Handbook-Non-Ferrous Metals

3 Flame-Shaping Brass. When brass piping systems are to be welded, the torch has often been used to shape openings in the pipe. To do this, lay out the outline of the desired opening with a templet, then paint a band of quick-drying iron cement (of the type used for caulking bell-and-spigot pipe joints) around the outline. (Mix the cement with water to the consistency of heavy paint, and apply with a brush.) Then melt through the brass in the center of the opening, using a flame angle of about 30 degrees until the edge of the opening has been reached, then changing to a 90-degree angle in order to get reasonably square edges. Melting sequence suggested for a hole about 5 cm (2 in.) in diameter is shown in Fig. 19-1. Be sure to use an oxidizing flame. Welding of Copper-Tin Alloys. In general, what has been said about the welding of copper-zinc alloys applies to the welding of the true bronzes, or copper-tin alloys. For repair work, where a precise color match is not essential, standard braze welding rod (such as OXWELD 25M) and brazing flux can be used. For good color match, use filler metal with the same composition as the base metal. The flame should be oxidizing, often strongly oxidizing. The exact degree of excess oxygen needed for good work varies from alloy to alloy. Strong excess will always produce a noticeable film on the surface of the weld puddle. Try to reduce the oxygen just enough to eliminate that film and maintain a bright surface on the puddle. Welding of Copper-Silicon Alloys. The copper-silicon alloys (”silicon bronzes” ) should usually be welded using a filler metal of similar composition and a special flux designed specifically for such welding. Even though there is often no zinc in a silicon bronze, use an oxidizing flame, and keep the weld puddle small. The silicon in the metal, combining with the flux, will form a transparent glass-like film on the puddle and prevent undue oxidation. Work as fast as possible. The metal is relatively weak at high temperatures (”hot short”) so tight jigging is inadvisable.