Silver Vein

Question:

I have a small furniture manufacturing company. I recently purchased powder coating equipment and have begun to bring all finishing in-house. I am having a terrible time spraying a color called “Silver Vein” a textured coating. I can get it to look great on a flat sample piece, but when I try to coat one of our chairs, it’s a disaster. The steel chair is comprised of many different thicknesses—from 16-gage tubing to 1/2 inch stock. Most of the tubing comes out great, but the thicker parts and the lower parts come out nearly completely silver (very little or no texture). I’ve tried going thinner and going thicker with very little success. I know it can be done, because the company that was coating for us before did a beautiful job. It seems the range between too thin and too thick is disconcertingly small, but maybe I’m doing something else wrong. I called my powder supplier and didn’t get much help. Any suggestions on where to go? Thank you in advance for your help. P. P.

Answer:

It sounds like your cure oven is not performing up to par. Often texture and vein materials require a minimal threshold temperature to form this look within the coating. If the top of the part is good and the bottom bad, maybe you have heat stratification problems. Stratification problems are defined as having a significantly different temperature at the top of the oven than at the bottom of the oven (difference of more than ten degrees F). Fixing this can be as simple as adjusting your ductwork outlets to as complicated as changing your air circulation fan. Consult the original oven supplier for help.

Similar problems can be caused on different-thickness materials on the same part, as you have in your chair. Heavier-thickness materials take longer to absorb the same heat as thinner materials of the same composition. If the thicker materials do not absorb enough heat to attain the texture or vein, then only your thinner parts will have the vein look and the rest will only be silver. Try raising your oven set point temperature or increasing your bake cycle time to ensure all the parts' materials (both thick and thin) get to the proper temperature. This should make your problem go away. If this does not work, then call your oven suppler to check if your oven has enough energy to heat all your parts to the desired temperature.