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: 16
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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This lesson introduces the fundamental classification of engineering materials into three main families: Metals, Ceramics, and Polymers. We will explore not just what these materials *are*, but how the way they are processed—from raw materials found right here in Ghana to finished products—defines their category. Understanding this classification is the first step for any manufacturing engineer, as it helps in selecting the right material for a specific job, whether it's building a car, a house, or even the plastic chair you are sitting on.
A. From Raw Material to Manufacturing Material Before we classify materials, we must understand the difference between what we find in nature and what we use in a factory. Raw Material: This is a basic, unprocessed, or minimally processed substance found in nature that is used as the starting point for production. Ghanaian Examples: Timber from the forest, bauxite ore from Awaso, gold ore from Obuasi, crude oil, cocoa beans, cotton from the farm, clay from a riverbed. Manufacturing Material (or Engineering Material): This is a raw material that has been processed to a point where it can be used to make products. The processing gives it specific properties (like strength, flexibility, or heat resistance). Ghanaian Examples: Wood/Lumber (from timber), Aluminium (from bauxite), Steel (from iron ore), Cocoa powder (from cocoa beans), Fabric (from cotton), Fired clay bricks (from clay).
The journey from a raw material to a manufacturing material is called processing. The type of processing needed is a major way we classify materials. B. The Three Main Classes of Materials METALS Metals are materials known for their strength, ductility (can be drawn into wires), malleability (can be hammered into sheets), and excellent electrical and thermal conductivity. They are typically shiny when polished. Raw Materials: Metallic ores (e.g., iron ore, bauxite, gold ore). These are rocks containing a high concentration of the desired metal. Key Processing Methods: Smelting/Refining: This is a high-temperature process used to extract the metal from its ore. A chemical reducing agent (like coke, which is derived from coal) is used to separate the pure metal from the other elements in the ore. Example (Ghana Focus): Iron ore is smelted in a blast furnace with coke and limestone to produce molten iron, which is then refined into steel. While Ghana has iron ore deposits, we often import steel for construction. A more direct example is the VALCO smelter in Tema, which uses immense electricity to refine alumina (processed from bauxite) into pure aluminium. Casting: Pouring molten metal into a mould to give it a specific shape as it cools and solidifies. Example: Local foundries or blacksmiths ("gye wu") in places like Suame Magazine (Kumasi) melt scrap metal and cast it into parts like corn mill grinding plates or coal pots. Forging: Shaping the metal by heating it and then hammering or pressing it into the desired shape. This makes the metal stronger. Example: A blacksmith forging a hoe or a cutlass from a piece of steel. Rolling: Passing the metal through heavy rollers to reduce its thickness and create sheets. Example: This is how roofing sheets (aluminium or galvanized steel) are made. Common Examples: Steel rods for construction, aluminium cooking pots, corrugated iron sheets (Aluzinc), gold jewellery, car engine blocks. CERAMICS Ceramics are hard, brittle, heat-resistant, and corrosion-resistant materials. They are excellent insulators of heat and electricity. They are made from inorganic, non-metallic compounds. Raw Materials: Clay, sand (silica), feldspar, cement raw materials (limestone, clay). Key Processing Methods: Mixing and Shaping: The raw materials are crushed into a fine powder, mixed with water or other binders to form a workable paste or slurry, and then shaped. Shaping can be done by hand (pottery), pressing into a mould (bricks), or casting (slip casting). Example: A potter in Vume (Volta Region) or Pankrono (Ashanti Region) mixing clay with water and shaping it on a potter's wheel. Drying and Firing (Sintering): After shaping, the object is carefully dried to remove water. Then, it is heated to a very high temperature in a special oven called a kiln. This process, called firing or sintering, causes the particles to fuse together, making the object hard, strong, and permanent. Example: Firing clay pots in a traditional kiln makes them hard and able to hold water. The production of cement at Ghacem involves heating limestone and clay in a huge rotary kiln to form "clinker," which is the key ingredient. Melting and Forming (for Glass): Glass is a special type of ceramic. Raw materials like sand (silica), soda ash, and limestone are melted at extremely high temperatures. The molten glass is then shaped by blowing, pressing, or drawing. Example: Manufacturing of glass louvre blades or bottles. Common Examples: Cement blocks, floor tiles, clay water pots, glass cups, spark plugs, bricks. POLYMERS Polymers are materials made of very long, repeating chains of molecules (called monomers). They are generally lightweight, flexible, and excellent insulators. They can be natural or synthetic. Raw Materials: Natural: Crude oil (for plastics), rubber latex from the rubber tree, cotton, wood, silk. Synthetic: Chemicals derived from petroleum. Key Processing Methods: Polymerization: This is the chemical process that links small molecules (monomers) together to form the long polymer chains. This is typically done in large chemical reactors at an industrial scale to produce plastic resins (pellets). Example: Ethylene gas (from crude oil) is polymerized to create polyethylene, the plastic used for "pure water" sachets and shopping bags. Moulding: This is the most common way to shape plastics. The plastic pellets are heated until they melt, and then forced into a mould to take its shape. Injection Moulding: Molten plastic is injected under high pressure into a mould. Used for making complex shapes like plastic chairs, buckets, and bottle caps. Blow Moulding: A tube of hot plastic is placed inside a mould, and air is blown into it, forcing the plastic to expand and take the shape of the mould. Used for making hollow items like bottles and jerrycans ("Kufuor gallons"). Extrusion: Molten plastic is forced through a die to create a continuous shape. Example: Used to make PVC pipes, electrical wire insulation, and plastic films. Vulcanization (for Rubber): Natural rubber latex is heated with sulphur. This process makes the rubber stronger, more durable, and elastic. Example: This process is essential for making car tyres, like those produced by formerly Bridgestone/Firestone Ghana Limited. Common Examples: Plastic chairs, PVC pipes, "pure water" sachets, rubber sandals ("chale wote"), car tyres, nylon ropes, foam mattresses.
Guided Practice (With Solutions)
Question 1: A local artisan in Bolgatanga is making a traditional water storage pot. Identify the material class and describe the main processing steps they would use. Solution & Commentary: Material Class: Ceramic. Processing Steps: Material Sourcing: The artisan sources clay (the raw material) from a local riverbed or pit. Preparation: The clay is mixed with water and kneaded to remove air bubbles and achieve the right consistency. Shaping: The pot is shaped by hand, often using a coiling or pinching technique. Drying: The shaped pot is left to dry slowly in the shade to prevent cracking. Firing: The dry pot is heated to a high temperature in a kiln or an open fire. This firing process is the key step that transforms the soft clay into a hard, durable ceramic pot. Commentary: This question connects the abstract concept of "ceramics" to a familiar, tangible Ghanaian product. The key is to identify *firing* as the defining processing step for ceramics.