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topic 54822

Black Trivalent Chromate heat resistance

April 15, 2010


We insert injection mold a black trivalent chromate plated metal plate. This involves placing the metal plate inside a mold and injecting molten plastic around the plate. The plastic is 600 deg F, the final part is removed from the mold within 60 secs and comes out around 150 deg F. We are currently experiencing blistering of the coating on some of the parts. We have made thousands of these parts in the past with no trouble. The supplier tells us nothing has changed. Any idea what the maximum peak temperature this coating should be able to withstand without delaminating?


Carl Rogers
Injection Moulding Project Engineer - Winnipeg, MB, Canada

April 16, 2010

Hi, Carl. Well, obviously something has changed despite what your supplier says :-)

Changed since when, though. Until a few years ago there was no common process called trivalent black chromate. But if things have only changed in the last few months, the plating shops process may not have changed much. Have you shortened delivery time so much that the black chromate is not fully cured (this is only about 24 hours though).

When you use the term "blistering", it pretty much impies a failure of the zinc plating to adhere, rather than a failure of the chromate. The zinc should be good for way over 150 deg. F. If you have not changed your injection molding cycle, the plater has for some reason lost control of the former adhesion he had achieved.


Ted Mooney,
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Ted Mooney, P.E.
Pine Beach, New Jersey
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