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Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)

by Larry Zitko, ChromeTech, Inc.
April, 2002

Adhesion Problems

Q. 1. I have noticed that some portions of hard chrome plated surfaces are peeled off during the final grinding, What is cause of it?

2. Can you give me suggestions on how to achieve quality finish of hard chrome process.

A. When chromium fails in post-plate grinding, this indicates an adhesion problem. You did not mention the type of base metal, whether you are plating "chrome-on-chrome" or whether you can see the base metal in the areas where the chromium deposit has peeled. I will assume that you are plating on steel substrates, and that the peeled areas go all the way down to the steel base metal.

This kind of peeling indicates poor adhesion between the chromium and base metal. The post-plate grinding is a pretty good test for adhesion, so often times a bond problem will present itself in the grinding operation.

Adhesion problems for chrome-on-steel seem to center around two areas:
1) Inadequate cleaning
2) Improper activation

You did not describe your cleaning or etching procedures, or the type or size of your parts, so I can't make suggestions that are specific to your parts. However, I have the following general comments:

Make sure that the plated regions of your parts are free of all oils, soils, films and foreign materials that would interfere with the chromium bonding. You may have to improve your cleaning operations. Perform the "Water Break Free" test after cleaning. If you are not already familiar with this common test, here is a brief summary:

Spray the cleaned and rinsed part with water. Observe the motion of the water as it runs down the plated area of the part. If the water runs down in an uninterrupted sheeting action, it is free of "water breaks", and considered clean enough for hard chrome plating. If you see any areas where the water diverts or gathers, this indicates areas which are not clean enough. If your parts are large and the plating cycle times are long, a good cleaning method is to scrub the parts with wetted pumice on an abrasive pad (3M Scotch-Brite), then rinse thoroughly.

The degree of reverse etch activation is critically important, because it will also affect bond strength. The degree of reverse etch is determined by both the current and duration during the reverse etch activation procedure. Defining the right etch is bath-specific, part-specific, alloy-specific, anode-specific and is also affected by any case hardening procedures that may have been performed on your parts prior to plating. Some parts cannot be reverse etch activated, and must be immersion etched or electroetched in other acids. Make sure that the parts are properly etched.



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