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44 • ROCK products • August 2016 www.rockproducts.com H ave you ever driven your truck when the front wheels are out of alignment? Toe in or toe out makes you wander all over the road, your tires wear and if you are keeping track, reduces miles-per-gal. The same things happen on your belt conveyor, even if it seems to be running fine. Shiny rolls are a good hint that your idlers are fighting each other and wear- ing. Even if the belt tracks correctly, you are likely wasting power and money that can be saved with a one-time tune-up. Figure 1 – Idler Angular Misalignment . Aligning Your Idlers Slots are provided in idler frames to allow easy adjustment of the idler angle. The hard part is knowing which way to adjust them. This is true for when idlers are first installed and most idlers are never moved after that. Sometime idlers are sighted in and then "knocked" to tracked the belt. At best, tape measures are used on the idler footpad to cross measure the frames. Both of these measures may incorrectly assume the frames were built precisely. Part and assembly dimensional variations in the conveyor structure and idler frames accumulate quickly due to rough and worn fixtures, hole clearances, part warpage, and other manufacturing and installation imperfections. The best align- ment is when the belt and rolls are used in the measurement but custom-build jigs necessary for this, until now, were only used on the largest conveyors. It is best to use the center roll because all of the rolls may not be in line and it carries most of the belt and bulk weight so it has the most influence on steering and power loss but it is the hardest to access. Alignment measurement is a problem because the important features, the belt line and roll centerline, are not parallel or near each other. This prompted the development of a new Alignment Verification Rig (AVR), see Figure 2. This device uses magnets to quickly clamp to the idler roll and uses a rotatable laser to locate a plane perpendicular to the roll centerline. The angular misalignment can then be seen by comparing the laser plane location to two points along the belt edge. This allows fine tuning idler alignment after the belt is installed, even after many years, as long as the belt edge is reasonably unworn. Measuring to widely spaced locations on the belt inherently gives very good accuracy and indicates which way one footpad of the idler should be moved relative to the other. The same approach can be used in new construction if another laser or piano wire is used to indicate the belt line. Figure 2 – Alignment Verification Rig (AVR) mounted to an idler and set to belt edge. Calculating Power Lost and Power Cost Let's say you have a 36-in./C belt full of limestone aggregate and that your idlers average being ½-in. off alignment. That is, one side of the idler is ½-in. ahead of the other. Divide that by the width of the idler frame. Typically that's belt width +9 in. or .5/(36+9)=.011 for the ratio of sideways movement to forward belt movement. Idler Misalignment on Belt Conveyors If Your Belts are Misaligned, You are Likely Wasting Power and Money. By Allen V. Reicks Importance of Alignment