" ELECTROSLAG and ELECTROGAS WELDING "

1. Read the Text:

Electroslag welding

Electroslag welding is a highly productive welding process developed in the United States during the 1930s. It involves the melting of the surfaces of themetal workpieces and the filler metal with a molten slag to cause coalescence. An electric arc is passed through the slag to heat it, but the arc itself is extinguished by the slag. Electroslag welding is commonly used to weld in a vertical orientation, and is particularly popular with steels. In the 1970s, it was used extensively in bridges, ships, and other large metal structures. However, in 1977 the Federal Highway Administration banned its use in welds for some structural members of bridges, due to concerns of weld imperfections and poor properties. Benefits of the process include its high metal deposition rates. Many welding processes require more than one pass for welding thick workpieces, but often a single pass is sufficient for electroslag welding. The process is also very efficient, since joint preparation and materials handling are minimized while filler metal utilization is high. The process is also safe and clean, with no arc flash and low weld splatter or distortion.

Electrogas welding

Electrogas welding (EGW) is a continuous vertical position arc welding process developed in 1961, in which an arc is struck between a consumable electrode and the workpiece. A shielding gas is sometimes used, but pressure is not applied. A major difference between EGW and its cousin electroslag welding is that the arc in EGW is not extinguished, instead remaining struck throughout the welding process. It is used to make square-groove welds for butt and welding, especially in the shipbuilding industry and in the construction of storage tanks. In EGW, the heat of the welding arc causes the electrode and workpieces to melt and flow into the cavity between the parts being welded. This molten metal solidifies from the bottom up, joining the parts being welded together. The weld area is protected from atmospheric contamination by a separate shielding gas, or by the gas produced by the disintegration of a flux-cored electrode wire. The electrode is guided into the weld area by either a consumable electrode guide tube, like the one used in electroslag welding, or a moving head. When the consumable guide tube is

used, the weld pool is composed of molten metal coming from the parts being welded, the electrode, and the guide tube. The moving head variation uses an assembly of an electrode guide tube which travels upwards as the weld is laid, keeping it from melting. Electrogas welding can be applied to most steels, including low and medium carbon steels, low alloy high strength steels, and some stainless steels. Quenched and tempered steels may also be welded by the process, provided that the proper amount of heat is applied. Welds must be vertical, varying to either side by a maximum of 15 degrees. Like other arc welding processes, EGW requires that the operator wear a welding helmet and proper attire to prevent exposure to molten metal and the bright welding arc. Compared to other processes, a large amount of molten metal is present during welding, and this poses an additional safety and fire hazard. Since the process is often performed at great heights, the work and equipment must be properly secured, and the operator should wear a safety harness to prevent injury in the event of a fall. EGW uses a constant voltage, direct current welding power supply, and the electrode has positive polarity. A wire feeder is used to supply the electrode, which is selected based on the material being welded. The electrode can be flux-cored to provide the weld with protection from atmospheric contamination, or a shielding gas can be used with a solid wire electrode. The welding head is attached to an apparatus that elevates during the welding process. Also attached to the apparatus are backing shoes which restrain the weld to the width of the workpieces. To prevent them from melting, they are made of copper and are water-cooled. They must be fit tightly against the joint to prevent leaks.

2. True or false:

1. Electrogas welding is less hazardous than electroslag welding.

2. Electroslag welding is more frequently used to weld in a horizontal

orientation.

3. Quenched and tempered steels are not welded using Electrogas welding.

4. The welding head is attached to an apparatus that elevates during the welding process.

5. The process is also safe and clean, with no arc flash and low weld splatter or distortion.

3. Answer the following questions:

1. What kind of electrodes are used in Electrogas Welding processes?

2. What structures can be welded by Electrogas welding?

3. Can thick workpieces be easily welded by Electroslag welding?

4. Why is Electrogas welding relatively unsafe and hazardous?

5. What is the difference between Electrogas and Electroslag welding?

4. Complete the following sentences:

1. The welding head is...

2. Electrogas welding (EGW) is...

3. A shielding gas is...

4. Electroslag welding is...

5. Electroslag welding is commonly used to...

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Дуговая сварка

"ARC WELDING"

1. Read and translate the Text:

Arc Welding(1)

Arc welding refers to a group of welding processes that use a welding power supply to create an electric arc between an electrode and the basematerial to melt metals at the welding point. They can use either direct (DC)or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert or semiinert gas, known as a shielding gas, and filler material is sometimes used as

well.

2. Read the Text:

Arc welding(2)

1. In a welding the workpieces are not melted by a flame. 2. They are melted by an electric arc. 3. In order to create the arc, a powerful electric current must be provided. 4. Otherwise the arc will not create enough heat. 5. The cables should be quite thick. 6. In other case they will overheat. 7. The transformer is used. 8. It shoud be switched on first. 9. The electrode holder contacts an electrode rod. 10. The electrode rod provides the filler metal to join the work pieces.

3. Translate the Text:

4. Match the sides:

5. Make up the sentences:

1. are,by,melted,work pieces, an,arc,electrical.

2. They,current,use,heavy.

3. are, cables,are,thick,the.

4. overheat,will,they.

5. feows,the,current,quickly.

6. Retell the Text:

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Типы дуговой сварки

TYPES of ARC WELDING