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Conveying


Modular components such as track-mounted pulleys can deliver slide-in / slide-out convenience.


By nature, spillage costs money. If people are cleaning up fugitive material, they’re wasting labour. If material is escaping, it’s wasting a valuable resource or product. While some operations can return the spilled material to the process, it often contains impurities that can raise product quality issues. In other facilities, the material must be discarded or washed away, a particularly expensive approach if the conveyor’s contents have already undergone some amount of refining by the time they reach the spill point. In an example not uncommon in bulk materials handling, one facility conveying 800 TPH was found to be literally washing an estimated $1.2 million worth of material down the drain every year. An effective system of fugitive material control that is properly installed can drastically reduce waste, often paying for itself in as little as 6-12 months. Another problem caused by fugitive material is flow restrictions. Chute or bin blockages can bring even a large-scale process to a standstill, causing thousands of dollars in downtime, corrective measures and lost production. Blockages can also cause material boilover and sudden surges, as large amounts of material suddenly break free and drop through a receiving vessel and onto the belt. Both conditions are major contributors to spillage, which can also introduce belt tracking error that can damage equipment and increase the risk of injury.


A well-designed conveyor system will often employ skirtboards for reducing spillage, used to contain the load as material is placed on the belt and until it assumes a stable profile. Skirtboards at each transfer point must be


20 September 2014 Solids and Bulk Handling


engineered to match the characteristics of the material, the receiving conveyor, drop height and transfer point design. Another form of fugitive material is dust, whether settled or airborne. In addition to the potential fall hazard, risk occurs primarily when fine, lightweight particles are sufficiently disturbed to launch them into the air, where their low mass causes them to hang suspended and travel in the wind. Dust inhaled by workers or members of the surrounding community can irritate airways and exacerbate conditions such as asthma. From a purely financial perspective, when equipment air intake includes significant amounts of dust, it can lead to more frequent maintenance and greater engine wear, causing operating costs to rise. Conveyor dust can also generate complaints from local residents and businesses, affecting community relations, creating obstacles to future operating permits or leading to increased scrutiny. As material escapes, it accumulates on idlers and other components, contributing to premature failure. Once a bearing seizes, the constant belt movement can wear through an idler shell with surprising speed, leaving a razor-sharp edge that poses a threat to workers and the belt itself.


Spillage can also contribute to the risk of fire by interfering with pulleys and idlers and by providing potential fuel. Most conveyor fires are ignited by friction-generated heat from a pulley turning against a stalled belt or a belt moving over a seized idler. A conveyor belt fire of any size is a serious issue, not only because the belt or its contents may burn, but also because the length and


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movement of the belt can spread a fire a great distance in a very short time. One overheated bearing and a small amount of powdered material can quickly turn into a large-scale event. Even worse, in confined spaces, airborne particles can create the right ingredients for an explosion. An elastomer edge seal is often used to prevent the escape of fines, typically constructed from steel plate. In addition to managing the bulk material to control spillage, the skirtboard and sealing system form a settling zone that contributes to effective dust management. In this zone, the air current traveling with the material stream is slowed and controlled, allowing airborne particles to fall back into the bulk material. When a conveyor has multiple loading points relatively close together, it may be advisable to install a continuous skirtboard between the loading zones. An experienced supplier of conveyor technology should be well-versed in the design options and able to provide sound advice on optimum features to suit an individual application. The symptoms of carryback are most often seen as return roller buildup that causes belt tracking problems. Often, an employee will try to clean the return roll while the belt is running, a highly dangerous and potentially fatal decision. Absent or inefficient belt cleaning is both a safety hazard (because an employee is typically required to somehow remove the carryback) and an efficiency drain (because this material isn’t getting delivered to the desired destination). While it may seem like a small amount of inevitable waste, in reality it’s a preventable loss. If it’s material that has already been processed in some way, then an even greater investment has been made without any return. Belt cleaning systems can drastically reduce the amount of carryback. Unfortunately, many bulk material handling systems exhibit symptoms of all forms of fugitive material: spillage, carryback and dust, complicating the effort to correctly identify the sources and apply effective remedies.


GUARDING


It’s essential that pinch points be equipped with well-designed guards to prevent accidental or unwise encroachment by employees. This includes rotating components like pulleys and idlers, as well as equipment that may create sudden movement, such as gravity take-ups. Many plants are beginning


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