MRO Magazine

Conveyor Surveyor Sees Solutions

Most conveyor belt maintenance activities and replacements are necessary because of mechanical damage, not wear. This article looks at system components and ways to avoid mechanical damage, reduce downtime and extend belt life.


April 1, 2004
By Steve Minett, Ph.D & Roy Dennis

Most conveyor belt maintenance activities and replacements are necessary because of mechanical damage, not wear. This article looks at system components and ways to avoid mechanical damage, reduce downtime and extend belt life.

There’s a tendency of many buyers to see conveyors as simple and to buy their components as commodities — especially the belt, says Lars Vistrand, president of the conveying division of Svedala — a Swedish-based, global mining and construction equipment group. Conveying systems are, in fact, rather complicated, he says.

In the majority of cases, belt replacement is required not because of wear but as a result of mechanical damage, says Vistrand. He has identified the typical causes of such damage and suggests their solutions.

Belt slippage: There are three main reasons why belt-to-pulley slippage occurs. The coefficient of friction between the belt and the pulley might be too low. The angle of wrap can be too small or the pre-tensioning of the belt may be too low.

Advertisement

The most cost-efficient solution to a slippage problem is to increase the coefficient of friction by using pulley lagging. With the right design the pulley lagging will also prevent the buildup of transported material and snow and ice on the pulley.

Material adhering to the belt: Sticky material can adhere to the belt, or dry material can get stuck in wear cavities on the belt. When the belt is running, material can fall off, building up under or on the conveyor. It can also cause damage to the underside of the belt and idlers.

Material buildup can be a particular problem where a double-pulley drive is used. Here, the belt is reversed onto one of the pulleys and material builds up in the centre of the pulley cylinder. This in turn distorts the belt. The splice is usually the first to fail.

This problem was originally solved by manual maintenance and the installation of a timber scraper. However, if the cause of the problem is sticky material, the answer can be a two-scraper system — a pre-cleaner and a T-cleaner. For cleated belts, a belt brush might be the answer.

Side spillage at loading stations: Material tends to tumble and bounce when dropping onto a conveyor belt, particularly if the transfer point is at a 90 degree angle to the receiving conveyor. Combined with the fact that the use of idlers leads to sagging of the belt between them, this may lead to spillage of material over the side of the conveyor belt in the transfer area.

This problem can easily be solved by installing a loading station combined with a sealing system. The impact bars prevent sagging of the belt and the low friction top cover offers a flat surface for the sealing blocks to seal against.

Impact damage to the belt: This is especially prevalent where the conveyor carries very coarse or sharp-edged materials that cause weak points, holes or even tears in the belt. In some occurrences the full length of the belt may be slit. Steel cord belt without rip-protection is especially vulnerable to this sort of slitting.

The answer to the problem is to use a loading station. Composite impact bars consisting of an aluminium track for fastening, special rubber for impact absorption and a low-friction top surface prevent damage to the belt.

Missaligned belts: Misstracking belts can result in major costs. A belt guiding system can cut maintenance costs substantially through actively controlling and guiding the belt back on the right track. Moreover, revenues increase as a result of higher conveying capacity due to reduced material spillage.

The risk of costly, unscheduled maintenance shutdowns due to belt damage can also be reduced considerably by installing a belt guiding system, providing a maintenance-free solution.

Unquestionably, a good working environment is important. Since material spillage is reduced with a belt guiding system, a cleaner working environment is obtained. In addition, the cost for continuous cleaning of the worksite can be minimized.

THE PROS AND CONS OF HIGH WEAR-RESISTANCE BELTS

The most important component of a conveyor system, whatever the on-site materials or operational problems, is still the belt itself. “Customers often tend to see belts as consumable commodities and are inclined to buy the cheapest available,” says Vistrand. “However, a 5% saving can be lost within half an hour of operation should a belt problem occur.

“Additionally, a belt that is 5 mm thick, as opposed to 3 mm, costs only 20% more, but will provide 60% more operational life.

“On the other hand, you may ask why you would buy an extremely wear-resistant belt when most belts fail because of mechanical damage. If you let the integrated conveyor systems and components take care of the mechanical damage, then it will be worthwhile buying a highly wear-resistant belt.”

This article was prepared by Minett Media. The Svedala Group, a unit of Finland’s Metso Minerals, operates in 50 countries and has over 11,000 employees worldwide. Since 1988 it has acquired some 300 brand names, including: Dynapac, Denver Sala, Trellex, Skega, MacNally Wellman, Reedrill, Allis Chalmers, Lindemann and Barmac. Metso Minerals (Canada) Ltd. has facilities across Canada. For more information, visit www.svedala.com.