II. Reading Activity and Speech Practice. II. 1 Before reading the text discuss with your group mates some questions:

Engineers in the field of machine construction design, build, operate and test machinery of all types. Moreover, they work on various kinds of structures. It goes without saying that engineers must know the most economical and valuable materials to use in the field of manufacturing. Mechanical engineers have to understand the properties of these materials and how they can be worked.

As is known, all engineering materials are divided into metals and non-metals. Metals are materials which widely used in machine-building industry because of their useful properties. All metals vary in density, hardness, heat and electrical conductivity, and weight; they can be formed by drawing, rolling, extrusion and hammering and worked using machine-tools such as lathe, shaper, grinder and a milling machine. We normally classify metals into ferrous and non-ferrous. The former contain iron and the latter do not contain iron. Iron is the world’s most common metal. Cast iron and steel, which are both alloys, or mixtures of carbon and iron, are the two most important ferrous metals.

Cast iron is a general term applied to iron-carbon alloys containing more than 1.7 % of carbon. Cast iron without the addition of alloying elements is weak in tension and shear, strong in compression and has low resistance to impact. However, grey cast iron is soft, easily machined, and only moderately brittle. Malleable cast iron is made by heating white iron castings for a period of several days in airtight pots filled with an oxide of iron.

Steel is a ferrous metal with carbon content. It is stiff and strong, but corrodes easily through rusting, although stainless and other special steels are corrosion resistant. Today the most important are alloy steels, which have a lot of special characteristics. Alloy steels are those in which some alloying elements in addition to the carbon are present. The principal alloying elements used in steels are nickel, chromium, vanadium, manganese, and to lesser extent, copper, tungsten, cobalt and beryllium. Heat treatment and mechanical working at cold or hot temperatures may give steel alloys superior qualities, such as hardness, strength, toughness, wear resistance and workability.

Among non-ferrous metals copper is the most essential one. Because of its high electrical conductivity this metal is used in electrical work. Three chief groups of copper alloys used in machine design are brasses, bronzes and nickel-copper alloys.

Wood, stone, rubber, concrete, ceramics and plastics are non-metals. However, plastics may be machined like metals. There are two types of plastics – thermosets and thermoplastics. Thermoplastics can be shaped and reshaped by heat and pressure but thermosets cannot be reshaped by heat because they undergo chemical changes as they harden. Ceramics are often employed by engineers when materials which can withstand high temperatures are needed.

So, it’s impossible to live without various engineering materials.

II.3 Now, give full answers to the questions given in exercise II.2 using the text.

II.4 Choose in the text the sentences about:

- metals and their use;

- characteristics of pure iron;

- the main alloying elements of steel;

- the chief groups of copper alloys;

- materials related to non-metals.

II.5 Find in the text the sentences to describe the main properties of ferrous and non-ferrous metals. Compare them and define the difference.

II.6 Put the items of the following plan in the proper order according to the text:

1. Metals and their properties.
2. Cast iron and iron-carbon alloys.
3. Steel and its alloys.
4. Plastics and their types.
5. Non-ferrous metals.

II.7 Express your opinion why it is so necessary for an engineer to know the engineering materials and their characteristics.