MATERIALS OF CONSTRUCTIONPresented By: Jayakrishna Shenoy Adithya Acharya Rishvik Sharma Preston Lobo Gary Naveen Lewis
Cast Iron• It is a type of iron which has 2-4% carbon content. It may also contain manganese , phosphorous, silicon & sulphur.• Manganese imparts hardness to cast iron but makes it brittle. So manganese is kept <0.75%.• Phosphorous increases its fluidity. But it makes cast iron brittle. If its amount is greater than 0.3%, cast iron becomes less workable and lacks toughness.• Silicon makes cast iron brittle and hard. Its mere presence causes rapid solidification of cast iron.
Manufacture of cast iron • It is manufactured by re-melting pig iron with coke and limestone. • This re-melting is done in a furnace called as cupola furnace. • It is more or less same as the conventional blast furnace but it is smaller in size. • Its shape is cylindrical with diameter of about 1m and 5m height. • The working too is similar to that of the blast furnace but the raw materials are fed from the top. • The air is forced from the tuyeres and the impurities are removed by oxidation. • The slag formed is removed from the top of the furnace at regular intervals of time. • It is led into moulds of required shape (AKA cast iron castings or ingots).
Illustrations of cupola furnace
Types of cast iron 1. Grey cast iron 2. White cast iron 3. Mottled cast iron 4. Chilled cast iron 5. Malleable cast iron 6. Spheroidal graphite iron. 7. Toughened cast iron
Grey Cast iron It is prepared from grey pig. It’s color is grey. It is soft and melts readily. It is extensively used for making castings.
White Cast Iron Its color is silvery white. It is hard and melts with difficulty. It is not easily worked even on a machine. Cant be used for delicate casting.
Mottled Cast Iron Intermediate variety between grey cast iron and white cast iron. The fracture of this variety is mottled. This variety is used for small castings. Mottled means variegated or smeared with spots.
Mottled cast iron looks like this from a 40x objective lens.
Chilled cast iron The chilling consists of making some portion of cast iron hard and the other portion soft. This variety of cast iron is hard to a certain depth from the exterior surface and is indicated by white iron. The interior portion of the body of casting is soft and is made up of grey iron.
Malleable Cast Iron The composition of cast iron is so adjusted that it becomes malleable. It is done by extracting a portion of carbon from cast iron making it less brittle. Its used to make railway equipments , automobiles , pipe fittings etc.
Ductile Or Spheroidal Iron Malleable cast iron is being replaced by ductile cast iron as it is much easier than malleable cast iron. Manganese content of carbon in iron and opposes the formation of free graphite.
Toughened Cast Iron This variety of cast iron is obtained by making cast iron with wrought iron scrap. This proportion of wrought iron scrap is about 1/4th to 1/7th of weight of cast iron.
Properties Of Cast Iron1. If placed in salt water , it becomes soft.2. It can be hardened by heating and sudden cooling but can’t be tempered.3. It can’t be magnetized easily.4. It does not rust easily.5. Its not ductile and hence can’t be used to absorb shocks and impacts.6. Its melting temperature is about 1250°C.7. It shrinks on cooling.
M A N U F A C T U R E O F WR O U G H T I R O N The wrought iron is almost pure iron and it hardly contains carbon content more than 0.15% or so. But the process is far more laborious and tedious. There are four distinct operations involved in its manufacture. They are: 1. Refining: The pig iron is melted and a strong current of air is passed over it. It is well agitated when the currents of air passes over it, oxidizing the impurities present in it. 2. Puddling: The conversion of pig iron into wrought iron by stirring it in a molten state is known as puddling. It is carried out in a reverberatory furnace as shown in figure. In this type of furnace, the metal does not come in contact with the fuel and flame from the fire is reverted back into the hearth. 3. Shingling: By this process, the slag contained in puddle balls is placed is removed. It may be achieved by forging the balls under a power hammer or by passing the balls through a squeezing machine. The shingling helps in binding or welding the different particles of puddle balls. The material obtained at the end of shingling is known as the bloom and it is still in red hot condition. 4. Rolling: The bloom is passed through grooved bars and flat bars of size about 4mm *100mm*25mm are obtained. These bars indicate wrought iron of poor quality. To improve the quality of wrought iron , these bars are tied together and they are heated and rolled. This process may be repeated till we get wrought iron of desired quality.
Properties Of Wrought-Iron 1. It becomes soft at white heat and it can be easily forged and welded. 2. It can be used to form temporary magnets, but cannot be magnetised permanently. 3. It fuses with difficulty. It cannot therefore be adopted for making castings. 4. It is ductile, malleable and tough. 5. It is moderately elastic. 6. It is unaffected by saline water. 7. It resists corrosion in a better way. 8. Its fresh fracture shows clear bluish colour with a high silky luster and fibrous appearance. 9. Its melting point is about 1500°C. 10. Its specific gravity is about 7.8. 11. Its ultimate compressive strength is about 200N/mm². 12. Its ultimate tensile strength is about 400N/mm².
Use Of Wrought-Iron The wrought-iron is replaced at present to a very great extent by mild steel. It is therefore produced at present. It is used where a tough material is required. The wrought-iron, at present, is used for rivets, chains, ornamental iron work, railway couplings, water and steam pipes, raw material for manufacturing steel, bolts and nuts, horse shoe bars, handrails, straps for timbers roof trusses, boiler tubes, roofing sheets, armatures,electro-magnets, etc.