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ball bearings and rubber seals

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  • ball bearings and rubber seals

    I have an application where a brushless model motor would be attached to an oil-filled gearbox. What are the chances that the rubber seal on the bearing would keep the oil from migrating through the bearing? Speeds would probably be in the 30krpm range, and the motor shaft is likely to be 3 mm or 1/8 inch. That's a pretty small bearing to start with, and it would be nice if its own seals were up to the job. This would be a step-down gearbox with about a 30 to 1 ratio, and the output shaft would also ride in a bearing needing to keep the oil inside. On the output side the shaft would be about 3/8 diameter.

    Is there a different seal used when oil instead of grease is used? Or does it simply boil down to using a separate seal independent of the bearing?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    Use a separate seal. The grease seals on bearings aren't oil tight. Especially if the gear box builds up a little heat. In fact, don't use sealed bearings. Put a shaft seal outboard of the bearings. Lube the bearings with the same oil.


    • #3
      At 30k rpm you aren't going to be using a traditional external contacting seal - it will burn up rapidly. But... the bearing seal will also - check the bearing manf data on max speed; often 7-8K max for contacting seals.

      There are non-contacting labyrinth seals for such uses.


      • #4
        Might be worth experimenting. My wood router has much larger bearings and it runs over 24k no load. With a tiny shaft OD like that and a good oil, the seals might not even get hot. Even if they stay intact they will seep though if the oil level is very high relative to the inner bearing race. If you use the system oil to lube the bearing (i.e. remove the inner seal) the oil shouldn't be at all deep, barely into the outer race. Even splash or mist from other components is probably sufficient. Personally, I wouldn't write it off without a trial jig of some kind.
        Last edited by chipmaker4130; 07-13-2013, 02:17 AM.