What are the Types of Engineering Materials

Types of Engineering Materials

The engineering materials are mainly classified as follows:

        1. Metals and their alloys

        2. Non-metals

1. Metals and their alloys

A) Ferrous metals

  • The ferrous metals are those which have the iron as their main element or constituent
  • Ferrous materials are the most important metals in the metallurgical and mechanical industries because of their extensive use.
  • The commonly used ferrous metals are as follows:

                 a) Cast iron.

                 b) Alloy cast iron

                 c) Plain carbon steel

                 d) Alloy steel

a) Cast Iron
  • Cast iron are the alloys of iron and carbon.
  • Generally, commercial cast iron are complex in composition and their carbon content is in the range of 2.3 to 3.7 % with other elements like sulphur, manganese, phosphorus and silicon.
  • Cast iron are formed by melting a metal and casting with or without machining to the desired final shape and size, hence called as cast iron.

Characteristics of cast iron

  • While manufacturing of cast iron, raw materials like pig iron, scrap limestone, coke etc. are used. All these elements are relatively cheap, hence the cast iron is the cheapest amongst all alloys.
  • The melting point of cast iron is low i.e. 110 to 1240 °C.
  • Due to high fluidity of melt, cast iron has excellent cast ability.
  • By altering the chemical composition, cast iron can provide a wide range of metallic properties.

Advantages of cast iron

  • It is a low cost material.
  • It can provide good damping capacity and high compressive strength.
  • Cast iron has high resistance to wear and abrasion.
  • It has high hardness.
  • Corrosion resistance of cast iron is fairly good.
  • It has excellent machinability.

Limitations of cast iron

  • It is brittle in nature.
  • Its mechanical properties like toughness, stiffness, resilience, etc. are poor.
  • Due to brittleness, it is poor against fatigue and impact loading.

Applications of cast iron

Cast iron are used in the following machine elements:

  • Machine beds, columns, hammers, road-rollers.
  • Pipe fittings, valves, farm equipment’s, automotive parts.
  • Camshafts, crank shafts, gears, ordnance parts.
  • Motor covers, pump bodies, furnace parts.
  • Engine frames, piston and cylinder, cylinder blocks and bearing blocks, etc.

Types of cast iron

Cast iron are classified as follows:

         1. While cast iron

         2. Gray cast iron

         3. Malleable cast iron

         4. Nodular cast iron.

b) Alloy Cast Iron
  • Generally, cast iron has low impact resistance, corrosion temperature resistance. Hence, to increase these properties certain alloying elements a p re added in suitable amount, resistance and
  • Usually, nickel, chromium copper, silicon, vanadium, molybdenum etc. are used for this purpose.

Properties of alloy cast Iron

  • It has high strength.
  • It has high oxidation resistance.
  • It has high wear resistance and corrosion resistance.

Applications of alloy cast iron

  • Alloy cast iron are used in the manufacturing of following parts:
  • Gears, automobile parts like pistons, piston rings, camshaft, crank shaft, cylinders.
  • Brake drum, pulleys, grinding machinery parts, etc.
c) Plain Carbon Steel
  • Steel is an alloy of iron and carbon with carbon content up to 1.6 % approximately.
  • Carbon content increases the strength and hardness of steel.
  • Plain carbon steel or carbon steel is defined as a steel which has its properties mainly due to its carbon content and does not contain more than 0.5 % of silicon and 1.5 % of manganese.

Properties of plain carbon steel

  • They are ductile in nature.
  • They have high fatigue and impact strength.
  • Their mechanical properties like toughness, stiffness, resilience, etc. are high.

Advantages of plain carbon steel

  • They have high tensile strength.
  • They have high resilience and toughness.
  • They can sustain fatigue and Impact load.

Limitations of plain carbon steel

  • The vibration damping property of steel is poor.
  • They cannot be cast into complicated shapes.
  • They have low wear resistance.
  • Its cost is more than cast iron.

Applications of plain carbon steel

Plain carbon steel is used in the manufacturing of following parts:

  • Stampings, fan blades, rivets, nuts, bolts, wires, structural steel, grill, shafts.
  • Gears, valves, crank shaft, camshaft, axles, screws, springs.
  • Cutting tools, milling cutters, blades, drill bits, musical instruments, agricultural applications, etc.
d) Alloy steel
  • To obtain the specific properties various alloying elements are added in steel.
  • The specific properties define the applications of steel.
  • The various alloying elements are as follows:

                    i) Carbon

                   ii) Sulphur

                   iii) Phosphorous

                   iv) Silicon

                   v) Manganese

                   vi) Nickel

                   vii) Chromium

                   viii) Titanium

                   ix) Tungsten

                   x) Molybdenum

                   xi) Vanadium

                   xii) Cobalt

Properties of alloy steel

  • They are ductile in nature.
  • They have high corrosion resistance.
  • They have high strength.
  • They are soft and having high toughness.

Advantages of alloy steel

  • They have high tensile and fatigue strength.
  • They have high wear resistance, corrosion resistance and creep resistance.
  • They have high toughness and resilience.

Limitations of alloy steel

  • Alloy steel cannot be cast into complicated shapes.
  • Their vibration damping property is poor.
  • They are costlier than steel and cast iron.

Applications of alloy steel

Alloy steels are used in the manufacturing of following parts:

  • Aircraft engine parts, heat exchangers, wrist watches, sanitary fittings.
  • Combustion chamber, furnace parts, gas burners, screws.
  • Valves, pumps, surgical instruments, razor blades, turbine blades missiles, structural components, etc.

B) Non-Ferrous metals

  • Non-ferrous metals are those which contain a metal other than iron as their main element or constituent.
  • Non-ferrous metals find wide applications in various industrial sectors because of following advantages:

                       Low density, hence light in weight.

                       High electrical conductivity.

                       Easy to fabricate.

                       High corrosion resistance.

  • The commonly used non-ferrous alloys are as follows:

                   a) Copper and its alloys

                                 i) Brasses

                                 ii) Bronzes

                   b) Aluminium and its alloys

a) Copper and its alloys
  • Copper is one of the most widely used non-ferrous metal.
  • Various alloying elements are added to copper to improve and add some properties.
  • Major alloying elements are zinc, silicon, aluminium, lead, manganese, nickel, phosphorous, tin, magnesium, etc.

Properties of copper

  • It has high ductility and malleability.
  • It has high electrical and thermal conductivity.
  • It is non-magnetic in nature.
  • It can be easily alloyed with other metals.
  • Its corrosion resistance is also high.

Applications of copper

  • Copper is used in the manufacturing of following parts:
  • Electrical parts
  • Heat exchangers
  • Household utensils, etc.

Types of copper alloys

            i) Brasses

            ii) Bronzes

i) Brasses

  • Brasses are alloys of copper and zinc with small amount of other alloying elements.
  • According to the percentage of copper and zinc, there are various types of brasses.
  • The properties of brasses can be changed by adding small amount of other alloying elements.

Advantages of brasses

  • It has high corrosion resistance.
  • It has high ductility and malleability.
  • Due to addition of zinc, it has high strength.
  • It has high machinability.

Limitations of brasses

  • It has low thermal and electrical conductivity.
  • Its cost is also high.

Applications of brasses

  • Brasses are used in the manufacturing of following parts:
  • Coins, needles, jewellery, condenser tubes.
  • Cartridge cases, headlight reflectors, springs.
  • Shafts, nuts, bolts, welding rods, machine parts, etc.

ii) Bronzes

  • Bronzes are alloys of copper and major alloying elements other than zinc or nickel.
  • But, generally bronzes are alloy of copper and tin.
  • Sometimes, it also alloyed with aluminium, beryllium, silicon, etc.

Advantages of bronzes

  • It has high corrosion resistance.
  • It is comparatively hard than brass.
  • It can be rolled into sheets, rods or wires.
  • It has high tensile strength.
  • It has high ductility and malleability.

Limitations of bronzes

  • The cost of bronzes is higher than the brasses.
  • The strength of bronzes is lower than the ferrous metals.

Applications of bronzes

Bronzes are used in the manufacturing of following parts:

  • Springs, gears, bearings, electrical appliances.
  • Bolts, rivets, pressure vessels, bells, marine containers.
  • Valve bodies, ordnance parts, gun barrels, pipe fittings, etc.
b) Aluminium and its Alloys
  • Aluminium is another widely used non-ferrous metal.
  • Aluminium can be easily alloyed with elements like silicon, copper, nickel, zinc, manganese, titanium, magnesium, etc.

Advantages of aluminium alloys

  • It has high thermal and electrical conductivity.
  • It has high corrosion resistance.
  • It has high toughness.
  • They are malleable and ductile.
  • It can be easily cast and rolled.

Applications of aluminium alloys

Aluminium alloys are used in the manufacturing of following parts:

  • Aluminium alloys are widely used in the aircraft industry.
  • Motor housings, pump castings, pistons, cylinder heads.
  • In food industry, food preparation equipment’s, refrigeration, storage containers, bakery equipment’s, etc.

2. Non-metals

  • Now-a-days use of non-metals is increasing in the industries because of following properties:

                   They are having low density.

                   They are light in weight.

                    Use of non-metals provides flexibility in the design.

                   They have high resistance to heat and electricity.

                   They have low cost.

  • The commonly used non-metals are as follows

                  A) Rubber

                  B) Plastic

                  C) Wood

                  D) Glass

A) Rubber

  • Rubbers or Elastomers are hydrocarbon and polymeric materials.
  • Rubber or elastomer is defined as a polymeric material which at room temperature can be stretched to at least twice its original length and after immediate release, it will return quickly to approximately its original length.
  • Now-a-days rubbers are widely used in engineering applications.
Properties of rubber
  • Rubbers are non-crystalline in structure.
  • They are non-conductors of electricity and low heat conductors.
  • Their chemical and corrosive resistances are also high.
  • They have relatively low softening temperatures.
  • They are ductile in nature.
  • They have high resilence and elasticity.
Types of rubber

Rubbers are divided into two major group i.e. natural rubber and synthetic rubber.

a) Natural rubber

  • Natural rubber is processed from rubber latex, a milky liquid obtained from certain tropical trees.
  • If sulphur is added to the raw rubber and the mixture is heated, then Vulcanization occurs. Hence, a much harder, stronger and rigid material is obtained.
  • The natural rubber has high strength, high resilience, high resistance to tear, abrasion and cracking; but it loses its strength at high temperatures.
  • Also it is a low cost material.

b) Synthetic rubber

  • The most commonly used synthetic rubber is styrene butadiene rubber (SBR).
  • Its most of the properties are improved by varying the relative amounts of styrene and butadiene.
  • Other synthetic rubbers are chloroprene, isonprene, polybutadiene, polyacrylate, pojysulphide, etc.
  • SBR is similar in properties to the natural rubber.
Applications of rubber

Rubbers are used in the manufacturing of following components:

  • Vehicle tyres, gaskets, erasers, pipes, tubes.
  • Belt conveyors, adhesives, tapes, seals, gloves, aprons, floor tiles, etc.
  • Brake liners, containers, wires and cables, engine mountings, etc.

B) Plastic

  • A large group of engineering materials which have increasing importance in industrial applications are composed of natural synthetic organic polymers (plastics).
  • Now-a-days in some of the applications, metal and wood parts are replaced by plastics, which have satisfactory properties and may be produced at lower cost.
  • Plastics are moulded into any required shape by the application of pressure and heat. For example toys, chairs, radiator fans, refrigerator equipments, etc.
  • The plastics can be cast, rolled, laminated and machined easily.
  • The word ‘trier’ means a unit; monomer stands for a single unit and polymer means many units joined together by a chemical reaction.
Characteristics of polymers/plastics
  • Low density and weight.
  • High corrosion resistance.
  • Low thermal, mechanical and electrical properties.
  • Low coefficient of friction.
  • Excellent surface finish can be obtained.
  • It can be produced in different colours.
  • It can be produced with close dimensional tolerances.
  • It has good mouldability.
  • It is more economical than the metals.
Limitations of polymers/plastics
  • It has low strength and rigidity.
  • It has poor tensile strength.
  • It has poor temperature resistance.
  • It has short life.
  • It has poor dimensional stability.
Types of polymers/plastics

Plastic or polymers are classified into two major categories:

        a) Thermoplastic or Thermoplasts (Soflen when heated and harden when cooled).

        b) Thermosetting or Thermosets (Soften When heated and permanently harden when cooled).

a) Thermoplastics (Thermoplasts)

  • Thermoplastic polymers soften when heated and harden when cooled.
  • These types of polymers are soft and ductile.
  • They have low melting temperatures and can be repeatedly moulded and remoulded to the desired shapes.
  • These polymers are usually fabricated by the simultaneous application of heat and pressure.

Applications of Thermoplastics (Thermoplasts)

  • These type of plastics are used in electrical insulations, toys, machine guards, musical instruments, fuel container coatings, hoses, photographic films, bottles, gaskets, packings, refrigerator parts, floor tiles, plastic lenses, etc.
  • Some of the commonly used thermoplastics are: Polyarnide, Poly-Tetra-Fluaro-Ethylene (PTFE), Poly-Vinyl-Chloride (PVC), Poly-Propylene (PP), Poly-Ethylene (PE), etc. 2. Thermosetting (Thermosets) polymers

b) Thermosetting (Thermosets)

  • Thermosetting polymers become soft during first heating and become permanently hard when cooled. Hence, these type of polymers cannot be remoulded or reshaped by subsequent heating.
  • These type of plastics are generally more stronger, harder, brittle and resistant to heat and solvents than the thermoplast.
  • If they are heated to high temperature, decomposition and degradation of the polymer takes place.

Applications of Thermosetting (Thermosets)

  • These type of plastics are used in telephone receivers, electric plugs, radio and T.V. cabinets, camera parts, automobile parts, switch panels, etc.
  • Some of the commonly used thermosets are: Phenolics, Epoxies, Aminos (Urea formaldehyde and melamine formaldehyde), Unsaturated polyesters, etc.
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