Corrosion Cause by Varnish and Countermeasures

How

1. When heat and RH are high, the bearing would rust after grease absorb corrosion gas that varnish volatilization inside the motor.

Why

1. Most happen to TEFC motor.
2. ODC motor wrapping with PE bag.
3. During manufacture and storage with high temperature and humid environment (ex. form rainy season to summer、RH at 70% ~ 80%).
4. When grease base oil consist of synthetic oil rust more easily compare to mineral oil and silicone oil.
5. Solventless based varnish rust easily than solvent based varnish.
6. Varnish improper drying time.

Characteristic

1. With direction, especially near the rotor and stator inside motor, same as bearing.
2. Interior rust more than exterior especially the parts contact with grease.
3. Grease with bad smell (even to unpleasant odor).
4. Rust pattern grow form point to line and final plane.

Prevent

1. Use solventless based varnish.
2. Use without contain non-acid solvent based varnish.
3. Adjust the drying time：low temperature with long drying time is better than high temperature with short drying time (ex. 130℃/3hr better than 150℃/1hr).

Suggestion

1. Do not install the rotor or stator into motor after varnish drying instantly, suggest that to storage at ventilation place let excess vapor vanish.
2. During storage and transportation, avoid heat and humid environment cause varnish volatilization.