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  1. #1
    Join Date
    Jan 2004
    Location
    Mackay North Qld
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    4,900

    Default Oilite bearings in Electric floor fan - continued

    As mentioned in the General MetalWork Forum I suffered a bearing failure in my floor fan.
    Complete disassembly showed it to be, not a oilite bearing, but a steel one and a semi spherical shaped one to boot.

    There was brown tarry crud present which I surmise was formed by cockatiel dust and light oil.

    Our local bearing emporium did not keep oilite bearing in that ID or configuration.

    Long story short, I decided to fit a ball race and duly spun up and adapter in the lathe.
    I had to fiddle about a few times with assembly and disassembly to get what I thought was the right end play.

    Now the strange part.I assemble the motor and was able spin the rotor freely and had about a mil and a half of end play.Switched the power on and it buzzed and locked up. Turn the power off and it was back to spinning freely. Does the rotor have to be in a precise axial location so the induced field can work properly?

    Can any one suggest what I might have done to cause this situation?

    Grahame

  2. #2
    Join Date
    Sep 2012
    Location
    North Yorkshire UK
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    2,665

    Default

    Hi Grahame,

    Two things pop into my mind, first is the front bearing OK and second are any of the laminations loose ?

    There is a third but there could be a voltage leakage to the frame via the bearings, I've only met this once or twice, but its most unlikely.
    Best Regards:
    Baron J.

  3. #3
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    4,900

    Default

    Quote Originally Posted by BaronJ View Post
    Hi Grahame,

    Two things pop into my mind, first is the front bearing OK and second are any of the laminations loose ?
    The front bearing ( the fan end ) is still the original and had not been removed and was still centered and crimped in place by the folded tags. The laminations are still ok. I threw the rotor up in the lathe and verified it was running true.

    I had suspected the shaft might have been bent, but it was still straight.

    One of the paper insulators had cracked and broke off the the one of the wire tails of the stator but apart from that there is no other physical damage.

    The original bearing was a steel semi spherical unit-basically a ball with flats at each end where the hole went through. It was not insulated from the exterior motor frame.

    Grahame

  4. #4
    Join Date
    Sep 2012
    Location
    North Yorkshire UK
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    2,665

    Default

    Hi Grahame,

    There is very little clearance between the rotor and stator ! Assuming that you have your new bearing accurately centred, then the only place you can get movement is the front bearing. Those balls with holes in them, the bearing, can move very slightly and if the rotor locks when the power is on, it is because the rotor has contacted the stator, the magnetic field sticking them together.
    Best Regards:
    Baron J.

  5. #5
    Join Date
    Jan 2004
    Location
    Mackay North Qld
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    4,900

    Default

    Quote Originally Posted by BaronJ View Post
    Hi Grahame,

    There is very little clearance between the rotor and stator ! Assuming that you have your new bearing accurately centred, then the only place you can get movement is the front bearing. Those balls with holes in them, the bearing, can move very slightly and if the rotor locks when the power is on, it is because the rotor has contacted the stator, the magnetic field sticking them together.
    Hi BaronJ

    I checked ffor side play in the front bearing (holder or what ever it is called).
    Sure enough it can be moved from side to side. The front bearing will get the same treatment as its running mate.Rip it out and and replace with a sealed ball race.

    Thanks very much for your advice, it was spot on.

    Grahame

  6. #6
    Join Date
    Sep 2012
    Location
    North Yorkshire UK
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    2,665

    Default

    Hi Grahame,

    I wish I had a pound for the number of times funny noises and locked rotors on induction motors that I had to sort out.

    One of the worst I remember, was a 100 Hp stirrer motor on top of a liquid chocolate tank. That motor never stopped, it ran 24/7. Anyway it started growling. Over a period of 2 or 3 months it got so loud that workers started complaining about the noise.

    They had a new motor but it had to be hoisted up around 30 feet to be able to swap it out with the old one. Now all I had to do was the disconnection and changing over of the wiring after the mechanics had done the swap. The old motor was isolated and disconnected then unmounted. Not a difficult job, could be done easily in the day. I did the re-connection of the wiring.

    A day or so later, I got dragged back to explain why the building was full of smoke and the smell of burning insulation.

    Not my fault, the motor must have been faulty ! That's my excuse...

    It turned out that someone had turned off the steam supply to the tank and the chocolate had set stopping the mixer blades and in turn the motor and causing it to burn out.

    There were three of these tanks all kept liquid by steam pipes inside them. If the steam went off line it was a major problem because the chocolate would start to set. I always wondered why there was never a reserve tank to cover this problem.
    Best Regards:
    Baron J.

  7. #7
    Join Date
    Nov 2008
    Location
    Sydney
    Posts
    86

    Default

    It turned out that someone had turned off the steam supply to the tank and the chocolate had set stopping the mixer blades and in turn the motor and causing it to burn out.

    There were three of these tanks all kept liquid by steam pipes inside them. If the steam went off line it was a major problem because the chocolate would start to set. I always wondered why there was never a
    reserve tank to cover this problem.[/QUOTE]


    Surely there would have been overload protection for the motor?

    Chas.

  8. #8
    Join Date
    Sep 2012
    Location
    North Yorkshire UK
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    Default

    Hi Chas,

    You would have thought so for a motor of that size and value, but smoke it did, and lots of it. My role in that job was as a contractor employed to isolate, lock off, and then uncouple the wiring from the motor and rewire the new motor. Maintenance was responsible for the motor swap. Lots of free chocolate though.
    Best Regards:
    Baron J.

  9. #9
    Join Date
    Jan 2004
    Location
    Mackay North Qld
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    Default

    This morning I made up a second adapter plate for the fan end of the motor.

    I had other priorities, this afternoon and did not get to install it,maybe tomorrow.

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