Q&A: Powder Coating
Temperature Requirements
What are the air, humidity and temperature requirements in a powder coating operation?There are two parts to this question. One relates to ambient air temperature and humidity; the other refers to compressed air.
Ideal ambient conditions are temperatures of 68 to 80°F, with 40 to 60% humidity.
Temperature and humidity of the compressed air are even more important. Here, for corona-charging systems, the pressure dew point of the compressed air should not exceed 35°F (3°C) at 100 psi (690 kPa) line pressure. For tribo-charging systems, even lower compressed-air humidity is desirable, with a pressure dew point below 32°F (0°C) at 100 psi line pressure.
Flow Control
When we set our powder regulators to the rate we need to get the minimum film build, we never get the same results we did the time before. Are we doing something wrong, or is it the equipment?No. At least not anything you can fix. It's very common for manual regulators to vary a lot each time they are readjusted. That's due to the device and the operator's ability to read and set the gauge. You can now purchase digital flow-control modules that are automatically set to the right flow rate. These are far more repeatable and can save money by applying just the right amount of powder without wasting any. The other advance in flow control is a "closed loop" device that adjusts the regulator automatically if the plant air changes, which it does.
Powder Coating Wood
We've been spraying metal parts for several years now and we want to start powder coating some MDF parts. Will we need to change any of our powder equipment?Usually the same equipment (booth, guns, etc.) can be used for wood. You will need good, clean air to fluidize UV-cure and low-temperature powders; they tend to be sensitive to heat and humidity. Some different preparation and application techniques may be needed, so you might want to contact a powder equipment manufacturer and do some testing in its lab. Of course, coating MDF may or may not require some different process equipment, so consult your powder manufacturer about what type of preheat and gel ovens and UV equipment they recommend.
Powder Output Rates
I have to use very high pump-pressure settings to get the right amount of powder to discharge from the gun. This limits our ability to adjust powder-output rates. What can we do to work at lower pressure settings?This problem is typically caused by one of the following:
• Worn powder pump venturi throats
• Excessive hose lengths between the pumps and guns
• Improper (too large or small) internal diameters of feed hoses
Inspect and, if necessary, replace the venturi throats of the powder feed pumps. Avoid having excessive hose lengths. Use hoses from the equipment supplier, or ask the equipment supplier about the recommended powder hose diameter.
Color Change Times
My company is a custom coater used to spraying a high volume of a single color. A customer just introduced a new product that requires frequent color changes. How quickly can we expect to change colors on our cyclone booth?With the equipment available today, you should be able to change colors in about 10 minutes. A few things that can help make color change faster include a cyclone system that makes it easy to clean out the cyclone, a feed center that makes it easy to change colors by pumping straight from the powder box, and a booth that's designed for fast cleanup. If it takes longer than about three or four minutes to wipe down the booth, you won't change colors in 10 minutes. Another tip is to look for a booth made of one of the newer materials that attracts the powder less, making it easy to clean. Powder clinging to the walls of the canopy makes quick color change much harder to accomplish.
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