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Read text B carefully. Pay attention to the words in bold type.

Text B. Metals: Use and Function (a Lecture).

Metals, metals everywhereÖ

Metals are remarkable things. And though man has worked them for many centuries they remain mysterious: a great deal is still unknown about them. They excite much wonder, interest and surprise.

Some metals and metal alloys possess high structural strength per unit mass, making them useful materials for carrying large loads or resisting impact damage. Metal alloys can be engineered to have high resistance to shear, torque and deformation. However the same metal can also be vulnerable to fatigue damage through repeated use or from sudden stress failure when a load capacity is exceeded. The strength and resilience of metals has led to their frequent use in high-rise building and bridge construction, as well as most vehicles, many appliances, tools, pipes in railroad tracks. They are also used in stomatology, space industry, vacuum technology industry, in electrical engineering, jewellery, chemical industry. Metals are indispensable to modern technology.

The automobile also remains a vehicle built primarily from metals. Let us examine some of the essential features of one to discover the approximate weight of metals used in its construction. In the typical European car, for example, the body consists of roughly 700 kg of steel. The cylinder block and gearbox require about 140 kg of cast iron although aluminium is being used more and more in engine compositions. Add 15 kg for the weight of aluminium pistons, the same amount of zinc for such things as door handles and the carburettor and some 10 kg of copper for pipes in the radiator and all the various electric cables. All automobiles need batteries and this increases the weight by another 5 kg. Adding up the weights of these different metals gives us a total of 885 kilograms or almost 2000 lbs.

The first step in manufacturing an automobile is the stamping, forging, casting, and machining of such materials as steel, aluminium, zinc, and plastics.

However, technology has not completely by-passed the automobile. As the price of fuel has risen and the demand for performance and reliability increased, so the overall weight of automobiles has decreased. This is particularly true in the case of many American vehicles which in the last few years, have moved closer in design and configuration to European models. In particular, the steel and cast iron content in some vehicles has fallen. On the other hand, aluminium content has more than doubled, while the use of plastics has increased. But it is worth noting, however, that the metal content of modern vehicles remains at around 80 percent of the total weight.

But is it really necessary? All these metals (and some of them are quite rare) are being used up at a frightening speed. Take the bumper. Itís shiny. Thatís because it is covered in chromium. Itís made of steel. The chromium is just there to make it look nice. Now that would be bad enough. But, you see, chromium wonít stick to steel, but it will stick to nickel, so under the chromium there is a layer of nickel.



But nickel wonít stick to steel either. Copper will, however, so there has to be a layer of copper to bind the nickel and the steel. So, thatís what is on the bumper: a sandwich of three rare metals. And what happens when it gets scratched or dented? We probably just throw it away.

Clearly, there are great possibilities for further reductions in metal weight content of passenger vehicles. There is also a need for this, since metals are expensive and some are becoming increasingly more difficult to obtain in large enough quantities to satisfy the growing demand worldwide for vehicles.


Date: 2015-12-18; view: 735


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