Text b Aluminium

The weldability of aluminum alloys varies significantly, depending on the chemical composition of the alloy used. Aluminum alloys are susceptible to hot cracking, and to combat the problem, welders increase the welding speed to lower the heat input. Preheating reduces the temperature gradient across the weld zone and thus helps reduce hot cracking, but it can reduce the mechanical properties of the base material and should not be used when the base material is restrained. The design of the joint can be changed as well, and a more compatible filler alloy can be selected to decrease the likelihood of hot cracking. Aluminum alloys should also be cleaned prior to welding, with the goal of removing all oxides, oils, and loose particles from the surface to be welded. This is especially important because of an aluminum weld's susceptibility to porosity due to hydrogen and dross due to oxygen.

UNIT 3

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Text A

Gas Metal-Arc Welding

Gas Metal-Arc Welding (GMAW), also called Metal Inert Gas (MIG) welding, shields the weld zone with an external gas such as argon, helium, carbon dioxide, or gas mixtures. Deoxidizers present in the electrode can completely prevent oxidation in the weld puddle, making multiple weld layers possible at the joint.

GMAW is a relatively simple, versatile, and economical welding apparatus to use. This is due to the factor of 2 welding productivity over SMAW processes. In addition, the temperatures involved in GMAW are relatively low and are therefore suitable for thin sheet and sections less than ¼ inch.

GMAW may be easily automated, and lends itself readily to robotic methods. It has virtually replaced SMAW in present-day welding operations in manufacturing plants.

Electroslag Welding

Electroslag Welding (ESW) deposits the weld metal into the weld cavity between the two plates to be joined. This space is enclosed by water cooled copper dams or shoes to prevent molten slag from running off. The weld metal is produced from a filler wire that forms an initial arc with the workpiece until a sufficient pool of liquid metal is formed to use the electrical resistance of the molten slag.

This process requires special equipment used primarily for horizontal welds of very large plates up to 91,44 centimeters or more by welding them in one pass as in large machinery and nuclear reactor vessels.

There are also variations of ESW where shielding is provided by an appropriate gas and a continuous arc is used to provide weld metal. These are termed Electrogas Welding or EGW machines.

Read and learn the following words and expressions:

carbon dioxide weld puddle versatile to lend oneself Electroslag Welding (ESW) cavity filler wire molten slag appropriate machinery relatively sufficient suitable

- углекислый газ - сварочная ванна - универсальный - применяться - электрошлаковая сварка - полость - присадочная проволока - расплавленный шлак, - подходящий, соответствующий - механизм - относительно - достаточный; - подходящий