Catastrophic belt damage – Taking care to reduce the risk.
It is estimated that in mining and quarrying especially, up to 80% of belts that are replaced prematurely is a result of accidental catastrophic damage. Such damage is regarded by some as being so impossible to avoid that they use cheap, low-grade ‘sacrificial belts’. Ironically, the cost of this surrender in time and money spent on regularly buying and fitting replacement belts, the loss of output due to stoppages to make repairs and the cost of the repairs themselves is actually a far more expensive option. Fortunately, there are several steps that can be taken that will significantly reduce the risk of severe belt damage.
It is not what you expect…
The biggest single cause of catastrophic conveyor belt damage is trapped material such as large, sharp rocks or foreign objects such as sharp pieces of metal. When lodged in a chute or some other part of the conveyor mechanism, they can puncture the belt cover and then penetrate the belt carcass, cutting the belt lengthwise as it is pulled against the object. Even the thickest, heaviest of belts can quite easily be ripped over their entire length in a matter of minutes.
One of the best ways to reduce the risk and minimize the extent of the damage is to identify where objects are most likely to become trapped and take preventative measures such as installing skirts or screening for example.
At the same time, areas where spilled materials build up need to be regularly checked and quickly dealt with. Apart from increasing the possibility of objects becoming trapped, waste build-up is a common cause of damage to components such as idlers and drums, which can cause a lot of collateral belt damage.
A significant proportion of belt damage is caused by incorrect installation of auxiliary equipment, damaged, protruding steelwork and components vibrating loose and becoming detached. The most effective way to avoid such problems is regular inspection (at least daily) backed up by a preventive maintenance regime that includes a policy of rapid replacement of worn or damaged components.
…it is what you inspect.
The importance of daily inspections cannot be over-emphasised. Regular, preventive maintenance, good quality components and a clean working environment all help to prevent damage and extend conveyor belt life. Other factors include making sure that any scrapers are correctly adjusted and that 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, having 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.
The loading point of any conveyor should always be a target for scrutiny because it is so often the source of damage problems. Key factors include making sure that loading is central and at the same speed and direction as belt travel. If necessary, reposition or redesign chutes to reduce the velocity of free-falling material. Incorporating screen bars into the back plate or chute or cutting a ‘V’ slot at the bottom of the chute when handling lumpy materials mixed with fines is another option because this allows the fines to form a bed (cushion) to help absorb impact. Another method is to use impact idlers and/or cradles.
Engineered for the task.
Having implemented such preventative measures, the risk of damage can be substantially reduced still further by fitting a conveyor belt that has been specifically engineered so that it will not be cut, torn or ripped to shreds under the slightest provocation. Specialist belts such as Fenner Dunlop’s UsFlex and Ultra X range, are proven to last up to four or five times longer than conventional multi-ply conveyor belts. This is because they use very high quality rubber and uniquely designed fabric plies that allow the transversal nylon strands to stretch. As the trapped object is being pulled through the belt, the strands gather into a bundle that eventually becomes strong enough to stop the belt in its tracks rather than propagate over a much long distance. The design of the fabric also allows the energy created by heavy impact to be dissipated over a much wider area rather than rupture the inner carcass.
Although the initial purchase price may appear high, specialist belts will, over their lifetime, cost substantially less than even the cheapest, thickest ‘sacrificial belt’. As they say, price is what you pay but cost is what you actually spend.
Bob Nelson
