Letter 27047

Risk of not phosphating?  

++++

Hello,

I will like to know if you can help me about the following question: I work with powder coating, but want to know what are the risks of not using the phosphate in the pretreatment process for metal parts? Thank you very much for helping me.

Eliseo Izquierdo
QA Eng. - Juarez, Chihuahua, Mexico

'Work with' is a little vague, Eliseo -- I'm not sure if you are the designer/specifier or the applicator. Without knowing the application and the exposure environment, and the type of powder coating, I really can't tell you whether it NEEDS phosphate or not. But phosphatizing is always a very good idea and should not be omitted unless the item is too difficult to phosphate, will see only interior exposure, and is otherwise well prepared.

You might want to consult R. Rausch's book ""Phosphating of Metals" [link is to info about the book at Amazon]" or Samuel Spring's "Preparation of Metal for Painting" [link is to info about the book at Amazon] for a full list of the many ways in which phosphatizing benefits the parts, but a starter list is: providing good key for paint adhesion, providing undercutting protection, and minimizing galvanic hotspots Good luck.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

++++ Hi Ted , It's very unfortunate to note many times your answers insult the person's question, who may be poor in, say, language or exact spelling or may be poor in a particular technical aspect.... your approach tends to first insult & then answer ..... Hope you can read between the lines & take this in a good spirit, Atul Bhide jobshop / applicator - Mumbai, India ++++ I appreciate you taking the time to point out your reading of my response, Atul. If Mr. Izquierdo was offended, I heartily apologize! My only point was that I did not understand his situation. We edit typographical and grammar errors, etc., so that our readers can read & understand the questions quickly, and so the questions are indexed properly in search engines. We very heavily edited Mr. Izquierdo's inquiry, so what you see here is very different than what he wrote; I was hoping that I did not misunderstand it or change its meaning, and was requesting clarification. I have rewritten my response to him and hope you find it less problematic. I greatly admire people who are multilingual! Anyone's English is far better than my knowledge of any other language :-) Ted Mooney finishing.com Brick, New Jersey

Dear Sir,

The general rule of thumb would be as follows to phosphate or not. For powder coated items that are to be sited outside (exterior) you will use a polyester powder. Having paid a little extra (poly vs e/p) it is wise to zinc phosphate. This is a preventative action in case the item gets damage (scratched) the phosphate will then prevent in the short term corrosion (rust creep) between the metal and powder.

For epoxy polyester powder coated items destined for internal use - iron phosphate is surficient - we class it as a very good surface cleaner - it will/may improve the adhesion of the epoxy polyester powder (?). Most coaters would only use this treatment if it is specified by the customer - why add to your processing costs?

Hope this answers the question you posted.

Terry Hickling Martex Paints Ltd    Birmingham, UK

July 18, 2009

can you please clarify the necessity of phosphating before electrocoating of paint in terms of Surface Activation-Phosphating-Electrocoat of Paint.

bhagwat mishra
paint shop employee - amdabad,gujarat ,India

Sir,
Can you please clarify which of two- zinc phosphating and iron phosphating,is preferable for car bodies,and how?

bhagwat mishra
paint shop employee - amdabad,gujarat ,India

Hi, Bhagwat. Unfortunately, readers virtually never reply to abstract flash-card style questions -- which will leave you, me, and the readers unsatisfied :-)

You work in the paint shop of one of the world's largest automobile manufacturers, which has surely acquired mountains of data on this subject. So, please: Start by telling us what phosphatizing process you presently use, and why you think it is best, or why you wish to consider switching.

If you put some meat on the bones of your question you will probably start an interesting dialog; but abstract questions almost always remain unanswered even after being viewed by thousands of readers. Good luck!

Thanks.

Regards,

Ted Mooney, P.E.  finishing.com Brick, New Jersey