Belt Tracking Question 1

[cavediver]

Hi guys,
I have a question that I am trying to find an answer to. I have been browsing the web looking for an answer and have found your site, hopefully you can help me out.

I am a field service tech looking for a comprehensive answer to provide to my enginneering team regarding belt tracking. I have found in the field that a belt (conveyor belt, or timing belts) tends to track towards the "tighter" side of the adjustment pully. Or, if I have a ballanced pulley/belt system, say a conveyor, and I tighten the right side, the belt tends to travel to the right, towards the tightened pulley.

This isn't making sense to me. By tightening the pully/belt on one side only (adjusting the adjuster bolt to increase the overall diameter of the one side of the belt) I would think that I am "tapering in" the other side, and the belt, being under tension would want to slid down away from that side, essentially reducing the tension on the belt....I'm confused, why is it climbing the pulley and becoming tigher????

You help is greatly appreciated in helping me cure this headache!!

Any links with discriptive answers are greatly appreciated,

Thanks in advance for your help, John

 

[cavediver]

Also, if it helps to describe my question. I've noticed that most belts have crowned pullies helping keep the belt centered.....Why/How does this work?

 

[JakubMech]

The crowning is a centering effect. Basically the high spot pulls the belt towards that area. By tightening one side of a roller it is simulating half a crown.

 

[btrueblood]

The reason for the centering effect is a bit difficult to describe, but a teacher once showed me a really great demonstration. Take two spheres mounted on axles (1" ball bearings with holes in 'em were what he used), and a wide rubber band. If there's any tension on the band, it will "climb" to center itself on the balls. If you watch carefully, you see that the edge of the band, when off-center, makes first contact with the ball surface slightly to the "high" side of where the rest of the band is running. As the belt continues around the ball, it walks its way up to center, just like winding a belt over a sheave flange.