Worm Gearbox efficiencies for hoists during raising/lowering

[tambraton]

Hello

I'm trying to determine if there is any difference in efficiences for a worm gear box used in a hoist system.

Details are as follows:

A hoist is used to lift a gate. The hoist drive train is composed of a 25hp motor, primary reducer (worm gearbox with 1/60 gear ratio) and two secondary reducers driven wire rope drums (one off each side of the worm). As the worm gearbox is self locking at this ratio, a torque input is required to lower the gate. Is the efficiency of the worm gearbox the same whether the gate is lowered or raised? I have not found any vendor information that clarifies this.

Anyone have any experience with this? Any incite or references would be greatly appreciated.

Regards,

 

[BrianE22]

Years ago I worked out the free body diagram for a worm and gear in contact. I found that the efficiency to lower the load was a less than the efficiency to raise the load. That's based on geometry only. The frictional force tangential to the worm thread reverses direction for raising versus lowering. The normal force stays in the same direction. This assumes the coefficient of friction remains the same in both directions. If, when lowering, the speed of the drive runs faster then the coefficient of friction might lower a bit. There's other stuff too if the speed is different - like windage losses in the motors and losses in the bearings.

You might want to try the FBD using your pressure angle and lead angle. You might find there's not much difference.