Torch brazing differs extensively from torch welding. With brazing, the flame should not be oxidizing and should be held much farther from the part than a welding flame would be. The flame for brazing should wrap around the entire joint (if possible) so as to evenly heat the whole joint rather than just a small portion of it. Sound hard? Not really. Let’s see how this might be achieved.
Figure 1 shows a typical example of a torch-brazing operation in which a joint is being heated for application of some brazing filler metal (BFM). The torch flame should be held at a convenient distance from the part so that the flame will wrap around the joint as much as possible and not just heat one small spot.
The flame is designed to bring the entire joint up to a temperature high enough so that when the BFM wire/rod is touched to the edge of the joint to be brazed (at the left side of the fitting in the photo), the heat in the base metal (not the torch flame) will cause the BFM to melt and be pulled into the joint by capillary action. Then, as the flame is moved slowly down the fitting (moved to the right in the photo), the molten BFM will be drawn through the fitting by capillary action because BFM likes to flow toward the hot spot.
Remember, the torch should NOT be used to melt the BFM. Too many torch brazers make the mistake of trying to melt the BFM wire using the torch flame instead of using the heat in the base metal to melt the BFM.