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1、编号：时间：2021年x月x日书山有路勤为径，学海无涯苦作舟页码：第1页 共1页1. Metals and Their UseIt is known that metals are very important in our life. Metals have the greatest importance for industry. All machines and other engineering7endVi5niEriN constructions have metal5metl parts; some of them consist only of metal parts.There
2、 are two large groups of metals:1) Simple metal- more or less pure chemical elements5elimEnt2) Alloys5AlCi- materials consisting of a simple metal combined with some other elements.About two thirds of all elements found in the earth are metals, but not all metals may be used in industry. Those metal
3、s which are used in industry are called engineering metals. The most important engineering metal is iron5aiEn, which in the form of alloys with carbon5kB:bEn and other elements, finds greater use than any other metal. Metals consisting of iron combined with some other elements are known as ferrous5f
4、erEs metals; all the other metals are called nonferrous5nCn5ferEs metals. The most important nonferrous metal are copper5kCpE, aluminumE5lju:minEm, leadli:d, zincziNk, tintin, but all these metals are used much less than ferrous metals, because the ferrous metals are much cheaper.Engineering metals
5、are used in industry in the form of alloys because the properties5prCpEti of alloys are much better than the properties of purepjuE metals. Only aluminum may be largely used in the form of simple metal. Metals have such a great importance because of their useful properties or their strength, hardnes
6、s, and their plasticityplAs5tisiti.Different metals are produced in different ways, but almost all the metal are found in the forms of metal oreC:(r) (iron ore, copper ore, etcet cetra.)The ore is a mineral5minErEl consistence of a metal combined with some impuritiesim5pjuEriti. In order to produce
7、a metal from some metal ore, we must separate these impurities from the metal that is done by metallurgyme5tAlEdVi.2. Plastics and Other MaterialsPlastics5plAstik, plB:stik have specific properties which may make them preferable5prefErEbl to traditional materialsmE5tIErIEl for certain uses. In compa
8、risonkEm5pArisn with metals, for example, plastics have both advantages and disadvantages. Metals tend to be corrodedkE5rEud by inorganic7inC:5Anik acids5AsId, such as sulphuricsQl5fjuErik acid and hydrochloric7haidrEu5klC:rik acid. Plastics tend to be resistant to these acids, but can have dissolve
9、d or deformed by solvent5sClvEnt, such as carbon tetrachloride7tetrE5klC:raid, which have the same carbon base as the plastics. Color must be applied to the surface of metals, whereas it can be mixed in with plastics. Metals are more rigid5ridVid than most plastics while plastics are very light, wit
10、h a specificspi5sifik gravity normally between 0.9 and 1.8. Most plastics do not readily5redili conduct5kCndQkt heat or electricityIlek5trIsItI. Plastics soften slowly and can easily be shapedFeip when they are soft.塑料具有特殊的性能。对于某种用途而言，这些性能使得塑料比传统材料更为可取。例如，跟金属相比较，塑料既有优点也有缺点。金属易受到无机酸的腐蚀，如硫酸和盐酸，塑料能抵抗这些
11、酸的腐蚀，但可被溶剂所洛解或引起变形，例如溶剂四氯化碳与塑料具有同样的碳基。颜色必定只能涂到金属的表面。而它可以跟塑料混合为一体。金属比大多数塑料刚性要好，而塑料则非常之轻，通常塑料密度在0. 9-1. 8之间。大多数塑料不易传热导电。塑料能缓慢软化，而当其还是在软的状态时，能容易成形。It is their plasticityplAs5tisiti at certain temperatures5temprItFE(r) which gives plastics their main advantages over many other materials. It permits the
12、large-scale production of moldedmEuld articles, such as containers, at an economic unit cost, where other materials require laboriouslE5bC:riEs and often costly processes involving cutting, shaping, machining, assemblyE5sembli and decoration.在某一温度下塑料是处于塑性状态的，这就使塑料具备超过许多其他材料的主要优点。它容许大量生产单位成本低廉的模制式器件，
13、例如，各种容器。于此，若用其他材料则需要大量劳力和往往需要很费钱的加工工艺，比如，切割、成形、加工、装配和装饰。Plastics not only replace other materials. Their properties can be exploitediks5plCit for entirelyIn5taIElI new applications. For example, plastics heart valvesvAlv and other human spare parts have make possible many recent developments in surg
14、ery5sE:dVEri.There is no single plastics material which is suitable for all applications. It is important that the most suitable plastics should be chosen, and if necessary adaptedE5dApt, for each particular requirement. It is also important that the properties of the plastics chosen should be explo
15、ited to the best advantage.A plastics article may need to differ in design and appearance from a similar article made from another material such as metal or wood. This is duedju: not only to the properties of plastics but also to the techniquestek5ni:k employed in fabricating5fAbrikeit plastics. The
16、se techniques include injectionin5dVekFEn molding5mEuldiN, blow molding, compression molding, extrusioneks5tru:VEn and vacuum5vAkjuEm forming.3. Casting and Die-Casting AlloysCasting5kB:stiN is one of the oldest metal working techniques known to man. Our country made metal castings as early as 2000 B.C., and the process used then i
