1. Answer the following questions

1. How many metallic elements do you know today?

2. How are the elements arranged?

3. Who elaborated the Periodic Table?

4. What are the most common properties of metals?

5. Are pure metals used in engineering practice?

6. What is the definition of the word «alloy»?

7. What classes are the properties of alloys divided?

8. What do we call «physical properties»?

9. What terms would you include in the description of the physi­cal behaviour of a material?

10. What are the main characteristics describing chemical prop­ erties?

2. Match the words on the left with their definitions on

the right
1) fracture	a) to put into order
2) solubility	b) transmission of heat or electric-
	ity by contact
3) to shape	c) a metallic substance containing
	more than element
4) alloy	d) surface shown by mineral when
	broken
5) to arrange	e) a property of being dissolved in
	some fluid
6) conductivity	f) to bring a mould into desired or
	definite form

30

3. Find out which sentences correspond to the contents of the text

1. The mechanical properties include those characteristics, which describe the behaviour of a material under the action of external forces.

2. Elements are complex substances which alloys are composed of.

3. Most of the elements are liquid at room temperature.

4. Only one-fourth of the elements are characterized by metal­lic lustre.

5. Metals have their own properties, which may be divided into three classes, i. e. physical, mechanical and chemical.

4. Render the following

Matter can exist in three physical states, namely, solid, liquid or gaseous. About one hundred elements are known at the present time. They are found to form almost endless combinations with each other. Metals are characterized by the appearance called metallic lustre, duc­tility and by relatively high conductivity for heat and electricity. These physical differences are accompanied by fundamental differences in their chemical behaviour. But the most useful classification is that elaborated in the Mendeleev's Periodic System in which the elements are arranged in periods and groups. It is necessary to know the proper­ties of metals as they play an important part in metallurgy.

5. Translate at sight

Металлы характеризуются металлическим блеском, термо-и электропроводимостью и способностью изменять форму без разрыва. В технике обычно используются сплавы. Сплавы - это вещества, состоящие более чем из одного элемента.

Свойства сплавов и металлов можно разделить на три ос­новные группы: физические, механические и химические.

Под действием внешних сил вещество проявляет механиче­ские свойства. Химические свойства включают такие, как способ­ность соединяться, коррозию, растворимость и так далее.

31

Unit 2

ADVANTAGES AND DISADVANTAGES OF CASTINGS

The shortest distance between raw material and finished part is called a casting. The casting process is finding many new applications simply because it is the most direct method, by which raw material is converted into a shape, which closely approximates the final shape and dimensions of a metal part. All metal processes begin with melting and solidification of the metal. In the casting process alone no additional steps such as forging, rolling, stamping, welding, etc. are required.

In many cases, the simplicity of the casting process makes it the lower cost method of producing parts. For example, a simple flat metal plate is rarely made as a casting. It is ordinarily more economic to cast a simple metal shape called a billet. A billet is rolled on highly auto­mated equipment into a plate of the desired thickness. It is then sheared to the length and width required. Each operation is performed at such low cost, that this process is considered to be less expensive than any operation of casting a plate directly to the shaped in the mould. On the other hand, if a plate were extremely thick, the casting process might become the lowest cost method.

Castings range in size from a few ounces to more than 100 tons. In function they range from decorator's trinkets to critical bridge struc­ture parts. Their cost varies from less then 10 cents per pound to more than 10 dollars per pound. Shapes can be as simple as small bars or as complex as diesel motor blocks. Metalworking always includes the casting process, which is of great importance.

Castings are used in vast volume showing the growing useful­ness of the casting process. Modern metallurgy and engineering ad­vances are raising the levels of quality and reliability.

32

Exercises