Bronze welding, while less common than steel or stainless fabrication, demands strict thermal discipline. The material's high thermal conductivity and narrow solidification range make preheat and interpass temperature control essential for sound joints.
Preheat in bronze welding serves two purposes: it reduces the cooling rate to avoid cracking, and it ensures adequate fusion between the base metal and the filler. For most bronzes, a preheat of 150-200?C is recommended. However, the exact temperature depends on the alloy composition and thickness. For high-leaded bronzes, preheat must be kept lower to prevent liquation cracking.
Interpass temperature control is equally critical. Exceeding 250?C risks overheating the weld metal, leading to excessive oxidation, loss of alloying elements, and reduced mechanical properties. In multi-pass welds, each pass should be allowed to cool to the interpass maximum before depositing the next bead.
Proper temperature monitoring using contact thermocouples or infrared pyrometers is a must. Relying on color change or touch is unreliable. A documented preheat and interpass temperature log should be part of the quality control plan for any bronze welding procedure.
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