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"Rack material for Iridite chromate conversion coating"

Current question:

December 16, 2021

Q. We have a large ordnance program requiring Yellow Chromate Conversion per MIL 7.3.1 of MIL STD 171 spec. on 6061 Aluminum. Color must meet Fed STD Color Spec ranges too.
Should we use titanium or aluminum racks?
If we go with titanium how do we mitigate possible galvanic corrosion between the parts, tooling, and chemistry?

Brian Isola
- Palatine, Illinois

Closely related Q&A's, oldest first:

September 14, 2020

Q. I need to build some custom plating racks for iridite baths.
What metal can I use to build them with that won't contaminate the bath?

Fraser Wilson
- Ville saint-laurent, Quebec, Canada

September 2020

A. Hi Fraser. 304 or 316 stainless would probably be fine.

But for the benefit of newbies trying to learn from the conversations, we should note that the Iridite process (a trade name for Mil-DTL-5541 [link is to free spec at Defense Logistics Agency, dla.mil] chromate conversion coating of aluminum) usually involves immersion is a sequence of alkaline cleaning, alkaline etching, and desmutting tanks before the Iridite. The desmut can be a number of different chemicals depending on the aluminum alloy you are processing. So while stainless is likely fine, there is a chance that aluminum or titanium would be a safer bet; aluminum would cost less, titanium more.

Another alternative would be to use plastic (PVC or polypropylene), or if high strength is essential, plastisol covered steel. I'm not clear on whether the parts would be delicately racked vs. dumped & jostled into baskets, sharp edges and all, which would be tough on plastisol coatings.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

September 14, 2020

thumbs up sign Thanks Ted,
Your info was very useful.
The cleaning sequences you mentioned would be used and the rack would be dedicated to certain parts and not a basket.

Fraser Wilson [returning]
- Ville Saint-Laurent, Quebec, Canada

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