subject: What Are Heat Treatment Processes? [print this page] Similar to soldering, brazing is the process of joining metal done by filler metals being heated and capillary actions used to share this between multiple, close fitting parts. This filler metal is heated just beyond melting point and a flux or atmosphere is used to protect it as it heats. Materials are then joined together by putting it over the base metal.
Parts must be close fitting and the base metal must be free of oxides as well as clean for correct brazing. Decontaminated brazing surfaces are needed so that the parts will join correctly. Before brazing, there are two ways of cleaning parts called chemical and mechanical cleaning. To help join the parts more easily a rougher surface is needed for mechanical cleaning so smooth surfaces are not as good as rough.
When looking at the quality of brazed joints, the temperature is a key factor. The higher the temperature, the better the joining process becomes. However, for certain metals it is vital that the temperature is the lowest possible past the melting temperature to minimise the heat effects once the product is joined together and to keep the costs of brazing down. Sometimes a higher temperature is chosen as it can help with things such as removing contamination of the surface.
The flux, mentioned earlier, is present to prevent oxides forming in the heated metal, as well as cleaning any contamination on the surface metal. There are many ways to put a flux onto the metal such as pastes and powders, and can also be applied using brazing rods covered in flux. This means that it flows right to the joint as it is heated. This should be removed once the work is complete though as it can damage the metal. Metals like certain types of copper are self fluxed and so there is no need for an added flux when joining copper to copper.
Depending on what it is used for, filler materials can be from a variety of alloys. Based on the desired functions, there are usually three or more metals chosen and used to create these alloys. Furnace brazing has an alloy present first whereas manual brazing uses wires and rods as these are the easiest to use while heating.
by: Madison J. Grant
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