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What determines required thickness for different chroming applications?
Hello,
I would like to understand why someone would specify a flash chrome vs. thick plated chrome. Does thicker chrome improve life vs a flash chrome and is their a point of diminishing return as you get thicker. I would also like to understand the relationship of hardness to wear resistance as it pertains between thin dense chrome and hard chrome. I realize that thin dense chrome is harder than hard chrome but has a much thinner coating.
How does this relate to my problem. I compression mold PTFE. We are looking at fabricating new dies and I think my old drawings have an overspecified chrome thickness. We are specifying 0.006 to 0.01 inches thick on each side. What am I sacrificing if I decrease my chrome thickness to 0.001 to 0.0015 inches thick on each side of hard chrome or would thin dense chrome possible be a better alternative.
Things to consider in my process. We pull our billet out of our mold so lubricity is important. Corrosion would be problematic - so if I chipped our dented the chrome. It would create brown spots in my final product. Depending on how well my supplier cleans their PTFE I can have trace amounts of HF which results in pitting of my dies.
Thanks for your help
customer/engineer - Hoosick Falls, New York
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Hi, Michael. "Flash" just means a very thin or very quick coating and has no real quantitative meaning. Thin Dense Chrome is a tradename for a proprietary, and some experts think highly of it while others are less impressed. You should talk to the purveyors and ask what the quantitative differences are, then talk to the doubters and decide for yourself how significant the technology is for your particula needs.
While the thickness of chrome has some effect on its corrosion resistance, the reason you specify a particular thickness usually doesn't have much to do with corrosion resistance but with wear life and providing enough thickness to develop hardness on the substrate in question. On a very hard substrate, a couple of ten thousandths of an inch may provide some wear resistance; on a soft substrate you may need several thousandths before you have anything truly useable. If your molds are copper, your 0.006 to 0.01 inch is probably not excessive. If they are hard steel, which I suppose they are because you worry about rust, I suspect that the 0.001 to 0.0015 might well do it.
Hopefully both of us will hear from experienced mold platers. Good luck.
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 Ted Mooney, P.E. finishing.com Brick, New Jersey |
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I also think your specified thickness is excessive. Some tool designers tend to think that a thicker coating is better, but this is not always right. Besides what Ted pointed, there's another issue with heavy electroplated coatings when applied to molds or tools: profile distortion. Thin dense chrome, due to its very low thickness, would not appreciably alter critical dimensions while conventional thick chrome will, thus requiring risky, expensive and tedious post grind or manual bench work to keep tolerances, eliminate negatives, sharp edges, etc. Now, if your resins are not blended with abrasive particles I think you should also consider high phos electroless nickel. More uniform, highly resistant to corrosion, fluorides and hard enough.
Guillermo MarrufoMonterrey, NL, Mexico