Calculating Pulley and Shaft Loads for an Existing System

[Stephen123]

Hi, i need to do a pulley/shaft check on an existing system.

Pulley is 840mm diameter and the motor has 47kw and 390 nm breakdown torque so to find the force from the belt can i assume that the force at the pulley o.d. distance is the force? So 390*0.84 will give the torque at that distance?

I also need to check that the shaft to pulley locking device is adequate. I have the rated Nm of the locking device but how do i find the load torque through the locking device?

Thanks.

 

[Baluncore]

So 390*0.84 will give the torque at that distance?

For pulley torque or force, the pulley radius is needed, not the pulley diameter.
Force at pulley radius is 390 Nm / 0.42 m = 930 N.
You should not need to know the locking device or shaft diameter. The locking device torque will be the same as the pulley torque.

 

[Stephen123]

For pulley torque or force, the pulley radius is needed, not the pulley diameter.
Force at pulley radius is 390 Nm / 0.42 m = 930 N.
You should not need to know the locking device or shaft diameter. The locking device torque will be the same as the pulley torque.

When you say the locking device torque will be the same as the pulley torque, what do you mean by pulley torque? The locking device locks the shaft to the pulley and is rated for 12,000Nm of torque. How can i actually find what the torque at the locking device is?

Thanks

 

[Baluncore]

Torque is independent of radius until you need to convert it to a linear force.
Tangential (force in Newtons) * (radius in metres) = (torque in Newton∙metres), Nm.

When you say the locking device torque will be the same as the pulley torque, what do you mean by pulley torque?

The tension in the belt measured in Newton, N, multiplied by the radius of the pulley, is the pulley torque. Since all parts are connected together the pulley torque, shaft torque and the locking device torque are all the same.

To work out the tangential force at the locking device you need the radius of the locking surface, but that is NOT needed in your example.
The 390 Nm breakdown torque is significantly less than the lock rating of 12 kNm so there should be no problem.

 

[Stephen123]

Torque is independent of radius until you need to convert it to a linear force.
Tangential (force in Newtons) * (radius in metres) = (torque in Newton∙metres), Nm.The tension in the belt measured in Newton, N, multiplied by the radius of the pulley, is the pulley torque. Since all parts are connected together the pulley torque, shaft torque and the locking device torque are all the same.

To work out the tangential force at the locking device you need the radius of the locking surface, but that is NOT needed in your example.
The 390 Nm breakdown torque is significantly less than the lock rating of 12 kNm so there should be no problem.

I understand what you mean now Baluncore, that makes sense. Thank you for the help!

 

[CWatters]

In case it matters...belts are pre-tensioned. The force calculated above is the difference in tension between the two sides of the belt.