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Zinc Cyanide over 12L-14 Steel

We perform quite a bit of zinc cyanide plating. We are having trouble with zinc plating on 12L-14 Steel parts. These are rack plated. On the stock material there is a heavy black smut or scale from the mill. This scale does not seem to be removed by alkaline soak, alkaline electrocleaner, and hydrochloric acid cleaning. We have even tried double cleaning and strip and replating. The result is that after a few weeks bleedthrough, staining, and corrosion occur. The machined areas of the part do not exhibit this problem. Is there a recommended process for this type of part?

Micheal Marchio
Co-Operative Plating - St. Paul, Minnesota
2006

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Try one of these: 1) fluoboric acid, 2) sulfamic + citric acid ⇦this on eBay or Amazon [affil links] or 3) methane sulfonic acid (MSA).
From a search for 'fluoboric leaded steel' on finishing.com

Note: This acid bath will need wastewater treatment capable of breaking the chelated lead complex.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2006

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I use 5% Sulfuric Acid + 5% Clorhydric Acid. An letting the part in the bath a little more time than usual.

Saludos

Guillermo Castorena G.
Jobshop - San Luis Potosí, México
2006