Q. I am getting ready to powder coat some brass parts. What temperature should I use, and how long should I keep the parts in the oven? —T.D.
A. The length of time in the oven and the cure temperature depend on the powder material, the mass of the part and the substrate material. You should refer to the Technical Data Sheet (TDS) supplied from the manufacturer of the powder material to find out what the cure cycle for the powder should be. It should have some flexibility so that you can use a lower temperature if you have more time. A typical cure curve might be 400°F for 12 min. If you lower the temperature to 375°F, the time must be extended to 15 min., or if you lower the temperature to 350°F the time might go to 18 min.
Keep in mind that the time listed means peak metal temperature. This is where the mass of the part affects overall time in the oven. If it takes 5 min. to raise the metal to the set point, the cycle time will include 5 min. of bring-up time plus the intended cure time. A heavier part will take longer to elevate to the intended cure temperature.
The substrate material may also be a factor. Steel is more tolerant of high temperature, so the shorter time and higher temperature may work well for a steel part. Castings and some other materials are less tolerant of higher temperature, so a lower temperature and longer cycle may be better. Brass is sometimes sensitive to temperature and may develop some pinholes due to release of trapped air or contamination in the porous surface. Find out how long it takes to bring the brass up to your cure temperature. Use a lower temperature if possible. You can consult the TDS to see how low you can go and still get a good cure. Add the bring-up time to the cure time and you have your cycle. Keep in mind that brass, like any surface, must be clean before powder coating. Ultrasonic cleaning is a good way to clean brass if it is available.