AC Motor shaft sheared 5

[TheElevatorman]

Just took apart a 1 year old Reuland 3 phase motor, 15hp, 284T Frame. Stopped working, and found the armature shaft sheared off going into rotor. Looked TOO clean, so asking if anyone can shed light on this. Tried to load 2 pictures

 

[itsmoked]

That docx crap doesn't cut it for about 80% of us. Any chance you can post a jpg in here?

You can use the

above for direct posts.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TheElevatorman]

Sorry. Was trying to post more than 1 picture at a time and the DOC was easier.

 

[TheElevatorman]

here's picture 2

 

[TheElevatorman]

OK, may have over done it, but I'll catch on

 

[dArsonval]

Tossing out a guess, it appears to be an [overhung load with rotational bending] fracture... based on the photos posted of the shaft break.

What is the motor's application? Is it a belt drive arrangement by chance?

And thank you for posting pictures!

John

 

[itsmoked]

OK thanks, that worked, as did the close-ups. Thanks!


Yikes. I see what you mean. Not clear on what we're seeing though. Is the bottom picture the shaft having left the rotor and heading into a machine (pump)? What kind of load is the shaft driving would help with the possible answers.

Typical shaft breaks are like this. Something stresses the shaft and then the stress fracture moves across the shortest path until the shaft fails. I could see the HAZ from welding the fan on being the precipitator.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Odd that the shaft sheared not on the outboard of the bearing but on the inboard at the rotor core end. What was that welding for?

Muthu

http://www.edison.co.in

 

[TheElevatorman]

The shaft sheared right going into the rotor. The other picture is of where the shaft goes out of the housing, and that flat end is what was attached to the rotor. It's a hydraulic elevator pump motor. As for the welding marks, have no idea. Was purchased as a new motor. Almost looks like it was "welded" to the rotor. That is almost too flat a fracture.

Thanks everyone

 

[waross]

Could you have had any power interruptions of a second or so?
Re-energizing out of phase with the residual EMF may cause torsional stress on the shaft.
That, combined with the local stress of the welding may have been a cause.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Bill; Don't motor shafts that fail typically shear off cleanly like this one?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

This is a shear failure rather than a torsional one. Such shear failures happen typically at bearing ends, not at rotor core end and most of them are due to tangential loads like V belt pulleys, gears etc. or due to stress risers at the inadequately radiused (?) shaft steps. OP should post the pics of the shaft on the outboard of the bearing.

Muthu

http://www.edison.co.in

 

[dArsonval]

This shaft break is interesting to me because somewhere in my archives of electric motor failures,
I have photographs of nearly the identical fracture as posted by the OP.

I still remember the color of the motor as green, it had aluminum end brackets with no bearing retainers etc.

Not to beat up on Reuland.... but to see this identical failure serves cause that...
perhaps this motor construction was unfit for the service it was engineered to provide.

Note the knurled shaft to provide a "fit" with the rotor laminations and the welds
to assist in holding it fast to the rotor. It's not a solid press fit.
It's not a motor that would endure a lot of mechanical stresses.

None of the above pinpoints the exact cause of the failure. Just highlighting that this particular
name brand of motor or its design has had this type of failure attributed to its history in certain applications.

John

 

[TheElevatorman]

OK, made a mistake. Motor was from a traction elevator. Couple more pictures to offer different view
First picture shows where the shaft is attached to the flange that couples the motor to the brake.

 

[jraef]

I'm wondering if the shaft failed or even just cracked a long time ago, and someone decided that rather than replace it, they would weld it onto the rotor, as in "We can't have the elevator be down for weeks waiting for a new motor from Rueland, so weld it for now and we will order a replacement and put it in when it gets here...".

Then some bean counter said "Is it working now? Yes? Then no need to spend money on a new one..."

Side note: now that we know there is a mechanical brake, it's likely that there is something wrong with the brake system. Elevator motors must have very heavy duty brakes capable of stopping a fully loaded elevator in free fall. If the brake engages while the motor is still energized, you can definitely break the shaft.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[edison123]

Agree it was an inherent crack which snapped the shaft when it was braked. If it is a 'new motor', OP should claim the warranty.

Muthu

http://www.edison.co.in

 

[desertfox]

Hi

Looks like a fatigue failure to me, I can see river lines going radiating from the large dark area which have may of been a flaw in the shaft.
I'll do some digging and post later.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[electricpete]

I'm a little confused, the first and 2nd pictures are both halves of the same break, right?
The 2nd pic shows a keyway.
I don't see the same keyway in the 1st pic. Is it hiding there at around the 6:00 position? Is the shaft keyed to the core? Why would the keyway extend beyond the core?

I guess there was welding between shaft and core endplate at 12:00 and 6:00 positions to prevent core migrating axially on the shaft? Seems to have deteriorated, any idea why? (maybe during the failure).

The plane of the shaft failure seems to be about 1/4" into the core.

What is the purpose of the evenly spaced axial grooves along the shaft? I'm not familiar with it. I get the wild idea that may have been done because they had difficulty assembling and this was easier than remachining the diameters to reduce interference / increase clearance.

Based on the odd location of failure my wild first guess fwiw is there is a manufacturing related stress riser of some kind. I didn't read the other responses closely, I apoligize if I ignored better answers (I don't think I'd know the right answer if I saw it in this case).



=====================================
(2B)+(2B)' ?

 

[waross]

Pete; Now that you mentioned it, take a close look at the 6:00 o-clock position.
I think that I see a keyway with a key still inserted. Not sure.
I suspect that whatever the cause, the welding stress may have contributed to the location.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[desertfox]

Hi

Here is an interesting link:-

https://www.efficientplantmag.com/2012/07/failure-analysis-of-machine-shafts/

I think its rotational bend failure

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein