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Adhesion failures

Problem: Powdered coated hot rolled steel. After curing we have ran cross hatch tests for adhesion. Parts pass. After sitting overnight, before shipping the next day. Cross hatch tests are ran again. Parts fail, temperature is below 60 degrees F. After parts sit in sun or warm up to 80 degrees and tests are run parts pass. WHY?, need help. Parts were ran through the following system:

Clean/phosphate, Rinse, Clean/Phosphate, Rinse, Dryoff oven, powdercoated, bake oven.

Horace Dudley
- Elk Grove, California, USA
2002

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2002

Hi Horace,

I must admit I have never heard of this before. However I would suggest that the parts are not curing properly. Test the cure of the powder coat by performing a MEK rub. The coating should withstand 200 double rubs at a downward force of approx. 2Kg, without any softening of the powder. If there is any softening you will need to cure the powders sufficiently. You can do this by either turning up the oven temperature or slowing your line speed.

Hope this helps,

Drew Devlin
- Lincolnshire