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Epistle on electric motor bearings part 1

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  • ogre
    replied
    This thread has been a huge educational trip to read from beginning to end. Thanks to all who said theyre piece!

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  • LHC
    replied
    Well I have been jumping around on the lathe tear down and only today got back to checking the bearings on the armature. I put it between centers on a lathe at a friend's place of business, and used a mag base with a dial indicator. There's absolutely no movement on the needle as we rotated and pushed and prodded each bearing. These things are staying put on the shaft and I'm just going to wash them out and re-pack them when the motor goes back together.

    Thanks once again for all the feedback and tips. The brake cleaner seems to be the only thing that will truely solubize this old grease, and using it on the end housings worked like a charm.

    Cheers,
    Lewis

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  • LHC
    replied
    Originally posted by Mcgyver
    looking at the pics again it seems the rotor was marked all the way around suggesting it is not bent or badly unbalanced...else the marks would be on one side. Are they similarly all the way around the stator? if so that would support the idea that something got in there
    Yes, the stator is scuffed all the way around as well, so that would support the theory of debris. Still easy enough to check the rotor for warp though and will do that in a day or so for "completeness".

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  • Michael C
    replied
    A few years back my 10ee took to making a screeching noise everytime I went above 1500 rpm. Couldn't for the life of me figure it out. Then the motor had a wire break inside. Took the motor to shop and they fixed wire and replaced the *looks good* bearings. Noise gone even at 3000 rpms. I guess every 50,000 hours the bearings need replacing even if they look good. Funny part was guys at motor shop insisted that my DC motor wasn't original to lathe that it must have come from an elevator. I quit arguing with them and let them be right.

    cheers
    michael

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  • Mcgyver
    replied
    looking at the pics again it seems the rotor was marked all the way around suggesting it is not bent or badly unbalanced...else the marks would be on one side. Are they similarly all the way around the stator? if so that would support the idea that something got in there
    Last edited by Mcgyver; 06-13-2012, 08:48 PM.

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  • LHC
    replied
    Originally posted by Mcgyver
    bearings are fairly cheap. And there is the issue that unless you match the greases one can be completely incompatible with another basically making it useless. Then there's the fact that slightly pooched bearings will still seem really smooth at hand turning speeds.

    imo its not worth not replacing them since you have it apart.

    as for noise and the marks on the stator, a contamination of some sort now cleaned out? Set the lathe up between lathe centres. In theory there should be negligible runout at the bearings (rotate rotor not the bearing race) but if there is a bit note it and compare it to runout in the middle, that'll give a hint if its bent/warped enough to rub.
    That's a great idea - thanks ! My lathe is too far apart to set up the rotor between centers - but - I can take it into my friend's place of work and do it there.

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  • Mcgyver
    replied
    bearings are fairly cheap. And there is the issue that unless you match the greases one can be completely incompatible with another basically making it useless. Then there's the fact that slightly pooched bearings will still seem really smooth at hand turning speeds.

    imo its not worth not replacing them since you have it apart.

    as for noise and the marks on the stator, a contamination of some sort now cleaned out? Set the lathe up between lathe centres. In theory there should be negligible runout at the bearings (rotate rotor not the bearing race) but if there is a bit note it and compare it to runout in the middle, that'll give a hint if its bent/warped enough to rub.

    Leave a comment:


  • LHC
    replied
    I'm back with a bit of success - or at least the hint of success. It's been a bit busy the last couple of days but I did manage to find a local source for the CRC Brakleen - original formulation (chlorinated). Did a quick test this morning before leaving the house and put some of the grease on a nail again, and gave it a squirt. Started to liquify it within a short time so that looks like it will work. Another test that I had tried was kerosene - and while it was a bit slower, it was definitely working to solubize the grease as well. After about an hour it was breaking it down and there were little bits left floating around.

    So, when I can get back to the workshop I think I'll try an overnight soak in kerosene and then a few sessions of blasting the brakleen and soaking with that.

    Will update when I get further along, but wanted to say thanks very much again for all the tips and suggestions. The more you learn the more you realize how little you know......

    Cheers,
    Lewis

    Leave a comment:


  • lakeside53
    replied
    Tighen the bolts on assembly.

    The grease is so the outside of the bearing can slide in the bell housing; they needs to move as the rotor expands with heat and allow the wave washer to do its job.

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  • LHC
    replied
    Originally posted by lakeside53
    If you use spray can BRAKLEEN brake cleaner in the red can (Tertachlorethylene - the non-California stuff) it will flush that old soapy grease out. I'd just replace the bearing and be done with it. As Jerry poined you early in these posts, heat (like from a hairdryer) can help.

    The end bells will line everything up. Put a dab of gas on the inside of the bearing housings.

    When you assemble, run it and tap the end of the shafts with a rubber hammer to get it running with minimum noise - this is just removing any assembly stresses by freeing things up so the wave washer (assumed you have one, and if not, you should) can preload the bearings slightly.
    Thanks. Yes, I do have a wave washer. Should I just snug up the 4 long assembly bolts that are holding the two end caps and the center portion all together, before I do the run up and tapping on the ends or tighten them down well? Might not matter much I guess seeing as the wave washer is providing the correct loading anyway.

    What's this "dab of gas" on the inside of the bearing housing business? (Sorry for the dumb question if I am missing something obvious here).

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  • lakeside53
    replied
    Originally posted by Abaker
    I never would have thought of that. I'm so used to the VFD whine I don't even think about it any more.

    I have found that if you run the motor at the max Hz setting of the VFD you get the least whine. If you still have the noise after all this then try that and see if the noise drops off.

    You can't just set it to max carrier unless you are operating within certain restricted parameters. Take care on old motors also.

    The new Hitachi WJ200 series has a nice feature. The carrier frequency can be set such that it is at max (set) until it needs to drop based on motor power and rpm. At lower power/speed it will be as high as 12kz; at high power/speed it will be at 2khz, but you will never hear it because of the machine noise.

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  • lakeside53
    replied
    If you use spray can BRAKLEEN brake cleaner in the red can (Tertachlorethylene - the non-California stuff) it will flush that old soapy grease out. I'd just replace the bearing and be done with it. As Jerry poined you early in these posts, heat (like from a hairdryer) can help.

    The end bells will line everything up. Put a dab of gas on the inside of the bearing housings.

    When you assemble, run it and tap the end of the shafts with a rubber hammer to get it running with minimum noise - this is just removing any assembly stresses by freeing things up so the wave washer (assumed you have one, and if not, you should) can preload the bearings slightly.
    Last edited by lakeside53; 06-11-2012, 01:45 PM.

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  • LHC
    replied
    Well I did a little test with a bit of the grease on the end of a toothpick and some gasoline in a little dish. The stuff did not "melt" as I was hoping, and after some time I swished it around but it still didn't have any effect. Tried mineral spirits next - same result. Based on this, a simple dunking and shaking around is not going to remove this grease easily, and will only end up leaving a bunch of solvents in the bearing. If I can't clean them out, I guess I am pretty much resigned to replacing them, or picking out most of the original grease where I can, adding more, then hope for the best.

    Taking this motor apart is somewhat mindless now that I have done it and see how it's constructed. These 3 phase motors are rather simple actually. I do have a question on putting it back together though - are there any precautions as to proper alignment or do the endbells sliding onto the bearings pretty much line everything up?

    I'm pretty sure the screeching and squeeking was not the vfd whine. It was too erratic at one point and certainly not the constant whine of a frequency drive.

    On the boring out of the endbells - I suspect that if this is in fact what has happened, it was something undertaken by the manufacturer, as the bearings are original England sourced bearings and the electric motor and lathe are all "made in England". The place I got it from bought it new back in the 60s and I'm pretty sure they never opened up the motor - or many other parts of the machine as I am learning as I take it apart.

    Also, picking up the stator assembly after I thought I had it vacuumed out, I could hear all sorts of little bits falling to the cardboard underneath I had on the bench. Here's a picture of rudest looking one.



    Will report back when I get a bit further along .... thanks for all the tips and advice.

    Leave a comment:


  • Abaker
    replied
    Originally posted by Chuck K
    Is it possible that the squealing you heard was the normal sound made by a motor powered by a vfd? I've used them on a few machines and each time the motors that ran quiet when powered by a rpc made an annoying squealing noise when powered by the vfd. Just a thought.
    Chuck
    I never would have thought of that. I'm so used to the VFD whine I don't even think about it any more.

    I have found that if you run the motor at the max Hz setting of the VFD you get the least whine. If you still have the noise after all this then try that and see if the noise drops off.

    Leave a comment:


  • Chuck K
    replied
    Is it possible that the squealing you heard was the normal sound made by a motor powered by a vfd? I've used them on a few machines and each time the motors that ran quiet when powered by a rpc made an annoying squealing noise when powered by the vfd. Just a thought.
    Chuck

    Leave a comment:

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