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topic 4805

Anodize bright dip


(2000)

Q. Hello all, I'm a hobbyist and I'm dye anodizing aluminum 6060 with great success. Can anyone recommend a bright dip solution I can mix and use immediately before anodizing. The parts are getting a lightly dull grey after etching.

Thanks.

Eirik Karlsen
- Norway


(2000)

A. Hi, Eirik. Don't etch so long; maybe not at all.

There are four metal finishing chemicals I hate, and aluminum bright dip is one of them (along with cyanide, hydrofluoric acid, and hexavalent chromium).

Bright dips contain nitric and phosphoric acid, and are wildly corrosive, toxic, and noxious. They operate at over 200 degrees Fahrenheit, and evolve clouds of mustard color toxic gas--not only from the bright dip itself but even the first rinse. In my opinion, a home hobbyist should not dream of bright dipping aluminum; way too dangerous and toxic.

However, there may be a semantics issue here. You may be inquiring about a "de-smut" bath as opposed to a bright dip. You may be able to de-smut with tri-acid salts or a dilute nitric acid dip.

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



May 18, 2015

Q. I process anodized aluminum parts, including bright dip. What exactly are the toxins in the bright dip gas, and what PPE's should be used by the processors. We currently use deep well tanks with an air curtain to keep gases down.

Derek Suddreth
- CLOVER, South Carolina, USA


July 2015

A. Hi Derek. My personal experience is limited to automated lines (programmed hoists) and we always put the bright dip tank at the end of the line, with it and the two rinses following it inside a "garage" exhaust hood (top, sides, and one end enclosed, and the other end with doors or hanging plastic strips or air curtain). My visual observation was that the orange clouds of NOx copiously evolved when the aluminum was immersed in the bright dip tank, and to a lesser extent when it was put into the first rinse, so the order of tanks is back wall of garage, bright dip tank, 1st rinse, 2nd rinse, door area.

I would seriously consider trying to automate the transfer of the racks into the bright dip and first rinse, to eliminate the personnel exposure. But NOx is indeed noxious and I don't think your operators are being exposed to much of it if they're not complaining when questioned. Most industrial ventilation companies are familiar with the issue and could come in and advise you what to do. I hesitate to suggest appropriate PPE or exhaust systems based on a verbal description of what you are doing to ameliorate the fumes.

Remember that the fumes must be scrubbed, and that it's not easy to scrub NOx -- I've sometimes seen two packaged wet fume scrubbers in series for this application, which in turn means a higher suction fan than usual.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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