Making blockages a less tense situation

Two fatalities in just one year, related to the same piece of equipment, led to important improvements in worker protection. However, arguably these did not go far enough. Now a solution from Renold Couplings helps to provide even greater safety.

Mining, as anyone who works within it knows only too well, is a dangerous industry. It is not just underground and at the coalface where serious - and even fatal - accidents can occur. One piece of equipment which has led to serious accidents is the inclined conveyor. But a solution from Renold Couplings promises to alleviate the risk, and Rio Tinto is just one company which has taken advantage of the innovation to protect its workers.

The mining industry would find it hard to function without the inclined conveyor to transport coal. However, in the event of a loss of power, their design means that they can run backwards out of control if in a loaded condition. For that reason, for many years they have been fitted with backstop sprag clutches. These work by allowing a shaft to rotate in one direction as the sprags slip. But, if the shaft tries to turn the other way - as it will do if the conveyor begins to run backwards - the sprags immediately stand up and lock.

These same safety components are also fitted to theme park rides to prevent cars from running downhill in the event of a power failure.

Although this effectively solves the problem it was designed for, another associated problem can also occur, for which it is not only no help, but also actually the direct cause.

If a blockage occurs between the lower belt and the return end shaft, the conveyor will stall. The backstop sprag clutch then comes into operation to prevent the belt from running backwards, but as a result tension builds in the upper belt, because the slack in the lower belt can't feed back through the drive.

The natural reaction of the operator is to remove whatever is causing the obstruction, to get the conveyor back in operation as quickly as possible. But if the tension in the upper belt isn't released first, the sudden release that occurs when the blockage is removed will cause it to pull the lower belt rapidly around the return roller with huge force. This force can be so powerful that it has been known to cause the load on the top belt to explode in all directions, and has even pulled the worker removing the blockage into the conveyor.

The answer developed by Renold is the tension release and torque limiting safety holdback sprag clutch, which has been designed to enable the extreme tension in the upper belt to be released in a controlled way, through controlled friction slippage of the sprag clutch element of the backstop.

With the tension released in this controlled manner, maintenance work can be carried out to remove the blockage and get the conveyor up and running again, quickly and safely. You can see the safety tension release mechanism in operation at www.renold.com and at www.youtube.com/user/renoldpic or contact the specialists at ERIKS UK for more information.

Increased safety goes hand-in-hand with additional capacity