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strength. Laboratory testing consistently reveals that so-called ‘economy’ belting is very rarely, if ever, ozone and UV resistant.
LOW-COST COMPONENTS Yet another connection between price and belt life is carbon black polymer, which is a key component of black rubber. Because it makes up around 20% of a typical rubber compound it is yet another target for cutting costs despite the crucial role that it plays. For example, carbon black prolongs belt life by helping to conduct heat away from the surface area of the belt. Tis reduces thermal damage and thereby slows the ageing process. It also acts as an important reinforcing compound. Good quality carbon black is costly, especially since the Russian invasion of the Ukraine. Premium-grade carbon black is more costly because it is created by a process of burning oil in a strictly controlled, low oxygen environment so that combustion is incomplete whereas cheap carbon black is usually produced by burning scrap car tyres. Burning old car tyres not only pollutes the atmosphere it also means that any oils and greases remain present within the ‘regenerated’ materials, which has a detrimental effect on the physical properties of the rubber. Belts offered with significantly lower prices are virtually certain to contain low-grade carbon black. Other methods to reduce the cost of the
rubber include the use of low-grade (reject) recycled rubber of highly questionable origin and cheap ‘bulking’ fillers such as chalk, which are used to replace part of more expensive rubber, despite the fact that they limit the life of the belt.
THE CARCASS Multi-ply construction are the most common type of conveyor belts. Tese consist of layers of fabric plies, usually
Lower-grade carbon black can be produced cheaply by burning scrap car tyres
polyester and nylon (EP). Polyester combined with nylon has the best balance of mechanical properties including allowing a conveyor belt to run straight and true, to trough, to flex round pulleys and drums, stretch, provide sufficient transversal rigidity, longitudinal strength and much more besides. All of which contributes to the working lifetime of the belt.
However, there are often huge
Quantum advances in conveyor belt technology have been made in recent years
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differences in the quality of the fabric plies between one belt and another because cheaper, lower quality fabrics are used where the more costly nylon transversal weft material is kept to a minimum. Although the required tensile strength may be achieved, rip and tear resistance are noticeably reduced and elongation (elasticity) will be too low. An even more dramatic cost-cutting method involves the use of totally polyester (EE) fabric plies in a carcass that is specified as having an EP (polyester/nylon mix) construction. Te fabric plies are a major cost component and because polyester (EE) fabric costs around 30% less than polyester/ nylon mix fabric (EP) it is a big help when trying to achieve the perception of a lower ‘like for like’ price. Te use of totally polyester (EE) fabric compromises a numerous essential mechanical properties*. Tese include low transverse elasticity, which reduces both the troughability and impact resistance of the belt as well as causing tracking issues, a reduction in rip resistance, fastener strength and greater risk of dynamic stress failure. Again, these detrimental physical effects have a significant impact on the life of the belt.
*Author’s note: Te use of fabrics made entirely of polyester (EE) has its place in
certain belt types and constructions – such as those used in saw mills, for example. However, in those cases the declared specification of the belt should clearly be EE and not EP).
A COMBINATION OF WEAKNESSES TO BE CONSIDERED A huge proportion of conveyor belts in mines and quarries are replaced prematurely because they have been irreparably ripped or torn. In these cases, the type of material being conveyed such as heavy, sharp rocks, is a major factor. For a belt carrying this type of material to provide a cost-effective life cycle means that it must be able to withstand the forces that rip and tear them apart. Such resistance is created by the combination of a high-quality inner carcass and high-quality rubber covers that are durable enough to protect that carcass. If either is lacking, then the belt is highly likely to be destroyed before it has paid for itself.
Knowing how the ultra-competitive
prices are often achieved makes it much easier to understand how good quality, European-made belts can consistently provide an operational lifetime that is up to four or five times longer. So, the answer to those two commonly asked questions – “how much does a conveyor belt cost?” and “how long do conveyor belts last?”– is that price ultimately determines the longevity, and it is the longevity that determines the true cost of a conveyor belt.
Leslie David is an independent specialist in conveyor belting solutions.
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