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Dark spots /staining after Potassium Stannate Tin Plating




June 14, 2011

We tin plate our power pistons to provide an initial (break-in) and continued (unit start-up and shut-down) bearing surface. On occasion within 12-24 hours after plating, small spots will appear at the plated surface. (see attached picture, 24 hr after plating).

57306-1

Too, we have noticed "staining" spots (usually larger in size) appear after 4-6 weeks in inventory. A preservative is applied - light tectyl prior. (see attached picture, 6 weeks storage).

57306-2

The piston material is either a ASTM A48 [affil. link] class 40 or ASTM A536 [affil link] Ductile (65-45-12).

I'm looking for the possibilities for these causes. I do not think they are process related. The "spots, I'm inclined to believe are created from base material porosity & post plating solution bleed back out. The staining....... I'm unsure of but might be related to the preservative application.

Any thoughts....suggestions???? All Welcome!!

Michael E. Marks
Manufacture - Houston, Texas



If these are aluminum pistons covered with immersion tin plate, then one possible cause is porosity in the aluminum. Some liquid gets into the pores and then leaches back out after plating. The immersion plate is fairly porous and has good wicking properties.

You can dye check the pistons for porosity before plating.

Lyle Kirman
consultant - Cleveland Heights, Ohio
First of two simultaneous responses -- June 16, 2011



Alkaline Tin plating solution surfactants are very tenacious and will not plainly rinse away, thus causing post staining. After tin plating and rinsing, then go back into an alkaline cleaner, then rinse again.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
probertbanner
Second of two simultaneous responses -- June 16, 2011




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