The $500,000.00 question.

[RollOver Pete]

Other than the obvious, can anyone tell me whats wrong with this picture? As you can see, the piece that failed is attached to a brake pad. When the threaded piece failed, the brake pad failed to do its job. So take a close look. Can anyone spot what to me is an obvious design flaw?



View attachment 86849

 

[Davvinciman]

Does that keeper pin in the block it broke off of come out? C'mon, Pete. You don't have to be a company a-hole. Hah! (from fellow Local 12 brother)

 

[Scrub Puller]

Yair...looks like may be there is insufficient clearance and the thread was flexing rather than the assembly pivoting on the pin through the square block?

What's the story?

Cheers.

 

[heavylift]

cheap all thread used... which probably isn't even a graded material

 

[tctractors]

Thread rod looks to be bent at the break point?? possibly the anchor pin location is to close to the metal backing of the shoe?? plus the wear segments often need to be in smaller section on external contracting bands???

 

[DigDug]

Needs twice the diameter bolt size for that amount of brake.

 

[rare ss]

is the block too big for the yoke so there not enough clearance when the rod trys to angle in a manner shown in the picture? if that makes sence?..

 

[Davvinciman]

One more try

I know this is probably because I haven't worked enough lately to see that many broken bolts but is the bolt made of aluminum? Sorry if blatant
stupidity is rearing its ugly head. I need to get back to work. And here is one for you. Why is this the $500,000 question? What do I get if I win?

 

[brianbulldozer]

Has the welded connection of the block to the stud affected the heat treatment of the stud and weakened it? Would a mechanical connection between the two be better? I am thinking eye bolt with a pin, tapped block with something to prevent the stud from rotating out, t-bolt, etc.

 

[John C.]

What I see is a brake band from a crane. The broken threaded rod looks nice and clean below the nut which I would think usually is the band adjusting nut. Why that thread is so clean and the open end beyond the nut is so dirty is very curious. The high price tag can only be because something got dropped because of the broken rod.

The other odd thing is that the rod is broken from one side to the other and was not pulled in tension. There is no thinning of the broken site, only a partial thread on the far side and the pull lip on the near side. This is a progressive crack failure that happened over a few cycles. One has to wonder that if the crane and linkages had been inspected before hefting a $500,000 load, the accident might have been prevented.

 

[John C.]

I think I missed that the nut on the band side of the rod is backed off all the way against the bottom of the thread. I would think that means there was no more adjustment left on the band. The clean threads on the broken side I would guess is from turning the nut back on the thread thus cleaning the dirt off as it is turned.

 

[Scrub Puller]

Yair...c'mon Rollover don't keep us in suspense.

The maker obviously recognised this was a critical component as the thread assembly has either been turned out of rectangular stock (unlikely) or the thread was inserted into the block and the weld radiused in a lathe. As John C. says it looks like the band has run out of adjustment...it's hard to determine the condition of the pads as the rivet holes are full of friction material.

Maybe the band was assembled with the incorrect component leading to insufficient clearance to pivot as other folks have pointed out?

 

[zlssefi]

I was going to say using a grade 2 thread where grade 8 should have been used.

 

[Haddy]

Like John C says , kinda interesting with the clean / dirty thread .

What activates the brake ? With two lock nuts where they are is there a collar or something similar between the two nuts ? This might explain the clean thread , maybe ?

Is whatever activates it putting even pressure on that rod , eg not trying to twist it ? Just my 2 cents worth - no expert

 

[RollOver Pete]

Does anyone think that maybe a fine tread should have been used?

The rig is rated and certified @ 140K lbs. At the time this happened, we were holding 55K lbs.

 

[OldandWorn]

Not really, it would make it a bit stronger because the threads are not as deep but I would just go up a size if it was that close to design limits. Is the threaded part that broke off bent? That would be a huge clue and would support some of the guesses.

 

[OldandWorn]

Does the brake on a crane have adjustable holding force or is it all off or on? If it's non-adjustable the weight would not matter with this sort of failure.

 

[Scrub Puller]

Yair...No way to the fine thread theory. Everything I've had a look at uses coarse in this application. As Oldandworn mentions the only difference would be a few thou. difference in the effective diameter of the rod. That would not be a game changer.

I still reckon the rod has been subject to flexing due to the geometry being altered by the band being adjusted past it's limits or some other factor such as incorrect assembly and it hasn't shown up untill the band is worn to where it is.

Cheers

 

[Nige]

Hard to say without some really good close-ups of the fracture face but it would appear as though the threaded adjusting rod failed in fatigue rather than a single cycle overload. This would lead me to believe that either there was a flaw in the threaded rod itself. Fine thread vs coarse thread would not have made a blind bit of difference, the grade of the steel in the threaded rod definitely would have.

I'm also at a bit of a loss to explain how everything is so clean. Cranes that use clutches & brakes are not normally like that. How long ago was the brake band fitted, and how does that tie up with the apparent amount of wear on the friction material..? Because the photos are not totally clear I'm going to hazard a guess here, judging by the amount of welding around the lug, that this may have been a modification of the adjuster designed to extend the life of the brake shoes for a few more hours when the original adjuster got to the end of its travel.

Incorrect installation if it was recently installed could also have been a factor.

 

[tctractors]

On the thread thing, on heavy lifting aplications the recomended thread is U.N.C. Metric thread has a hard point > at the base of the pitch, U.N.C. has a radius at the base of the pitch form, in critical heavy lift situations Metric tread is not allowed.