On brazed joints, to make good joints you must what?

• A. Cool Quickly
• B. Clean
• C. Brush With Solvent
• D. Solder

Answer: (B)

In brazing, the filler metal must wet the base metals and be drawn into the joint by capillary action. That only happens when the surfaces are clean and free of oils, grease, dirt, and oxide films. Contaminants act like a barrier to wetting, trapping air and creating voids, porosity, or leaks in the joint. While flux is important to protect the joint from oxidation during heating and to help wetting, it can’t fix a dirty surface on its own. Proper surface prep—thorough cleaning with solvents or degreasers, mechanical cleaning to remove oxide, and then drying—sets the stage for a strong, leak-free brazed joint.