Bleed-Out and Lap Seams
Q. We are plating assemblies with spot-welded seams. A major problem is bleed out and the corrosion it causes on the assemblies. Do you have any suggestions for how we can solve this problem? T.L.
A. The problem you are having is fairly common and has to do with the rinsing steps after plating. Spot-welded lap seams typically have very little clearance and are almost impossible to properly rinse. The seams function as capillary channels and as a pathway for bleed-out.
The first thing I would suggest is to try to improve your rinse steps. Try longer soak times in the rinses and alternate warm and cold rinses. The alternate warm and cold rinses create a “pumping action” that can help clear the seams.
Another thing you might try is to open the lap seams ever so slightly so that you can insert a sheet of copier paper into the seam. This should give you better drainage of the seams.
Also, make sure that the parts are thoroughly dried before they are put into storage or shipped.
An alternative product for passivation...
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Masking is employed in most any metal finishing operation where only a specifically defined area of the surface of a part must be exposed to a process. Conversely, masking may be employed on a surface where treatment is either not required or must be avoided. This article covers the many aspects of masking for metal finishing, including applications, methods and the various types of masking employed.