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Why should our hard anodizing start at 20 volts and not 0?

We are a Anodize shop and are in the process of ordering a new rectifier for our hard anodize. Our control panel has a voltage offset that we set at 20v. The rectifier mfg asks why we need that and wants to charge $1100 more to have it. The problem is that none of us knows why we start at 20v and not 0v, and if we need it. I have looked at many of the aerospace standards, along with guide books and cannot find the reason that we start at 20v. Any insight on this would be greatly appreciated!

Thanks

Eric Robert
production mgr - Pomona, California
March 16, 2011

Start at zero voltage and let it climb smoothly for 15 minutes up to the ampere setting that is equivalent to 24 or 30 amps per square foot. Never mind that stuff about 20 volts, start at zero. The voltage you will be at switch-over (24 ASF) is a function of the free acid.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

March 18, 2011

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