Lesson Notes By Weeks and Term v4 - SHS 3
Classification of Materials
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Classification of Materials
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Subject: Manufacturing Engineering
Class: SHS 3
Term: 1st Term
Week: 17
Grade code: 2.1.1.LI.2
Strand code: 1
Sub-strand code: 1
Content standard code: 2.1.1.CS.2
Indicator code: 2.1.1.LI.2
Theme: Manufacturing Materials and Technologies
Subtheme: Classification of Materials
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Welcome, future engineers! Look around our classroom. The desk you are sitting at, the metal legs of the chair, the glass in the windows, and even the plastic pen in your hand are all made from different materials. But have you ever wondered how we get from a tree in the forest to a wooden desk, or from reddish-brown rock to a strong steel rod? This lesson is about understanding the main families of engineering materials—Metals, Ceramics, and Polymers. Most importantly, we will learn how the unique way each material is processed (shaped, heated, and finished) helps us to classify it.
A. Introduction: What are Materials and Material Processing? Material: A substance from which a thing is or can be made. In engineering, we choose materials based on their properties (strength, hardness, flexibility, etc.) and cost. Material Processing: The series of operations that transforms a raw material into a finished product or component with desired properties and shape. The processing method is a key identifier for a material class.
We will focus on three major classes: Metals, Ceramics, and Polymers. B. Class 1: Metals
Metals are elements or alloys that are typically hard, opaque, shiny, and have good electrical and thermal conductivity. They are known for their strength and ductility (ability to be deformed without breaking). Common Examples in Ghana: Steel (from iron ore or scrap), Aluminium (from bauxite), Gold, Iron, Copper. Think of roofing sheets, car bodies, cooking pots, jewellery, and concrete reinforcement bars. Key Processing Methods: Metal processing usually involves high temperatures to melt or soften the material. Smelting: This is the process of extracting a metal from its ore by heating it to a high temperature. Example (Ghanaian Context): Iron ore (a reddish rock) is heated in a blast furnace with coke (a form of carbon) and limestone. The intense heat separates the pure iron from the rock. This molten iron can then be further processed into steel. While Ghana doesn't have a large-scale blast furnace, the principle is used in steel mills like those in Tema that melt down scrap metal to produce steel bars. Casting (Founding): This involves melting the metal into a liquid and pouring it into a mould of a desired shape. It is then left to cool and solidify. Example: Making cast iron cooking pots ("dadesen") or engine blocks for cars. A mould is made in the shape of the pot, molten iron is poured in, and once it cools, the solid pot is removed. Many local foundries in places like Suame Magazine in Kumasi use casting to make spare parts. Forging: This is the process of shaping metal by heating it and then hammering or pressing it. The heat makes the metal soft and workable. Example: A blacksmith making a hoe or a cutlass. They heat the metal in a fire until it is red-hot and then hammer it into the desired shape on an anvil. Rolling: This process reduces the thickness of a metal stock by passing it through one or more pairs of rollers. Example: Manufacturing aluminium or steel roofing sheets. A large, thick slab of metal is heated and passed through massive rollers repeatedly until it becomes a thin, long sheet. C. Class 2: Ceramics
Ceramics are inorganic, non-metallic materials. They are typically hard, brittle, and good insulators of heat and electricity. They can withstand high temperatures and harsh chemical environments. Common Examples in Ghana: Clay pots ("asanka"), bricks, cement, glass, floor tiles. Key Processing Methods: Ceramic processing involves mixing powders, shaping them, and then heating them to a high temperature to bond the particles together. Mixing and Shaping: Raw materials (like clay, sand, feldspar) are crushed into a fine powder and mixed with water to form a workable paste. This paste is then shaped. Example: A potter in Vume (Volta Region) or Pankrono (Ashanti Region) mixes clay with water and then shapes it on a potter's wheel to form a bowl or pot. For bricks, the clay mixture is pressed into rectangular moulds. Drying: The shaped "green" ceramic is carefully dried to remove most of the water. This must be done slowly to prevent cracking. Example: The freshly shaped clay pots are left in the sun or a shaded, airy place for several days to dry. Firing (Sintering): This is the most critical step. The dried ceramic is heated to a very high temperature in a special oven called a kiln. The heat causes the individual particles to fuse together, making the object hard, strong, and permanent. Example: The dried clay pots are stacked in a kiln (which can be a simple pit or a modern oven) and heated for many hours. This is what transforms soft, fragile clay into a hard, usable cooking pot. The same process is used for making bricks and tiles. D. Class 3: Polymers