Metal finishing Q&As since 1989
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Black or Greyish stain after zinc plating
Black or greyish stains are visible after zinc plating. Despite going through several rounds of degresing at high temperatures, black stains are still stuck at the cold-roll steel part.
Part goes through tig welding process of a pin onto it before sending for zinc plating.
What causes the black unremovable stain to appear ?
Some of the parts have this problem but some doesn't, why is it so?
What is the solution to ensure part will be of zinc plating finish.
Consumer - Singapore
2007
2007
Lim,
Do the black stains appear after the chromate? How do they look? Spots or stripes?
Saludos
Jobshop - San Luis Potosí, México
It's possible that the fault you describe is caused by oil/grease being 'burned' into the steel by the welding process. No amount of degreasing after it's welded will remove the 'stain'. The part of the plating process you need to ensure is adequate is the acid dip stage (correct concentration, temperature and immersion time).
John Martin- Wales
2007
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