MATERIALS HANDLING
Total avoidance is not possible
but reducing the chances of it happening and minimising the extent of the damage if it does occur is very achievable. The first step is identifying where objects are most likely to become trapped and taking appropriate action to minimise the risk by installing skirts or screening for example. At the same time, areas where spilled
materials build up need to be regularly inspected and quickly dealt with. Apart from increasing the possibility of objects becoming trapped, waste build-up is a common cause of failure of components such as idlers and drums and also a major contributor to premature belt wear. The importance of daily inspections
cannot be over-emphasised. The old management adage, ‘It is not what you expect, it is what you inspect’ certainly applies to conveyors. Regular, preventive maintenance, good quality components such as idlers and rollers and a clean working environment all helps to prevent damage and extend conveyor belt life. Other factors include making sure that any scrapers are correctly adjusted, and drum linings (where applicable) are in good condition. Belt tracking is also important because a mis-tracked belt can catch on the conveyor framework. Again, a clean environment is important because mis-tracking is often caused by material build-up on the bottom side of the conveyor belt or drums and pulleys.
EARLY WARNING SYSTEMS On some applications, the fitting of an early warning facility in the
Double trouble – a damaged component and an unclean environment
Diagram 1
form of a rip detection system can certainly help minimise the extent of the damage by allowing the belt to be stopped as soon as rip damage starts to occur. Rip detectors work by using detection loops that are embedded at predetermined intervals in the belt during the manufacturing process. A transmitter and receiver are positioned on the conveyor structure opposite each other on either side of the belt (Diagram 1). This is usually behind the loading position to provide protection in the area where there is the greatest exposure to risk. Multiple detection locations are also possible. The transmitter sends electro-
It is not what you expect, it is what you inspect
magnetic signals to the receiver at regular intervals. When a signal is not received by the receiver, caused by a damaged detection loop for example, then an alarm is triggered or, depending on the type of system, the conveyor is automatically stopped. Even if this facility is part of the system and the conveyor
drive automatically stops the belt for optimum safety they should still be physically monitored. A second method of condition monitoring is to continuously scan the integrity of the steel cords for breaks or damage. This also permits monitoring the behaviour of splices, checking for anomalies, and identifying damage or even impending failures. This method of scanning is typically combined with the rip detection. Having the detection loops fitted
during the manufacturing process is, of course, an additional expense and the detection systems themselves can also be quite costly. These costs need to be weighed against the cost of a major repairs, replacement belt(s) and the loss of output while the conveyor is out of service, which can be several weeks if you do not have a spare belt on site.
NOT WORTH THE SACRIFICE Despite the undisputed importance
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