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Unit 6: Wood Unit 7: Metals Unit 8: Plastics Unit 9: Safety in the Workshop Unit 10: Marking Out Unit 11: Cutting & Shaping Unit 12: Bending & forming Unit 13: Joining | |||||||||||||||||
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Unit 6:Wood Conversation of Timber There are many methods of converting timber The first two methods are plain sawing and quarter sawing. Plain Sawing In plain sawing, the log is cut into planks by parallel saw cuts. This is a very quick and simple way of sawing. There is very little wastage of timber. Plain sawn timber can shrink and warp easily. Usually lousy quality timber which is used for packing cases and pallets is sawn this way. Quarter Sawing Timber sawn this way is usually more expensive because more labour is involved and there is a greater wastage of timber.Quarter sawn timber usually does not warp easily. For this reason, musical instruments such as guitars and violins are made from quarter sawn timber.Quarter sawn timber can also be used for making wooden floors. Seasoning of Timber Seasoning is the process of removing of excess moisture from freshly-cut timber. We must remove the moisture before it can be used. Seasoning is necessary because seasoned timber has greater strength is less likely to warp is less likely to be attacked by fungi and wood boring insects can be easily work with tools and can be polished and painted Air Seasoning In air seasoning the timber is stacked in a way that allows the air to flow freely around the timber. The moisture in the timber will gradually evaporate into the air. The timber is mostly stacked in an open shape as the concrete floor helps to prevent moisture from the floor affecting the timber.Air seasoning is a very slow process and the rate of seasoning depends on the thickness and the kind of timber. It may even take as long as one year or more to be properly seasoned. Kiln Seasoning In kiln seasoning the timber is placed on trolleys. The trolleys are used to be pushed into huge ovens called kilns.The hot air and steam in the kiln are used to dry the timber. The amount of hot air and steam and the temperature in the kiln is controlled so that the timber will season evenly. The hot air and steam will also kill the insects in the timber. Kiln seasoning is faster than air seasoning and it depends on the type of timber and its thickness. This method of seasoning timber takes only a few weeks to season the timber. Types of Wood ? | |||||||||||||||||
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Unit7: METALS Pure metals can be minded from the ground, on the surface and even below the seabed. They come in the form of ores and have to be taken out from inside the ore using the blast furnace. Different metals are obtained from different ores. Sometimes a metal can be combined with other metal or element to form a new kind of metal which is called an alloy. For example, steel is an alloy of iron and carbon. Copper combines with zinc to another kind of alloy called brass. Some pure metals are weak and are not used commonly. However when it is being alloyed, the metals become stronger. Thus the main purpose of alloying is to improve the properties of the metals. For example, aluminium is a soft metal which has been alloyed with manganese, copper and magnesium to form a new alloy called duralumin which is strong enough to be used in aircraft construction. Ferrous Alloys STAINLESS STEEL Stainless steel is made by alloying steel with chromium and nickel. It is a hard and tough metal and is also non-toxic, it dose not rust. The kitchen utensils and cutlery are commonly made of stainless steel. It is also used for making surgical instruments as it is non-toxic and also antirust. High Speed Steel High speed steel is an alloy of steel, tungsten and chromium. Generally, most metals lose their hardness at high temperatures but this is not with high speed steel. This steel can retain its hardness at temperatures as high as 700 degrees celcius!!! Hence, tools made of high speed steel can last longer than those made of high carbon steel. Some of the cutting tools such as twist drills and lathe cutting tools are widely made of high speed steel. NON-FERROUS METALS Lead Lead is a very heavy but soft metal. It has a dull-grey colour and has a resistant to corrosion. We must be very careful when we use or work with things that contain lead as it is toxic. Lead is commonly used for making the plates in car batteries and in the manufacture of soft solders. It is also used as a protection against X-rays and radiation. Being a heavy metal, lead is used to make fishing weights. Zinc Zinc is a bluish-white metal. When the metal is being exposed into the air, a layer of oxide is formed and this oxides protects the metal from corrosion. Zinc is widely used in the manufacture of batteries. It is also commonly used for coating mild steel sheets to make galvanised iron sheets. Galvanised iron is particularly suitable for making air-conditioning ducts and roofing sheets. NON-FERROUS ALLOYS Brass Brass is an alloy of copper and zinc. It is golden-yellow in colour and tarnishes easily. However, the tarnished surface can be polished to make it shiny again. Brass is a good conductor of heat and electricity. Brass is commonly used to make the pins of electric plugs, keys, hinges and barrel bolts. It can also be used to make costume jewellery and musical instruments. Bronze Bronze is an alloy of copper and tin. It is reddish-yellow in colour and is harder and tougher than brass. It is also resistant to corrosion. Bronze is commonly used to make bells, gears, musical instruments, ship propellers and sculptures. Duralumin Duralumin is an alloy of aluminium, copper and maganese. It is greyish-white in colour. Although the metal is light in weight, it is tough and hard. Duralumin is commonly used where strength and lightweight are required, such as making aircraft and vehicle parts. It is also used for making window and door frames, grille, letter boxes and ladders. Pewter Pewter is an alloy of tin, antimony and copper. It is soft and can be shaped easily. The metal has a colour of silver. Pewter is commonly used for making ornaments such as plaques, vases, mugs and souveniers for display. | |||||||||||||||||
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