Welding of bronze
The main difficulty in the gas welding of bronze arises from the burnout of impurities, especially tin. Tin begins to form in the form of balls at a temperature of 500 to 600 ° C, which are burned to form tin oxides. On the surface of the welding bath, the foam forms during the evaporation of tin, the seam becomes porous, and the strength of the metal decreases. Welding of aluminum bronze is difficult due to refractory alumina, which is heavily removed from the weld pool. In addition, bronze becomes brittle during the heating process above 500 ° C, loses its viscosity. When welding, molded products are heated unevenly — this can lead to significant internal stresses and the appearance of cracks. Therefore, cast bronze products are recommended to be welded with preheating to 450 ° C. At the time of welding, it is impossible to lift and rotate hot products, since brittle bronze in such a state can give a crack.
As such, a composition similar to the basic one is taken. As a rule, cast rods are used, Ø 5−8 mm and length 400−500 mm. It is better if they contain phosphorus (up to 0.4%), since it prevents the oxidation of tin, thereby the seam becomes pore-free. Before welding, the surface of the bars must be thoroughly cleaned.
It can be used the same as when welding copper. In the process of welding aluminum bronzes, the same flux is used as for the welding of aluminum alloys (sodium chloride — 20%, sodium fluoride — 15%, potassium chloride — 45%, barium chloride — 20%), since this flux is able to remove the formed aluminum oxides .
The burner flame should be normal. Excess acetylene can lead to the appearance of pores in the seam, and excess oxygen contributes to the oxidation of tin, copper and other components of bronze. Welding should be done quickly, without interruptions. For this, a second burner is used (as in the case of copper welding), which heats the metal, moving ahead of the welding. During the welding process, the flux is permanently introduced into the weld pool by dipping the bar end. The end of the burner core should be at a distance of 6 to 10 mm from the surface of the molten metal. The power of the tip of each burner should not exceed 100 l / h per one mm of the metal thickness. At the end of welding, the part is heated to 450−500 ° C and cooled in water.
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