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www.rockproducts.com ROCK products • August 2016 • 45 Figure 2a – Movement of the AVR laser for angular alignment to belt edge. Figure 2b – Alignment target for improved accuracy. Multiply by the load on the idler and a friction factor of .5 to convert to the sideways push at each idler (some push one way and some the other way). This force times the belt speed and operating hours is the energy lost. At 1600 tph and 600 fpm on a 300-ft. conveyor with a belt weight of 10 lb./ft., we get 3 hp or 2.2 kW wasted power. If you run 3,000 hours per year you are wasting $646 every year on this short conveyor compared to a more precise idler alignment of 1/16 in. This and the intangibles that go with it only costs a few hours from your maintenance crews. Longer and bigger belts save more. To review: Cost of idler misalignment=idler misalignment/ idler bolt spacing*friction factor*(conveyor tph*2000/60/ belt speed + belt weight*2)* conveyor length in ft.* belt speed *.000023*hours per year*power cost $/kWhr. Or ( 1 / 2 - 1 / 1 6 ) / ( 3 6 + 9 ) * . 5 * ( 1 6 0 0 * 2 0 0 0 / 6 0 / 6 0 0 + 1 0 * 2 ) *600*300*.000023*3000*$.10=$646/year (or, download a spreadsheet calculator from avr4idlers.com.) Idler alignment is identified as one of four main friction losses in CEMA's belt book, 6 th and 7 th editions (see below). Misalign- ment design categories show average conveyor idlers have misalignments ranging from ¼ in to 1 ½ in. depending on the application. This range is wide because it may take more than a tape measure to get good alignment and the effect on the bottom line has been underestimated over the years. Bottom line, the more conveyor length you have, and the worse your idlers are aligned to the belt the more you can save, if you have a way to get very good alignment. How Well are My Idlers Aligned? Why Does My Belt Track Fine? Belt alignment is an important element of conveyor operation but is not the same as idler alignment. While idler angular misalignment can have a strong influence on belt lateral tracking, individual idlers typically counteract or fight one another. The good news is that there is usually not enough side push on the belt to counteract the gravity centering in the trough and you get decent belt tracking. As a test measurement of your conveyor, measure the idler spacing on both stringers for a section of 10-20 idlers. Subtract the spacing of one side versus the other for each pair. Some of the differences will be negative and some positive. If you average all of them, the result should be small if the belt is tracking well. If you drop all of the negative signs (absolute value) before averaging, the result will be larger and is an esti- mate of your sliding idler misalignment. See example in Table 1. Table 1 - Example of Misalignment Estimate- 5 ft. spacing Idler spacing (in.) Difference (in.) North Side South Side Mathematical Actual 59.75 59.75 0 0 60.0625 60 0.0625 0.0625 59.9375 60.125 -0.1875 0.1875 60.0625 59.625 0.4375 0.4375 59.8125 60.5 -0.6875 0.6875 60.3125 60 0.3125 0.3125 60.125 59.9375 0.1875 0.1875 59.75 60.1875 -0.4375 0.4375 60.375 60.125 0.25 0.25 Average Alignment -0.007 0.285 Net Alignment Affect On Tracking On Power This method does not include the variability in the frame assem- bly but only installation variation. The AVR can do this more accurately, quickly and easily from one side of the conveyor, both to assess the benefit to adjusting and to measure for future adjustment. Its low cost makes this a practical approach.