Subject : Basic Technology
Class : Basic 9 / JSS 3
Term : 1st Term / First Term
Topic: Production of Materials – Metals
Behavioural Objectives : By the end of the lesson, learners will be able to
- Define metals
- Mention processes that are involved in the production of metals
- Say the properties of metals, steels and alloys
Meaning of Metal
Metals are materials used in producing some equipment used in everyday life. Metals are usually solid but a few ones are in liquid or powder form. They are made from raw forms called ores. We will discuss how metals are produced from ores and metal alloys are formed. Metals come in different forms such as rods, tubes, plates, wires, bars liquid (e.g. mere) ferrous metals contain iron but non ferrous metals do not.
Metals are materials of choice for building and builders because metals are strong and durable.
This topic has three units:
- Production of metals: smelting and casting, etc.
- Carbon properties of steel
- Metal alloys:
Metal: Production of metals: smelting and casting, etc.
Most metals do not occur in pure state. They are usually combined with other metals and earthly impurity to form what is called mineral ore. When the ore is mined, the required metal is extracted from it. Some of the impurities removed from the ores are manganese, phosphorous, silicon, etc.
Stages of producing metals
Stage 1: Extraction Stage
The rock containing the metal is dug from the soil with drilling and excavating equipment. The rock and the metal mixed together is called the metal ore (the impure metal).
Stage 2: Smelting Stage
The metal ore is heated in a furnace until the metal melts into liquid form. This process is called smelting. It is then separated from other impurities that have mixed with it.
Stage 3: Casting Stage
The hot molten (liquid) metal is poured into containers of different lengths and sizes called moulds. It is left there to cool and solidify to take up the shape of the mould. This is called casting. This is round bars, square bars, wire and others are produced.
Section 2: Carbon Properties of Steel
Steel is a strong metal that is made up of the mixture of iron and carbon. This raw and impure iron is called pig iron. From pig iron, other forms of steel (iron) are produced.
- Cast iron
This is produced by refining pig iron in a furnace called cupola it contains 2% to 5% of carbon.
The pig iron scraps and some limestone are put in the furnace and burnt together with coke fire. The molten pig iron is then put into moulds to form either white cast iron (in form of iron carbide) or grey cast iron (in form of graphite).
Cast iron is brittle, and can easily break is given a hard blow.
- Wrought iron
This is produced by removing the impurities that come with the pig iron. As it melts in the furnace, it is stirred with a puddling pole so that the carbon content escapes as carbon (II) oxide gas.
Wrought iron has fibrous nature. It is able to withstand sudden shock. It can resist corrosion. It is used for making couplings, chain, gates, railings, etc.
- Tool Steel
The strength of steel depends on the quantity of carbon it contains. When the carbon content of steel is increased beyond 0.8%, it means it can be hardened by heating. Such steel is called tool steel or cast steel. It is produced by high induction furnace.
This is classified by its carbon content. Some are low carbon steel having 0.05% to 0.15% carbon. Medium carbon steel contains 0.2% to 0.5% carbon. They are also produced from pig iron in an open furnace. They could be black or white.
Section 3: Metal Alloys
An alloy is a metal that is obtained by mixing two or more metals together
- Brass: is an alloy. It is made up of a combination of copper and zinc. It can easily be worked on hand tools. If the copper content is up to 65%, brass can be ductile and can be bent when cold. It resists corrosion. It is therefore used for taps, valves, pipes, screws, etc.
- Duralumin: is an alloy of aluminium. It contains 4.5% copper, 0.5% manganese, 0.5^ magnesium, and 94.5% aluminium. It becomes hardened with age. It is used to make aircraft and sheets.
- Gilding metal: is also an alloy of copper and zinc; here copper takes as much as 90% while zinc takes 10%. It is used for making bowls, jugs, ashtrays and jewelry.
- D. Bronze: is an alloy of copper 80% and tin 20%.
The Topic is presented step by step for easy assimilation by the learners.
Step 1 : The teacher revises the previous topics that had been taught during the precious lessons
Step 2 : The subject teacher introduces the new topic of the learners
Step 3 : He or she allows the students to give their own contributions and he corrects them when the needs arise
- State the stages of producing metals
- Mention four types of metal alloys
The class teacher encourages the students to form notes by making use of the available reference materials and books. The subject teacher collects their notes and mark. The teacher does the necessary corrections on their notebooks when the needs arise