Post By rusty ripple
Post By motion guru
Post By tdmidget
Post By gmatov
Post By scphantm
Safety lesson. Lifting heavy weights
Here's a non-fatal crane accident. Mechanical failure - coupling to load brake apparently.
I'd like to be a fly on the wall of THAT "lessons learned" meeting. I wonder who got fired: the negligent in the maintenence chain of command or a scapegoat
Last edited by Forrest Addy; 06-22-2012 at 08:47 AM.
Ouch!!!!! that will leave a rather expensive mark.
i think the most important lesson here is that no matter how trivial the lift may seem, you should always videotape it.
When we installed our bridge crane and went through the rebuild of the hoist - I heard several crane service people comment on the differences between older hoists of American and Japanese design and newer hoists of predominantly European design.
The biggest difference is in the braking systems. Older hoists had an integral mechanical braking element built into the hoist gearing / drive train that braked the hoist drum until released by torque supplied by the motor. In other words, the hoist motor had to introduce a raising or lowering torque to mechanically release the brake on the hoist. In addition, the motor itself also had an electric shaft brake that required releasing before the motor could spin. This redundant braking system was standard in US / Japanese designed hoists for many years.
In recent years (decades?) European hoist manufacturers like Demag have hoist designs that dispense with the actual hoist brake and rely upon the motor shaft mounted brake. As a result, any failure of the motor brake or drivetrain components (coupling in the case of the crane above) results in a complete loss of load control and the hoist drum freespools and drops the load without resistance of any kind.
The Hitachi hoist that we rebuilt has a mechanical brake within the hoist itself along with the motor shaft mounted brake. The motor output shaft is splined to drive the input shaft of the hoist gearbox (no coupling). It is a severe duty hoist and I can see the benefit of this design in light of the failure mode of the crane that dropped the turbine assembly . . . yikes!!
Best part was the guy in the hard hat just about crawling around under the load while it was flying. Bet he had to change
his shorts after the fall.
BTW am I the only one who thought "gee, doc says I've got a small hernia starting here, better what out
for lifting heavy things..." when the thread popped up...?
Not quite as bad as dumping 2 of them at the bottom of the harbour...
WOW, that's going to be expensive.
It is painful to read this . Demag is the descendant of what is like the first german heavy engineering company.... ever ! (Mechanische Werkstätten Harkort & Co zu Wetter an der Ruhr -- F. Harkort ist essentially the father of a big part of German heavy industry)
Originally Posted by motion guru
Unbelievable they take that kind of shortcuts....
Some 30 plus years ago I worked a couple of summers in a machine shop. One daybtheynhad a huge boring mill delivered and the riggers used a crane to lift it of the trucks it was brought in on. This was just outside the shop's main door. I was standing just inside the door at the stock rack looking for a piece for the next job as the riggers were lowering the mill to the ground. I guess the crane couldn't handle the load because when they got the mill a couple feet off the asphalt the cranes mast gave way and the mill slammed into the ground. I can still remember the sound of the mill hitting the ground. It dug into the parking lot about a foot. By some miracle nobody was hurt. As I was siting here recalling this story I also remember the shops overhead crane had no brake and we had to pulse the motor in the opposite direction to get it to stop. They also had a tow motor that had no brakes, which was scary to drive out in the sloped parking lot. Today OSHA would,shut that shop down in a minute.
In 1975 while working at the 6" G&L at the South end of the shop, I looked over to see four guys yaking it it up. I looked up to see that they were standing directly below the hooks of the bridge crane. The crane leaked oil so I always wore a hat during a lift or just stayed away from underneath the crane. The crane was normally operated by the one eyed union steward but today on the afternoon shift for the first time there was an apprentice up in the crane. He was 'practicing' running the hooks up and down, generally moving the controls and the bridge for practice. That would be enough to get me to skedaddle out of the way. But those guys were deep in a conversation, probably about the Bears or White Sox as this was the South side of Chicago and nothing but the forman could have moved those guys. Machinist union by the way. Unknown to the guys on the floor, there was a little problem with the limit switch. So maintenance had removed/disabled it. The apprentice while running the small hook up overshot the location of the limit switch. There was enough torque to shear the cables. The crane operator turned on the siren and I looked up from my job to see three guys run as the small hook dropped. The fourth just stood there, undecisive about which way to go. The small hook came down and nailed him. The bolt on the side plate opened him up from the back of his head all the way down his back. He laid face down in a pool of blood struggling to breath. It was more than anyone knew how to help. Finally an ambulance arrived and took him away. The first two hospitals refused to treat in the ER, the ambulance took him to the third hospital. They found that the breathing difficuly was his false teeth were lodged in his throat from the impact. He actually survived the injuries, but never fully recovered. One inch either way, dead, or it would have missed him.
Some things stay with you for ever. Not too many overhead cranes anymore, but I always tell the apprentices, know here your hands are at all times.
I spent my last fifteen years working on cranes dating to 1938, when they built the Irvin Works, US Steel, Dravosburg.
EVERY crane had TWO brakes per hoist, redundant, as one could hold the load, BUT safety first, and not necessarily the safety of the workers, more for the safety of the load.
The brakes are in series with the motor. When you make a lift motion on the controller, it tries to open the brake. If the brake is properly adjusted,it WILL open. If you crank it down too much, you will have to go to second notch on the lift to open the brake.
Most had a brake on the outboard end of the motor and the outboard of the reduction gear. If the motor brake failed, the gearbox brake would hold, vice-versa.
A couple badly made cranes had the brake on the end of the shaft outside the jackshaft. Shaft snapped. We had to re-engineer to put it back in service.
Down was open the brake, again series wound, but the motors became generators, "dynamic braking", into resistor banks.
I have never worked on a crane that had "mechanical brakes". You make it sound like pawl and ratchet setup.
"Unknown to the guys on the floor, there was a little problem with the limit switch. So maintenance had removed/disabled it."I seriously doubt that, and if they DID, I don't think you would ever have heard of it. That would probably be a million buck OSHA fine.
ALL my cranes, about 85 of them, were in good shape at the end of my shift. Next AM, half of them needed rewired, burnt off brake leads, or the tension reset.
Most of the problems in my mill were that my crew did not understand that the torque was specific, 16 inch wheel with 200 HP motor, 100 ton crane, crank the pullrod down, back off the specified flats, and that is what Cutler and the like speced. Back off 1 turn and 3 flats. Set the holding torque,NOT set to MAX, but to hold the load.
When you hear brakes slamming shut, they are tightened too much. They also will not open on notch one of the controller. When you hear brakes go "clank-clank"", when applying, they are maladjusted, one is wound tighter than the other.
They should NEVER slam shut. They CLOSE, if properly adjusted, silently. It IS a release of current that lets the magnet release the armature.
Mebbe that is enough to explain how a crane works. You wanna know more, ask.
My dad's friends with the crew that was working this job...
Crane Collapses at National Cathedral | NBC4 Washington
repairing the cathedral after the earthquake last year. We learned a little background that was never reported in the press from the guys on the crew.
1st, the press crucified the operator stating for weeks afterwards that it was operator error and he screwed up the counter balance weights. I asked the engineer on the crane that day and he goes, you have to understand something, we got that crane off the boat from Germany about a month before this job. it was brand new. prior to be set up at the cathedral, the only time it was assembled was when the company rep helped us put it together in the yard to train everyone how to use it. With this particular crane, its NOT POSSIBLE to fudge the counter weights. It is a completely automatic system with absolutely zero input from the operator. the crane has about 3 safety systems on the counterweights that move them when necessary, and if you exceed the limits, the hoist stops. you couldn't fudge the counterweights if you wanted to, the lever literally doesn't exist.
when asked then what brought it down, jack laughed and said the factory didn't anneal one of the assembly pins correctly. the op dropped his load, pivoted around and that pin snapped. when that pin snapped, there was nothing that could be done. it was just dumb luck it fell right where it did.
he said when they looked at the wreckage, he saw the pin (when i say pin, i mean like 6 or 8 inches in diameter) and just from the way it looked after it snapped he knew it was too hard. he called the factory rep and the factory rep showed up, looked at it, went OH F*** and opened up his check book. he even paid to re-sod part of the grass that was tore up by the thing falling. paid every penny and then some, bought the crane back at full price and even refunded the shipping from germany to america. he said by the time the cops got there, that crane was already on the boat heading back to germany, by the time the feds got there, that crane was already being used to cap bottles of fine german beers.
Originally Posted by Zonko
Humans are pretty tribal, and we take great pride in good stuff our tribe does, and are aghast and ashamed at bad stuff our tribe does. I can assure you that similar lapses in judgement have happened in America, Canada, the Netherlands (obviously) and Japan. Even in France, though they may not admit it.
I was glad to read that this was not a total loss. Not so for the guy we dropped 35m down the smokestack we were building. Winter. Late in the day (sun was setting, low light, operators tired). Guy (inspector) is in a bosun's chair. His walkie talkie battery failed. They pulled the block into the pulleys at the end of the crane and he went straight down when the cable snapped.
The turbine, and the loss of life case both point out that one has to think through a the failure modes and not just the success modes of major operations. And failure modes change as the scale of operations change. Folks here might enjoy Henry Petroski's books, specifically "To Engineer is Human", in which he discusses how we can learn from failures.
Thanks for posting this, Forrest.
It was a multi-million dollar lawsuit won by the plaintiff. I did hear about it as my father was Chief estimator at John Mohr and Son in Chicago at the time of the accident. Later on he was Works manager.
Originally Posted by gmatov
100 ton crane, the limit switch is about the size of a chest freezer. Wires are about 2" D, with insulation. You don't do splicing with this stuff.
Only an Idjit would wire the limit switch out of the circuit. You have to have a fat guy just to open the limit, to allow you to WORK on the crane. BIG ones have about 150 pounds counterweighted arm.
Limit does not always work. I have seen lots of big cranes break inch and an eighth wire, when run up too fast.