Crane and the like unwind resistance

[Dan68c]

Hi all,

I was thinking about cranes, any type. What brake or mechanism is used to stop the cable unwinding when a load is on the end. Is it the just the resistance and gearing of the motors or is there a physical lock. Small detail but something i cannot find any detail on.
Thanks

 

[hydroman247]

I have seen various braking systems but drum brakes seem more common than others.

 

[Dan68c]

Thanks for the reply. I figure thats what is. I image the resistance of the motors and the gearing would provide some sort of friction to stop it unwinding.

 

[fegenbush]

Many overhead gantry cranes and jib cranes (specifically the hoists attached to such cranes) use a self locking worm gear arrangement. When the loads become larger, external braking devices such as the drum brakes mentioned by hydroman247 are employed.

 

[RolMec]

The selflocking worm gears have quite a low efficiency for the driven direction of the worm gear, this leads to an increased power requirement in order to do the normal operations. Distinct braking systems are, in my experience, obligatory requirement for lifting applications. Then usually you have an operational mode based on speed performance, controlled braking will give you the system behaviour you need. If there's persons involved (in the lift operation or onboard the lifted device) or dangerous goods (molten metal, nuclear, ..) there might even be two+ independent braking systems required. Most often, brakes (drum brakes) are mounted on the high speed shaft (motor side). In cases of safety concerns, the failure of the drive shaft shall be considered, this leads to disc brakes with a disc mounted on the rim of the rope (or chain) pulley = low speed application. However, smaller disc brakes are used for high speed application too, they need less space per torque output.
R.