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Hardchrome plating - stripping

Sir,

While stripping the Hardchrome plated coatings with HCl in chemical method, how to decide the stripping time when there is a vast variation in coating thickness, around 10 - 40 microns.

Is there not a possibility of substrate material attack at the lower coating thickness areas till we wait for the higher thickness coating to dissolve. Is there any metallurgical deterioration due to this attack and what is the remedy?

K.Chandrasekaran
Metallurgist - Coimbatore, India
2005

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Stripping chrome in an uninhibited Hydrochloric acid solution will give you all sorts of problems. You do not say what your substrate is, but assuming it's steel or aluminium then you will get base metal attack. Furthermore, if it is steel you have the potential to cause embrittlement, which would need removing by stoving at an appropriate temperature (normally 135 °C for carburised or nitrided steels, 195 °C for other steels greater than 1100 MPa) for an appropriate length of time (this is normally based on the strength or hardness of the steel, the higher the UTS or hardness the longer the stoving times).

You could consider stripping chrome from steel using a 10% caustic soda [affil links] solution anodically at about 2-4 volts. There should be little or no attack of the base material, although de-embrittlement is still recommended. All I can advise about stripping from aluminium is BE CAREFUL.

Brian Terry
Aerospace - Yeovil, Somerset, UK
2005

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July 22, 2010

is that 10% caustic to 90% water?

Bruce Conner
- Klamath Falls,Oregon, USA

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Hi, Bruce. Probably 10% by weight, but I doubt that it's critical -- the electricity does the work.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 22, 2010