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Structure opening issue - oil patch kind

December 3, 2009

Dear All,

We have patches appearing on panels after curing. we are using structure powder (siemens Grey, 7032 powder). Patch appears like oil mark where structure has not opened and it is smooth on patch. Powder is coated with proper thickness (70 to 100 microns).
Coating Guns are Nordson make Vantage manual Guns.
Recoating and curing would make patch diappear from the panel.

We tried following
- We have re-made the degreasing bath (we use hot degreasing) thinking patches are because of oil residues but it is not helping
- zinc phosphating is happening properly and nail test is showing good phophate coating
- chemical concentrations in Degreasing and phosphating are as recommended by manufacturer
- PH vaues of water is also in range

Not having any clue as to what is causing the problem. Any pointers towards causes would be very helpful.

Chandra Vishwaraju
powder coater - Bangalore, India

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