How screwed am I?

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@kcurbanloggers, do you still have the machine? Can you take a close up picture of the broken ends? If there was a crack in the weld before you started using it, you will see it on both sides of the fracture. If it's obvious enough you might be able to point it out to them in an effort to not blame you.
fracture-mechanics-failure-analysis-lecture-fatigue-35-638.jpg fluctuatingloadsnotes-160306040949-thumbnail-4.jpg 108-010-failureanalysisgearsshaftsbearingssealsmaintenancemanual-14-638.jpg
 
Another thing I would point out is that rod failed at the weld, not above it or below it. It's a poor quality weld. The weld if done right is the strongest part. I hope you have a copy of the rental agreement and the insurance coverage you paid for. I'd be combing the fine print.
 
He stated he had not paid for ins.:cool:
Oh, thought I read he did opt for it. Damn. Well if they said it only covers catastrophic failure of the machine anyways it would not have been worth it by the sounds of it.

The more I lool at it the more the failure looks like a brittle fracture. Brittle fractures on shaft in tension are fairly flat and straight across the cross section of the shaft. You can see the center is raised a little which is more typical of a ductile failure. That profile is what I would expect from that section of the shaft that has been welded on. A sudden shock load in tension on the rod would cause that. The welding of the rod ends to the shaft makes the steel brittle in the heat affected zone and would not penetrate all the way to the center of the rod. That is why the center is more raised. Crack propagation in brittle steel occurs instantaneously where as in ductile steel you will see the striations across the rod until the cross section is reduced enough where it conpletely fractures. A tiny flaw in the weld is the likely initiator for the failure. By chance did you try pushing a stump on the corner of the blade (opposite side of the ram)?

See how there is no "necking" (narrowing of the shaft) in a brittle failure? Just like your shaft, no necking is present.
Fracture-Surfaces-.jpg
 
I went back and read that he did indeed by the ins., not sure if it covers the damage done though. Now, back to your regularly scheduled program, sorry for the error, Marshy!:cool:
No worries. I skipped most of the posts except his replies. Haha.
Not that you guys don't have good advice.
That shouldn't be an expensive fix at all. Just weld it back on! I would have been tempted to have it fixed and not told them. Could have made a call to a traveling welder and had it back running in an hour or two hehe.
 
@kcurbanloggers, do you still have the machine? Can you take a close up picture of the broken ends? If there was a crack in the weld before you started using it, you will see it on both sides of the fracture. If it's obvious enough you might be able to point it out to them in an effort to not blame you.
View attachment 632029 View attachment 632030 View attachment 632031

I finished the job and left the machine on the job site, so that’ll be all for pictures.
I’ll let you guys know what happens with the rental company. I’ll mention the grease and the fact that it broke on the weld. The rental agreement is pretty clear that I am responsible for damages, but if they think that retaining my business is more important than not paying for the break, then maybe they will let me off the hook. I’m not to keen on paying for breaks attributable to poor maintenance. Thanks for all the advise. I will let you all know what the rental company says when I hear from them tomorrow. In the meantime, if you have any talking points I could mention to them that might encourage them to cover this, please let me know.



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No worries. I skipped most of the posts except his replies. Haha.
Not that you guys don't have good advice.
That shouldn't be an expensive fix at all. Just weld it back on! I would have been tempted to have it fixed and not told them. Could have made a call to a traveling welder and had it back running in an hour or two hehe.

I was tempted too, but on the off chance they did notice that, I think I would have been in a lot deeper s***. I think it’s best if I disclose it and do what I can to have them cover the loss... despite the rental agreement.
 
I wouldn't classify that as poor maintenance. If it was a broken pin I would agree. Pulling the head off a cylinder rod like that is a combination of things. Because where it broke, actually at the weld, its a flaw in the weld that let go once it was stressed enough. I wouldn't go as far as to say it was from operator abuse either. Could of happened to anyone that loaded it enough.
 
I wouldn't classify that as poor maintenance. If it was a broken pin I would agree. Pulling the head off a cylinder rod like that is a combination of things. Because where it broke, actually at the weld, its a flaw in the weld that let go once it was stressed enough. I wouldn't go as far as to say it was from operator abuse either. Could of happened to anyone that loaded it enough.

Wouldn’t the rust and lack of grease put extra side to side strain on the piston? It seems to me that if the joint doesn’t move freely, then the piston would take quite a load from the side, which it was not designed to do. A defect in the weld was probably gave it the greater propensity to break, and the rust in the joint was what set it off. Correct me if I’m wrong though. That’s just what it seems like to me.


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Standard fluid power specifications for cylinder rod are 50-55 Rc surface hardness with a case depth of 0.050″ min deep. The case hardening keeps the outside from deforming easily. The soft inside gives it toughness. The .45% carbon would allow one to through harden and temper it to about 50RC. That would want to be avoided in this situation. Lots of things are case hardened, induction case hardened today (like your chainsaw bar rails) but not the pretty color-case hardening like the Starrett tools and firearms of old.
Kcurbanloggers- I hope things work out for you man. Hopefully with this crash course on cylinder repair you have gained some insight that will help you at the bargaining table. Good luck.
 
You're confusing case hardening with deferentially hardened, cased hardening is adding carbon to mild steel. deferential hardening, is hardening specific spots on med to high carbon steel.

know what never mind, I'm not a machinist anymore and I like it, 150 people in on shop not one of em know the difference between annealed, hardened, normalized, stress relieved or tempered, let alone case, through or differential hardening.
 
I would weld it but i wouldnt exspect it to stay glued together on that hardened shaft.

Looks like a newer machine. Ram just failed it happens on all machines in the dirt.

Good luck
 
Wouldn’t the rust and lack of grease put extra side to side strain on the piston? It seems to me that if the joint doesn’t move freely, then the piston would take quite a load from the side, which it was not designed to do. A defect in the weld was probably gave it the greater propensity to break, and the rust in the joint was what set it off. Correct me if I’m wrong though. That’s just what it seems like to me.
If the pin is seized it would create a bending moment on the rod. The highest stress point would be where it broke. The back and forth movement of the blade would cause fatigue and it would eventually fail in the same location if that was the case.

That is true however, the fracture does not indicate a fatigue failure from bending. The dull grey surface that resembles granet crystals on the surface of the fracture is indicative of a rupture of the material. Instantaneous fracture from a load that is beyond the yield point of the material propert.

When looking at fracture due to fatigue there are two zones to look for. One is the fatigue zone and the other is the rupture zone.

In a situation where a small crack develops (from fatigue) and slowly spreads through the rod, the crack leaves striation marks which are like the material ripping apart little by little until the cross sectional area of the rod is too small to support the load then it ruptures.

The striated zone from crack propagation is the fatigue zone.

The surface where it ruptures looks identical to the surface in your one pic.

The striated surface from crack propagation will be dull from the surfaces moving back and forth and rubbing over each other. If the crack growth is slow the fatigue zone may be corroded also depending on it's environment.

The amount of overstresing can be determined by the size of the fatigue zone compared to the rupture zone. A large rubture zone and small fatigue zone indicate highly overstressed.

Remember, a fatigue faikure will have both zones. From your picture we can only see approximately 80-90% of the surface but, all of the visible surface I see indicates a rupture type failure.

It's possible there is a fatigue zone but without a better picture straight on I cannot tell. If there is no discernable fatigue zone it means it still failed due to highly stressed. I'm not an expert but my experience and education tells me this was certainly overstressed. A legitimate failure analysis would look a lot closer identify a manufacturing defect thst would cause a stress riser. If none is found then it could be concluded it failed because the load was greater than the materials ultimate strength. They would also test it's hardness to see if the welding changes it's mechanial poroperty and contributed to a brittle faikure.
 
If the pin is seized it would create a bending moment on the rod. The highest stress point would be where it broke. The back and forth movement of the blade would cause fatigue and it would eventually fail in the same location if that was the case.

That is true however, the fracture does not indicate a fatigue failure from bending. The dull grey surface that resembles granet crystals on the surface of the fracture is indicative of a rupture of the material. Instantaneous fracture from a load that is beyond the yield point of the material propert.

When looking at fracture due to fatigue there are two zones to look for. One is the fatigue zone and the other is the rupture zone.

In a situation where a small crack develops (from fatigue) and slowly spreads through the rod, the crack leaves striation marks which are like the material ripping apart little by little until the cross sectional area of the rod is too small to support the load then it ruptures.

The striated zone from crack propagation is the fatigue zone.

The surface where it ruptures looks identical to the surface in your one pic.

The striated surface from crack propagation will be dull from the surfaces moving back and forth and rubbing over each other. If the crack growth is slow the fatigue zone may be corroded also depending on it's environment.

The amount of overstresing can be determined by the size of the fatigue zone compared to the rupture zone. A large rubture zone and small fatigue zone indicate highly overstressed.

Remember, a fatigue faikure will have both zones. From your picture we can only see approximately 80-90% of the surface but, all of the visible surface I see indicates a rupture type failure.

It's possible there is a fatigue zone but without a better picture straight on I cannot tell. If there is no discernable fatigue zone it means it still failed due to highly stressed. I'm not an expert but my experience and education tells me this was certainly overstressed. A legitimate failure analysis would look a lot closer identify a manufacturing defect thst would cause a stress riser. If none is found then it could be concluded it failed because the load was greater than the materials ultimate strength. They would also test it's hardness to see if the welding changes it's mechanial poroperty and contributed to a brittle faikure.
Holly cow, that’s a lot of typing to say it busted!:cool:
 
Here is a pic showing fatugue zone and rupture. The stress is unidirectional in this case but had it been bidirectional you can have a fatigue zone opposite of each other.
20180212_125014.jpg
 
Lmao, she done did broke!
Pushing stumps out ain't no joke. Use the center of the blade and leave the stump tall for leverage!
Dig the roots out with the corners of the blade first then push with the center of the blade, for scarifying most of the guys out here use a shovel or a push arm style cat for this reason.

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Dig the roots out with the corners of the blade first then push with the center of the blade, for scarifying most of the guys out here use a shovel or a push arm style cat for this reason.

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A big excavator does a good job too.
 

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