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STAINLESS STEEL SOLDERING Soldering and brazing differ only in the temperature used to melt the alloy being used to join the material being soldered or brazed. The material being joined is not melted by joining processes. Soft Soldering: Soft soldering of stainless steels is not much of a problem when the requirements of the job are understood. The biggest problem is breaking through the passive film with a flux so that the solder will wet the stainless. Soft solders are weak as compared to stainless steel. Consequently, if strength is required, the edges should first be riveted or spot welded, then soldered for a tight seal. Stainless steel must be perfectly clean before soldering is attempted. This can be accomplished by a clean white pickling with acid, or it can be done with mechanical polishing. Do not expect the flux to do the cleaning. Stainless steel is resistant to the corrosive attack of most soldering fluxes, and unless the flux etches the surface, it will not function. On smooth surfaced parts, such as cold rolled strip, it will be difficult to get the flux to spread and completely cover the surface. Therefore, the soldering area should first be roughened by acid etching (50 : 50 muriatic acid and water) or mechanical polishing. This rough surface will take the flux quickly and the solder will flow evenly. Use fluxes prepared especially for soldering stainless steel. Apply the flux with a brush to the area to be soldered and rub until the surface is wet. All flux must be properly and completely removed after soldering to avoid continued corrosion. Be sure to remove all splattered flux with soap and water. Stainless steels are slower to absorb heat, and it is, therefore, necessary to use a larger and heavier iron, it is not necessary that it be hotter, just bigger and with more heat capacity, so it will heat a sufficient area to allow the solder to flow freely. “Tinning” the joint will also assist in making the solder flow more evenly. Keep moving as fast as the solder fills the joint. Ordinary half-and-half solder applied from the top of a well-tinned copper is satisfactory, but for brighter, stronger joints use 67% tin, 33% lead dairy solder. In general, the higher the lead content, the more quickly the joint will darken on exposure to the air. |
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