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Hardcoat Anodizing thin parts(.047)

I am a plating supervisor and we have been doing a lot of anodizing on thin material. .047 to be exact. We are experiencing burn problems on the parts. We have an additive in our tanks to correct this (supposedly). We are running about 14 % sulfuric acid and about 30 degrees. Thanks for your responses

Chris

Chris Mace
plating shop supervisor - Waynesboro, Va, USA
July 1, 2009

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July 1, 2009

Hi, Chris. Hardcoated parts have a large amount of power pumped into them and heat up very readily. I think you will find that for thin parts like this, the problem is that some spots don't have intense agitation to quickly convey away the heat. Look carefully at your agitation system.

Regards,

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

thanks for the response . We experience a random burn on all parts from time to time now...All parts show good contact and the tank concentration and temperature is right. I have heard its contact...can you have too much contact on one part? We usually rack them in spring clips and there is a part per run that usually will burn. Any suggestions?

Chris Mace
- Waynesboro, Virginia, USA
September 22, 2009

Hi, again. If the burning is random rather than at one position, I agree that that is evidence that the problem is contact rather than insufficient heat removal. People have used some exotic solutions, like contacts made of indium, but I wouldn't abandon your simple spring-clip racks without really trying hard to get them to apply sufficient pressure through sufficiently sharp contact points, while completely preventing any wiggle.

The reason that contact is so critical is that hard anodizing starts at low voltage to keep the current within bounds, but as the insulating anodized coating builds up, the voltage must be raised quite high so current will continue to flow. If you have a part that didn't make good contact at low voltage, and now makes contact at high voltage while it has no insulating coating, it will burn. It is possible for this breakthrough to happen at a low enough voltage that the bulk of the part anodizes properly, but the high current density edges burn.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 23, 2009

I am running my hard anodizing tank at the appropriate temp. and concentration with medium agitation yet I always have one part burn past the point of salvaging. Just looking for suggestions on why this might be happening

Chris Jones
anodizing technician - Calgary, Alberta, Canada
September 23, 2009