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
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)
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.
cheap all thread used... which probably isn't even a graded material
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???
Needs twice the diameter bolt size for that amount of brake.
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?..
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?
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.
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.
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.
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?
I was going to say using a grade 2 thread where grade 8 should have been used.
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
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.
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.
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.
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
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.
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.
yap
Yair ... . With all due respect tct and josh...I doubt that European and Japanese lifting devices use National Coarse...I doubt the thread form is a factor in this failure. I think Nige above is thinking along the same lines as me. Cheers.
I always thought that the profile (V-shape) of any thread could be changed within certain limits by the method of manufacture. For example a rolled thread is always stronger than a machine-cut thread. The root and apex of the thread form are slightly rounded when compared to a machine-cut thread. Although a large number of lifting shackles used in Europe are quoted as metric dimensions you will always find that they are conversions from inch sizes, including the thread size.
ANSI standards for metric threads typically call for either a *rounded* or flat root on external threads. Strangely enough, ANSI specs for UNC and UNF threads call for a flat root at the bottom of the thread, with a rounded root being *optional*. ANSI UNRC and UNRF specs mandate the rounded root profile. I don't have any ISO specs handy but I'm quite sure that cutting sharp V threads anywhere hasn't been acceptable for at least a century. To quote from Machinery's Handbook: "UNR external screw threads: To reduce the rate of threading tool crest wear and to improve fatigue strength of a flat root thread, the Design Profile of a UNR thread has a smooth, continuous, non-reversing contour with a radius of curvature not less than 0.108P (pitch) and blends tangentially into the flanks and any straight segment..." Common indexible inserts for single point threading tools are ground with a root radius for both metric and inch threads. If someone is single-pointing a thread with HSS tooling and grinding the tool by hand, then you are taking your chances on the profile. In short, off the shelf inserts or rolling machine dies should both give you the same profile, allowing of course for the usual tolerances. I'm not making any guesses whatsoever regarding this failure, but will say that a cut thread of any type is inferior to a rolled thread, both in ultimate tensile and especially fatigue, to due the grains/fibers in the material being cut instead of being formed to follow the thread profile. A cut thread is typically more accurate though. Just my $.02 Marv
No expert here but looks like that cotter pin was causing a bit greif. muzy
I would not think for 1 second that the Metric or what ever thread is anything to do with this "little snag", but on a few high spec' lifts I have been involved with, it was in the lift technical spec' about the grade of the bolts fixing the lifting points io the load, I was told about the non use of any metric fasteners on the bolted down hoist points, the reason given was the thread form??? I know less than nothing about nuts and bolts, but possibly its a U.K. thing that this point was made, its just something that sort of made me wonder why.
The piece that failed was a factory part installed at our shop by a factory technician 7 months earlier that year. The rig was also re-certified at that time. The adjusting rod was one of two that attach to an equalizer bar. From there, the linkage attaches from the operator control. I'll try to dig up some detailed blue prints. Anyways, as you can see in the top pic, the kelly brake is resting on the bottom which is where it went when the adjusting rod failed. The two that were up on the up on the rig jumped clear and no one was hurt. We had already cemented the 1400' well and were in the process of swabbing. When the kelly came down, it destroyed the table, swivel, bent the kelly, cracked the derrick in a few places and bent the main frame. The rig was as good as totaled. It's been a little over a year and the insurance company's are still battling it out. Kinda ironic....our Howard Turner rig built in the 50's still drills a straight hole and never had any of these kind of problems.
Some close-up photos of the fracture faces both sides of the adjusting bolt break would be good, if you can get hold of them.
Is that threaded rod actually bent at the break? It certainly looks like it is but it's hard to say for sure. If it was me, if at all possible, I would be re-assembling that brake on the draw-works and looking to see if there is some kind of interference causing that thread to be bent sideways. I can't quite picture the equalizer bar setup, but is it possible that the brake was adjusted improperly? As in only one band being taken up to adjust for wear, resulting in the equalizer being thrown off center and causing a side load? Where were the adjuster nuts positioned on the other band? My money would be on something like this happening. With a side load, it wouldn't be long before it let go. Marv
All of the parts are back at the manufacturer. They admit that their part failed but they don't want to pay for new draw-works and a new derrick. The frame was bent beyond repair so how is it that the draw- works and derrick were not damaged? We have had problems with the draw-works from the start. Each time the manufacturer would send their people down to remedy the problem but there was always an alignment issue. We are not ready to load up a rebuilt or repaired derrick with 140,000 lbs unless the manufacturer x rays and certifies it. For some reason, they won't go there. Same with the draw works. We want new, they want to give us the old stuff. When this slammed into the casing, all of the cat walks on the front of the rig were either broken or laying on the ground. I was told that the front of the rig jumped 3' into the air and by the looks of the cribbing, I wouldnt doubt it. Oh well.....it's been an ongoing money draining battle between the manufacturer and the insurance companys. The only one making any money is the lawyers. I don't think that we'll ever see this rig back in the yard. It's just as well. They just don't build them like they used to.
Oh....the threaded rod was just as straight as can be. No bends.
don't get me started liers and insurance companies ! in 2002 i installed a pair of out side oil tanks. in 2007 loader o pperator hits one tank cleaning snow .drains tank oil company fills tank it drains again . long story longer they end up demo'ng the building and have the nerve to name me in the 1.5 mill law suit .supposed to go to court this march. by the way tank never leaked till ahole hit with loader! sorry to hijack your thread just had to vent tks tb
first rule of law suits is name everyone under the sun with any sort of assets or cash you can seize. Then drop them one by one as you realize you cant get blood from a turnip
Boy,that's good to know.The good old USA,huh?Wow!.Ron G
That's one of the joys of having a business, and it is especially true in CA. At a recent meeting with one of the lowlife scum masquerading as a lawer said to me "It doesn't matter that you didn't do anything wrong, you are still going to pay".
Luckily it has only cost me $50,000 to day in legal fees only to be dropped from lawsuits. I started adding a line to all my contracts that stipulates that any disputes be handled through arbitration. The courts will very rarely side with the big bad contractor.
So did the 500000 question get answered? I'll put in my .02...granted its a factory weld and all but...would rapid cooling ie..bucket of water or getting the rod to hot when welding could have caused this?
OK i'l try one more, The drill line looks bad, so the blocks smacked the crown and when the steel came down some part hit the brake and snapped the rod you show. muzy