Materials / 1 1 MATERIALS Engineering is a branch of science which deals with the optimization of material, cost and time of a product. For these optimization, an engineer should have a good knowledge of materials and their properties; so that he can choose the right material. A material is something which consist of matter. It comprise a wide range of metals and non-metals which can be operated upon to form the end product. Classification of Engineering Materials: (R.G.P.V., – June 2009) Engineering materials Metals/alloys Ferrous Organics Composites Semi-conductor Non-Ferrous Steels Plain carbon steel Ceramics Cast iron Alloy steel Grey cast iron White cast iron Malleable cast iron Ductile cast iron (nodular iron) 1. METALS : Elements whose atoms can loose electrons to form positively charged ions are called metals. They are good conductors of heat and electricity. Properties of metals : 1. They are hard. 2. 3. They are malleable. 4. 5. Good weldability. 6. 7. They are stiff. 8. Examples : Iron, copper, Aluminum, Zinc etc. They are ductile. Good machinability. They are rigid. Good castability etc.
2 / N.S.D. Basic Mechanical Engineering Metals are further classified as : Metals Ferrous Non-Ferrous (a) Ferrous Metals : Ferrous metals are those which have iron as the main constituent of the material. Examples : Cast iron, Wrought iron, steel etc. (b) Non-Ferrous Metals: Non- Ferrous metals are those which have a metal other than iron as their main constituent. Examples: Aluminium, Copper, brass etc. 2. Ceramic Materials: They are rock or clay mineral materials. Ceramic usually consist of Carbides, Borides, Oxides, Nitrides or Silicates of various metals. Properties of Ceramic Materials: 1. They are brittle. 2. They are hard. 3. Rock like appearance. 4. Corrosion resistance. 5. Resistance to high temperature. Examples :- Sand, Glass, Concrete, Cement, Insulators, Plaster etc. 3. Organic Materials : They are polymeric materials composed of carbon compounds. Polymers are solids composed of Long Molecular chains. Properties of Organic Materials : 1. Light in weight. 2. Soft. 3. Ductile. 4. Combustible 5. Poor conductors of heat and electricity. Examples : Plastic, Rubber, Paper, Wood, Lubricants, Fuels, Textiles, Paints etc. 4. Composites : Composite are mixture of two or more materials. The properties of composite materials depends upon base materials. Example : Fibre Glass. 5. Semi-Conductors: Semi-Conductors have conductivity between conductors and insulators. Example : Germanium, Silicon, Carbon etc.
Materials / 3 Ferrous Materials : The main constituent of ferrous materials is iron. It generally occurs in ores in the form of chemical compounds such as oxides or sulphides. After extraction from its ore, iron is obtained in different forms such as pig iron, wrought iron, cast iron steel etc. Iron ore Blast furnace Pig iron Cupola furnace Puddling furnace Wrought iron Cast iron Block diagram showing extraction of iron from its ore. Pig Iron : Pig iron is the first product in the process of converting iron ore into useful metal. This product is obtained when the impurities such as Sulphur, Phosphorus, Silicon, Manganese and Carbon in the iron ore get reduced by burning in a blast furnace. Pig iron is regarded as an impure form of cast iron and it is the raw material for practically all iron and steel products. Composition of Pig Iron Composition (%) Composition (%) Carbon Silicon Phosphorus 3–4 1–3 0.1–2 Sulphur Manganese Iron 0.4–1 0.1–1 Remaining Wrought Iron : Wrought iron is the purest form of iron. It is prepared from Pig Iron by burning out Carbon, Silicon, Manganese, Sulphur and Phosphorus in a Puddling furnace. Composition of Wrought Iron:Composition (%) Carbon Less than 0.03 Silicon 0.02–0.10 Phosphorus 0.05–0.25 Sulphur Less than 0.02 Manganese 0–0.02 Slag 0.05–1.5 Iron Remaining * Slag - It consist of Oxides and Silicates of calcium, magnesium, manganese and iron.
4 / N.S.D. Basic Mechanical Engineering Properties of Wrought Iron :1. It possess a high resistance towards corrosion. 2. It contain very low carbon due to which its melting point is high, so it cannot be used as casting alloy. 3. It is malleable, ductile and can be easily bended without any crack. Uses of Wrought Iron : 1. In building construction works, it is used as electrical conduit, underground service lines and vent. 2. It is used for making plates. 3. Due to good weldability and high impact strength, it is used for making crane hooks and chains. 4. It is used for making pipes, boiler tubes etc. Cast Iron: Cast iron is an alloy of iron and carbon. It is obtained by re-melting of Pig Iron with coke and Lime stone in a Cupola furnace. Composition: Carbon 1.7 - 4.5% Silicon 0.5 - 3% It also contains small amount of manganese, phosphorus and sulphur. Properties : 1. It is hard and brittle. 2. It cannot be rolled or forged. 3. High compressive strength. 4. Good in machinability. 5. Good in castability. 6. It has good damping capacity. Uses : Tool bodies, Fly-wheels, pipes, Automotive Cylinder block heads, piston and piston rings, pulleys, levers etc. Cast iron may be further classified as :- Cast iron Grey cast iron 1. Grey Cast Iron : White or chilled cast iron Malleable cast iron Ductile or Nodular cast iron Alloy cast iron (R.G.P.V. June-2008) It is grey in colour due to the fact that the Carbon is present in the form of free graphite.