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Crane failures 8

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Cast iron jaw coupling in a hoist? at 3.24. This might be allowed under the design rules for a light duty crane, but specifying a light duty crane in a turbine hall where the load can easily be worth much more than the crane seems like an unwise cost choice (not even considering the safety aspect).
 
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I don't work in heavy industry so those of you who do can correct me as necessary:
1. Isn't the broken part a cable sheave? The system failed when the sheave fracture from its hub and the lift cables went from constant tension to sudden impact loading on the upper support structure.
2. Isn't this probably a fatigue failure and not an issue with improper specification or procurement of parts? The crane is built to the specification required for the turbine hall. This wasn't an ad hoc decision to do the lift. This would all be planned for and checked before the lift.
3. Isn't this a safety training video illustrating never go under a live load even if the equipment is rated for the lift, you trust your team, and you have done the same thing many times before - unexpected failure can occur?
This seems like a case of a critical part failing not because of ineptitude or malice but because it developed a hidden defect. More info would be needed beyond the short video to make a knowledgeable decision.
 
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xx said:
1. Isn't the broken part a cable sheave?
Click to expand...
The failed part looks (to me) like a jaw coupling, which is a part I would expect between the hoist motor and the hoist gearbox.
gc-guardex-curved-jaw-coupling-3631058608_dusmhc.jpg

The lower grade of these couplings is made from cast iron, note the brittle fracture surface. These couplings can be obtained in steel, which is less likely to fracture.

It is unusual for a crane of this size to have a mechanical load break, so failure of this coupling results in complete loss of load control, but the load will accelerate slowly as it is still connected to the inertia of the gearbox. I would expect much faster acceleration if the hoist rope failed.

XX said:
2. Isn't this probably a fatigue failure and not an issue with improper specification or procurement of parts? The crane is built to the specification required for the turbine hall. This wasn't an ad hoc decision to do the lift. This would all be planned for and checked before the lift.
Click to expand...
The difference between a light duty crane, a heavy duty crane, and a port or steel mill duty crane is the design expected duty cycle. Turbine hall cranes tend to be designed as light duty, as the expected number of capacity lifts over the life of the crane is small. CMAA Class A, FEM 1C[sub]m[/sub], ISO Class M2. Note the lifetime cycles and infrequent capacity loading in the table below.
Screenshot_from_2022-07-30_12-01-54_ficu66.png


XX said:
3. Isn't this a safety training video
Click to expand...
But it looks like a real event (although some of the video could have been staged after the fact).
 
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There are more broken pieces than just the jaw coupling, it is not obvious what they belong to. Perhaps a bearing housing supporting the coupling??
 
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Yes, an extreme misalignment between the motor and gearbox would break the coupling in this manner. This coupling failure is a result of the load dropping, not a cause.
 
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The jaw couplings for the container cranes I have worked on were typically GGG Spheroidal cast iron. Its also common to have redundant brakes, typically 1 on the motor side and one the low speed side of the gearbox.
 
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FacEngrPE - typically what is used to actuate the e- brake system? A single-shot latching circuit reading acceleration from an encoder on the drum shaft? An inertial switch on the drum shaft?
 
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It's been 20 years since that job, so my memory is a bit fuzzy, this list might not be complete.
Emergency breaks set
[ul]
[li]Emergency stop signal.[/li]
[li]Loss of power.[/li]
[li]Hoist drive fault[/li]
[/ul]
We did not use an overspeed switch as the total available lift distance was too short to allow discrimination between normal fast motion and likely failure conditions. A container crane might make a different choice, as the lift is much longer.
The brakes themselves are spring to set on loss of power to the actuating coil (or air cylinder in the case of the pneumatic version).
 
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...are those disc brakes? I didn't know they used them on hoists. [ponder]

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik
 
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In my opinion, I would think for such a mission critical device that cranes are, that top quality materials would be used. There should be nothing made of cast iron or similar material on any crane.
It is evident that in the above example some corner was cut in the design department.
How many crane failures happen that we never hear about?

Was any sort of engineering involved in the design of these cranes?



At the 0:37 area.
 
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If a casting is broke then it is evidence that it could not handle the load. Then if cast iron is the choice increase the amount of material to handle what ever is thrown at it. That goes for engine blocks as well.
Yes the added weight makes it a bad choice to use.
 
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On container cranes disc brakes are the norm on the main hoist, I've seen drum brakes on the boom hoist (on the motor side of the gearbox, band brakes or disc brakes on the rope drum side) drum or disc on the gantry and trolly travel. Cast iron couplings are very popular, check out Bubenzer or Tschan most of their products come in cast iron.
 
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Thanks CC... didn't know that they used disc brakes for any cranes... I've never encountered them.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik
 
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