Conveyor belt expert Leslie David explores advances in the technology and the benefits they afford to industry
Written by: Leslie David
In the mining industry, as with many other industries, conveyor belts are critical components that play an essential role. Their reliability and efficiency are essential to success. It is therefore surprising to find that, in a world of continual technological advancement, the basic construction of rubber conveyor belts has not fundamentally changed since 1905 when mining engineer Richard Sutcliffe invented a belt made from layered cotton and rubber. Since those early days, the rubber is now almost entirely synthetic, and the multiple layers of cotton have been replaced by layers of synthetic (usually polyester and polyamide) fabric ply material with a thin layer (skim) of rubber in between each layer. In principle, the heavier the application, the more layers that are used.
This multi-layered carcass structure is protected by an outer layer of rubber. Known as ‘multi-ply’ belts, they are by far the most common type of conveyor belt. But that is where the new thinking seemed to end, until now.
Ever decreasing life cycles
Primarily due to the focus given by Southeast Asian manufacturers on gaining a price rather than a performance advantage using a market saturation strategy, the vast majority of belts no longer provide a cost-efficient working lifetime. General wear, especially rip, tear and impact damage, cutting, gouging and rubber degradation caused by exposure to ozone and ultraviolet light are all reasons why more than 80% of all conveyor belts are replaced considerably sooner than they should be. In an increasing number of cases, within months rather than years.
To many in mining and quarrying, the catastrophic damage caused by trapped objects is considered inevitable. Consequently, growing numbers are falling into the trap of using low price imported ‘sacrificial’ belts, resulting in ever decreasing cycles of fitting, repairing and replacing.
However, one conveyor belt manufacturer, Fenner Dunlop Conveyor Belting in Europe and North America, part of the Michelin Group, sees things very differently and is bringing about a radical change of thinking. Since the hugely successful introduction of its single and dual-ply UsFlex belt more than two decades ago, it has continued to develop the concept. Known as the X Series, it not only replaced thick, multi-layered belts, it also provided numerous advantages. Although thinner and lighter, Fenner Dunlop’s single and dual-ply belts are actually much more robust and resistant to damage than their multiple ply counterparts.
In theory, a higher number of inner plies should result in a stronger belt. However, the greatest influence on the strength and other essential physical properties of a conveyor belt is the design and quality of the ply material used to create the carcass. The big advantage Fenner Dunlop has is that it has its own fabric weaving facility in the US. This is where the company has been able to develop a range of unique super-strength fabrics for single-ply belts (Ultra X and Nova X) and the longer established single and dual-ply UsFlex constructions. The carcasses possess a longitudinal rip resistance that is more than five times greater than multi-ply belts of equivalent rating, they also have up to three times greater impact resistance compared with conventional belting. This is quite a breakthrough. So, how does it all work?
It’s all about the fabric
The whole working principle of being able to create advantages from using single and dual-ply belts centres on the fabric. Having already developed rubber cover compounds that are well-recognised as being the hardest wearing and longest lasting, the company’s engineers focussed on the design of the fabric. The starting point was to ensure that the individual fibres and yarns were of the highest possible quality and strength. Next came the weave pattern, which is where fabric technology becomes difficult to explain.
The X Series has (so far at least) three versions of fabric. Ultra X features a specially woven ‘Crimped warp’ carcass, combining crimped polyester warp yarns with strong binder and filler yarns, creating exceptional strength, stability, and impact resistance. The higher tensile strength Nova-X (available in North America and coming soon to Europe) uses an even stronger crimped warp fabric with binder yarns to lock the carcass, providing excellent rip, tear, and impact resistance under load. The even heavier duty UsFlex employs a ‘Straight warp’ carcass, made of high-tenacity polyester fibres protected by polyamide weft lines.
What all X Series fabrics have in common is that they consist of longitudinal strands lengthwise and heavy strands running crosswise, held in position by a strong yarn. The strands are completely straight in both directions and not interlocked as in conventional fabric. This allows the weft to float free from the warp. A shock absorber effect is thereby created by dissipating impact energy over a larger area, allowing the belt to withstand the kind of punishment that would destroy a normal multi-ply belt. Arguably even more important is the ability to resist rip and tear damage.
When penetrated and being pulled through a trapped object such as a large, sharp rock, the unique weave design allows the strands to gather in a bundle that can eventually become strong enough to stop the belt or even expel the object causing the damage.
Strange as it may seem, synthetic plies are usually more effective than steel when it comes to minimising the length of a rip. In fact, the UsFlex fabric is so strong that Fenner Dunlop uses it as a breaker ply in its steel cord belts. As one quarry manager was testified: “We used to replace our belts every three to six months before we started fitting UsFlex belts. Now it can be four or five years before we need to fit a replacement.”
Defying convention
For some, the very idea that a single or dual-ply construction belt can provide the necessary tensile strength while possessing considerably more resistance to damage is difficult to comprehend. The answer lies in a combination of the innate strength of the fabrics together with a higher level of splice efficiency. Although a step splice can be used to join a dual-ply UsFlex, single-ply constructions require a finger-splice joint (depending on the application, mechanical fasteners can also be used on X Series single-ply belts). The enormous advantage of finger splice joints is that they retain up to 90% of the belt’s tensile strength. By comparison, a two-ply step splice only retains a maximum of 50% and a three-ply step joint only achieves a maximum tensile strength of 67%. Single and dual-ply belts joined by a step splice create equivalent tensile strengths and belt safety factors that are more than comparable to three or four layer conventional belting. For example, an Ultra X3 single-ply belt can pull up to 56t. A significant additional benefit of this method is that finger splice joints are stronger and more durable so the need to repair and re-splice joints is much less frequent.
Another advantage is that X Series single and dual-ply belts are more flexible, so they are also better suited for use on mobile conveyors, which are notorious for having small diameter pulleys where the continual flexing places greater dynamic stress on the inner carcass and splice joint, therefore seriously limiting what can normally be fitted.
Better for the environment
The reduction in environmental impact is also considerable. Having only one or two layers rather than three, four or more layers helps to reduce energy consumption (they are typically 10% lighter) and maximise production efficiency. It also means that less rubber is used, including a corresponding reduction in the chemicals and additives used to make it, together with a dramatic reduction in non-bio-degradable synthetic fabric. The superior toughness also means that the fabric need to be replaced far less frequently, meaning that some 50% fewer conveyor belts have to be manufactured in the first place.
A cultural change?
Having sold countless thousands of metres, Fenner Dunlop management claim that have not had one single complaint or technical issue. This seems to be supported by the evidence. Ultra X and UsFlex are now the belts of choice in a fast-growing number of mines and quarries on both sides of the Atlantic. Fenner Dunlop believes that single-ply and dual-ply belts are the future. Given the evidence, who could argue?
About the Author: After spending 23 years in logistics management, Leslie David has specialised in conveyor belting for over 18 years. During that time, he has become one of the most published authors on conveyor belt technology in the world.
For more information, visit: www.fennerdunlopemea.com
