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Casing Research PLYWOOD Plywood is a manufactured board. It is used to case speakers. Birch-faced ply is a light coloured, high-quality plywood that colour-stains and varnishes easily. CHIPBOARD Chipboard is also a manufactured board. It is cheap and will not warp or curl. Chipboard comes in two forms, plain and woodgrain, both of which are usually coated in plastic 'foil' or veneered to improve the finish and looks. MDF MDF (Medium Density Fibreboard) is another manufactured board. It used to fabricate boxes, and close-textured MDF is cut and sanded to make moulds for vacuum forming plastics. MDF must be glued using PVA carefully and precisely, and requires coating with paint many times to give a good finish, as it absorbs liquids readily. Mild Steel Mild steel can be found in many different forms. Sheet steel, for example, is made into casings and a variety of brackets an fixings. Bright drawn steel is made into round, square, tubular, angled and flat bar versions. Mild steel can be cut and shape into components that are to be permanently fixed to the product.
Acrylic becomes malleable when heated and can be easily machined. It is also possible to cement pieces of acrylic together using methylene chloride glue. When polished, acrylic must be handled carefully as its surface dents and scratches easily. POLYSTYRENE Polystyrene comes in many forms. One such form is a thin sheet of polystyrene that is used in vacuum forming machines to fabricate a casing. It has a low melting point and is fairly weak, but unlike acrylic it is not brittle. Polystyrene is also an excellent insulator, minimising any chance of electrocution by the product. It can be cut and assembled rapidly, but it takes time, precision care and effort to manufacture a quality product casing. Plastic casings can be made in a variety of ways. Injection moulding is the most common method of manufacturing casings in industry. The machine makes a casing in three stages: Step 1: The mould is warmed and the thermoplastic substance is placed in the heating chamber.
Step 2 A heating element is pulled across the top of the plastic sheet, heating it until it crinkles, then becomes taught again. Step 3 The platform is raised, and the mould is pushed into the plastic. Step 4 The air is then pumped out of the chamber, and air pressure (now greater than inside the machine) presses the sheet over the mould. Step 5 The sheet is removed from the machine (assisted using a taper, which angles all vertical sides of the casing). Excess plastic is trimmed from the casing. The mould is usually constructed from layers of MDF. It is solid because air pressure given no resistance can crush hollow moulds. If the mould is too far down, webbing (plastic sticking together in corners) occurs, not leaving enough plastic to give a full coating on the mould. The mould is smoothed to avoid bumps and lines on the casing. Air pockets are prevented by drilling holes in the mould, allowing excess air to flow into the vacuum.
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