced

plastic is a fiber reinforced polymer made of a plastic matrix reinforcedby fine fibers of glass.

Aramid-

Aramid fiber a class of heat resistant and strong synthetic fibers. They

are used in aerospace and military application.


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Application of composite materials

1) Composite materials to be used in certain application like spacevehicles.

2) Aircrafts.

3) Rockets.4) High pressure vessels.

5) Building construction.

6) Aerospace.

7) Fuel efficient automobiles.


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Types & uses of materials

Reinforced plastic with fibreglassmakes the material to withstand highcompressive as well as tensile stresses


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References1) Bhandari, V. B. Machine Design data book, Tata McGraw Hill

Publication Co. Ltd.

2) Material Science & Metallurgy For Engineers, Dr. V.D. Kodgire & S.V. Kodgire,Everest Publication.

3) Engineering Metallurgy, Higgins R. A., Viva books Pvt. Ltd., 2004.

4) Material Science & Engg. Raghvan V., Prentice Hall of India , NewDelhi. 2003.


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Non Metallic Materials Used for Machine Elements