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What is phosphating?

What is phosphating? I am completing a wastewater discharge permit for a Jobshop that paints metals and plastics. Prior to painting, the parts are dipped in a cleaning solution to remove oil and grease. This cleaning solution contains phosphates. Is this phosphating, or is phosphating a different coating procedure?

Robert Adams
1998

Dear Bob, phosphating is the process of providing a conversion coating for iron bearing metals and/or etching/activating for non-ferrous metals. When the metal comes in contact with the phosphate solution, a chemical reaction takes place (also called pickling). The phosphate coating is deposited. The topcoat will now have a better substrate profile in which to adhere to. Remember that aluminum does not accept a conversion coat unless phosphate chrome is used. The aluminum will still receive an etch that will accept good adhesion.

Bob Utech
Benson, Minnesota
1998

Dear Sir:

Many heavy duty cleaners contain phosphates as part of their makeup. You need to determine if the job shop is just degreasing the part or actually applying a phosphate coating.

Phosphate cleaners are typically alkaline, phosphate conversion coatings are typically acidic.

Finally, it is possible to apply a phosphate conversion coating (zinc or iron) to aluminum.

Edward Koneczny
- Birmingham, Michigan
1998

please tell me in detail about accelerators used during phosphating as a paint base; also tell me about the post treatments regarding the phosphating process.

abhijeet.p.bapat
1999

I am a chemist from Pakistan. I need some know how about metal pre-treatment system. Is there any gentleman who gives me information about alkaline cleaners, pickling solutions, phosphating chemicals. God bless you.

syed Iqbal Saleem
- Pakistan
2000

2000

Hello, Mr. Bapat. Hello, Mr. Saleem,

There are entire shelves and even aisles in technical libraries which attempt to answer your questions, so it is hard to recommend just a single book, but Samuel Spring's Preparation of Metal for Painting [affil link on Amazon ] is a book that I can recommend.; or try "Phosphating of Metals" [on Amazon or AbeBooks] by Rausch. or "Phosphating & Metal Pretreatment" [on Amazon or AbeBooks] by Freeman. Good luck.

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

What is the difference between phosphate cleaner and phosphate conversion?

harish mehra
employee - delhi, India
September 22, 2011

September 22, 2011

Hi, Harish. Phosphates, such as trisodium phosphate [on eBay or Amazon], are sometimes used as detergents to assist cleaning. But phosphate conversion coating, sometimes called phosphatization, is a pretreatment process for metal which improves its corrosion resistance and provides a good base for the adhesion of paints or absorption of oils. If you can provide some context rather than an abstract question, we can probably assist in more detail. Thanks.

Regards,

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

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