The British Construction Equipment Forum  

Go Back   The British Construction Equipment Forum > EQUIPMENT > Technical Q&A


Reply
 
Thread Tools Search this Thread Display Modes
  #1   IP: 82.132.231.146
Old 16-05-2017, 02:40 PM
volbar1 volbar1 is offline
Secret Master
 
Join Date: Dec 2011
Posts: 82
Default Rod failure

Had the rod snap inside the dipper ram of my 30t excavator the other day, not had anything like that happen before, bit at a loss to see how it happened as the machine hasn't been miss treated or the dipper being contantly banged against the end of stroke but it has done 12000 hours.
I don't know if anyone can see from the picture if it was a manufacturing defect? The top 1/3 of the rod end where there are lines visible is really smooth and the other 2/3rd's is jagged, to me it looks like the jagged bit was holding it all together?Studio_20170516_143837.jpg
Reply With Quote
  #2   IP: 81.147.99.180
Old 16-05-2017, 04:19 PM
hiluxman hiluxman is offline
Elect of Fifteen
 
Join Date: Jul 2015
Posts: 583
Default Re: Rod failure

Looks like a floor in it.

Could of just been a crack slowly getting deeper and deeper until the rest couldn't take the pressure any more...

But I know bugger all about metal and stress
__________________
If in doubt hit it.
Reply With Quote
  #3   IP: 213.78.124.22
Old 16-05-2017, 05:01 PM
EngconUK's Avatar
EngconUK EngconUK is offline
Secret Master
 
Join Date: Aug 2016
Location: Tewkesbury, GL20 8TD
Posts: 51
Default Re: Rod failure

That looks like a standard case of crack propagation. The crack is likely to have started at the 1.30 o'clock position for whatever reason and gradually it opens up with repeated cycling to the point where the remaining material cannot withstand the stress and fails catastrophically. The crack area is relatively smooth because it's been rubbing over the years whereas the break portion has not. Not able to say what caused it - it looks as if you have a dent on the outer ring in the same place but that may just be coincidental.

My opinions, not Engcon's - it's just that I studied Metallurgy and Engineering at Uni too many years ago

Robert
Reply With Quote
  #4   IP: 82.132.228.226
Old 16-05-2017, 06:53 PM
volbar1 volbar1 is offline
Secret Master
 
Join Date: Dec 2011
Posts: 82
Default Re: Rod failure

Thank you Hilux, Robert. The damage around the outer ring was caused when the rod broke out from the cylinder, was suprised how slowly it pulled itself apart, bit of a brown trousers moment though!
Reply With Quote
  #5   IP: 31.49.119.206
Old 16-05-2017, 07:49 PM
V8Druid's Avatar
V8Druid V8Druid is online now
Knight of the Rose Croix of H.R.D.M
 
Join Date: Jun 2013
Location: Druid central, just East of Pandy, Nr. Abergavenny, S. Wales, UK, 3rd rock from the Sun
Posts: 13,429
Default Re: Rod failure

I take it that is right at the shoulder of the machined part of the rod that the piston is screwed onto? ..... the end of the thread ??

as said a crack has propagated from that stress point, where the cutting tool, (creating the thread, has been withdrawn from the cut) and over the years, has rubbed smooth through use ... the rest has just given up the un-ending struggle to do what it should all have been doing, full time !!

bet that was a WTF moment, when the dipper started doing its own thing

IMHDO of course



apologies for adulterating yer pic

Studio_20170516_143837 marked.JPG
__________________
If it's got tracks, wheels, t*ts, or an engine, at some point it's gonna give you trouble!!
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by V8Druid; 16-05-2017 at 07:56 PM.
Reply With Quote
  #6   IP: 82.132.229.54
Old 16-05-2017, 09:32 PM
volbar1 volbar1 is offline
Secret Master
 
Join Date: Dec 2011
Posts: 82
Default Re: Rod failure

Hello Druid, yes that was the end of thread area👍
your not wrong about the wtf moment, I did go cold at the thought that a few days before I had 3.5t concrete panels hanging of the end of the arm, I dont think the cab would stop that coming very well!!
Reply With Quote
  #7   IP: 81.147.99.180
Old 16-05-2017, 10:00 PM
hiluxman hiluxman is offline
Elect of Fifteen
 
Join Date: Jul 2015
Posts: 583
Default Re: Rod failure

Would you compare it to a tree and say it's opened up the crack 17times?
__________________
If in doubt hit it.
Reply With Quote
  #8   IP: 31.49.119.206
Old 16-05-2017, 10:17 PM
V8Druid's Avatar
V8Druid V8Druid is online now
Knight of the Rose Croix of H.R.D.M
 
Join Date: Jun 2013
Location: Druid central, just East of Pandy, Nr. Abergavenny, S. Wales, UK, 3rd rock from the Sun
Posts: 13,429
Default Re: Rod failure

Quote:
Originally Posted by volbar1 View Post
Hello Druid, yes that was the end of thread area��
your not wrong about the wtf moment, I did go cold at the thought that a few days before I had 3.5t concrete panels hanging of the end of the arm, I dont think the cab would stop that coming very well!!
think I'd have pushed the right stick through the windscreen ..... if I had the time

I'd say that the termination of the thread had set up a stress point in the rod ..... dare say that anyone losing a piston off their dipper rod would find a similar break point ..... other rods are mostly under compression when most highly stressed on 360 M/cs

It's why, when turning, if a diameter change is required, the corner of the step is left radiused slightly ... if possible, to relieve the stress point caused/set up by the change in diameter



http://www.amesweb.info/StressConcen...derFillet.aspx


" Stress Concentration Factor: Dimensional changes and discontinuities of a member in a loaded structure causes variations of stress and high stresses concentrate near these dimensional changes "
__________________
If it's got tracks, wheels, t*ts, or an engine, at some point it's gonna give you trouble!!
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by V8Druid; 16-05-2017 at 10:19 PM.
Reply With Quote
  #9   IP: 86.158.217.11
Old 16-05-2017, 10:20 PM
JD450A's Avatar
JD450A JD450A is offline
Knight of the East
 
Join Date: Jan 2011
Location: Not really sure
Posts: 4,719
Default Re: Rod failure

Quote:
Originally Posted by V8Druid View Post
think I'd have pushed the right stick through the windscreen ..... if I had the time
You'd of made it worse
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


Quote:
To Be Continued.....
Reply With Quote
  #10   IP: 31.49.119.206
Old 16-05-2017, 10:22 PM
V8Druid's Avatar
V8Druid V8Druid is online now
Knight of the Rose Croix of H.R.D.M
 
Join Date: Jun 2013
Location: Druid central, just East of Pandy, Nr. Abergavenny, S. Wales, UK, 3rd rock from the Sun
Posts: 13,429
Default Re: Rod failure

Quote:
Originally Posted by JD450A View Post
You'd of made it worse
how would dropping the boom possibly have made it worse Rory
__________________
If it's got tracks, wheels, t*ts, or an engine, at some point it's gonna give you trouble!!
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

 
Partner Links



All times are GMT +1. The time now is 11:53 AM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.