The considerable length of inclined conveyors at mines often results in mining companies having to prevent reverse running, owing to loss of drive, says industrial chain, gearboxes and couplings provider Renold Clutches & Couplings applications engineer and sales section leader Philip Parsons.

The weight of material on an inclined conveyor at any time can be enormous, he adds.

Parsons states that Renold’s SH Series of sprag clutch holdbacks, with central torque arm, is the suitable solution for arduous, heavy-duty applications, such as inclined belt conveyors and bucket elevators, where reverse running could result in catastrophic consequences.

Should drive be lost, the clutch holdbacks instantaneously prevent any runback, he says.

“Since first manufactured in the 1950s, the SH Series of sprag clutch holdbacks have benefited the minerals industry. Throughout the years, the clutch holdbacks has been upgraded to meet the changing needs of the industry,” says Parsons.

He explains that, usually, if a drive stalls and the conveyor back-drives, it accelerates because of gravity until the entire load on the conveyor has been dumped at the bottom.

“Although this is not a problem for the conveyor and the bearings, it can be a big problem for the components on the other side of the gearbox, as the out-of-control conveyor drives the gearbox the wrong way and changes its speed, reducing its role to one of a speed amplifier.”

Parsons says this will overload the components in the drivetrain that would have been sized for normal operating conditions when the conveyor belt moves forward.

“Further, if a fluid coupling is fitted to provide a ‘soft’ start for the conveyor, its aluminium casing would be put under massive centrifugal loads, sufficient to make the casing explode, spreading shrapnel and hot hydraulic oil everywhere.”

To prevent this from happening, Parsons says, the SH Sprag Clutch Holdback is positioned on the end of the conveyor headshaft. If the drive fails or is stopped when the conveyor is loaded, the clutch holdbacks instantaneously prevent any runback.

“This is because of the high-quality sprag elements of the clutch being in constant contact with the inner and outer races of the clutch element of the holdback. It prevents damage to plant and equipment, the resultant downtime that would have followed and any potential accident risk to personnel,” he explains.

Parsons says these components ensure long unit lifetime and low operating costs, adding that the clutch holdbacks can accommodate large bores of up to 20 inches and have a high-torque capacity within a compact design, adding that the dimensionally interchangeable one-piece central torque arm of the clutch holdbacks is conveniently designed for ease of replacement.