A metal is a product from iron ore. Iron ore is the raw form of iron dug from the ground. When in this raw form, it contains impurities. To change iron ore into usable forms, the impurities have to be removed and some other substances added. Different processes are involved in the removal of impurities and adding of other substances.
Metal Processing Methods
Metal processing industries process metal ores and scrap metals to obtain pure metals.
The metal processing methods are:
- Smelting: The removal of impurities from iron ore and adding of substances to convert it to a metal type is called smelting. The iron ore is converted into a liquid form by heating it to a very high temperature in a furnace. A furnace is a large installation in which iron ore can be turned into liquid.
- Casting: This is a process of moulding metals into different shapes when it is in the liquid state (molten state). In order to cast a metal, the molten iron ore is poured into a mould that has been prepared in the desired shape and size to form a solid.
- Hammering: This is the process of pressing metals into the shape of a die. This will strengthen the metal, making it harder to deform.
- Welding and cutting the sheet metal.
- Sintering: This involves transforming metal powder compacts (or loose metal powders) into coherent solids at temperatures below their melting point.
- Shaping the metals on a lathe.
Advantages and Disadvantages of Different Processing Methods
The smelting process is the chief among the metal processes. It helps to extract metals in a purified form and enhances better workability while using suitable reducing substance.
Disadvantages of Smelting
- It requires a very large temperature and iron rich in ore.
- It produces toxic air pollutants.
- Waste products from smelting include liquid waste which may leak into water supplies.
- As a result of the pollution from a smelting plant, acid rain may be produced.
- Workers at smelting plants are exposed to toxic chemicals everyday, which can harm the workers’ health.
The casting process produces excellent dimensional accuracy, smooth cast surfaces and thinner walls cast. It reduces or eliminates secondary machining operations, has rapid production rates and low fluidity metals.
Disadvantages of Casting
It is very expensive and the process is limited to high-fluidity metals. Also, the final casting will have a small amount of porosity, hence, it is only suitable for parts in which softness is acceptable.
Examples, Properties and Uses of Metal Alloys
An alloy is a material composed of two or more metals and non-metals. We have seen that different processes are used to produce a metal from iron ore. The processes involve removing impurities and adding some other substances. The smelting process thus produces different metal types such as pig iron, wrought iron and cast iron.
When substances are added to the molten ore after impurities are removed, the resulting product is called an alloy. A common type of metal alloy is steel. Other types of metal alloy are:
- Pig iron: This is formed when carbon is added to the smelted iron ore. Pig iron mainly contains saturated iron and carbon. It is not very strong, therefore, it breaks easily.
- Wrought iron: When the amount of carbon contained in pig iron is reduced, the resulting product is a wrought iron. It is a soft metal, which can be easily bent. It does not break or rust easily. It is mostly superior than cast iron which is overly hard.
- Cast iron: Cast iron is a pig iron containing about 3.5% carbon. There are two main types of cast iron; grey cast iron and white cast iron. They are both heated to a very high temperature but the white cast iron is allowed to cool rapidly.
- Steel: Steel is a mixture of three basic elements namely ferrite (a pure iron), cementite and pearlite an (alternate layer of ferrite and cementite).
There are three types of steel based on the carbon content. These are:
- Low carbon steel (Mild steel): This contains about 0.1% of carbon. It is mainly made up of ferrite and a little quality of pearlite. It is a very soft steel with a low tensile strength. It is used in the manufacturing of car bodies and light structures since it cannot be hardened.
- Medium carbon steel: It contains about 0.5% carbon. It is relatively hard and strong. It is used in the manufacture of light strings and power transmission cables.
- High carbon steel: The carbon content of high carbon steel is about 0.85% to 1-2%. It is made up of mostly pearlite. It is very hard and used for metal cutting tools, files, punchers, tapes, dies and chisels.