# Tension in Conveyor Belt due to weight placed on it

1. Jun 15, 2015

### achan88

Hello,

I am trying to determine the tension in a belt conveyor transporting material to calculate the motor power required and also tensioning force needed on it. I wanted to know how the material weight that is being carried affects it. I considered the tension to be equal to the friction force due to material weight as well as the belt weight. So assuming the material wt. = Wm lbm and belt wt. = Wt lbm, the frictional resistance will be = (Wm+Wt)x g x μ. Is this correct? What other forces do I need to take into account?

I have attached a schematic diagram of the problem.

Thank you.

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2. Jun 15, 2015

### Baluncore

If the material is placed continuously along the belt then you have a catenary between supporting rollers.
As the sag allowed between rollers increases, the tension in the belt rapidly reduces to a reasonable value.

3. Jun 15, 2015

### billy_joule

A free body diagram will show that If the belt does not sag the tension due to the weight is infinite..
So clearly the belt will sag - And how much it sags will define the tension.

What friction are you trying to find? The bearing friction in the rollers? The belt-roller interface friction?
These may help for the former:
http://www.roymech.co.uk/Useful_Tables/Tribology/Bearing Friction.html
http://www.skf.com/group/products/b...ings/principles/friction/skf-model/index.html

For the latter, the belt-roller friction is really only important for the driven roller (assuming that's how it's driven), the belt-roller friction at the idler rollers should only become relevant during bearing failure - assuming your bearing selection is acceptable.

4. Jun 15, 2015

### achan88

Oh, I forgot to mention that the belt is traveling over a 3"x3" mesh support grid of 1/8" SS rods. So the sag is pretty much negligible. The frictional force that I am considering is the resistance to the belt sliding over the mesh while carrying a constant layer of material. The speed is also pretty slow, about 2 ft/min.

I also found this webpage : http://www.brighthubengineering.com...nsite-calculations-for-conveyor-belt-systems/

Does this equation account for the friction resistance or do I need to add it to calculate the total effective tension?

Thanks.

5. Jun 15, 2015

### Baluncore

That is a game changer.
That is enough to estimate the tension if the belt only moves material horizontally.

6. Jun 16, 2015

### Staff: Mentor

A couple of things:
1. A conveyor belt that is allowed to sag is not being properly supported. They should never be allowed to sag.
2. Even if it did sag, that has nothing to do with the power needed to make it run because the sag tension is a constant force that is equal everywhere and is static: it exists whether the belt is moving or not and isn't affected by the motion.