With regard to pulley plate failures, there are a number of possibilities, including:

* excessive belt tension,

* too short of a transition zone (although this normally manifests itself in either pulley or belt wear),

* excessive lateral force from belt mistraining or the pulley being out-of-square with the system,

* loose taper lock, or other pulley-to-shaft attachment, on one side,

* pulley out of balance, and

* faulty welding.

Seam cracks across the face of the drum are normally due to excessive belt tension, pulley balance problems, or poor welding.

Hope this helps.

regards, ■

Engineering of the pulley assy. assumes the engineer has adequately identified the forces.

Sometimes the engineeer's design criteria does not include features such as: belt misalignment, material buildup allowance, drive load sharing imbalance, pulley mfg tolerances, idler transition induced belt forces, proper force load pattern acrosspulley face, lagging wear differential shape , errors in steel cord placement, ............

Pulley failure, on the shell near the end disk, is caused by:

a) improper treatment of the shell axial seam weld

b) improper shell thickness which cannot handle the cyclic fatigue

c) improper shell thickness variations due to machining after form.

d) the transition stress field from shell to end disk is complex and often misunderstood leading to inappropriate selection of material thickness compatability - shell to disk

We have seen many such failures. The cause can usually be identified upon inspection and analysis from the above. CDI has published a number of articles in Bulk Solids Handling , SME papers, and other forums. Contact us for need info.

Lawrence Nordell

Conveyor Dynamics, Inc.

Bellingham, WA 98225

ph 360/671-2200

fx 360/671-8450

email nordell@conveyor-dynamics.com

website www.conveyor-dynamics.com new format to be released 2002 ■

Such failures are common in pulleys having wide faces and small diameters. the cause is typically failure to analize all stresses and the fatigue strength for those stresses. The fatigue strength is influenced by the juncture and welding details.

The writer experienced pulley failures due to circumferential cracks that, in each case, began at an internal disc, welded in the pulley to insure roundness. The intermittent filet welds run circumferentially. Their shrinkages stresses combine with the operating axial stresses (due to primary bending) to set up a triaxial stress state. This has the affect of raising the yied stress to the ultimate stress, elliminating the normal ductility of steel. Failures occured at relatively low operating stresses. AISC (American Institute of Steel Construction) assigns its the lowest fatigue allowable to this weld detail when subject to complete stress reversal. AISC fatigue allowables are reduced to as low as 3000 psi for 2 000 000 cycles. At a conveyor pulley, it takes about 500 hours (about three weeks of continuous operation) to reach 2 000 000 cycles. ■

A second posting to my earlier comment.

The failure you allude to is usually caused by the weld stress riser on the inside junction between end disk and shell. This location is difficult to treat correctly unless the end disk to shell is welded from the inside. If not welded from the inside, the irregular weld penetration and metalugical zone created at the weld inside tip creates an undefinable stress configuration. Too many factors are at play to produce a meaningful analytic criteria or treatment. To compenesate, many manufactures reduce the triaxial fatigue stress limit to about 10% of yield (3500 psi). The normal principle fatigue stress limit can be increased to about 40% of yield when welding a T-section butt weld at the shell only connection or fillet welding inside and outside. In this latter case, see the British Welding Standard for the appropriate stress level which is not associated with the yield strength of the metal. Of course this assumes you can accurately make this analysis. As Mr Joe Dos Santos states, this also occurs at the inner reinforcement disks which is usually attached by stitch welding. The end disk stress is complex in that the hoop or tangential stress is converted to a shear stress at the inner edge of the end disk. See our website for references to publications we offer that provides more in-depth discussion and treatment.

Lawrence Nordell

Conveyor Dynamics, Inc. ■