Letter 27047

Risk of not phosphating? [Mexico] 

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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. Without knowing the application and environment, and the type of powder coating, we 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, and will see only interior exposure, and is otherwise well prepared.

You might want to consult a book about phosphating like R. Rausch's book "Phosphating of Metals" [also available used from this link at Abebooks] or Samuel Spring's "The Preparation of Metal for Painting" [available used from this link at Abebooks] 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, NJ

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 problem with my response, Atul. If Mr. Izquierdo was offended, I heartily apologize! My only point was that I did understand his situation.

We edit typographical and grammar errors, etc., so that our readers can read & understand the questions quickly. We very heavily edited Mr. Izquierdo's inquiry, so what you see here is quite 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, P.E. 
finishing.com
Brick, NJ

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 surfice - 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

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