Handbook-Brazing & Soldering

Fig. 19-1. To illustrate capillary attraction, two glass plates are

clamped together, with a thin spacer between the plates at the

right- hand side, and then inserted in a dish of colored water.

What metals can be brazed? Almost every metal, and some combinations of metals that cannot be successfully fusion-welded together. While the silver-based brazing alloys are the most widely used, there are also families of brazing alloys based on aluminum and magnesium (for use with those metals), on copper and phosphorus, on copper alone or copper and zinc, on nickel, and even on gold. Brazing alloys are designated by the American Welding Society with the letter ”B” followed by the chemical symbol or symbols of the major element or elements. ”BAg-1, BAg-2”, etc. are alloys based on silver (usually about 50% ). The copper-phosphorus alloys are designated ”BCuP-1, BCuP-2”, etc., nickel-base alloys ”BNi-1”, etc. In the ”BAg” group there are no less than 19 different compositions, all of which contain copper as well as silver; some also contain zinc, some cadmium, and a few contain tin or nickel. In virtually all brazing applications, heat is applied directly to the parts which are to be brazed, not directly to the brazing alloy. Many different heat sources can be used; flames, furnaces, electricity (through resistance or induction heating), radiant (infrared) sources, even molten salt baths. When gas flames are used, the process is termed torch brazing. Do not think of that word ”torch” as necessarily implying a hand-held single-flame device like your welding torch. Most production torch brazing is done with fixed multiple-flame burners.