2. Answer the questions to the text.

1. What is brazing?

2. What is the difference between brazing and soldering?

3. What metals and alloys may be brazed?

4. What groups do brazing materials fall into?

5. What is the main purpose of using flux in brazing?

6. What requirements must the flux meet?

7. How is heating provided?

8. Is it possible to heat metals to be brazed by induction heating?

9. Where does brazing find its application?

10. Under what temperature are brazing materials usually melted?

11. What factors does the clearance between brazed surfaces depend upon?

12. What fluxes are used in soldering?

13. How is the strength of soldered joint determined?

14. Where does soldering find its application?

3. Give the short summary of the text.

Text 3.

Electro-slag welding

New words and word combinations.

1. flux-coated consumable nozzle – расходуемый наконечник с флюсовой обмазкой

2. vertical welding – сварка вертикальным швом

3. due to – благодаря, из-за

4. groove – выемка, канавка

5. to retain – удерживать

6. water-cooled copper blocks – водоохлаждаемые медные блоки

7. butt or fillet-joint geometry – форма и размеры стыкового или углового соединения

8. to weigh – весить

9. to ensure – гарантировать

10. uninterrupted single run weld – непрерывный однопроходный шов

1. Read the text and try to understand it.

The electro-slag welding process employing a bare consumable nozzle was first developed in the Ukraine at Paton Institute.

The electro-slag welding process with flux-coated consumable nozzle has recently become popular because of its simplicity for vertical welding thick plates. In this process the wire and base metal are melted by heating due to the electric current flowing through the nozzle wire and slag. The wire is fed through a flux-coated consumable nozzle which is fixed relative to the base metal along the centre axis of the groove. The nozzle is melted by the slag bath during welding, and is thus consumed. The molten metal and slag are retained between work parts by means of water-cooled copper blocks. The copper blocks must have a suitable shape and size adaptable to butt or fillet-joint geometry. They are firmly fixed on the base metal by means of wedges or magnеts, and then water cooling is circulated.

The copper cools the metal at the bottom of the pool thus forming the weld.

As solidification occurs, the electrode wire is fed vertically into the slag maintaining the end of the wire at a constant distance from the molten metal pool. Both AC and DC welding are possible for this process. In DC welding, reversed polarity seems to be more desirable than straight polarity.

The welding equipment consists of a welding head, a wire reel and an operating box, all of which are fitted at the top of the joint to be welded. The whole equipment weighs about 12-15 kg and can be easily carried about by one operator. The nozzle consists of a mild steel tube and flux coating of thickness 2 mm. The flux is used as the starting flux as well as the coating on the nozzle. The flux-coating prevents any possible short-circuiting or arcing between the nozzle and base metal or copper blocks, thus ensuring stable and easy welding. It also serves to replace automatically the flux that solidifies; thus any additional supply of flux is not necessary during welding.

Preparation of the equipment for welding is simple. After creating the arc between the nozzle and base metal, and the start of welding. no change of adjustment is usually required.

This process is now well established for the welding of thick plates. In fact its unique capability of producung an uninterrupted single run weld in any thickness has made it the more attactive the greater the plate thickness. Parts more than 2 inches in thickness can be welded with a single stationary electrode. When the electrode is moved back and forth horizontally, or when two or more nozzles are used, welds of 6 to 8 in may be made.

Notes to the text.

1. because of - из-зa, вследствие

2. due to — благодаря; из-за, вследствие