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White patches under the powder coated film

We are doing clear powder coating(Polyester base) on a buffed and polished aluminium die cast component. The pretreatment process is a clear chromating operation. The component is fully open to atmosphere. After putting component in use, we are facing a problem of white patches under the powder-coated film(Specifically near coastal areas). This problem starts only after a month's time. There is no damage in the powder-coated film also. What could be those white patches are? could it be a corrosion product or something else. Please send your opinion on the root cause for this problem and remedy to overcome this problem.

Saravanan Kanakaraj
Premier products - Gurgoan, Hariyana, India
2004

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Dear Saravanan Kanakaraj

This problem may be appear due to pretreat you are doing mainly degreasing & chromotising step pl look care fully these steps. Temp, time, concentration of bath as recommendation by the pretreatment chemical supplier.Pl check the water break test after the degreasing stage, the water film should not break.This is the important. Or you check that the casting you are you are using is coming with white mark.

Rakesh Sharma
- Gurgoan, India
2004

WHat do you mean by water break up test. please explain.

Manish
- India
2004