Coal Age

JAN-FEB 2019

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40 January/February 2019 operating ideas Proper Tension Improves Belt Cleaner Performance Given the number of conveyor-related ac- cidents that occur during routine main- tenance and cleanup, every bulk material handler has a vested interest in technol- ogies to help reduce hazards and prevent injuries. Seemingly mundane tasks such as adjusting belt cleaners and removing spillage often require employees to work in close proximity to moving conveyors, where even incidental contact can result in serious injury 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 cre- ate the right ingredients for an explosion. The buildup of fugitive material can oc- cur with surprising speed. As the table be- low illustrates, spillage in an amount equal to just one sugar packet (about 4 grams) per hour will result in an accumulation of about 700 g (1.5 lb) at the end of a week. If the rate of escape is 4 g/min, the accumu- lation will be more than 45 kg (nearly 100 lb) per week, or more than 2 tons per year. If the spillage 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 lb) of fugitive material every day. Although there are a number of belt cleaning technologies available to convey- or 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 reg- ularly adjusted and periodically replaced to maintain effective cleaning performance. The ability to maintain the proper force required to keep the blade edge against the belt is a key factor in the performance of any cleaning system. Blade-to-belt pressure must be controlled to achieve optimal clean- ing with a minimal rate of blade wear. There is a popular misconception that the harder the cleaner is pressing against the belt, the better it will clean. But research has shown that there is an optimum range of blade pressure, which will most effectively remove carryback material. Increasing tension be- yond this range raises blade-to-belt friction, thus shortening blade life, increasing belt wear and increasing power consumption — without improving cleaning performance. Operating a belt cleaner below the op- timum pressure range also delivers less ef- fective cleaning and can actually accelerate blade wear. A belt cleaner lightly touching the belt may appear to be in working order from a distance, whereas in reality, exces- sive amounts of carryback are being forced between the blade and the belt at high ve- locity. This passage of material between the belt and the blade creates channels of un- even wear on the face of the cleaner. As ma- terial continues to pass between the blade and the belt, these channels increase in size, rapidly wearing the blade to a jagged edge. A common source of blade wear that often goes unnoticed — even with a prop- erly installed and adjusted cleaner — is running the belt empty for long periods of time. Small particles embedded in the empty belt's surface can create an effect like sand paper, increasing the wear rate of both the blade and the belt. Another potential source of wear is when the cleaner blade is wider than the material flow, causing the outside portion of the cleaning blade to 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." As urethane cleaner blades wear, the surface area of the blade touching the belt increases. This causes a reduction in blade-to-belt pressure and a correspond- ing decline in cleaner efficiency. Therefore, most mechanically tensioned systems re- quire periodic adjustment (re-tensioning) to deliver the consistent pressure needed for effective carryback removal. To overcome the problem of the blade angle changing as the blade wears, a radi- al-adjusted belt cleaner can be designed with a specially engineered curved blade, known as "CARP" for Constant Angle Ra- Material loss from conveyors can add up quickly. As the center of the blade wears unevenly, the outer edges create a 'smiley face' or 'mooning.'

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