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Surface texture improvement by phosphating?

We do powder coating of heavy machinery parts of steel. We use polyester powder after primer application on shot blasted surface with Ra about 8-10, Rmax about 50-60. The total DFT is about 120-150 microns. The powder coated surface appears not very smooth and most of the problem visibly is due to shot blasted finish. I want to know if iron phosphating or zinc phosphating will improve the surface finish to say Rmax of 25-30? Will the powder coated surface appear smooth after this additional process of phosphating?

Thanks

Srinivasan Subrahmaniyan
- Indore, M.P., India
2004

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2004

Mr Srinivasan Subramanium.

It is creditable that the powder coat adheres so far without an undercoat.

It is necessary for good adhesion to apply either a medium Zinc phosphate , or in rarer cases an iron phosphate. A third route is gaining understanding. This is the application of Alkaline Zinc coating as a pre ttreatment over steel prior to paint..

The advantages of Alkaline Zinc over phosphate.
- Improved adhesion due to better surface coverage.
- Improved corossion resistance due to complete zinc thickness and coverage all over the surface.
- Greater thicknesses possible in lesser timings. ( Thicknesses translate to read grammage per unit area , of Zinc.

Therefore please consider your needs in the light of this information.

Regards

Sincerely

Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016

adv.