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Performance of powder coating on blasted surface

I would like to know whether the powder coating film will show same performance on blasted surface as that of Phosphated surface?

ASHISH KULKARNI
- Pune, India
2006

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It is possible to achieve this goal Mr. Kulkarni.

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina
2006

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I don't think I'd quite agree with that Sheldon. There may be very high quality powder coatings that can deliver good performance without a phosphate pretreatment, but I believe that including the phosphate will always improve the coating system -- not only because of improved bonding, but because of the power of phosphatizing to neutralize the galvanic hotspots that fabrication always produces.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

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First of two simultaneous responses --

I agree with Ted on this issue completely. Not only prevention of galvanic corrosion, phosphated surface will also give added adhesion, which may be a problem on a plain blasted surface due to irregularities.

Amit Amembal
- Mumbai, India
2006

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Second of two simultaneous responses --

Dear Mr. Ashish Kuklarni,

Phosphate coating chemically changes the metal surface by forming a non-metallic, non-conductive, insoluble phosphate coating. The phoshate coating becomes integral with and firmly adherent to the treated surface, and insulates the metal against electrochemical corrosion. The most important reason to use a conversion coating is to prevent or retard the spread of corrosion under paint, including the areas near a ruptured film.

The primary use of conversion coatings, however, is for the bonding of paint. Conversion coatings produced on metal are not only stable and chemically inert toward organic finishes, but they are also absorptive and bind organic finishes to the metal.

Failure of coatings in service with problems such as corrosion and blistering are nearly always caused by inadequate pretreatment.

MOST FINISHING PROBLEMS ARE NOT FINISHING PROBLEMS AT ALL: THEY ARE USUALLY STARTING PROBLEMS. THE PRETREATMENT IS AS IMPORTANT, IF NOT MORE IMPORTANT,THAN THE FINAL FINISH.

Please phosphate the components and then only paint the surface; you will save a lot of money and save your reputation also.

S. MEENAKSHISUNDARAM
- CHENNAI, Tamil Nadu, INDIA
2006

I thank all of you for your guidance on the Performance of powder coated film over Blasted Surface. I would like to know specifically that can I use blasting as a pretreatment for powder coating where I want Salt Spray of 500 Hrs. (As per ASTM Method)

ASHISH KULKARNI
- Pune, India
2006

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Unless someone has already done this type of testing and can provide an answer based on their data, it would probably be a good idea for you to do it. Use sample panels made from a substrate that is comparable to your production material, blast each sample or set of samples with different media and grit, paint the samples and send them out for salt spray testing. The results will tell you what you need to know. Keep in mind that product from a high volume production line(if that's what you have, or are thinking about installing) will probably not perform as well as the samples do. A conveyorized 5 stage spray wash, cleaner-rinse-multimetal phosphate-rinse-DI, will give you 500+ hours with steel, 700+ with aluminum. If you decide to do the blast testing, please post the results. Good luck.

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina
2006

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Good reply, Sheldon! Thanks.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007