Е. С. Закирова, П. А. Красавин Английский язык для технических вузов
MODULE 7 ELEMENTS, COMPOUNDS, MIXTURES, AND COMPOSITES
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- MODULE 8 DIFFERENT KINDS OF CASTING
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ELEMENTS, COMPOUNDS, MIXTURES, AND COMPOSITES Taking into consideration the chemical composition of materials, that is the chemicals they contain, and how the chemicals are combined, we may distinguish the following main categories of materials: elements, compounds, mixtures and composites. Pure materials in their basic form are called elements. They cannot be bro- ken into separate constituents. The most common elements widely used in engineering are iron, aluminium and carbon. Materials which consist of two or more elements combined by chemical reaction present a category of compounds. An everyday example is water — a compound of hydrogen and oxygen. Mixtures include two or more elements or compounds which are mixed together but are not chemically bound. The most common mixtures used in engineering are alloys. Steel, an iron-carbon alloy, can include in small quan- tities other elements such as chromium, manganese and tungsten. A composite material is a matrix with a reinforced material inside it. Fiber- glass, correctly called glass-reinforced plastic, is a composite with a plastic matrix reinforced with fiberglass. Composite materials are considered to be hi-tech materials. MODULE 8 DIFFERENT KINDS OF CASTING The casting process is subdivided into different kinds according to the mold material, such as sand or metal, and pouring method, such as gravity, 276 vacuum or pressure. Only some kinds of casting are mentioned here: sand cast- ing, shell-mold casting, die casting, spin casting. Sand casting is a metal casting process characterized by using sand as the mold material which is relatively cheap and sufficiently refractory even for steel foundry use. Shell-mold casting uses resin covered sand to form the mold. As compared to sand casting, this process has better dimensional accuracy, a higher produc- tivity rate, and lower labour requirements. During die casting the molten metal is forced under high pressure into a mold cavity. The mold for die casting is created using two hardened tool steel dies. While spin casting, the centrifugal force is utilized to produce castings from a rubber mold. Typically, a disc-shaped mold is spun along its central axis at a set speed. The casting material, usually molten metal or liquid thermoset plastic is then poured in through an opening at the top-centre of the mold. The filled mold then continues to spin as the metal solidifies or the thermoset plastic sets. жүктеу/скачать 4,38 Mb. Достарыңызбен бөлісу:
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