×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

motor failure with locked rotor

motor failure with locked rotor

motor failure with locked rotor

(OP)
i have had  two failures with single phase capacitor start motors connected to a  conveyor.  the motor is wired 22o volt  through a drum reversing switch.   in both failures the  rotor was locked  when  the  motor was disconnected from the gear reducer.  the  reducer and drive chain spin free when the  motor is not connected.  when new motor is  installed  machine runs normally and  amperage reading is below  full amp rating.  is the failure  due to end user  overloading conveyor  or is there another  electrical cause such as reduction of  voltage by power  utility ?

RE: motor failure with locked rotor

All I have are questions for now...  are the two failures of the same motor location or separate conveyors?  

Did the motor fail electrically or mechanically?  (in other words, why was the motor rotor locked up?)  a bearing failure? electrical failure internally?  what type of coupling is used (& how does it look after a failure)?  how is the coupling aligned?..

Is the customer giving you all the information on the loading of the conveyor?  who has access to the drum reversing switch and how is it used when the conveyor is running?  does the customer monitor the motor temperature at all during operation?  

RE: motor failure with locked rotor

Also, what conditions exist in the area the motor is located? dusty, wet, gritty, etc? Does the motor nameplate indicate TEFC?  

RE: motor failure with locked rotor

(OP)
pablo
   thanks for responding       the motor in question is  a  c face  mount, tefc   the shaft when examined shows  no remarkable  damage and its'  removal from the reducer quill is  easy ... there is no smell of  burnt insulation  and  yes  the  failures occurred on the  same  conveyor   the customer of course is not monitoring the  temperatures  the conveyor is used to bring  product  from  a street  level loading  area  to the basement   the  conveyor is used by a wide range of personnel.   there is  starting and stopping  under  load  but this  not  unusual  for this type of  conveyor application     the  switch  shows  no sign of damage and the contacts  show  continuity    i was wondering if it  were possible that there is a flaw in the motor manufacture  either  with the  bearing  or the windings    or perhaps if  incomplete engagement of the  switch when used  frequently by store personnel  were creating a low voltage  condition   i checked the  incoming  power and  it is within the  nameplate range

RE: motor failure with locked rotor

It sounds most likely like a bearing failure.
There are of course numerous possible causes of bearing failure.  Disassembly/inspection might cause some clues. Some items that come to mind:
- The gearbox is imposing excessive radial loading on the motor bearings.
- contamination of the bearings by the environment
- improper greasing of the bearings - overgrease, incompatible grease, etc
- severe operation causes high temperatures which cause all the grease to run out of the bearing.


RE: motor failure with locked rotor

I, like pete, think it might be a bearing failure... it might be that the gear reducer is worn (you mention starting and stopping frequently under load) -- check the gear reducer where the motor connects for any play axially or radially in the shaft...  I think your motor inboard bearing is wearing out and gauling enough to lock it up (but it's only a guess without taking the motor apart...

RE: motor failure with locked rotor

When you removed the motor was it STILL locked?

If the windings are not burned I would suspect a bearing failure.

Can the motor be banged around in any way to put it out of alignment? Could it be hit by personnel or objects?

Make sure personnel are FULLY engaging the drum switch!

Have you confirmed the voltage AT the motor leads, WHILE she is LOADED?

Does the motor come with a manual overload?

RE: motor failure with locked rotor

good points Pablo and Steve.

Street level- is it outdoors? TEFC does not necessarily mean the motor is suitable for outdoor use... It needs suitable degreee of ingress protection, something like IP55 or better to make sure the bearings are suitably protected from the environment.

RE: motor failure with locked rotor

(OP)
thank you everyone for your repsonses   the motor in question does retain the rotor  lock  when removed from the  gear reducer  there is  no apparent  play  in the  reducer  quill after removal     since it is installed in a  fruit  store in nyc  it is  difficult  to  monitor  use and all personnel    the most striking  problem is that the  failure has occurred  twice  within  2 week sof each other with brand  new  motors  and a new reducer   the reducer turns  freely  by hand  and  no apparent  binding is evident    i can't  see how a bear could  fail so quickly  and  without  resultant  noise or other evidence   at  present  i'm  inclined towards  the  incomplete contact within the  drum switch  cause   can a locked rotor  be caused  by a voltage problem  such as  this?   unfortuneately it is  impractical to disassemble the  motor  for inspection

RE: motor failure with locked rotor

A reversing switch not making good contacts can make a motor sound like it is locked up.

Disassembly of the motor would be most revealing as to what happened. I suspect you will find either just the run or start windings burned and have melted the insulation so as to lock up the rotor!

Before you replace the drum switch (replace it with one that is twice the HP capable), do a conveyor load test. Load it up and stop it repeatedly and confirm that it can start the conveyor under those conditions each time!

A motor with a manual overload is what I suggest. This of course means running a line leg through the overload first and then back to the switch.

RE: motor failure with locked rotor

I have never heard of insulation melting in a fashion as to lock up the rotor. But then again I work with large industrial motors, not small ones.

RE: motor failure with locked rotor

Hello conveyorman53

From the information of the previous posts it seems that your motor is failing due to siezed bearing/bearings.
In some cases motors can burn up and some wire strands gets caught on the rotor cage fins causing locking.If this was the case,the bearings would not necessarily be faulty.
I don't think you have mention that anywhere.
There is a possibility (albeit remote) for C flange motors to fail with drive end bearing siezed.It happens because of a lot of slop (looseness)on spigots causing motor to be badly misaligned when it is bolted down.This misalignment
can be severe enough to preload the DriveEnd bearing to destruction.
We have to rebuild spigots on large Generator Armatures for that same reason.After a few assemblies and disassemblies,spigots can get fairly sloppy.Your motor most likely has a shaft Spline that inserts in  the Gearbox.They will not tolerate too much misalignment.  

GusD

RE: motor failure with locked rotor

Pete..

Smaller motors I have seen have a slot liners and top stick that look like plastic... and when the motor is overloaded, they sure do MELT like plastic. ;)

RE: motor failure with locked rotor

Have personnel been trained on proper use of reversing switch?  Or, is it possible that starting circuit is improperly wired so that the start-winding and/or its associated capacitor are not adequately connected?

RE: motor failure with locked rotor

Finally someone asked about the run and start capacitors.  I don't think that a fault in this area would cause bearing failure though.  At this point should opt for misalignment and  check for it.  Be agressive. Cut the motor open with a cutoff wheel or something.  Especially if it occurs again.  See if motor burn or bearing.  Home in on the symptom.  Speculation could go on indefinitely.  

RE: motor failure with locked rotor

(OP)
thanks for the  responses     after having  changed the motor  the  problem  has not  reoccurred in the  past  few weeks     the  theory of  misalignment is weakest i think  the  reducer is  new  as  was the original motor and there is  no  slop in the  fit  at the quill....  it would  also seem less likely that the  failure was due to  the  bearing  since  the  wear time on the  motor  was only  a few  weeks...  of couse the porblem  here is that  to get  credit from the motor  supplier  cutting open the  motor  or  disassembling it to  examine it  are  not possible.... this  has  been  a problem  that  has occurred regularly in the  conveyor  industry  with small  floor to floor  conveyors  operating on  single phase motors...  at this point the  burnt  insulation  wrapping around the rotor  to " lock " it  would seem  the  most  plausible

RE: motor failure with locked rotor

Suggestion to the original posting marked ///\\\
i have had two failures with single phase capacitor start motors connected to a  conveyor.  the motor is wired 22o volt  through a drum reversing switch.   in both failures the  rotor was locked
///This can be of a mechanical origin or electrical origin.\\\
  when  the  motor was disconnected from the gear reducer.  the  reducer and drive chain spin free when the  motor is not connected.
///The conveyor still may be the culprit as well as the motor mechanical internals.\\\
  when new motor is installed machine runs normally and amperage reading is below  full amp rating.  is the failure  due to end user  overloading conveyor  or is there another  electrical cause such as reduction of  voltage by power  utility ?
///If the motor is sensitively protected (this has not been addressed yet) and the power quality is right, then the motor electrical portion will not show major symptoms, e.g. burned wiring, smell, etc. Even, if there is some wiring melt, it should not be catastrophical to lock the motor. If the motor is not sensitively protected, then the wiring melt may cause the motor to be locked.
The mechanical failures have been addressed in the above postings. The single phase motor may have a centrifugal switch that might disintegrate and potentially lock the motor. Also, the rotor cage might experience mechanical malfunction that may lock the rotor.\\\

RE: motor failure with locked rotor

I would suggest that you observe how the switch is used to operate the conveyor.  My guess is that someone is using the switch as a form of speed control, jogging, by either teasing the switch or worse by switching it on and then hitting reverse to stop the belt rapidly.  In either case the 'on-time' of the motor will be short and the cooling fan won't reach full speed causing overheating.  Also, the reduction ratio wasn't stated but there may be a lot of 'wind-up' in the gear box before the belt starts moving or changing direction.  The net result is a lot of mechanical stress on the motor which in combination with overheating is a formula for early motor failure.

RE: motor failure with locked rotor

Suggestion to the previous posting: Such operation would probably burn the motor winding. This would be easily detected.

RE: motor failure with locked rotor

jbartos, an open in the stator winding would probably not result in a locked rotor; however, it would be an indication of very abusive, high heat conditions inside the motor housing.  Induction motor rotors can have cast aluminum rotor bars and end connections which become overheated and deform and/or melt, which in combination with constant reversing or plugging, may cause an unbalanced rotor and contact with the stator.  Also to be considered is the construction of the rotor shaft, how the laminations are attached, and whether the bearings were intended to take any thrust loading due to end play.

Conveyorman should cajole (hey, we're from NYC!)the motor manufacturer to disassemble the end-bells and check the bearings, if the rotor moves freely so much for my overheating theory.  If not then saw the motor in half lengthwise and see where the rotor failed.

Here's a thought that just occurred to me- is any type of crud getting sucked into the external cooling fan housing and jamming the rotor?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources