Thread moved from General Aspects to proper forum selection ■

A good metallurgist can complete a root cause analysis for you and determine the reason for the failure.

Other possible reasons for failure can be.

1 - lack of lubrication.

2 - improper lubrication.

The bearing would go first and possibly cause a shaft failure. ■

Dear Mr.Subhas,

If the machine is getting overloaded, usually it would be visible. Hope this screen is operated by V belts. V belts would have been slipped. This may be of fatigue failure, though fatigue failure cannot be taken for granted. Was there any maintenance or modification carried out recently on this machine?

Thanks & Regards, ■

Dear Mr.Subhas,

From your reply, my conclusion goes for fatigue only. Shaft getting sheared due to fatigue is a nightmare for maintenance engineer. The worst part is, it is never predictable. I had asked honorable forum members is there any predictive method ? But I think it is not existing, as I did not get any reply.

All you have to do is to ensure is very good design and good quality of materials used in the machine, as for as to avoid fatigue failures.

Regards, ■

It would be very difficult to tell the reason for failure from a picture. Fatigue would start from a crack and progress to point of failure. A good metallurgist could tell the progression my microscopic examination and analysis.

If you want a proper answer hire a metallurgist. If this is critical to your decision making I would not determine the mode of failure based on comments from a photograph posted on a forum. Professional analysis requires the correct profession person to do the correct professional examination. ■

Originally Posted by Subhasbec2002

Dear Roland/Gary,

Thank you for the reply.

We normally change all the gear in set if anyone is damaged.Here in this case, bearing was not damaged as it was installed just 10 days back with new bearings.

I am not concluding anything from the comments ........

Regards.

Subho

This is the best feedback we've had in a long time.

I presume that if the bearing was installed 10 days previously and all gears and bearings appeared undamaged then the gouge marks in the casing were not present either at that inspection juncture.

If this was indeed the case then overload due to faulty rebuild, or inspection, is the closest you'll get.

Have you already sent the shaft away?.....you must have plenty of cash! ■

Originally Posted by Subhasbec2002

Dear Mr. Blenkhorn/Mr.sganesh,

Thank you for your reply.

The screen is run by V belt and drive pulley is fixed on top shaft (right side).It then rotate other four shaft by gear drive. The shaft below the main drive shaft was broken. V belt was not slipped and motor was not tripped.Also Recently there was no modification.

The surprising thing is all the bearing (8 nos.) are in good condition and we can rotate it smoothly after failure.All the gear are in good condition also.

Could you please tell whether from the analysis of the fracture surface pattern,is it possible to tell whther this failure is due to the fatigue or over loading?

As we dont have any belt scale to measure how much material is coming to the screen, its very difficult to tell whether the screen was overloaded though it may be one of the possibility which can be checked only after installing belt scale.

Regards,

Subhas

Dear Mr.Subhas,

From your last post, we understood that all the bearings were replaced 10 days back. What were the reasons for replacing those bearings? What are the recommended bearings by the original equipment supplier and what were the bearings fixed before 10 days for this machine, particularly at the sheared end.

Please reply at the earliest, so that we may further analyse about the possible reasons.

Thanks & regards, ■

This vibrating mechanism is unnecessarily complicated. After 10 years and shaft and gears failures I would suggest replacement of long shafts. One of the reason of failure could be incorrect installation of gears.

8 bearing vibrator is too complex(unreliable) and too expensive - I would suggest design simpler mechanism.

Regards

Ziggy Gregory ■

Dear Subhas,

would you please send a sketch for arrangement of drive, shafts, bearings and unbalance weight on the screen as well as springs?

Meanwhile is there any welded point on the shafts? there are some signs in the photo.

what is the connection of gear and shaft?

first of all, loads on shaft should be analyzed, then speak about overload or fatigue. I mean first load should be defined then overload.

Is the load of material will be on shaft, may not.

In vibrating screen, when you have too much material, first of all the amplitude of screen is decrease and screening become weak. you had this problem? ■

Originally Posted by ziggy

This vibrating mechanism is unnecessarily complicated. After 10 years and shaft and gears failures I would suggest replacement of long shafts. One of the reason of failure could be incorrect installation of gears.

8 bearing vibrator is too complex(unreliable) and too expensive - I would suggest design simpler mechanism.

Regards

Ziggy Gregory

Without knowing why that complex gearbox was installed in the first place I am with Ziggy all the way.

Regarding replacement with a simpler machine consider that:

You've had your money's worth;

Repairs to the expensive drive don't work;

We don't know why those repairs don't work;

Present repairs probably might not last very long;

A metallurgical review might cost as much as a new simpler screen mechanism;

What is the life expectancy of your plant?

It is also noted " There is no data in design document.". What data were you really looking for?...and in what design document?

What about an answer on the gouges? Are there marks in the cover? ■

I second the opinion of Mr.Ziggy Gregory. Unbalanced shafts mechanism is outdated and replaced by exciter gearboxes. Replacement of gearboxes would be faster than replacing the shaft at the site. Repair work of exciter gearboxes can be done at workshop.

In unbalanced shafts machine also, manufacturers suggest to keep total vibrating unit as a spare. However replacing of total unit will take much more time compared to that of replacing exciter gearbox. It would be very bulky.

The decision of replacing present machine by exciter vibrating machine is left to the end user, depending on the economical viability and site conditions.

The wrong tolerance or fitment procedure would have caused the fatigue failure.

If the shaft were locally made( not by OEM ), not following stress relieving dimensions or improper material would have also caused this shearing.

Mr.Subhas is requested to post the root cause of the failure.

Regards, ■

Originally Posted by sganesh

.....

....

Mr.Subhas is requested to post the root cause of the failure.

Regards,

Originally Posted by Roland Heilmann

...... "Could be fatigue", but fatigue cracks grow thanks to insufficient local strengh. Your shaft's broken end surfaces are partly worn away, so as Gary says, its a specialists job for crack analysis --> $. Metallurgy will at least find out whether the material was faulty, but yes, it's $ again. Following Mr. Ganesh, I put the same issues on the shafts: ....

is there by any chance already some feedback? It would be most kind to share your findings, so that one could learn and also check on someones own input.

There is agreement that the shaft has failed and very little other coherent information. We could rephrase the question thus "What might be the cause of the root failure?"

Although the unbalanced shaft design might be out of fashion and complex it is 10 years old and has worked OK for that time. The trouble can only be due to old age (what is the design life?), misuse or faulty maintenance. For me, the last option sticks out like an examination cheat. ■

follow this LINK, quite interesting reading: hope this helps.

http://www.maintenancetechnology.com...achine-shafts/

...............................................

Originally Posted by Subhasbec2002

Dear Experts,

Recently we have one shaft failure in our screen. Please see the pictures.

Now as I understand, there can be two reasons for shaft failures..

1. Fatigue failure

2. Overload

Is it possible to tell after seeing the shaft fracture surfaces whether the shaft fails due to fatigue or due to overload?

Our shaft in screen exciter is running for last 10 years...So I am thinking it may be due to Fatigue failure also.

Could you please tell How much is normal fatigue life for shaft in screen exciter? There is no data in design document.

How to proceed for Root cause analysis? Microscopic analysis can reveal anything whether its fatigue failure or overload failure?

Regards,

Subho

■

Originally Posted by Subhasbec2002

Dear Experts,

Recently we have one shaft failure in our screen. Please see the pictures.

Now as I understand, there can be two reasons for shaft failures..

1. Fatigue failure

2. Overload

Is it possible to tell after seeing the shaft fracture surfaces whether the shaft fails due to fatigue or due to overload?

Our shaft in screen exciter is running for last 10 years...So I am thinking it may be due to Fatigue failure also.

Could you please tell How much is normal fatigue life for shaft in screen exciter? There is no data in design document.

How to proceed for Root cause analysis? Microscopic analysis can reveal anything whether its fatigue failure or overload failure?

Regards,

Subho

The damage is due to fatigue and continued use ending in a shaft failure.

It all depends on the duty cycle of the screen and the loading which affects

the shaft life so that is not an easy thing to determine unless you can provide

us with the needed information.

Its time you changed the bearings, shafts and gaskets to prevent any more issues.

I hope you looked at the oil and put a magnet in it before you drained it and

disposed of it.

The Bearing life B-10 life in one example is affected by the operating speed,

the lubricant used and the duty cycles and shock loading.

It is time to tear the screen down; replace the shafts, all the tapered barrel roller bearings,

and the side plates of the screen and then put it back into service.

The pictures speak volumes to me as the bearings are not at all healthy, Which manufacturer

of bearings was used to replace the old bearings?? ■

Originally Posted by Roland Heilmann

Hello Mr. Zaharis,

would you be so kind and share some of the content of those volumes, quote: "The pictures speak volumes to me as the bearings are not at all healthy"?

I'd very much like to learn something here!

Thank you very much in advance, & with

Kind regards

R.

==================================================================================================== ====

Hello Roland,

I would hope you are not interrupting your evening reading

this like most of us "Bulkoholics", haha!!

If you enlarge the pictures Roland and look closely at

one or more of barrel bearings you will see gaps and the

metal in the bearings does not shine at all.

The other major item that jumps out is that there are gaps

between the bearings and there should be none period!!!

It all comes down the bearings metallurgy, the shaft(s) metallurgy,

the duty cycle, screen loading or overloading that we do not know

yet or may never know. ■

Hi everyone

I think it is fatigue failure, it is obviously seen from the picture, half of broken shaft is smoothy, and half of broken shaft is rough, this is meet the feature of fatigue failure.

fatigue failure is formed from the scratch of surface of shaft or crack of shaft, so during the fabricating of shaft(if it is very important) , some measures should be taken including heat treatment, aging treatment.

BR

■

Originally Posted by Roland Heilmann

Hello Leon,

well, I take this forum to be part of my professional input into this world ;-) & also very much of a training (honestly!), so instead of smoking there's this other habit...

Making something of those pics provided kindly by our OP (hopefully not scared away but listening at least), & concerning the bearings, I'd think:

The larger daylight overview pic has perhaps been done some days (weeks) after the event. Whereas the smaller detail pic of the shorn shaft & resp. bearing has maybe been made rather earlier...

But independent from that, my comments on these pics:

Attachment 43871Attachment 43872

But I see no gaps except for what is provided for by the cage. Pls. point me to the point... Some scratches may have been due to bits of the shaft, and the bearing seems indeed rather fresh, on the detail pic. Pls. see my comments on the pics.

P.S. On the shaft / Mr. Jiang:

I'm not sure. The broken surfaces have imo run against each other for some time still, thus perhaps the smooth appearance. I miss those nice wavelike lines of rest.. and the velvet smoothness. Perhaps it's an overload event, together with a brittle failure mode. But it's a guess again, see further up the line..

Thanks, & Kind regards

R.

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Hello Roland,

I quit smoking 25 years ago when the they were $1.85 USD a pack and

smoking heavily.

Roland-look closely at the end shaft to inner race mating surface on all four bearings

and the outer races of all four bearings not good, not good, not good in my opinion

There should be no space exposed space period.

Look at the bearing at the top right-look closely very closely, what do you see perhaps a metal chip???????????????

The circlip does not appear to be fully seated on the top right bearing.

Old shafts and new bearings bad idea, new shafts and old bearings bad idea.

installing new bearings with old bearings is a bad idea, poorly made bearings bad idea.

Still suffering from the lack of information withdrawal.

As we have no idea what the unexposed shaft ends/seals behind the bearings look like

that is another issue for us to ponder. ■

Basically I would like to know more about this type of screen: 8-bearing vibrating screen

Is there any text?

I have not found anything in VSMA nor Google. ■

I quit smoking on 21st July 1978 when Chesterfield Filter were dirt cheap. The accupuncturist saved 3 other guys from the drawing office before his receptionist's husband shot him dead because of their affair. Perhaps this thread should be buried. Unlike the receptionist's husband we seem to be shooting in the dark. (He shot him in the clinic during working hours.)

Mohandes has sort of hit the nail on the head. I've never seen nor heard of that type of screen either. It might have some historical interest, but I'm nearly historical anyway. ■

Hello,

Fatigue, fatigue strength and fatigue life is an age old subject.

I suggest you to see the mechanical engineering textbooks (graduate and post graduate level) which will certainly have the chapter on the subject matter. These describes the calculation for service life in number of revolutions and resultant time duration. I have a book which has 60 pages chapter on this, including low cycle fatigue, high cycle fatigue, and so on.

In your case, the screen exciter shaft has already achieved ten years of service life. Is this not adequate ? Instead of waiting for failure, it is better to indicate service life and preventive replacement prior to such failure. This will avoid damage and risk to the life. This will avoid blame for failure and also will have satisfied customer and spares sale.

As is generally known, the fatigue life is also sensitive to sudden change in cross section, notches, surface finish, etc.

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

Author of Book: ‘Belt Feeder Design And Hopper Bin Silo’

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India. Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

John your lucky I was fully seated in my chair when I read your post HAHA.

====================================================== ■

Originally Posted by I G Mulani

Hello,

Fatigue, fatigue strength and fatigue life is an age old subject.

.............

In your case, the screen exciter shaft has already achieved ten years of service life. Is this not adequate ? Instead of waiting for failure, it is better to indicate service life and preventive replacement prior to such failure. This will avoid damage and risk to the life. ...........

Dear all,

As per my experience, shaft shearing due to fatigue failure is nightmare for me. Because shaft fails without any indication. But i doubt the fatigue as the MAIN reason for this failure. The end user had changed the bearings only 10 days prior to the breakdown. There could have something gone wrong during assembly or its procedure or bearings selection. The vibrofeeder bearings are having special clearances and tolerances for fixing at bearings outer race and inner race.

Mr.Subhas needs to answer such questions for my interest.

Regards, ■

Originally Posted by lzaharis

John your lucky I was fully seated in my chair when I read your post HAHA.

======================================================

"Fatigue, fatigue strength and fatigue life is an age old subject."

I beg to differ. Fatigue came to prominence in the early 1950's when airliners began falling out of the sky in big pieces. De Havilland Comets were rather good examples but there were others: Fairey Delta was another. As kids we used to play in an shot down plane in the field behind my home without even knowing the cause for failure or the whereabouts or origins of the pilot. I was the one to presume that it must have been a British model because a German fighter couldn't reach Liverpool. Everybody thought I was very clever so I didn't tell them that I'd gleaned the information from a radio documentary about the Lutwaffe. Does it matter if the shaft failed from fatigue, overload or dodgey steel? It's failed and some answers have been offered before the originator lost interest, realised the options or fired the maintenance foreman.

This thread is, as often, degenerating into repetetive texbook theory. We have no data on operating stresses, stress cycles, previous service history (beyond a 10 day farce), working conditions at site nor any worthwhile replacement history. I think I already mentioned shooting in the dark....but I'll mention it again for this old timers sake. ■