Before brazing, which step involves cleaning the pieces to be brazed?

• A. Check for proper fitting
• B. Clean pieces with a wire brush or sand cloth
• C. Assemble pieces
• D. Start nitrogen purge

Answer: (B)

In brazing, surface cleanliness is essential because the molten filler metal must wet and flow between the surfaces to form a strong joint. Oxides, oils, and other contaminants on the metal create barriers that prevent bonding and lead to weak joints or porosity. Cleaning with a wire brush or sand cloth mechanically removes these films, producing a fresh, clean surface that the filler metal can adhere to and spread over by capillary action. This cleaning step sets up the joint for successful brazing, while other steps like verifying fit, assembling the parts, or initiating a nitrogen purge relate to preparation, alignment, and processing during heating, rather than cleaning.