4. Answer the questions:

1. By what properties are metals distinguished from nonmetals?

2. What common metals are produced in great quantities?

3. What metals are called light?

4. What properties do nonmetals have?

5. What is done to protect metals from corrosion?

5. Read and retell: Greeks and Romans

From about 600 B.C. the Greeks began to study their world. Great philosophers (thinkers) such as Pythagoras developed the “scientific method” – the principle of observation and experiment that is still the basis of science today. The Greeks studied mathematics and astronomy and invented simple machines. At around the same time, the Romans used Greek scientific ideas to help them build great structures.

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The wheel was invented in about 3500 B.C.

The pump was invented in the second century B.C.

Hero of Greece built the first simple steam engine in the first century A.D.

Lesson four Text: Welding

I. Find equivalents:

spot welding hammer welding workpiece arc welding butt welding to create combustible gas thermite welding to join gas welding fusion welding fusion state flame electric resistance welding to melt

a. дуговая сварка b. горючий газ c. соединять d. пламя e. газовая сварка f. плавиться g. электрическая контактная сварка h. создавать i. сварка плавлением j. кузнечная сварка k. точечная сварка l. стыковая сварка m. термитная сварка n. расплавленное состояние o. деталь

II. Translate the international words:

Process, contact, transmission, filter, classify, reaction, specific, theme, normally, tube, form, section, intensity, granite, graphic, pneumatic, standard, electrode, shock, sort, watt, ton, transform, leader, limit, local, function, formula, detail, diffusion.

III. Read and translate the text:

Welding is a process of joining together metallic parts by heating the place of contact to the fusion state.

Welding processes are classified according to the source of energy employed for heating, the metals and the state of the metal at the place of welding.

There are different types of welding such as hammer welding, thermite welding, electric arc welding, gas welding, etc.

Hammer welding is a process in which two heated metal parts are joined and fused together by force from a power hammer.

Thermite welding is a process consisting of a chemical reaction. It I used in repairing large sections such as rails, frames, etc.

Resistance welding process forms a whole group consisting of many types of welding such as spot welding, butt welding and others.

In arc welding the workpiece are not melted by a flame. They are melted by an electric arc. In order to create the arc, a powerful electric current must be provided. The current must be at least 60A, otherwise the arc will not create enough heat.

In gas welding, it is necessary to use a mixture of two gases. To create a hot flame, a combustible gas must be mixed with oxygen.

Gas welding is normally used to join steel to steel.