Coal Age

NOV 2012

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conveyors continued design would have the brace perpendicular to the wing, and at the center, not the ends where it could block material from exiting the pulley. For example; a steel disc at the center could tie the wings to each other. If the gusset angle does not make a difference on the cleaning ability of the wing pulley, what does? Comparing the existing "self- cleaning" pulleys provides insight to the problem. The wing pulley has straight wings and will throw material back onto the belt when used as a tail or take-up pulley. The spiral drum has a bar wrapped around a drum at a very slight angle, a helix, that augers the materi- al out away from the center of the pulley. It does the job, but takes many turns to get the material out. The bar is only 1 inch high, so it cannot handle much of a lump size. It can easily become overload- ed with material and can plug. Solution The answer is a cross between the wing and the spiral drum. Take the wings and angle them to the axis of rotation. Then Table 1—Pulley Diameter vs. Belt Speed for Centrifugal Force when the wing throws the material, it will be perpendicular to the wing and NOT the axis of rotation. The more the wing is angled, the better, up to a point. After 45° of wing angle, the material can start to hang up on the wing, sliding along the sur- face of the wing, instead of being thrown. But, how can this be done and maintain the strength of the wing pulley? Conventional wings span the distance between the hubs with one continuous member, the wing. But in an angled wing pulley, the wings on each side will be angled backward, such that the material is thrown to the side. There will be no single wing to span the distance between the hubs; even if it did there would be a bend in the middle, reducing its strength against the belt load. Therefore, a member has to be added at the base to support the wings. A tube is needed to provide the foundation for such a pul- Figure 3—Wing pulley build up at the tail. November 2012 www.coalage.com 47

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