Recently I encountered a problem of oil leakage from different driving systems SERVO gearboxes. The transmitted mechanical power ranges from 2 to 8 kW, while the motor speed (the gearbox input speed) varies from 1440 to 3000 RPM. Most of the units are 1 stage planetary gearboxes although some of theme are helical-bevel gears.
Despite the gearbox manufacturers (several European companies) are well-known and having significant heritage in this field, these gearboxes all begin to leak from their input seal before reaching 3000 hours of operation. Replacing the oil to grease improves the amount of leakage, but the phenomena still exists. Adding breathers / pressure relief valves, hardening the gearbox input shaft (which acts against the input seal), and replacing the seal material to viton - all made just a small improvement. Furthermore, the same happens even in our air-conditioned lab - so the problem doesn't seem to be related to harsh environmental conditions.

I suspect the root cause is the continuous operation profile (the system runs for 24/7) - which kills the seal many hours before the units operation life.

Inspecting the seal and the shaft of a leaking gearbox did not show strong indications of wear. As suggested here, it may also be a vibration problem, probably coming from the motor.

Any ideas how to improve it? Are there instances out there for SERVO gearboxes running continuously for more than 3000 hours before leakage?

  • $\begingroup$ Well, other questions also come to mind - such as is the environment dusty? Is this causing extra friction on the outside surface of the seal causing it to fail prematurely? $\endgroup$
    – Solar Mike
    Aug 24, 2018 at 10:50
  • $\begingroup$ Actually, the same happens even in our air-conditioned lab - so it doesn't seem to be related to harsh environmental conditions. $\endgroup$ Aug 24, 2018 at 11:13
  • $\begingroup$ Add that info to your original question... $\endgroup$
    – Solar Mike
    Aug 24, 2018 at 11:15
  • $\begingroup$ Have you inspected one of the failed seals? That would give you an idea of how they failed. What is the running temperature of the gearbox? If it's too hot that could fatigue the seal quicker, maybe use a viton seal? If there is vibration between the motor/gearbox, even a small amount of wear would contribute a lot to leakage, minimise that and maybe use a seal with a garter spring. $\endgroup$
    – CraigC
    Aug 24, 2018 at 14:14
  • $\begingroup$ Primarily, find a servo rated for 3000h or more, and if it fails earlier, you can make it the manufacturer's problem. They are probably better equipped for that, know the device better and will be able to pinpoint and fix the problem. $\endgroup$
    – SF.
    Aug 24, 2018 at 17:19


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