What Does a Crowned Pulley Mean?

August 6, 2019

The key to keeping conveyor belts centred, some would say, is to use crowned pulleys. Not complex electronic guide systems or flanging mechanisms, just pulleys that impart an arch to their belts. Ultimately, by adopting this drum surface profile, system designers can solve equipment tracking hardships without adding a potentially unreliable tracking attachment. This is due to the fact that flat but pliable carrier belts can be made to self-track.

Introducing Middle Hump Self-Tracking

If someone pinches a broad elastic band by its right edge, it bends right. Pinch it on the left edge, and then it bends to the left. On scaling up that elastic band and applying tension straight down its centre, the pliable material ribbon straightens out. Crowned pulleys simply imitate that centre-tensioning effect. By putting a raised hump right on the centre of the drum cylinder, then making sure this raised centre tapers down to the slightly narrower end caps, elastomer ribbons track true. In effect, with balanced lateral forces stretching down from the mirrored declination line, the belt steering lateral forces split exactly in two. As a result of this centring action, those opposing lateral forces promote belt carriage parallelism.

Optioning Multiple Crowned Pulley Outlines

If an imaginative person were to conjure up a mental image of an average crowned pulley, it would probably look like two conical cups joined together by their widest edges. The taper drops down to the cylinder ends, so this is a convex crowned cylinder. There’s also a concave variant, which looks a little like a fattened hourglass. Completing the range, the centre hump sometimes widens to provide an alternative set of tracking features. Typically, flat centre section variants work well when steering narrower conveyor belts. On the whole, the tapering angles, centre flat crowns, and choice of concave or convex drum surfaces vary depending on the length of the cylinder and the end cap diameter. Incidentally, just to clarify matters, concave crowning isn’t in common use, not even in trough-shaped material conveyance equipment.

In the final analysis, centre drum peaks improve pulley tracking. The raised cylinder apex slopes down in a straight line in both directions to create a tapered profile. To match this shape, the end sections of a pulley are fitted with smaller caps. Again, by dividing belt tension in two, the crowning shape also divides the applied lateral forces in two. Using this design, conveyor belt self-track and no supplementary guides are needed to pull off this impressive feat. Tuning this centring action somewhat, the tapering angle and centre flats alter to accommodate alternative loading scenarios and singular drum dimensions.

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