Coal Age

SEP 2017

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Page 35 of 51

34 September 2017 conveyor maintenance Optimizing Conveyor Belt Cleaner Tension to Maximize Performance and Service Life Maintaining correct and consistent blade pressure is key to effective belt cleaning by alan highton and todd swinderman Given the number of conveyor-related inju- ries that occur during routine maintenance and cleanup, every bulk material handler has a vested interest in technologies to help reduce hazards and prevent injuries. Seem- ingly mundane tasks such as adjusting belt cleaners and removing spillage often require employees to work in close prox- imity to the moving conveyor, where even incidental contact can result in serious in- jury in a split second. Further, spillage can contribute to the risk of fire by interfering with pulleys and idlers and by providing potential fuel. Even worse, in confined spaces, airborne particles can create the right ingredients for an explosion. The buildup of fugitive material can occur with surprising speed. As Table 1 illustrates, spillage in an amount equal to just one sugar packet (about 4 grams) per hour will result in an accumulation of about 700 grams (1.5 pounds) at the end of a week. If the rate of escape is 4 grams per minute, the accumulation will be more than 45 kg (nearly 100 pounds) per week, or more than 2 tons per year. If the spill- age amounts to just one shovelful per hour (not an uncommon occurrence in some operations), personnel can expect to have to deal with more than 225 kg (nearly 500 pounds) of fugitive material every day. Belt Cleaning to Reduce Carryback Although there are a number of belt-clean- ing technologies available to conveyor operators, most designs in use today are blade-type units of some kind, using a ure- thane or metal-tipped scraper to remove material from the belt's surface. These de- vices typically require an energy source — such as a spring, a compressed air reservoir or a twisted elastomeric element — to hold the cleaning edge against the belt. Because the blade directly contacts the belt, it is subject to abrasive wear and must be regu- larly adjusted and periodically replaced to maintain effective cleaning performance. Typically, the blades of a cleaner do not cover the full width of the belt, be- cause the full belt surface is not generally used to carry material. CEMA specifies the minimum blade coverage based on belt width, as shown in Table 2. Various belt cleaner suppliers have their own standards for blade width. Some manufacturers opt for more than the min- imum coverage, but rarely does the blade size need to be equal to or greater than the belt width. For optimum cleaning, the dirty portion of the belt's carrying surface should be observed or calculated and the cleaner's size matched to it. Installing a blade that is wider than the material load on the belt can lead to undesirable wear patterns. The center sec- tion of the blade may wear faster than the portion of the blade on the outside area of the belt, because there is more abrasive cargo in the middle. The outside portion of the cleaning blade will then hold the center section of the blade away from the belt. As a result, carryback can flow between the belt and the worn area of the blade, accelerating wear on this center section. Eventually, the process creates a curved wear pattern sometimes referred to as a "smiley face" or "mooning." Table 1—Material loss from conveyors. Table 2—CEMA minimum blade coverage based on belt width.

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