JSS2 Basic Technology Lesson Note on Processing of Materials

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WEEK EIGHT:        Processing Of Materials

TOPIC:          METALS

CONTENT:

• Production of metals: smelting, casting, etc.
• Carbon properties of steels
• Metal Alloys
• Clay, ceramics and glass

Metallic materials are materials which are referred to as good conductors of heat and electricity. Metals are gotten from Iron ore which is the raw material for metal production. The Iron Ore is dug from the ground along with the impurities (coke, hot air, limestone with Iron Ore).

When the Iron Ore is dug up from the ground, it cannot be used as it contains some impurities, it undergoes certain processes during which these impurities are removed and other substances are added. Since these impurities cannot be removed from iron-ore in its solid state, it is converted into a liquid state by heating. This process is known as smelting. The equipment used for this process is called a furnace. After removing these impurities from Iron Ore, the product left is called Pig-Iron. The Pig iron in its ordinary state cannot be used without further processing; this is because pig iron contains saturated iron and carbon. This is weak and can break easily. Hence, it forms the basis of all ferrous metals containing about 45% carbon.

In order to render pig iron usable such as cast Iron, steels and wrought Iron, the amount of carbon it contains must be reduced.

1. Cast Iron: This is obtained when pig Iron is put into a cupola furnace. In this furnace, the carbon content is reduced to about 3.5%. The molten Iron is then poured from the furnace into a container, called mould, so as to solidify it. This process of pouring molten iron into a mould to solidify into a described shape is called casting, hence, the name cast iron.

Examples of cast iron

1. Ductile (chilled) cast iron
2. Malleable cast iron
3. Grey cast iron
4. White cast iron.

Steel: This is obtained when the carbon content of pig iron is reduced to 1.5 or less. Steels are named according to the carbon content present in them. These steels are called Plain Carbon Steels because they are made up of carbon and iron.

Low carbon steel: (mild steel) this contains about 0.3% or less of carbon.

Medium carbon steel: This contain between 0.3%- 0.5% of carbon.

High carbon steel: This contains between 0.6%- 1.5% of carbon.

Furnaces used are open hearth and Bessemer converter.

Wrought Iron: The wrought iron is obtained by removing the carbon content present in the pig iron. It is soft, easily bent and does not break or rust easily. This is almost pure iron with little slag on it. The wrought iron has no carbon content in them. It is almost rust proof. It is malleable and ductile and can be easily forged into the required shape. Wrought Iron is used in the manufacture of chairs, boilers, plates, gears and so forth.

Casting: This is the process of melting and pouring molten metal into the mould where it cools down to solidify.

Smelting: This is the process of extracting metals from its iron-ore to a liquid state by heating. In this process, all impurities are extracted from the Iron- Ore to form pig-iron.

Annealing: This is the process by which metals can be softened.

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