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topic 4944

Having problems hardcoating aluminum


We are having problems hardcoating our aluminum. We can't get it to repeat.

My question is what is the best way to test the density of the acid tank and what should it read "avg".?

we are using a float hydrometer to test it now but have no idea what the reading should be. We are running it at 17 now. How to calibrate it for the temperature changes etc. I hope this makes sense. Any information on hardcoating aluminum will help



Specific gravity can be used decently to control a chromic acid anodize tank but can not be used on a hardcoat line. First the density changes with temperature, so you would have to wait till the tank was cold to test it or develop a fudge factor. Second, Anodizing is concerned with the amount of sulfuric acid in the tank. You gradually build up aluminum and other contaminants that contribute to the specific gravity and give a false high reading. Switch to wet lab testing. It is accurate and does not take a lot of time (a lot more than a SG reading tho). You can also do a test for the amount of aluminum which you should be controlling also. This is not as easy a test to get repeatable data on, and rarely will two different people get the same answer on, but it is relative. Control the aluminum and your life will be better.

James Watts
- Navarre, Florida


We might be able to help if you're willing to look at PVD approaches. To that end, What hard coating are you trying to apply, and what is the application?

jim treglio portrait
Jim Treglio
PVD Consultant - San Diego, California


In this context 'hardcoating' has a specific meaning: it's a synonym for hardcoat anodizing, Jim.

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

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