5 Replies Latest reply on Oct 6, 2014 11:36 PM by Daniel Andersson

    is dynamic balancing needed?

    Walid Abid

      Dear All,

      We have a 90kW electrical motor. we overhaul the motor by replacing the bearing, dust seals, stator cleaning...

      this was done because of bearing damage.


      The stator and stator shaft seems to be OK without any crack, wear or damage.

      Could you please advise whether a dynamic balancing for the rotor is needed or not?

      when such balancing is neede?


      thank you in advance.

        • Re: is dynamic balancing needed?
          Daniel Andersson

          Not that much of a Solidworks  question. ..


          What brand is the motor?

            • Re: is dynamic balancing needed?
              Walid Abid

              of course, that is right. But sure there are some people who have a good experience on it and can help.


              Please note that we have one Leroy Somer SL315 motor that we replace the bearing on January 2014. Now, and after 3300hours running time after maintenance, we found some abnormal sound.

              When we dismount the motor, we found the NDE bearing lock nut little loosen and the ball bearing cage was damaged.

              The rotor and bearing seats are in a good condition and no damage is there.


              I would like to ask if any damaged can happen to Leroy Somer SL315 motor which is running continuously for 24 hours during one month.

              Can this affect the motor rewinding, motor bearing, rotor, bearing lock nut…?

              Is dynamic balancing required for the rotor?


              Your quick reply is highly appreciated.

                • Re: is dynamic balancing needed?
                  Walid Abid

                  Could you please advise if any specialized maintenance forum that I can look for help there?

                  many thanks

                  • Re: is dynamic balancing needed?
                    Daniel Andersson

                    In general I would say that you should balance the rotor. You have already put some money into the overhaul and adding balancing is a good preventive action in order to not have more surprises once you have installed the motor. I design electrical motors (for a competitor to Leroy Somer) that goes into applications that is time consuming and have a high cost to disassemble so we always recommend to re-balance the rotor for our applications. But this might be different depending on manufacturer, motor type, application etc...


                    To be able to do balancing you need to have information from the manufacturer. Balancing method and acceptance criteria's is needed and is different between designs. So I can not give you more details than that.


                    Emerson seems to be the company that have the brand Leroy Somer. Try their web site and see if you can get any phone number to call. Or try your local dealer.


                    Your second question about the damage is hard to speculate at. Failure may be for many reasons and sometimes with combinations of different failures.

                    It could be changes in the driven equipment (gearbox, coupling, fan, wheel, etc etc.) that makes the motor to fail. E.g. increased axial force is not that good for a axial locating bearing. Or it could be that the bearing was not really all the way down in its seat after assembly (shaft or shield). Did you install bearings with the correct designations, keep in mind that the bearing clearance might be different from a standard bearing (C2, C4 clearance etc.). Recommend to see the manufacturers manual for details. Be also sure that you apply the correct grease. It might also be that the motor was not properly aligned.

                    There is alot of stuff that might go wrong...


                    I think you could get vibrations if the rewinding went bad. But I have not seen it myself during my 6,5 years as a mechanical engineer of rotating electrical motors. However, I think that this should have been captured in the routine test of the motor. It is also quite easy to make a simplified test by running up the motor and then shut off the power. During the run up and run out of the motor you could listen for vibrations and noises and get a feeling for what is happening. Note that I say feeling, since my experience is that you do not always see what you expect and the cause is not always what you think. E.g sometimes the motor behaves different during run out since it passes different speeds slower than during run up.


                    I could go on... but without seeing the damages and the motor it is hard to tell.

                    Therefore I recommend that you get in touch with a Leroy Somer workshop or after sales person and have a good look at the complete line of the driven equipment.


                    // Daniel

                • Re: is dynamic balancing needed?
                  Stephen Crook

                  90 kW (120 HP), I would *think* so, though this is not my area of expertise, as any vibration due to out-of-balance condition could be hard on the bearings, (possibility a contributor to or even the original cause of bearing failure?).

                  A better forum to ask this question might be: Engineers Edge Engineering Forum

                  Oh, I see you already have posted there! Good.