Parts aren’t drying in the oven, so the operator cranks the temperature from 80 C to 120 C. The surface looks dry. Pull it out and the inside is still wet. You just baked a skin over the moisture and trapped it.
Drying isn’t just heating
Moisture has to migrate from inside the part to the surface, then evaporate into the air. Crank the surface temperature and the outer layer dries first, forming a dense skin. That skin seals the remaining moisture inside. The part feels dry but isn’t.
What actually controls drying is relative humidity and air movement, not raw temperature.
Vent the wet air
An industrial oven has fresh air inlet and exhaust. Open the damper and pull the moist air out. At 80 C with proper venting, parts dry faster than at 120 C with the door shut. The oven saturates quickly; if you don’t exchange the air, nothing evaporates.
Compare exhaust and inlet temperatures. A big gap means you’re exhausting properly. If the whole oven reads one temperature, the air isn’t circulating.
Air velocity
Still air forms a saturated film next to the part. Moisture can’t cross that film. Add fans and blow air across the parts, and cut the drying time in half.
Watch thin parts. Too much air velocity and they blow around or warp.
Don’t trust the touch
Use a moisture meter or weigh the part. When the weight stops changing, it’s dry. The operator who feels “warm to the touch” and calls it done will come back to trapped moisture later.
