Rubber belts with a ‘multi-ply’ synthetic textile reinforced inner carcass are the most commonly used type of conveyor belt. The inner carcass serves as the belt’s core structural element and provides the inherent characteristics of every conveyor belt, such as its tensile strength and elongation (elasticity or ‘stretch’ under tension). Its primary function is to transmit the tension required to lift and move the loaded belt, while also absorbing the impact energy generated as material is loaded onto the belt.
The rubber covers, rather than the carcass, are widely considered to have the biggest bearing on operational performance and longevity. This is perhaps because the thick outer covering of rubber makes the carcass invisible to the eye. Whatever the reason, the fact remains that the carcass is the heart of every conveyor belt. Its importance should never be underestimated because deficiencies can be extremely costly.
Fabric quality
Almost without exception, rubber multi-ply belts use synthetic fabrics. Currently, the most commonly used type is a combination of polyester and nylon (polyamide), referred to as ‘EP’. Even in belts that have low quality (low cost) fabrics, it is unusual to find a fabric that has inadequate tensile strength. However, although the amount of material used in the longitudinal strands of the fabric may be sufficient to achieve the required tensile strength, to reduce cost, the use of the more costly nylon transversal weft material is kept to a minimum. As a consequence, rip and tear resistance are reduced and elongation (stretch) is low, which can cause problems with transition distances and a general inability to accommodate the contours of the conveyor and its drums and pulleys. Ultimately, this can lead to the premature failure of the belt.
A common deception
Unfortunately, due to price competition, it is becoming increasingly common for some manufacturers, traders, and importers to supply belts that have totally polyester (EE) fabric plies in a carcass that is declared to be a polyester/nylon mix (EP) construction. The reason for this deception is that EE fabric costs some 30% less than EP fabric. This is significant because, after rubber, the fabric is the highest cost component, so using cheaper polyester fabric is a big help towards achieving the perception of a lower ‘like for like’ price.
This is a preview of an article that was originally published in the April 2025 issue of Global Mining Review.
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