Yellow Tint

[CuloMalo]

I have recently begun to notice a yellow tint on our lighter colored and metalic powder coat jobs. I think it is because my "painter" is using too much clear. However, he believes it is caused by a mythical smoke that is present in our shop when he removes the parts from the oven.

Can anyone shed some light on this problem? Will applying too much clear to a part cause it to yellow?

[Popeye]

Is the oven well ventilated? Not sure about to much clear but it almost sounds like it's over-cured and possibly cured at to high a temperature.

[CuloMalo]

The oven is 10'X12'X30' and well ventilated. We cure the clear at 375 for 15 minutes per the manufacture's instructions. The problem is not over the entire part, just on the thicker metals. When the part comes out of the color oven and goes into the clear spray booth, it is still very hot. When we apply the clear to the thicker metal (3/8") it instantly gels and becomes translucent. However, on the thinner metals, (12 ga.) the clear remains a milky white.
I think the painter is going back over the thick metal until he has a uniform milky white color before putting it back in the oven, thereby overcoating with clear.

[Harleydad]

Originally Posted by CuloMalo

The oven is 10'X12'X30' and well ventilated. We cure the clear at 375 for 15 minutes per the manufacture's instructions. The problem is not over the entire part, just on the thicker metals. When the part comes out of the color oven and goes into the clear spray booth, it is still very hot. When we apply the clear to the thicker metal (3/8") it instantly gels and becomes translucent. However, on the thinner metals, (12 ga.) the clear remains a milky white.
I think the painter is going back over the thick metal until he has a uniform milky white color before putting it back in the oven, thereby overcoating with clear.

The thinner metal is cooling faster. I think that would explain the milky white. As far as yellowing I've always associated that with overcure. If you're applying the clear that hot it's already flowing out. Try 10 minutes at 375.
Why do you apply the clear hot? Have you tried at room temp?

[bzer1]

I was also told by a few suppliers that almost all clears are are moving to low cure temps. I have a 5lbs box with a cure cycle of 325 for 10 min. I would suggest that you check with your supplier to see if you need to update your cure cycle.

[CuloMalo]

Guys,

Ya'll were right. We recently started using a new clear and no one checked to see if the cure time and temp had changed, but of course it has. I reduced the temp to 330 as suggested and it works like a champ. Thanks for the insight.