Powder on Anodized Aluminum


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Q. We are thinking of trying powder coating on the hydraulic valves we manufacture for the aircraft industry. The valves are made of aircraft grade aluminum (2024 and/or 7075) and anodized to either Type I or Type II, depending on the end users’ requirements.
We have a couple of concerns right now, and I am sure there is more that we just don’t know about yet. Is there a powder coating that will hold up to Skydrol 500 B4 and Skydrol LD4? 

Will we be able to remove the powder coating from the parts when they come back in for rebuild or repair so that can inspected the parts? What kind of cure temperature and time are we looking at for cure of the powder? We need to make sure it does not affect the base material. —T.R.

A. I think the powder will handle the hydraulic fluid (Skydrol) fine. Most powder materials have good chemical resistance and you should talk to the powder supplier about the specific products that the finish on your valves will need to be able to tolerate. During material selection you should work with the powder supplier to make sure they understand the level of resistance you need and the specific material that you use. 
The anodized surface is a bit of a concern that should be tested. Powder does not always adhere well over some anodized surfaces. Consult with your supplier and do some testing on adhesion. The cure temperature you use will depend on part on the powder you select. It will most likely be between 325°F and 400°F (160°C to 200°C), but there are some epoxy formulas that can be cured as low as 250°F (120°C). 

Powder can be removed with chemicals, high heat, abrasion or some combination of the three. The high heat is not a good option for aluminum. Look into chemical stripping materials. There are some products that are reasonably safe and effective for powder removal. Do your research and testing and you should be able to effectively use a powder coating material for your valves. 


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