I have visited shops that experienced greater than normal rejects from their brazing furnaces, and they did not understand why. When the process was investigated, it was discovered that they had been using alcohols and acetones to remove the lubricants from the surfaces over the years, but they did not realize that when their suppliers switched from using the petroleum-based/mineral-oil based lubricants and began using only water-based (aqueous) lubricants, their pre-braze cleaning procedures were no longer effective, and their degreasing solutions (alcohols/acetones, etc.) were no longer effectively removing the oils from the surfaces to be brazed, resulting in increased braze-failures in their shop. The same was true for shops that had been using vapor-degreasing processes.
Important: Match your degreasing solution to the type of lubricant you are trying to remove!
Synthetic, silicon-based, lubricants – Danger! These lubricants, if allowed to dry on the surface of parts, can render them non-brazeable. Silicon is not a good actor in brazing, and must be kept away from your brazing areas. A number of shops have found that they need to either burn-off, or machine-off, any of the hardened silicon-based lubricants from the faying surfaces of parts they received from a supplier, since attempts to braze those surfaces did not work even after normal degreasing processes were tried, and they did not realize the difficulty that silicon-based lubricants presented.
B. Oxide Removal. As shown in the bottom half of Table 2, the removal of any oxides is also very important. Surface oxides can come from many sources, and must be completely removed prior to brazing. Perhaps the metals themselves easily react with oxygen in the air to form surface oxides at room temperature or at slightly elevated temperatures. Iron, steel, aluminum, and titanium alloys are common examples of these. Or perhaps the oxides have been added to the surface via surface-prep, such as grinding, grit blasting, etc. Aluminum-oxide is a common material used for grinding wheels or for grit blasting, and residues from those processes will remain on the surfaces, potentially ruining any hopes for effective brazing. Tumble-deburring, likewise, leaves a surface film from the tumbling media that is used (alumina, stones, walnut shells, etc.).
Recommndation: Grit blast or tumble-deburr using only pure metallic material, not oxides. Thus, use a metallic grit, or a stainless steel grinding wheel, or stainless BB’s when tumble-deburring, etc.
C. Rinse Water. As shown in the last line of Table 2, the water that you use in your cleaning operations is very important. I strongly recommend that you use deionized water in your shop, and not well water or city water. City water can go bad upon occasion, whereas having your own deionizer in your shop is an excellent safety measure. Well water may be great for drinking, but it contains minerals (calcium-oxide, magnesium oxides, etc.) that are strong braze-inhibitors.
Equipment for cleaning. The equipment you use can be simple or formidable, depending on your budget. Cleaning can be done in a simple bowl on your work-bench, or in a larger, floor-mounted aqueous cleaner (such as shown in Fig. 1), or perhaps via ultrasonic cleaning methods, such as shown in Fig. 2.