Q: I was wondering if you would be able to help explain the gel time of an epoxy powder coating for me. I am having some issues with requirements in a current specification.
Specifically, can you tell me in your opinion what the variation of a powder should be? We currently state that the gel time is 52 + 8 seconds.
A: First of all, gel time is a rather subjective test. Results can be very operator related. The gel time range you’re proposing is 44-60 seconds, which is a fairly wide range. If the same operator was running the test, this would be too wide. Taking operator variation into account, however, this may make sense.
What I would do is have three or more operators run the test multiple times to identify the swing in results with a known standard. Then I would consider establishing a target gel time and collect SPC data on a number of batches. Set up arbitrary min and max values, and adjust as you collect more data. I would begin with a +/- 6 second range. Be sure to run the test carefully and in control. Use a consistent quantity of powder and measure and record the surface temperature of the gel plate before each measurement.