Rock Products

MAR 2013

Rock Products is the aggregates industry's leading source for market analysis and technology solutions, delivering critical content focusing on aggregates-processing equipment; operational efficiencies; management best practices; comprehensive market

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MATERIAL HANDLING CONVEYING two positions over a conveyor belt, mostly depending upon belt speed. If the belt is moving fairly slowly (300 ft. per minute or slower), then pulling tramp metal out of burden depth should not be an issue. Therefore, it is recommended that the SE magnet is positioned in a cross���belt fashion upstream of the head pulley. Because of this downtime, the trend today is to spend more upfront to install the SE magnet and continue to operate the magnet during the cleaning process. Self��� clean models have a short belt conveyor built around the magnet to automatically remove tramp iron from the magnet force. When the belt is traveling faster, it���s better to have the SE magnet mounted just over the stream of material leaving the head pulley. Material coming off faster���moving belts results in a higher trajectory free���fall off the head pulley, clear of any burden. The SE magnet can capture the tramp metal as it flies off the head pulley. (A non���magne��� tized head pulley is recommended in this case.) The self���clean system, like the one offered by Eriez, fea��� tures a rubber conveyor belt, bearings, rugged but simple continuous channel frame, adjustable take���ups and shaft��� mounted reducer with V���belt coupling to a TEFC motor. Standard vs. Custom Components SE magnets consist of several standard components to provide the magnetic force necessary to collect large pieces of tramp metal. The coil, core, backbar and steel enclosure provide an efficient and effective magnetic circuit for collecting this tramp metal. Ninety���nine percent of SE magnets built come with coils that are always fully immersed in cooling oil. Heat and moisture, the greatest enemies of electromagnets, are ef��� fectively controlled by the oil. The oil takes heat ��� gener��� ated by the coils and core ��� and moves it away to the outer surfaces of the magnet box where air currents cir��� culating around the magnet will cool it. Aluminum coils are the standard among SE magnet manufacturers. However, some customers like the idea of copper coils because they generate more power in less space. Copper coils ��� although more expensive ��� can be incorporated into the SE magnet design upon request. A small percentage of SE magnets are air���cooled and contain no interior coil or oil; the inside of the magnet is completely dry. This type of SE magnet is generally used in mining or other dusty areas considered as hazardous locations. The air���cooled SE magnet costs more to build and is most often rated by a third���party underwriter, such as UL or CSA. The customer must specify that the working environment is hazardous and work with the SE magnet manufacturer to ensure the air���cooled magnet meets all underwriting guidelines. Today���s SE magnets are built to withstand harsh weather and operate for long periods with low maintenance. Two factors that reduce magnet holding force over time are oil contamination and reduced power. During routine inspection, operators should check the cleanliness of the oil by taking a sample, submitting it for inspection and noting any contamination. Any sort of contamination in the oil can reduce its ability to take heat away from the coils and core, thereby reducing the magnet���s ability to attract metal. Keep up with routine lubrication and adhere to your manufacturer���s instructions on proper oil amount. (De��� pending on the size of the magnet, oil capacity can range from 30 gal. up to several hundred gallons.) If the SE magnet is losing power even with clean, filtered oil, operators should check the power source to make sure the magnet is receiving an ample amount of power. In most cases, the cause is a blown fuse inside the recti��� fier. This simple change���out can bring the SE magnet back to optimum holding force. Since many factors may impact the choice, installation and operation of an SE magnet, it���s best to consult with an SE magnet manufacturer and go over any design compo��� nents needed for the job. Eriez, for example, has 23 SE magnet sizes, 69 standard models and hundreds of spe��� cial designs available for unique applications. Bill Dudenhoefer is manager, separation products for Eriez. Manual Clean vs. Self-Clean Some mining and quarrying operations prefer the less expensive manual clean SE magnet if there is a low vol��� ume of tramp metal generally found in the conveyed material. With a manual clean model, there is some downtime as operators turn off power to the magnet, move the magnet away from the conveyor line, then clean any accumulated tramp. ROCKproducts ��� MARCH 2013 45

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