Q: I have a question for you about allowable oven temperature variation. Our ovens were recently calibrated and were 1° off from our control unit reading to what was measured inside. Due to our ISO regulations, I may possibly need to shut them down until it is exact.
I know we need to keep temperature variations minimal, but this sounds ridiculous. Our powder manufacturer’s technical data sheets are specific in their writing of proper cure (20 minutes at 400°).
What is your knowledge on what is acceptable and what is the best way of documenting this? Should I approach all of our manufacturers and have them revise or state what is acceptable?
A: Yes indeed, this is way overkill. Virtually all industrial ovens in the coatings industry cycle over a reasonable temperature range. Tuning an oven to an exact temperature is outside of the design of an industrial oven or the needs of curing a coating, powder or otherwise.
Although technical data sheets do not explicitly state that a temperature range is acceptable, a reasonable swing of +/- 5°F is acceptable. What is most important is the actual part temperature, which, in turn, affects the curing condition of the coating that was applied.
Even with an oven cycling temperatures over a modest range, the part temperature changes less than the oven air temperature due to the mass of the part. For example, if your oven cycles +/- 5°F, the parts (depending on their mass) may be cycling +/- 2°F – which is totally acceptable for conventional powder coating technology.