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Parts Burning During Hard Anodizing

What could cause parts to burn during hard anodizing?

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Q. From time-to-time, a few parts on some loads burn during hard anodizing. I make sure all anodizing conditions are ideal. However, sometimes on the same spline or on the same section of rack where there might be 50-100 pieces, there are one or two burnt parts (literally dissolved), even though all contact points are securely fastened. What could cause this? T.K.

A. Perhaps this is an air agitation issue. The air may not be vigorous enough, or one or more of the air holes in the sparger line may be plugged up. Lots of evenly distributed air agitation is required for hard anodizing. Even if the agitation looks good on the solution surface, there could be places near the bottom of the tank that have little or no agitation. If you pump the tank and turn on the air, you may find the source of the problem. Remove the air lines and clean them out, or make up new air lines and have them ready to install when the tank is pumped. We always make the air line spargers removable from the air header by using threaded connections and a threaded cap on the end. This way, the sparger can be removed and cleaned, and then reinstalled. 

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