What goes around: Longer haul distances are one of the reasons that energy use in mines is increasing globally by 6 per cent per year. It is not surprising, therefore, that mines are looking for ways to counter the associated increase in energy cost. But there is a new material that could help to make conveying minerals energy efficient and reliable.
Most minerals travel a long way from their point of extraction to their point of use. Typically, this journey involves trucks, steel conveyor belts, endless belts, steel conveyors, trains and/ or boats. For short haul distances, truck transport offers a flexible solution. But this transportation option is heavy and requires a lot of fuel. As a result, there has been a noticeable shift towards conveyor transport.
What is more, distances within mines are typically increasing, because the longer a mine is in operation, the further away extraction moves from the processing point (such as a power plant built next to a coal deposit). An additional challenge that mines are facing relates to their licence to operate from society. People are increasingly critical about the use of fossil energy and carbon emissions.
Reinforcing Conveyor Belts
About a century ago, the first conveyor belts were small, and at that time, rubbers were typically reinforced with cotton. Today, natural cotton fiber has been replaced by modern man-made materials, such as polyester (PET) and polyamide (PA) or endless steel belts. These materials are light, strong, resilient and abundantly available. However, they have one serious drawback - low stiffness modulus.
Long belts have extreme elongations. A 5 km conveyor installation, for example, has a 10 km looped belt. If this belt elongates by 3 per cent under running tension, 300 mt of excess belt length is formed, which needs to be taken up. That is why long belts are normally reinforced with steel, in the form of embedded cables.
However, steel belts not only have a high modulus but also characterized by a substantial density (7.8 kg/L). In any moving system, more weight means more energy consumption. So, are there any solutions that can help lower the weight of conveyor systems?
Aramids – Strong and Light
Aramid fibers may embody the perfect solution to this problem. The name aramid derives from aromatic polyamide. Like any man-made high-strength fiber, its strength is achieved by carefully aligning strong molecular chains along the direction of the force. The result is a fiber that is almost as strong as steel, but a lot lighter.
Aramid fibers have a density of just 1.45 kg/L—five times lighter than the steel. Aramids are also three times stronger than polyester, which is also a frequently used as a reinforcement material in conveyor belts. Refer to the Figure 1 that compares the tenacity and elongation of steel with that of three man-made fibers.
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