Cement Americas

APR 2019

Cement Americas provides comprehensive coverage of the North and South American cement markets from raw material extraction to delivery and tranportation to end user.

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30 CEMENT AMERICAS • Spring 2019 • www.cementamericas.com FEATURE G iven the number of conveyor-relat- ed accidents that occur during rou- tine maintenance and cleanup, every bulk material handler has a vested interest in technologies 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 the moving conveyor, where even incidental con- tact 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 create the right ingredients for an explosion. The buildup of fugitive material can occur with surprising speed. As the table below 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 lbs.) at the end of a week. If the rate of escape is 4 grams per min- ute, the accumulation will be more than 45 kg (nearly 100 lbs.) per week, or more than two tons per year. If the spillage amounts to just one shovelful per hour (not an uncommon occur- rence in some operations), personnel can expect to have to deal with more than 225 kg (nearly 500 lbs.) of fugitive material every day. Belt Cleaning to Reduce Carryback Although there are a number of belt cleaning technologies available to con- veyor operators, most designs in use today are blade-type units of some kind, using a urethane or metal-tipped scraper to remove material from the belt's surface. These devices 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 regularly adjusted and peri- odically replaced to maintain effective cleaning performance. Tensioning The ability to maintain the proper force required to keep the blade edge against the belt is a key factor in the perfor- mance of any cleaning system. Blade- to-belt pressure must be controlled to achieve optimal cleaning with a mini- mal 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 actually an optimum range of blade pressure, which will most effectively remove carryback material. Increasing tension beyond this range raises blade- to-belt friction, thus shortening blade life, increasing belt wear and increasing power consumption -- without improv- ing cleaning performance. Operating a belt cleaner below the optimum pressure range also delivers less effective 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, excessive amounts of carryback are being forced between the blade and the belt at high velocity. This passage of material between the belt and the blade creates channels of uneven wear on the face of the cleaner. As material 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 properly installed and adjusted clean- er – is running the belt empty for long periods of time. Small particles embed- ded in the empty belt's surface can cre- ate an effect like sand paper, increasing the wear rate of both the blade and the belt. Even though the cargo may be abrasive, it often has moisture in it that serves as a lubricant and coolant. 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." Time to Mention Tension Optimize Belt Cleaner Tension to Maximize Performance and Life and Achieve Cleaner, Safer, More Productive Conveying By Mark S. Kuhar

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