Dear Mr. Paul,

You are referring to uneven wear of rubber lagging. Such wear simply implies that belt is pressing more where there is more wear. The more pressing of belt can occur due to; 1) Belt central portion is worn out but it is thicker at edges, (2) Belt center line and pulley center line are not perpendicular, (3) Loading on belt is not central, (4) Carcass is somewhat weak wherein permanent elongation is not uniform across the width, (5) Abrasive material contamination in particular zone of the belt.

Issue is somewhat comparable to wear of car tyres (not exactly).

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

May I add to the above:

1. spiral wrapped bias - lagging is often vulcanized to pulley shell using a fabric wrap wound around in a spiral to apply pressure during the autoclave cook. This wrap can result in a screw action if not dressed propertly. The belt is forced to one side and countered by pulley alignment, or side travel restraint that does result in asymetric wear.

2. normal wear - is lagging center located due to abrasion of material carried

3. symmetric edge wear as Mr. Mulani states is from excessive edge pressure that can be associated with:

a) improper troughing idler transition design

b) lagging dimensional errors causing local differential shear

c) belt local tension member misalignment in the vertical plane

d) construction biases in belt pretension

e) and so on ....

Lawrence Nordell

Conveyor Dynamics, Inc.

website: www.conveyor-dynamics.com ■

Paul

In addition to Mr. Nordell and Mr Mulani's comments. You can also experience lagging wear due to poor splicing ie: the splice is not perpendicular to the centerline of the belt. This can cause the belt to travel axially on the pulley when the splice goes around and can cause the wear patterns that you see on both sides of the pulley.

In some cases you can actually see the belt moving across the pulley as the splice comes near the pulley and then travel back after the splice goes by.

Good luck,

Gary Blenkhorn ■

Hello Paul,

The points you refer to are associated with poor belt construction in the factory. Some manufacturers do not control the edge cords to a sufficient degree. Look at the belt cords in cross-section across the width. The horizontal and vertical placement should be within 1 mm of the theorectical positions. Often the edge cords migrate significantly from the proper position. This migration has to do with the manufacturing process and lack of good quality control of the machine and raw stock tolerances. All excess rubber, in the form of edge flashing must move past the edge cords. Pressure, cord tension control, cook control, etc. may allow cord migration in some belts.

Vertical errors can produce unusually large differential radial pressure on the pulley lagging. which translated into a shear gradient. The shear gradient can create localized wear both from heat and abrasion associated differential velocity. These errors can be visually observed. It is best to set up a quality control program that forces the manufacturers to maintain proper control.

I have been through many production plants and have observed these errors. Checking the QC samples I have called to the mfgrs. attention these errors that they were oblivious too. THey shug with lack of knowledge on the importance of the errors.

Varition in pretensioning does produce some of the same effects. This can ocurr at any place across the width.

Ask how the cord placemet and tensions are controlled. What tolerances are specified. What practice is implemented to reject. Are samples used to educate the production operators with visual clues.

Lawrence Nordell

Conveyor Dynamics, Inc.

website: www.conveyor-dynamics.com ■

Added clarification,

Pretensioning is related to the mfg. production press cord bridle tension control. Often this is a hydraulic action conrolling many cables from one hydraulic piston. Since the cord mfgr. does not have good control of the weave uniformity, significant variations in elongation can ocurr between cords in the belt. Lack of individual and uniform cord tenion will create both variations in tension and placement.

Some mfgrs. do understand this and make the proper effort. Aside from pulley lagging wear differential you can observe these errors in tracking errors and edge flap anomolies.

LKN

Conveyor Dynamics, Inc. ■