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Hard Coat Anodize - Type III per MIL-A-8625 _ Cracking/Crazing

Hard Coat Anodize - Type III per MIL-A-8625 _ Cracking/Crazing

Hard Coat Anodize - Type III per MIL-A-8625 _ Cracking/Crazing

(OP)
I have a few small parts that have cracking/crazing in the surface after a Hard Coat Anodize process (Type III per MIL-A-8625).

Do these cracks/crazing constitute a failure to meet the spec? (Reference MIL-A-8625, Para 3.13, "...coating shall be...uniform in appearance, free from...breaks, or other defects which will reduce the serviceability of the anodized part..."

What's the difference in a crack VS a craze...depth?

Also, what is visual inspection defined as? Is there any magnification allowed at all or it is just strictly the unaided eye? I couldn't find anything that defines visual inspection...

What is the best way to ensure this coating is truly acceptable or not? The abrasion resistance test MIL-A-8625, Para 3.7.2.2?

Lastly, I had another batch of parts Hard Coat Anodized per MIL-A-8625, Type III with a PTFE seal that did not exhibit this cracking/crazing issue. Could the PTFE prevent or reduce the cracking issue?

Any help is greatly appreciated...especially from Kenvlach.

One part is shown below, approx 0.090" DIA (hopefully).
 

RE: Hard Coat Anodize - Type III per MIL-A-8625 _ Cracking/Crazing


Hi.

Cracking/crazing comes from differences in coefficients of expansion between the aluminum and ceramic surface.

PTFE adds should have no effect on outcome.  

If you can't isolate cause (the large temperature variation), keep in mind that cracking/crazing is an appearance issue, only.  

If you need more information about anodic coatings, see:
<a href="http://www.industrialcoatingsworld.com/Wear-Resistant-Coatings/Anodizing-.html">Anodizing</a>

Good luck!

William Gunnar
http://www.IndustrialCoatingsWorld.com
 

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