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HARD ANODIZING HELP

I AM A BEGINNING ANODIZE AND I AM HAVING TROUBLE WITH HARD ANODIZING.
CAN'T GET THICKNESS BUILD-UP ON 7075 OR 6061 BEYOND .001 INCH.
I CAN'T BUILD UP 2024 BEYOND .0005 WITH BURNING.

ANY TIPS WOULD BE WELL APPRECIATED. ACID CONCENTRATION IN THE TANK IS AT LOW END AND AIR AGITATION IS POOR BUT I SUSPECT THE PROCEDURE I WAS LEFT WITH .

TRIED DPS STANDARD PROCEDURE - DON'T WORK EITHER THAT WAS WORST HELP

PLEASE

ROD BEST
METAL FINISHING - COMPTON, CALIFORNIA
2003

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Hard anodizing is quite a bit more difficult than conventional anodizing. The solution must be very cold to keep the acid from dissolving the anodic film faster than you can build it. But it must be cold not just in general, but right at the part interface where all the heat is being pumped in. Vigorous air agitation is what keeps fresh solution there to achieve this cooling. So if the air agitation is poor, the situation is hopeless :-( Fix that and then get back to us.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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Dear Rod,

In your first few words you already have answered your own question= beginning and alloy. 7075 and 2024 are a few of the most sensitive alloys to anodize/hard coat. I know of many shops,very large shops who will not do those alloys because of the problems. Most that do, have their own "tricks" in doing that type work. I prefer to go back to the basics and work form there.1) Temp must be consistent through out the bath (prefer 32 f). 2) Air must be VIGOROUS and extremely even. 3) All contacts must be secure (bolted preferred). 4)Acid concentration should be close to 200 grams per liter or higher and other parameters must be maintained within guidelines.5) Segregate alloys and don't mix batches.6) Use aluminum cathodes 6063T6 at a ratio of 3-1.7) Anodize by asf not voltage. 8) Use a quality additive! 9) Most important call a supplier that really knows todays anodizing from chemistry to equipment !

Drew Nosti, CEF
Anodize USA

Ladson, South Carolina

2003