Gas Welding & Brazing

Sticking metals together with heat is a lot older than automobiles, but few consumer service industries use the “hot wrench” more than auto repair. Oxy-acetylene are still the gases of choice, and controlling the heat is the key to strong, neat-looking welds. Using the right size, clean tip for the job is important, as is adjusting the “feather” properly. A moderate blue cone inside a yellow flame should do (consult the handy pocket guides or wall charts from your gas supplier). Don’t weld with a cutting torch, and don’t knock off a cut assembly with the torch tip, either, since molten material will clog the small oxygen jets.

Cleanliness is very important, since inclusions and voids in the weld give cracks a handy place to start. Strong oxy-acetylene welds should ideally begin with shiny metal. For long welds, tack the joint in several places before running a bead: welding heat produces expansion forces in metals which usually overwhelm the force of C-clamps or Vice-Grips. Align with clamps, then tack. Wire brush or grind any contaminants away from the tack welds, then sew up the joint. Use commercial filler metals, since they’re designed to deliver the correct compatibility and tensile strength for the material you’re welding. Resist the temptation to use that handy coathanger. It might work in a non-critical application, by why not do it right?

Brazing is nothing more (and nothing less) than soldering at a higher temperature, with a high-temperature solder, usually bronze. The key to a strong braze is cleanliness, since the natural oxides on metal surfaces keep the liquid bronze from wetting the surfaces and drawing into the joint by capillary action. Fluxes break up the oxides, and if your joints are rough with a “dripped on” look, grind back and clean thoroughly. Fluxes coat conventional ferrous (steel) brazing rods, but for some tough jobs, you may need flux pastes or powders. Be sure to clean off any residual fluxes after brazing, since the aggressive oxide-breaking action won’t stop just because you’re done. And always wear the proper safety gear, even if you’re just heating a stubborn fastener. But you knew that already, right?