Belt Drive vs. Direct Drive 1

[ChE51]

Hey,

I am purchasing a particle-size reducer and need to decide the type of drive I want to use. The piece of equipment comes standard with a belt drive. I know belt drives are usually cheaper but usually have lower performance. Are there any other advantages/disadvantages? Such as maintenance, product/seal leakage, reliability, etc..
Any suggestions would be of great help.

Che51

 

[jbartos]

Suggestion: The direct drive is better
Belts will:
1. Age and deteriorate
2. Have bigger losses
3. Cause vibrations
4. Break in time
5. Cost money when replacing
6. Have availability and lead time factors to be remembered
7. Etc.

 

[mvcjr]

I'm not saying I am for belt drives but some of the advantages I can see are:
1. Belts absorb some of the shock during starting (something analogous to a fuse, sacrificing the belts rather than the driven equipment? ) in the drive train.
2. Belts allow you to mount your motor in a more accessible location, thus resulting to ease of installation & maintenance.
3. Some loads operate at speeds not directly possible with direct drive set-up.

God bless!

 

[electricpete]

I agree with all the above. Belts can have some advantages in terms of motor intial cost and efficient oeprating speed. The speed can also be adjusted relatively easy for fine-tuning on site.

We have only <5% of our machines belt drive. We tend to have relatively lot of problems with them and more difficulty aligning and sometimes takes a few attempts to get the right tension. Then again, it is partly a function of our expertise... if we had more belt drives we would be better at it.

 

[jOmega]

Also look at the ratio of the sheaves; motor... load.

Typically you get a mechanical advantage if the load sheave is larger than the motor sheave.

If you were to go to direct drive... this factor would have to be evaluated... and the motor would have to be sized to provide the necessary torque to the load that the belt drive did.

As an example, a 5 hp 1750 rpm motor develops 15 ft.lbs of torque. Couple the motor to a 2:1 belt reduction and you now deliver 30 ft.lbs torque to the load at 875 rpm.

If you remove the belt drive, and couple the 5 hp motor direct to the load... you may not have enough torque to support the load; particularly if the load torque is greater than 15 ft.lbs....

In this case you could opt to replace the 5 hp 1750 rpm motor with a 5 hp 875 rpm motor.... and have enough torque for the load.

But 5 HP - 8-pole motors are not that common and so, are more expensive.

if the ratio of the sheaves .... motor to load.... is 1:1...then the above consideration is not necessary.

The belt drive vs direct drive argument is usually one of ongoing maintenance costs that are elminated with direct drive.

jO

 

[SteveKW]

Given the option I would get the belt drive since you can troubleshoot it easier and get a replacement motor cheaper & faster than say a motor that is C faced.

 

[jOmega]

C-face motors are relatively common.... and the C-face bracket is a standard option and usually available from stock from most NEMA Frame motor manufacturers.

 

[edison123]

Assuming speed reduction, a direct drive low speed motor will have a lower efficiency, lower power factor, bigger size and higher cost as compared to belt driven higher speed motor. Of course, belts themselves have plus and minus points as pointed out by mvcjr and jbartos. When a load requires a RPM not obtainable directly from ac motors (without use of VFD), then belt drive may be the only cheaper option.

 

[ChE51]

Thanks for the help. I believe I am going with the belt driven motor.

Che51

 

[jbartos]

Suggestion: Belts can help the motor to achieve the higher than synchrounous speeds.

 

[jOmega]

JB:

Joseph,

How do &quot;Belts can help the motor to achieve the higher than synchrounous speeds.&quot;

Please explain.

(I know this is gonna be good!)

Or perhaps you meant that belting can run the load at a speed higher than the synchronous speed of the motor ?

j

&#937

 

[jbartos]

Clarification: The belts help motor to bring the load to the higher than synchronous speed over a proper ratio of pulleys.

 

[macmil]

All the above information is valid. I used V belt drives for years with relatively little problem. In more critical applications, I also used timing (cogged) belt drives with good success. They are a little more expensive, but are more tolerant of temperature variations, and dirt causing slippage, and typically require less belt tension, reducing the load on the drive end motor bearing.