Hi etse51815,

Check your shaft calculation on our free beam deflection spreadsheet on www.cospire.com / Engineering Tips / Quick Structures.

It all depends on your drive arrangement. On the pulley side the main consideration is bending stress limits. Deflection as such is not a major controlling component.

However, high shaft deflection can cause local stresses in your gearbox - hence high wear of bearings.

Use a stepped shaft to give you extra stiffness - resulting in reduced deflections. Or add an extra internal diaphragm in the drum, so the drum face provides the required stiffness.

Regards - John.Rz ■

Momentary belt tensions can be factored in a similar way to structural steel methods. We have written specification on the pulley stress analysis method that includes a load reduction for momentary forces of 25%. Thus, when the high momentary T1, T2, ect. values are divide by 1.25 and then are still larger than the high normal loaded operation, the resulting T1/1.25 will be used.

Care must be taken to include the combined T1 & T2 resulting force as they occur in operation and not from their separate maximums. ■

Good point lads.

What do you mean by start up tensions? Is that real, or hypothetical?

1 - A drive motor has a certain maximum torque. This varies with the details of the motor windings, and the starter kit.

2 - Are we looking at a cold start empty, or from an emergency shut where the whole belt is full and overflowing?

3 - Do a What If Analysis http://www.cospire.com/browse.aspx?id=4317 . Is your mathematical catastrophe certain, probably, or only theoretically possible [belt, braces, and tin hat. What if a failure did occur? Would the sun stand still? Would you be sued?]

4 - Don't get tied up in knots by the politics of "Safety Factors". We are trying to assess realistic probablities of failure, and their monetary and safety consequencial damages.

5 - What can we control, or change? Starting time ramp on the PLC?

It is OK to use your engineering judgement at times - that's what you are paid for [just watch out for the legal bullies - they can be real snakes-in-the-grass].

Regards - John.Rz ■