2. Answer the questions to the text.

1. Where was the electro-slag welding process developed?

2. Where do we use this welding process?

3. How is the molten metal retained between work parts?

4. What materials are the blocks made of?

5. Are the blocks water-cooled?

6. How are the copper blicks fixed on the base metal?

7. What current is used in electro-slag welding?

8. Which polarity is more desirable?

9. What can you say about the equipment for electro-slag welding?

10. Is the electro-slag welding equipment portable?

11. What components does the nozzle consist of?

12. What does the flux-coating prevent?

13. What are the main advantages of electro-slag welding?

14. Have you ever seen the machines for electro-slag welding?

15. Describe briefly the process of electro-slag welding.

3. Give the short summary of the text.

Appendix 1

1. Ultrasonic welding

New words and word combinations.

1. grease – смазка, солидол

2. minute – мельчайший

3. void – пустота, пузырек, полость

4. to accomplish – совершать, выполнять

5. foil or sheet gauge aluminium – фольга или тонколистовой алюминий

6. transducer – преобразователь

7. coupling system – соединительная система

8. heat exchanger – теплообменник

9. lateral – боковой, поперечный, горизонтальный

10. array – установка

11. to devise – придумывать, изобретать

12. power input – подводимая мощность, затраты энергии

13. installation – установка

Ultrasonic vibrations are extensively used in engineering, medicine biology, chemistry and in other branches of our industry.

In the last few years, the use of ultrasonics has grown greatly, and has reached production status in at least two applications. The minute, extremely rapid vibrations clean grease and dirt from parts, and locate large and small voids in various metal products.

A new joining method is now added to the list of ultrasonic application in industry. Metals difficult to weld by conventional means can now be welded by the application of ultrasonic mechanical energy. They include several types of stainless steels, zirconium and its alloys, molybdenum, tantalum, and others. It is also possible to join dissimilar metals and thin sections. Both spot and continuous seam welding can be accomplished with commercially available equipment.

The most extensive application of ultrasonic welding is joining foil or sheet gauge aluminium. Strong welds can be formed since there exists no heat-affected zone. There appears to be no practical limit to the minimum thickness of aluminium that can be welded.

Welding mechanism. Electrical energy is transformed into ultrasonic vibrations in a type of transducer. The special coupling system transfers ultrasonic vibrations to the welding tip. The welding tip is vibrated vertically at frequency ranging from 16,000 to 25000 cycles per second. The energy delivered to the weld zone results in a temperature rise which, though not small, does not cause melting. The vibrations destroy an oxide film on the surface of the metal to be welded and produce a weld with a solid-state metallurgical bond over half its width. The remainder is a mechanical bond. The surface of the metals are reliably joined together by the forces of molecular attraction.

The ultrasonic process was first used for joining foil gages. Since 1955, it has been looked at in connection with metal joining problems of heat exchangers, atomic reactor elements, electrical and electronic hardware, and a large number of everyday items. Its capabilities are being rapidly extended by the development of more powerful and effective transducer-coupling systems.

There are several basic arrangements, two of which are the laterally driven reed type and the lateral-drive type both introduce ultrasonic vibrations through a welding tip. The welding array consists of the ultrasonic transducer-coupling, its force-insensitive mount, and a reflector anvil for concentrating of vibratory energy within the workpiece. Force-insensitive mounts prevent the resonant frequency from shifting with force applied to the system, and largely, prevent energy losses to the support systems. A hydraulic, pneumatic, or spring system for applying static force to the weldment, and an electronic timer to control the duration of the ultrasonic pulse are usually included as well as a power supply and driving unit.

Such are some present capabilities of the ultrasonic welding process particularly in the joining of high-temperature and corrosion resistant materials and plastics. The future of this new method is limited only by the power of the equipment now in use; however, more powerful machines (for welding heavier gauges) are being devised constantly, and power inputs approaching 6,000 W have been applied to the transducer in some heavy installations.

Questions to the text.

1. What applications has the use ultrasonics reached progress in?

2. What metals may be welded by the ultrasonics?

3. What does the energy delivered to the zone of welding result in?

4. Is it possible to melt metals by ultrasonics?

5. What ultrasonics systems are used for joining metals?

6. What units does the welding array consist of?