Welding Practice - The Hong Kong Polytechnic University
Welding Practice - The Hong Kong Polytechnic University
Welding Practice - The Hong Kong Polytechnic University
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<strong>Welding</strong> <strong>Practice</strong><br />
Details of a Weld<br />
In order to obtain coalescence between two metals, there must be a combination<br />
of proximity of surfaces and sufficient activity between the molecules of the<br />
pieces being joined to cause the formation of common metallic crystals. Such<br />
proximity and activity are often impeded by an oxide layer or a thin layer of<br />
absorbed gas on the oxide surface. <strong>The</strong>se contaminant layers must be removed<br />
by mechanical or chemical means in order to obtain satisfactory welds.<br />
In summary, in order to obtain satisfactory welds it is necessary to have a<br />
satisfactory heat and/or pressure source, a means of protecting or cleaning the<br />
metal, and avoidance of, or compensation for, harmful metallurgical effects.<br />
2. <strong>Welding</strong> Processes<br />
<strong>The</strong> field of welding can be divided into two main classifications fusion and nonfusion.<br />
Fusion welds are usually made without the assistance of mechanical<br />
pressure. Non- fusion welds generally necessitate the assistance of mechanical<br />
pressure to bring the heated surfaces into intimate contact.<br />
When parts are joined by fusion the method is very similar to a casting process<br />
since the surfaces being welded are heated until they melt and run together. If a<br />
filler is added this is melted along with the metals being joined and run into the<br />
space which it is necessary to fill.<br />
2.1 Gas <strong>Welding</strong><br />
Gas welding comprises the group of welding processes in which the heat<br />
necessary for welding is obtained from the combustion of a fuel gas oxygen<br />
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