Hard Chrome Plating and Etching

Q. Can you give me some guidelines for etching prior to hard chromium plating? V.P.

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A. Here are some basic guidelines for etching:

Etching is generally not a cleaning process. An acid etch will not remove oils and greases very effectively. Etching is performed to “roughen” the surface to get better adhesion of chromium to the base material.

A separate tank should be used for the etching step. Using your plating bath as an etch tank is not considered good practice. Doing so will increase the iron concentration in the plating bath, thereby causing plating problems.

Your etch time should not exceed 45 sec, with most operators limiting the time to 10–30 sec. Remember what the etching process does: It removes base material. Overetching can be counter-productive and can damage your parts.
Many people use only chromic acid in their etch tank (no sulfuric acid). This allows for better control of the etching step. A concentration of 32 oz/gal chromic acid is recommended.

If you want more information on hard chromium plating, the best reference book on the subject is The Handbook of Hard Chromium Plating by Robert K. Guffie. The book is out of print, but if you can find a copy, get it by all means.