9. The nature of plastics

Plastics are the wonder engineering materials of the modern age, provided that they are properly employed. They are known to possess a great variety of valuable properties and can be used in a wide range of things. An engineer should know how to utilize plastics taking advantage of their desirable properties.

To solve this problem successfully it is necessary to know the nature and behaviour of plastics, while for selection a suitable plastic for the design of plastic parts it is important to know their general advantages and disadvantages.

The advantages of the plastic material include:

a) The ease of fabrication and adaptability to mass production methods at low unit cost.

b) Resistance to corrosion as most plastic parts are inert to rust, rot and corrosion.

c) Plastics are good thermal and electric insulators. Plastics are poor heat conductors and if they were exposed to a high temperature for a short period, the interior temperature of the plastics would remain lower than would be the case with metals.

d) Plastics easily combine with other materials like wood, fibres, paper and combine light weight with good strength as well.

Plastics have now invaded all branches of industry, agriculture, household needs, medicine and even art. In the building industry plastics find application as structural material and in fittings. They are also extensively used for finishing the interior of buildings. Plastic materials, with and without glass fibre reinforcement, are being increasingly applied to aircraft production.

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10. Transistors

It is well known that the quick development of electronics began with the invention of transistors. They replaced electronic tubes due to their numerous advantages. One of the main advantages of the transistors in comparison with the vacuum tube is absence of filament power loss. One of the principal causes of damages in electronic circuitry is high temperature. The heat causes breakdown of tubes and other circuit elements that are very sensitive to this influence. The transistor, on the other hand, does not heat its surroundings.

Another advantage of the transistor is its long life. The life of the average transistor is more than ten thousand operating hours. Because of its long lifetime and ruggedness, the transistor is very reliable and has much better efficiency in professional equipment.

Transistors replaced electronic tubes due to their numerous advantages. One of the advantages of the transistor is its small dimensions. Because of their small size, the absence of heating and other properties, transistors make it possible to produce compact, small-dimensioned electronic devices which consume very little power.

Transistors revolutionized many fields of technology. Today they are successfully used for direct transformation of heat energy by means of thermal elements. They are also used to convert radiant energy into electricity with the help of photocells or solar batteries. Light sources and lasers are built on the basis of transistors. They find wide application in computers, automatic devices, aviation, communication, etc.

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