Every few months, the drive motor for an extruder has to be replaced. The replacement is complicated by the fact that the extruder must be shut down half a shift to cool enough to permit safely replacing the motor. It's further complicated by the fact that when the extruder loses its drive it overflows with melted plastic and the resulting mess coats the motor.
The mechanical maintenance supervisor says there are no problems with the gearbox, and the motor is clearly big enough to drive it. He mentioned that since the thermal overloads don't blow, he doesn't see that heat is a problem.
What should you look at?
Motor thermal overloads aren’t temperature-measuring control systems, so not blowing doesn't mean the motor isn't overheating. The motor probably is overheating, but resizing the overloads won't solve the downtime problem.
Carefully examine the thermal environment. Use a thermal imaging camera to measure the heat exchange between the motor and ambient air. Use this as your baseline to compare with measurements after implementing some changes.
If the motor isn't cooling enough to stay below its temperature rating, maybe you could replace it with one that has a sufficiently high temperature rating. For optimal reliability, combine this change with improvements such as these:
Design a mechanical drive system that moves the motor into cooler ambient air
Install a thermal shield between the motor and the extruder
Duct cooler air to the motor
After each change, use the thermal imaging camera to measure where the motor is in relation to its thermal specifications.