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Epistle on electric motor bearings part 1

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  • Epistle on electric motor bearings part 1

    Folks –

    Sorry in advance for what might be a bit of an epistle. I tend to get long winded at times….

    I have taken the 3 phase electric motor apart on my Raglan 5” lathe restoration project. I had connected a vfd (inverter) to it and ran it up a little when I initially removed the motor from the machine some months back. It seemed to run but there was an annoying squeak that turned into a bit of a screech as the rpms increased. I shut it down and set it aside for later, resigning myself to the fact that I would at least have to open it up and inspect the “innerds”.

    Later finally arrived, and I took it apart a few days back. It’s an open frame style motor and as a result, there’s 50 years of dust and a few chips that were found inside. I gave it a good vacuuming, then wiped down the inside of the end caps with some mineral spirits to clean it up. Here’s a picture of the bits and pieces –



    The squeeking and screech that I heard might be traced to the surface of the armature that looks a bit scuffed, but otherwise in reasonable shape. There’s a few dings here and there, maybe as a result of chips and/or handling during assembly. Here’s a picture of the armature and a closer shot of the surface





    Here’s a picture of the inside of the stator. Fairly decent, with some of the varnish obviously scraped from the surface in spots. There’s a large area of black “grunge” on the left side of the windings that looks like the first point of contact of oil/swarf that made its way inside the motor.



    ----continue to part 2 posting----

  • #2
    Epistle On Electric Motor Bearings - Part 2

    And here’s the inside of an end cover after I wiped it down with mineral spirits.



    The bearings seem to be silky smooth rotating them by hand. The grease has not gone stiff and appears to be in good shape, but I am going to have to replace it as it’s a good many decades old – if it ever was replaced, and the lathe itself is about 50 years old. Like many things on this lathe, there’s a general sense of light use and decades of inactivity.

    Looking at the rims on the bearings I am able to make out some specifications but not all the numbers / letters are visible. The rotor end bearing is larger than the rear end of the motor.

    They both look to be single shielded or single sealed – I am not sure how to tell myself but someone may be able to advise me on this. I can take some more detailed pictures if needed.

    Here’s an example of the bearing at the rotor end. The sealed/shielded ends are the ones towards the inside of the motor, with the open ends being protected by the counter-bored recess in the ends caps.



    -------------------------------------
    Rotor End Bearing Markings
    120P V3
    ENGLAND
    HOFFMANN
    -------------------------------------
    Rear End Bearing Markings
    ?2037
    ENGLAND
    6 PT
    --------------------------------------

    I do not want to pull the bearings off and replace them as they appear to be in great shape. I do however want to wash out the grease and re-grease them. This brings me to the list of questions that have come to mind.

    1 - How to flush out the existing grease without removing the bearings ?
    My thoughts here are to immerse the ends in a little jar of gas (petrol) or mineral spirits and let it sit and/or slosh it around with a small brush to assist. Any other tricks or tips people can provide here? I guess the trick is to make sure the assembly is completely dry afterwards to ensure no contamination with the new grease being placed in the bearings. (I have read about the problems with mixing different types of grease). I have no problem letting things sit for a period of time to dry if needed – I’m not on any clock here.

    2 - How much to pack into the bearing by hand when re-greasing?
    From my diggings it seems to be 30-50% but I was thinking of using a syringe and poke the grease in that way, around the cage and roller elements. I understand the main purpose of the grease is to contain the oil for the bearings and too much will end up overheating etc.

    3 – A friend of mine has recommended the use of NLGI-2 grease for this application and sent me a great .pdf from Exxon Mobil explaining the ins and outs of greasing electric motor bearings. I’m going to search out this stuff later this week. However, looking though this document revealed that the greasing “ports” on my motor are not like the standard industry things on the larger HP motors. There’s a single port with a little screw in the end that you take out for adding grease, but there’s no “exit” port to allow for flushing the old grease etc. In fact, the design on the inside of the end cap shows a very small opening where the grease could get into the open side of the bearing. This has me to wondering if it’s even of any use. I mean you can only jam in so much grease with no exit being provided for ! Being ignorant on this subject, I must admit that I poked some oil in these before I ran the motor up for the first time. Anyway, if anyone has some comments on all this – fire away.

    Here is a picture of single port on each end for grease. Note that the orientation on the machine is as shown here – the electrical fitting coming out the bottom and the grease port/tube running horizontal. Not exactly a gravity feed system !



    Here’s the inside of an end plate showing the grease entry point into the open side of the bearing – not that large really. And again – nowhere for the grease to exit.



    Sorry for the long posting – I tried to get all my thoughts questions and pictures together in one place ! Better than not enough info I guess...

    Thanks very much for any help people can pass along.

    Cheers,
    Lewis

    Comment


    • #3
      Well I've never seen a ball bearing set up like that to be greased without removal. Where does the excess grease go? Nowhere except back into the housing in front of the bearing. The inward face of the bearing might well be sealed, which would be evident by seeing a rubber-faced disc pressed into the end of the bearing rather than a steel-faced disc. The steel-faced 'end cap' is a shield rather than a seal. I can't really tell from the pics, but if they are seals, then grease should not be able to get through. If they are shields, they can be washed through from the open side.

      I would not use any solvent that has additives that could be left behind once dry. That eliminates gasoline, but white gas would be ok, or any of the other normal solvents could be used. My favorite of late is brake clean, since it's easy to blow into bearings to get the dissolving action spread into the bearing carriers. You definitely have to be careful of it splashing back into your face or on your cloths.

      Also my favorite of late has been synthetic wheel bearing grease. I just work it in with my fingers from one side until it looks clean coming out the other side, then wipe out the excess from both sides and call it good. I've had pretty good luck at removing and re-installing the shields or seals without damage, but that's a learned skill as well. With one side open already, you might be able to poke a wire through to push the other seal out. In your case the seal would stay on the motor shaft, but at least you get to clean the residual gunk away. Snapping the seal or shield back in is easy, but make sure you get it fully re-seated.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

      Comment


      • #4
        Ain't got a clue mate, never seen inside an electric motor before ...........
        .

        Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



        Comment


        • #5
          Personally I would remove the bearings and replace with modern sealed types, if the rotor rubbing was caused by bearing wear then then they need replacing anyway after 50yrs use.
          Mic the OD ID and width and any local bearing co will come up with the equivalent.
          Max.

          Comment


          • #6
            Darryl -
            Thanks for the tips. I'll take a closer look at the inside face of each bearing and see if it looks like metal or rubber. It seems to me it's metal, which as you say would indicate it's a shield. I agree, the fact that there's no exit point for the grease is odd. Perhaps the end cover castings are some sort of universal thing and the ports are not even meant to be used. White gas = mineral spirits ?

            Max-
            My plan "B" (distant one at that at the moment) is to remove the bearings and replace with modern ones, but I don't really have the gear to do that, and from the always accurate and never wrong youtube site - I see these fancy things called induction bearing heaters just so that you can slip them over the shaft when installing them.

            Comment


            • #7
              Originally posted by John Stevenson
              Ain't got a clue mate, never seen inside an electric motor before ...........

              Now you have !

              Comment


              • #8
                From this far away, those bearings don't look bad. I am tending to think that the worn markings you're seeing on the armature and field is due to foreign material having gotten in there and rubbed around all these years. But it certainly is possible that the armature is not centered within the field- the endbells could be allowing for that if they don't center perfectly or without play when re-assembled. Of course, if the bearings aren't a snug fit in their bores, that would allow the armature to go off-center as well.

                An aside- I just took apart a dust collector motor that had failed. The bearings were still fairly good, at least they weren't sloppy and gritty. This particular motor had some areas where the windings has shorted to the field laminations. A couple of the lamination tangs had been blown to bits and the copper windings blown to bits in spots. I wanted to save the field laminations for another project, so I had to remove the windings. With any well-made motor this would involve cutting into the wire bundles as there would normally be a varnish or whatnot impregnated into the windings. Not so here- this was a typical shi**y chinese motor with no varnish and only minimal 'string' holding the bundles together. The string had all gone rotten- it was all over the inside of the housing in small pieces, and what remained on the wiring was breaking off easily just by wiping with my fingers. Pair of side cutters and five minutes I had all the wire removed. It should not have been nearly that easy.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                Comment


                • #9
                  Darryl -
                  No issues with lack of varnish on this motor - there's residue all over the place and the field windings look like they are really tight and glued together with it.

                  I just ran out to the workshop and checked - the closed end of each bearing is metal - not dark rubber. So it looks like I have single side shields on these bearings. There`s no hint of grinding or rough running when turning the bearings by hand - they are as smooth as silk.

                  And an unrelated question to the bearings - is there an easy way to wash off the black goo that has accumulated on the inside of the field windings in one spot over the years? I seem to recall that WD-40 would work but I don't want to use something that's going to strip off the varnish. I could just leave as is if there's any doubt as there is not that much of it.

                  Thanks,
                  Lewis

                  Comment


                  • #10
                    There are various spray-on cleaners/washes, like "Electro-Wash" and the mass air flow sensor cleaning sprays. They are made of materials which don't damage most electrical stuff. Electro-Wash would be my first choice.

                    As for the greasing, there are supposed to be TWO ports..... you remove the covers/plugs, put a fitting on one, and pump in grease until it comes out the other one. Then remove fitting and replace plugs.

                    The two are normally located so that you won't fill the bearing, which would be bad.

                    You don't have two grease ports, so I reckon your plan of removal and manual re-greasing is best. The new grease should last a good long time.

                    The new Departure manual suggests a hot solution of "Oakite" cleaner, which sounds similar to purple cleaner, a strongish base. Possibly it is washing soda based. Another suggestion that I am told works quite well is pine-sol.

                    Yes, these are water based, but you can do a WD-40 dunk, or another light oil wash-thru, and/or use a hair dryer to dry them, while manually spinning them to assure the water is gone. Using hot solution helps also.
                    Last edited by J Tiers; 06-10-2012, 12:50 AM.
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #11
                      -'while manually spinning them'- this avoids the temptation to see how fast they will spin up using compressed air. Something to be avoided unless you want to destroy the bearing.
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                      Comment


                      • #12
                        Originally posted by darryl
                        -'while manually spinning them'- this avoids the temptation to see how fast they will spin up using compressed air. Something to be avoided unless you want to destroy the bearing.
                        I can remember once a long time ago in a friend's place of work using the compressed air to spin up an old turbine and marveling at the gyro forces at play as we held it in our hands.....

                        Comment


                        • #13
                          Originally posted by LHC
                          Folks –

                          It seemed to run but there was an annoying squeak that turned into a bit of a screech as the rpms increased.

                          The squeeking and screech that I heard might be traced to the surface of the armature that looks a bit scuffed, but otherwise in reasonable shape.
                          I didn't see anyone addressing the squeak or screech.
                          I'm guessing that it was the bearing races spinning in the seats.
                          John M...your (un)usual basement dweller

                          Comment


                          • #14
                            Originally posted by Deja Vu
                            I didn't see anyone addressing the squeak or screech.
                            I'm guessing that it was the bearing races spinning in the seats.
                            I was wondering if I was the only one concerned about that.

                            The bearings and grease look fine to me, I think the over riding problem is to figure out why the rotor looks like it has been rubbing on the stator.

                            Dave

                            Comment


                            • #15
                              I'm suspecting that the "rub" on the rotor was caused by an excessive radial load on the motor shaft at some time in the past.
                              Those aluminium end caps/housings (I think that's what they are) would have enough flex under heavy side loads to cause the rub.

                              I've seen motors that this "rub" appearance was actually a final tweaking of the rotor during assembly to achieve clearance.

                              Otherwise, as previously stated, debris got in the motor and spun around in there causing it.
                              Last edited by Deja Vu; 06-10-2012, 10:53 AM.
                              John M...your (un)usual basement dweller

                              Comment

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