Definition Of Metals
Metal is processed from a natural solid mineral found beneath the earth called iron-ore. In its natural state iron-ore contains a lot of impurities which is removed through smelting.
Processing of Metal
Iron ore is the first material needed for the processing of metal. The iron ore and other materials such as coke and limestone are loaded into a device called BLAST FURNACE .The blast furnace produce a blast of hot air which heat the limestone and iron ore to produce a molten iron. The molten iron is then transferred to a Ladle which will be used to transfer the molten iron to the mould. Here in the molten iron will be allowed to cool down and form the first metal called PIG IRON.
Methods of Processing
- Blast furnace: The blast furnace is a smelting (heating or burning) plant used for changing iron – ore into pig –iron. To smelt iron – ore in the blast furnace, other chemicals like coke (which serves as fuel) and limestone (which removes impurities) are added to the iron – ore so that most of the impurities may be removed.
- Pig – iron: Pig –iron is derived from iron- ore. It is the product, derived from the blast furnace. Further processing of pig – iron gives birth to steel. The furnace used for this purpose is called “Bessemer Converter”.
- Bessemer Converter: This is the furnace used for smelting pig – iron into steel by further burning off of impurities in the right percentage. Since steel are categorized into three categories, the Bessemer converter is used for this purpose.
Other Methods: Other furnaces used for smelting iron – ore into steel are:
- The basic oxygen furnace
- The electric furnace: For producing cast iron products
- The open-hearth furnace: Is one of a number of kinds of furnace where excess carbon and other impurities are burnt out of pig iron to produce steel
Note: This three methods listed above make use of iron oxide at high temperature (16000 C) to remove impurity.
Classification of Steel
Steel is produced from pig – iron. However pig – iron contains 3 to 5% of carbon. This percentage of carbon is too high for any steel since the metal will be too weak for any engineering work.
The three basic elements of steel are Ferrite (pure iron), Cementite and Pearlite.
Classes of steel
- Low Carbon Steel: The content of carbon In a low carbon steel is about 0.05% – 0.3%. it contains mostly ferrite. It has low tensile strength and is used for car bodies and light structures.
- Medium Carbon Steel: This class of steel mainly contains cementite. This property makes medium carbon steel hard and ad of great strength. It is mainly used in making lighter springs and power transmission devices. The carbon con tent is about 0.3% – 0.6%.
- High Carbon Steel: This is the steel that contains mostly pearlite. It is usually very hard and it is used for making cutting tools like files, punches, chisels, dyes, etc.
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