A job came into the shop that entailed brazing a broken brass casting. This piece is an antique of unknown brass alloy. Brazing rod needed to be used for a good color match. The repair consisted of grinding a vee at the break, filling the vee with brass, grinding back to shape, and polishing. I tried brazing with a torch but porosity was a problem. Something was outgassing from the casting. And I couldn't boil it away with the torch. So I tried TIG, both AC and DC. AC worked best for laying down rod. It cleaned the surface of the weld of dirt from the casting and zinc ash. DC worked best for leveling the weld and for boiling out the impurities. The technique that worked best for me was to keep the tungsten as far away as possible from the work and to use the lowest amperage possible. I warmed the part first with the TIG and then watched for the blue cloud that meant the zinc was vaporizing. I backed off on the pedal then and pulled the tungsten away a little. Keeping the blue cloud as small as possible is the trick. Form a puddle and push the rod into the puddle from the side. Raise the tungsten away from the work when feeding in rod to prevent the rod from getting too hot and vaporizing the zinc. Since I would be grinding down the weld I didn't care about losing a little zinc from the surface of the weld. Anyway, it worked and the customer will be happy. ERS
- posted
17 years ago