Easy,

Basic mechanics, if the chain slips on a smooth headwheel (i.e. no teeth) then the T1/T2 tension ration across the headwheel to too great for coefficient of friction between the chain and wheel.

Options :-

1) Fit a toothed wheel at the head so you're not reliant on friction for a drive.

2) Reduce the T1/T2 tension ratio by using a gravity weight tensioning system and adding extra weight.

3) Increase the angle of wrap at the head wheel by fitting snubbing wheels (only possible with side mounted buckets). ■

I had a figure, but can't find it at the moment.

But at Webster you'll have access to some chain and wheels. Do what I did 20 years ago -

1) mount a wheel on a shaft.

2) put a 180 degree wrap of chain around it.

3) attach a spring balance to each end of the chain.

4) put some tension into the chain.

5) rotate the wheel so the the chain slips on the wheel.

6) record the values on the spring balances.

7) add more tension and repeat, several times.

8) plot the tensions on X and Y values of a graph.

9) the slope of the graph is the T1/T2 ratio.

Oh, and don't work up to the limit you have measured! ■

Buy a sprocket for the head shaft top drive end and forget your problems. ■

I'm fascinated by the original concept. Without very high tensions the drive seems impractical...Unless... the top wheel grips the back of the buckets..in which case it would be quite clever. After all a dangling belt does not contribute to drive friction. What is the drive geometry in regard to bucket height, drum diameter & bucket pitch?

A single sprocket at the head end will not provide adequate torsional restraint. Is there a wearing/worn section at the inner face of the buckets? If the buckets cleverly provide the friction then they must support the chain against bottoming in the groove. If not then the chain slips, wears away the root of the groove until the buckets can contact the drum. Then the buckets wear until the chain contacts the drum and the whole thing settles down.

If there is inadequate torsional rigidity this twist contributes to increased pressure on one side of a bucket which alters the drive torque temporarily. Have you examined this scenario? ■

Strange as it may seem, friction drives on chain & bucket elevators work quite well.

Really, the only difference between the friction drive on a belt conveyor and a friction drive on a chain & bucket elevator is the coefficient of friction you use. As you use the appropriate value for a belt, similarly you use an appropriate value for for a chain. The friction theory remains the same. ■

There is nothng wrong with friction drives

Spillage is a problem....generate heat, wear chain links etc

U need to investigate when it happens - what is the scenario....starting, running , after a surge from the upstream equipment.

Pls note that the max. capacity is > design capacity eg bucket fill level is typ. 75%.

Coal can contribute to lower co-ef of friction > hence, more tendency to slip.

Suggest adding more weight to the tail stn...make it free and not screw....need to check FOS on your chain.

Cheers

James ■

I measured the coefficient of friction on my chain/wheel setup at 0.34.

Make of it what you will :-)) ■