What substance is recommended for cleaning surfaces before brazing?

Acetone is recommended for cleaning surfaces before brazing because it is an effective solvent that removes oils, greases, and impurities that may be present on the surfaces to be joined. A clean surface is crucial for brazing as it ensures proper adhesion of the filler metal and helps achieve a strong, reliable joint. The use of acetone minimizes the risk of contamination, which can lead to weak joints or failures during the brazing process.

This makes it a preferred choice, as it evaporates quickly and leaves no residue, further ensuring that the surface remains clean and ready for the brazing operation. Other substances, like alcohol and water, may not be as effective for cleaning metal surfaces due to their different chemical properties. Oil, on the other hand, would be counterproductive since it could leave a film on the surface, preventing proper bonding during the brazing process.