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1,2 4.




5. , :

1. Who is the worst environment pollution caused by?

2. What diseases are linked to air pollution?

3. What materials can be reused?

4. What materials cannot be absorbed by the earth?

5. What problem do people face?

 

a. Plastics cannot.

b. By manufacturers who put chemical wastes into rivers and seas.

c. The problem of preservation of environment.

d. Paper and glass.

e. Asthma and eczema.

 

6. , :

1. The worst environment pollution is caused by manufacturers....

a) who reuse chemical wastes.

b) who put chemical wastes into rivers and seas.

c) who don't put chemical wastes into rivers and seas.

2. Many materials like paper and glass....

3. Many materials, especially plastics.....

a) can be reused.

b) cannot be reused.

c) cannot be absorbed by the earth again.

4. People face the problem of preservation of environment because....

a) many materials like paper and glass can be reused.

b) air and water are becoming seriously polluted.

c) natural resources and energy are getting more expensive.

19

1. :

 

1. spot welding a.

2. hammer welding b.

3. workpiece c.

4. arc welding d.

5. butt welding e.

6. to create f.

7. combustible gas g.

8. thermit welding h.

9. to join i.

10. gas welding j.

11. fusion welding .

12. fusion state 1.

13. flame m.

14. electric resistance welding n.

15. to melt .

 

 

2. :

process, metal, metallic, contact, classify, energy, type, gas, chemical, reaction, section, form, electric, normally.

3. :

 

WELDING

 

1. 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.

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

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

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

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

6. In arc welding the workpieces 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 60 A, otherwise the arc will not create enough heat.

7. 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.

1,4,6,7.

5. , :

 

1. What kind of process is welding?

2. How are welding processes classified?

3. What is hammer welding?

4. What is arc welding?

5. What is thermit welding?

6. What gases are used in gas welding?

 

a. It is a process when two workpieces are melted by an electric arc.

b. A mixture of a combustible gas and oxygen.

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

d. It is a process consisting of a chemical reaction.

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

f. According to the source of energy, the metals and the state of the metal at the place of welding.

6. , :

1. Hammer welding is a process.... a) consisting of a chemical reaction.

2. Thermit welding is a process.... b) when two metal parts are melted by an electric arc.

3. Arc welding is a process.... c) when two metal parts are joined by force from a power hammer.

4. In gas welding a combustible a) hydrogen

gas must be mixed whith b) oxygen

c) methane

 

20

1. :

 

1. arc welding a.

2. to melt b.

3. flame c.

4. to overheat d.

5. electric circuit e.

6. earth clamp f.

7. to appear g.

8. to attach securely h.

9. to strike the arc i.

10. holder j.

11. electrode rod .

12. filler metal 1.

13. deep penetration m.

14. surface quality n.

15. to fall onto .

 

2. :

 

electric, cable, transformer, electrode, type, position, metal, class.

 

3. :

 

ARC WELDING

 

1. In arc welding the workpieces 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.

2. The current must be at least 60 A, otherwise the arc will not create enough heat. For thicker workpieces, the current may be 250 A. In order to carry this current, the cables from the transformer should be quite thick or else they will overheat.

3. To supply the necessary current the transformer is used and to complete the electric circuit an earth clamp is used, which is attached to the workpiece. Then the current flows around the circuit and the arc appears. It must be securely attached, otherwise an arc will appear between the clamp and the workpiece. To strike the arc, the transformer should be switched on first.

4. The electrode holder contains an electrode rod which provides the filler metal to join the workpieces. As the current flows between the electrode and the workpiece, the tip of the electrode melts and falls onto the workpiece. The electrode must be moved across the joint continuously, if it is moved too quickly neither the electrode nor the workpiece will melt.

5. While choosing an electrode type it is necessary to know:

a. Position to which the workpiece is to be welded.

b. Type and thickness of metal used.

c. Type of welding current.

d. Class of work: deep penetration, surface quality, etc.





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