Brazing

Brazing, or SOLDERING, is the process of uniting together two pieces of brass, two pieces of copper, or one of each, by means of a hard solder, partaking more or less of the composition and properties of ordinary brass. The edges or parts of metal to be joined are first filed bright, so as to be thoroughly clean, then there is strewed over the joint a mixture of the solder and borax. The solder employed varies in composition according to the kind of work, and may be rendered more fusible by the addition of a larger amount of zinc. Hard solder, or 'spelter solder,' for brass consists of 1 part of copper to 1 of zinc; for copper or iron it is usually 1 part of copper to $\backslash frac\{3\}\{4\}$ths of a part of zinc. The proportions, however, vary, 3 of copper to 1 of zinc being about the hardest solder. After the solder is made it is again heated and granulated in a mortar for use. The borax is employed to form a glaze over the brightened surfaces, and thus prevent the oxidation of the metal, which would seriously interfere with brazing, and even stop the operation. An outward coating or layer of charcoal is likewise serviceable in the exclusion of the air during the brazing of large pieces of metal. Where a very high heat is required in the process, a little powdered glass is mixed with the borax. The mixture of solder and borax may be applied dry, but it is better to moisten it with water, and to lay it on the filed surfaces with a spoon. The whole is then gently heated, when the water evaporates and leaves a crust of borax and solder. The work may now be strongly heated by a bellows, blowpipe, or over a clear charcoal or coke fire, and at a bright red heat the solder fuses and the zinc begins to burn with a pale-blue flame. At this stage the solder flushes or becomes liquid enough to permeate the joint or crevice; but should it be tardy in acting thus, several slight taps will insure the proper result. The whole is now cooled, and, towards the close, the articles may be introduced into cold water for more rapid reduction in temperature. Pieces of metal which have undergone the process of brazing are so firmly united that they may be rolled and re-rolled without the parts yielding. Steel is brazed with a solder composed of 19 parts silver, 1 of copper, and 1 of brass. See SOLDER.