Aluminum Brite Dip Chemical Composition / Effective Polishing Techniques

A. Hi cousin Bharat. These solutions run at near boiling, say 200-210 °F, although some people claim it can be done at 185 °F.

But no, you did NOT "read all these articles and question & answers" or you wouldn't have done it because we never fail to suggest that this process only be done inside a garage type hood with automation -- never manually out in the open with conventional exhaust systems :-)

You can try the proprietary fume suppressants to see how much they help, but even with them I doubt that it is safely workable on a manual line. In 40 years of frequent visits to plating & anodizing shops I only saw three shops which did aluminum brite dipping, and all three were automated and did their small manual bright dipping experimentation within a lab hood.

If your solution is being held in other than a fluoropolymer lined 316L stainless tank or a double-walled 316L stainless steel tank, leakage onto the floor may be just around the corner, and your problems only beginning. Electropolishing might be an alternative :-(

Luck & Regards,

I guess the first thing to say is if you have been working anodizing shop for any extended length of time, then you should be glad that your nose is still able to be offended by the fumes.

Bright dip temps can vary depending upon what type of jobs you are processing. polished parts might need to be around 210 °F but up to 220 will work fine as well especially if you are bright dipping reflectors. Non polished parts can be processed the very lowest 185 °F as Ted wrote but that could almost be pushing it which could result in an etching type process as opposed to brightening.

Lastly again Ted is correct. Ventilation is critical. All work loads will generate differing amounts of fumes or orange smoke. Wearing a ventilator is not a good remedy. Ventilation along with fume scrubbing is critical. you may be getting yourself in deeper than you want to go. Proprietary chemical brightening chemicals may be the way to go with having fumes that are much less noxious.

A. Hi Daniel. Wernick, Pinner & Sheasby [adv: this book on AbeBooks, Amazon & eBay] has a 94-page chapter on chemical and electrochemical brightening of aluminum that will explain everything you could imagine -- no secrets. Generic bright dip is composed of nitric acid & phosphoric acid and operates at 190-210+ °F. A typical formula is 80% by volume phosphoric acid & 3.5% nitric acid.

People probably don't say much about brite dipping chemistry for a number of reasons.
First, very few anodizers do brite dipping, which limits the amount of response we can expect.
Second, there are a number of proprietary suppliers, and people may not be sure if a composition they know of is generic knowledge or is actually a proprietary trade secret they can get in trouble for publishing.
Third -- and most important to me personally -- those who are familiar with it realize this is a really, really, really, nasty solution that requires specially designed garage-door type fume containment (not conventional lip exhaust or push-pull exhaust), plus rather special unconventional fume scrubbers to deal with the wild NOx fuming and the high solubility of nitric acid which conventional fume scrubbers can't fully handle, and very well engineered secondary containment because it is extremely aggressive even to expensive construction materials. This stuff running out on the floor after eating through a 316L stainless tank would be a major concern!

So speaking for myself, while I'll cheerfully give anyone a few minutes of my time, when we get into aluminum bright dipping, it's just so chock full of "Why in the name of hell didn't you warn me about THAT?!" issues that it's a topic that cannot be quickly dispatched. I, and maybe others, tend to not want to be pulled into a discussion when I see such a very long very rocky road in front of me. Are you willing to invest in full automation? ... a totally enclosed ventilation system? ... special custom-design double fume scrubbers? ... the consequently required higher pressure exhaust fans to push the fumes through double scrubbers? ... double-walled 316L stainless steel process and rinse tanks? -- If not, please understand that I want to discourage you from working with this chemistry, not encourage you :-)

This is perhaps a good area to start with a proprietary solution from a vendor who will give you some hands-on help. I believe Albright & Wilson may be one; search for their Phosbrite bright dip.

Good luck.

A. Typical home-made solution is as follows:
Phosphoric Acid 73-83% (vol)
Nitric Acid 2-5% (vol)
DI Water 14-23% (vol)

Heated to a temp of 200-210 °F.

Like Ted said: extremely nasty stuff, and use with caution. This bath works well on wrought alloys, not castings (or alloys with high silicon content). Nitric acid content must be kept stable, or you'll have undesirable results. Also heed his advice on finding a supplier of pre-made brite dips. They are much easier to work with, but if you're intent on making your own, the above recipe works well. Use double walled 316L tanks to contain your solution (I would even coat the inside with a fluoropolymer coating).

A. Bright dip for aluminum:
phosphoric acid(d=1,75) 65%
nitric acid(d=1,5) 25%
acetic acid [on eBay or Amazon] 10%
30-60 sec, 80-110 °C temp.

A. I know of 2 basic formulas for bright dipping aluminum.
The typical R5 process consists of 80% phosphoric acid, water, and HNO3. specific gravity should be around 1.65
You need 1000 ppm of copper (as copper sulphate) and diammonium phosphate or urea (2%) as a fume suppressant.
The nitric acid concentration is the 3 to 4%, water should be about 10%, the balance is the phosphoric acid. Make sure you use 80% phosphoric acid.

The second formula, similar to the phosbrite 174, is a mixture of phosphoric acid and sulfuric acid. the specific gravity should be about 1.70. Also use copper and the fume suppressant. Same concentrations as before : Nitric 2 to 4 %, about 10% water, 15 to 20% sulfuric, the balance is 80% phosphoric acid.

Operating temperature should be over 212 °F, as the b/d generates water. With the heat you control the specific gravity of the solution (also by adding water when necessary).
The immersion time should be from 1 to 3 minutes (depending on the alloy).

To formulate a B/D bath is pretty simple - I provided you with the "secret" ingredients. The real deal is to know how to operate it in a production line.

The operating parameters are very tight, if you don't keep accurate controls, you are bound for disaster.

Daniel. This is a good topic. Bright dip anodize is what they used on aluminum car parts. I restore them and send my parts out to get bright dip anodized. I would like to do my own and this here has given me a lot of information. Thank you all for commenting.

A. Hi Alfredo. The nitric-phosphoric acid bright dip requires high temperature; moreover, it's a very dangerous mix.

What is the alloy? Are the products castings with silicon, which would require fluoride chemicals? Are you sure it's not more practical to mechanically polish the products?

Regards,

A. Hi Alejandro. From my own experience, I don't think you'll find a chemical bright dip free of nitric acid. However, you can electropolish the aluminum to similar brightness with electrolytes that are free of nitric acid.

Regards,

adv.
I think Accu-Labs, Inc. [a finishing.com supporting advertiser] may have what you may be looking for:
213 ALUMINUM BRIGHT DIP

A. Thanks Alexander! We don't print brand or source suggestions in this public forum ( huh? why?) ... so when products from our supporting advertisers are mentioned, we mark it as an advertisement :-)

The data sheet says it contains 2-4% nitric acid, but with a fume suppressant to deter NOx fumes.

Regards,