Text 18

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Superhard materials from powder

The development of a number of industries is unthinkable without materials with special properties. Powder metallurgy helps to obtain such materials.

The operational principle of powder metallurgy is very well known — an article of necessary size is mod­elled, in a mould, out of very small metal grains and is put into an electrothermic furnace where the grains get sintered together.

The coefficient of the use of metal grows by five times and the time of operation of powder articles increases greatly. The sintered articles have already shown their advantages in outer space, in deep sea conditions and inside various machines. The antivibration alloys of the "iron-copper" type made it possible to double the life of drilling tools. This increased the labour productivity by 20 per cent.

Soviet scientists were the first to develop a new super-hard material out of boron nitride. The priority of the USSR in developing the first article out of so-called viscous ceramics has been recognized in a lot of countries.

Answer the questions:

1. What is the operational principle of powder metallurgy?

2. What is the coefficient of the use of metal?

3. Where can we see the advantages of the sintered articles?

Text 19

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Lasers today and tomorrow

The laser has become a multipurpose tool. It has caused a real revolution in technology.

Atoms emit rays of different length, which prevents the forming of an intense beam of light. The laser forces its atoms to emit rays having the same length and travelling in the same direction. The result is a narrow, extremely intense beam of light that spreads out very little and is therefore able to travel very great distances.

The most common laser is the helium-neon laser in the laser tube, there being 10 per cent helium gas and 90 per cent neon gas. At the end of the tube there is a mirror, and at the other end there is a partial mirror. The electrons get energy from a power supply and become "excited", giving off energy as light. This light is reflected by the mirror at one end of the tube. It can only escape through the partial mirror at the other end of the tube.

The first laser having been built in 1960, scientists developed several types of lasers which make use of luminescent crystals, luminescent glass, a mixture of various gases and finally semiconductors.

Answer the questions:

1. What prevents the forming of an intense beam of light?

2. What is the helium-neon laser?

3. Where do the electrons get energy from?

Text 20

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Electro-ionizing laser (eil)

The 20th century has been often called the age of the atom, the age of polymers, or the space age. It would be equally correct to call it the age of the laser.

It is impossible to list all the jobs a laser can do. It has become a part of our life being used in various industries, medicine, biology, etc. It should be mentioned that all the methods we know of processing materials with lasers were suggested not long ago. Physicists knew of the tremendous capabilities of the laser beam, but they could not be realized until lasers of adequate capacity were developed. To make a laser really useful the radia­tion intensity had to be increased (since capacity deter­mines productivity) and high beam efficiency created.

Creating highly effective laser is still one of the main problems of quantum electronics. In a gas laser all one has to do in order to increase the capacity is to increase the volume and the pressure of the gas. This sounds simple, but the doing of it is not.

Answer the questions:

1. How is the 20^th century called?

2. What jobs can laser do?

3. What is necessary to do to increase the capacity of a gas laser?

Для спеціальності МЕХ

text 16

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Cold Bonding of Silicone Rubbers with Metal and

Other Materials with the Help of Heat-Resistant,

Cold Setting GUM KT-30

Gum KT-30 is 80 % solution of silicaorganic resin in toluol. It is used for bonding of silicone rubbers with metal (steel, titani­um, duraluminium, etc), plastics, glass-cloth, glass and other ma­terials.

10-15 minutes before bonding the surface of the rubber is clea­ned with gasoline. The surface of the metal is also cleaned with the help of metal sand or emery paper. This operation is followed by deoiling by means of gasoline. The prepared surface of the metal is covered by a thin layer of gum and then it is dried during 10-15 minutes. Subsequently both sur­faces are connected and put on pressure with the help of a screw clamp or weight.

Optimum bonding strength is achieved after keeping the bond­ed articles under pressure within 48-60 hours.

The gum KT-30 provides re­liable bonding within tempera­ture range between -60C and 300C, It stands long ageing un­der temperature of 200C—300°C and it is moisture resistant.

Answer the questions:

1. What is Gum KT-30?

2. What is it used for?

3. How is the surface of the rubber or the metal prepared for bonding?