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Flat Belt Pulley Traction

Flat Belt Pulley Traction

(OP)
We build hundreds of 3" wide transfer belt assemblies every year. We have been building our own drive pulleys and lagging them with rough top belting but the whole pulley assembly has become quite expensive. I have been messing with a cast pulley with traction ribs cast in but by the time the foundry is done shot blasting the surfaces all sharp corners are rounded and the traction just isn't there. I need a quick and cheap way to add traction. The draft angle on the pulley face would make traditional lagging difficult. Is there a spray on grit (thermal spray) coating I could use? Urethane sleeve or band? It's 12" OD and I haven't fount a sleeve that large. All ideas are welcome.

RE: Flat Belt Pulley Traction

My idea is to make sure you test the heck out of whatever it becomes before units go to the field.

RE: Flat Belt Pulley Traction

What you really need is for the teeth in the belt to not climb out of the grooves and I don't think that increasing the friction will help; it might make it worse as the increase will allow the teeth to climb a higher angle.

Several alternatives:

1) Look at Plaster Rubber Molding. It is probably more expensive than what looks like sand, but doesn't need draft and doesn't need post-cast finishing except maybe the bore.

2) You might also look at extruding the part as well. More metal to remove if you want the narrow hub.

3) Make a series of die plates and press the cast pulley through it to shave the outer shape to finished condition.

RE: Flat Belt Pulley Traction

(OP)
Thanks for the ideas. There are no teeth on the belt, the grooves are there for texture/traction. It is a sand cast part to keep costs in line.

RE: Flat Belt Pulley Traction

The grooves are clearly not helping with traction, so don't call them traction grooves; that's imaginary engineering.

Have you tried just rough turning the OD to a plain or crowned cylinder shape?

If that's not rough enough, you can have the OD flame sprayed/ arc sprayed/ metal sprayed with most anything, including tungsten carbide, but you'll have to explain to the spray supplier that you actually want a rough surface.


Mike Halloran
Pembroke Pines, FL, USA

RE: Flat Belt Pulley Traction

I would recommend bonding or overmolding a rubber material to the pulley surface. Rubber on rubber would give a better coefficient of friction than metal on rubber. Plus there would be less belt wear than using a rough carbide coating on the pulley surface. And it would be extremely quiet.

RE: Flat Belt Pulley Traction

(OP)
Many years ago I had a sample on my desk of a surface that had been flame/arc/metal sprayed with what I think was tungsten carbide. The sample is long gone and I've been unable to find anything like it online. If you have a source I'd be grateful If you'd share.
The overmolding idea is something else I've looked into but the cost is prohibitive, at least with the vendors I've looked at so far. Part of the problem is shipping costs. A typical run would involve several thousands of pounds of castings. Shipping them around for secondary operations can get pricey. Is it possible to do this in-house?

RE: Flat Belt Pulley Traction

For large numbers of parts, it would be far less expensive to overmold the pulley OD with an elastomer layer than spraying with something like carbide. The carbide would be more durable, but since it is also abrasive it would significantly increase belt wear. The overmolded elastomer layer on the pulley OD would give excellent traction and provide long belt life. It would also be easy to replace the overmolded elastomer layer if it degrades in service.

Obviously, it would require a specific piece of molding equipment and tooling to perform the operation in-house. But the same is true for spraying the pulley OD with carbide.

RE: Flat Belt Pulley Traction

I think the tooling for gravity casting polyurethane around the pulley, like an overmold, could be relatively inexpensive.

Look at the early history of making plastic skateboard wheels for inspiration.

Mike Halloran
Pembroke Pines, FL, USA

RE: Flat Belt Pulley Traction

I come from rubber belt conveyor engineering, there the rule was the Euler - Eytelwein - Formula

and there's 3 parameters:
- initial pull: we achieve by prestressing the belt via take-up devices
- friction: we achieve by lagging with rubber (profiled in herringbone or diamond pattern) or in extreme cases ceramic tiles, very rarely in PE / PU (only for really special cases)
- wrap angle: we achieve by a deflection pulley placed in a way to wrap the belt more than 180 deg around the drive pulley
Ceramic tiling exists in different types and usually is vulcanized onto the pulley. But there's also cold bonding of sheet like / wallpaper roll like pre-fabricated tilings.
Profiling of lagging doesn't improve friction as such, it only gives spaces for the odd dust, water, dirt etc in order to get away from the pressure area between belt and outer lagging surface.
Regards

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