Cleaning for Wire Plating

Q. I have a few questions about cleaning wire prior to silver plating. We run round wire mostly 0.0641" to 0.0403" with 1.25 -10 percent plating.

We are struggling to plate wire that is drawn to 0.0179" and flattened to 0.1006" by 0.0025" (40:1). After flattening, there are small bare patches that appear to follow a line along the length of the flattened wire. We are almost certain this is not caused by the flattening process, as round wire supplied by some other companies does not have this issue. We don’t see this problem when flattening 20:1-30:1 or when drawing to ultra-fine sizes.

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It was suggested that the failures might be caused by small, local spots of poor cleaning. We have questioned whether our cleaning process was robust enough. For this product we clean with a wash tank, about 30" submerged at 75 fpm and 14 amps. Do you think poor cleaning could be the cause of this? Thanks.—J.G.

A. Based on your description, the first thing you need to do is definitively determine the root cause of the defect you are finding in this flattened wire. It is not clear to me that the cleaning process is the cause of this problem, especially since the failure is so localized and repeatable. It could be due to a tooling problem that is rolling a “fold” into the flattened face that makes consistent cleaning and plating impossible.

I suggest contracting a metallurgical laboratory that can effectively determine the cause. I would offer a cross section of the part to examine the profile under magnification and consider a scanning electron microscope to determine if there is a metal fold from the flattening process in the defect area or if this is simply due to poor cleaning. If you do not find any metalworking-related cause of the problem, you may need some additional time or possibly increased temperature to more effectively remove whatever contaminant is causing the plating problems. Additionally, you could try to find these spots ahead of time and perform analysis and cleaning trials in those areas to determine if it is a different contaminant and how it can best be removed.