Broken Tail Pulley Shaft
Broken Tail Pulley Shaft
(OP)
Couple of days ago we had a failure on one of our conveyor's tail pulley shaft.
I added a picture of surface. The speed of the pulley is approximately 120 rpm.
I did a little bit search and it looks like rotating bending fatique? Can anyone who is experienced on failure analysis help me on the type of failure.
Thanks,
I added a picture of surface. The speed of the pulley is approximately 120 rpm.
I did a little bit search and it looks like rotating bending fatique? Can anyone who is experienced on failure analysis help me on the type of failure.
Thanks,





RE: Broken Tail Pulley Shaft
The red frame in the attached picture. It is done simultaneously from both housings. I'm not sure if too much tihtening played a role here,
RE: Broken Tail Pulley Shaft
How many decades did the shaft survive before fracturing?
As for overtightening, it happens, but usually not with experienced millwrights, unless the design was wrong from the start.
As an engineer, you can estimate the power required to drive the conveyor, turn that into belt tension, and do a free body diagram on the shaft.
The most obvious general question is the distance by which the drive pulley extends past the closest shaft bearing; ideally it's zero, but a couple of shaft diameters is usually OK. I can't guess anything about the shaft arrangement or the belt drive from photos provided so far.
Mike Halloran
Pembroke Pines, FL, USA
RE: Broken Tail Pulley Shaft
RE: Broken Tail Pulley Shaft
RE: Broken Tail Pulley Shaft
This was a newly installed conveyor, it just run 1,5 months and then we have faced with this failure. To be honest i don't think it is a design issue, thats why i didn't go through with the calculations. But i will for sure now.
Lukin
I added another photo, it is broken just from the pulley to shaft bushing. I'm not sure if they were tighten equally, this happened in a weekend and guys replaced the pulley immediately. There is a big chance that operation group tightened them unequally...
Gearcutter
thanks for the information,we started to think that too much tightening is the issue here. I'm sure it is not fair to ask this question but When you say very very few loads are you talking about hours?
Thanks to everyone
RE: Broken Tail Pulley Shaft
No, I'm talking about load cycles. In this case..........rpm under load.
RE: Broken Tail Pulley Shaft
http://www.eng-tips.com/threadminder.cfm?pid=330
Keep the question you post specific to the fracture zone and its appearance.
Be careful that you do not copy this post and then re-post in other forums as this is not allowed, it's called cross-posting.
RE: Broken Tail Pulley Shaft
Link
Thanks,
RE: Broken Tail Pulley Shaft
Was this a new machine, or reconditioned, or just a "good used" machine.
RE: Broken Tail Pulley Shaft
RE: Broken Tail Pulley Shaft
Walt
RE: Broken Tail Pulley Shaft
RE: Broken Tail Pulley Shaft
As for fatigue, assuming just 10/24 and 6/7, we look at +2,5*106 cycles and are well placed for relevant failure. Pls. see attached.
As for overtightening, I would not think that anyone should have been retightening the taper lock device, pulleys being normally delivered as an ready-to-use integral unit of pulley shell + shaft + locking devices. This is, at 1,5 month from delivery, entirely within the scope of mfgrs warranty.
As for checking, this calls for a full blown investigation into
- loadbearing capacity of the shaft zone affected, considering all stress raisers
- metallurgical exam & crack analysis
- load amplitudes and cycling characteristics
- operations (extraordinary events, op. history until failure)
- design environment and influences from pulley bearing & support design
and check this back against the design calculations.
No one should accept to work with a system where such failure might occur again & at random. And from a legal p.o.v. you are now "in" to know there's a weakness which may have severe effect at least for operations material , if not for the operators. What if the belt does really start to burn & starts a fire, which is a real (in my prof. experience) risk with such failure mode?
In belt conveyors, the rule is: "Protect the belt", it's the major item in capex.
Regards
R.
RSVP
RE: Broken Tail Pulley Shaft
Best of luck for you to find the root cause!
It would be very kind to offer your findings & conclusions to the forum!
Thank you in advance,
Kind regards
R.
RSVP