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Thread: Pulley Lagging Wear

  1. #1
    Paul Allardice - Downer EDI Engineering, Australia Guest

    Pulley Lagging Wear

    I have seen many pulleys that are lagged with natural grooved rubber which have a wear pattern worn around the circumference and out towards the edge of the pulley - basically where the edge of the conveyor belt runs around the pulley.

    Some pulleys have the wear pattern worn into the lagging on both sides of the pulleys face while others only on one side.

    What are the possible reasons for the lagging wearing in these areas?

  2. 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

  3. #3
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc. [eDir]

    Conveyor Dynamics Inc.

    Professional Experience 58 Years / 8 Month Lawrence K. Nordell has 58 Years and 8 Month professional experience

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    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

  4. #4

    Pulley Lagging Wear

    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

  5. #5
    Paul Allardice - Downer EDI Engineering, Australia Guest
    Thank you all for your feedback.

    Larry,

    Could you elaborate further on the following points you listed?

    " 3. Symmetric edge wear ......
    c) belt local tension member misalignment in the vertical plane
    d) construction biases in belt pretension "

    Is point 3. c) related to overtensioning of the belt?

  6. #6
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc. [eDir]

    Conveyor Dynamics Inc.

    Professional Experience 58 Years / 8 Month Lawrence K. Nordell has 58 Years and 8 Month professional experience

    Discussions 2608 Lawrence K. Nordell acceded to 2608 discussions, Articles 0 Lawrence K. Nordell wrote 0 articles, Publications 0 Lawrence K. Nordell Nordell released 0 publications

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    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

  7. #7
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc. [eDir]

    Conveyor Dynamics Inc.

    Professional Experience 58 Years / 8 Month Lawrence K. Nordell has 58 Years and 8 Month professional experience

    Discussions 2608 Lawrence K. Nordell acceded to 2608 discussions, Articles 0 Lawrence K. Nordell wrote 0 articles, Publications 0 Lawrence K. Nordell Nordell released 0 publications

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    Know-How Design (1521) Lawrence K. Nordell used this tag 1521 times, Pipe Conveyor (238) Lawrence K. Nordell used this tag 238 times, Chutes (119) Lawrence K. Nordell used this tag 119 times

    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.

  8. #8
    Owbridge - Sandvik Guest

    Pulley Lagging Wear with Fabric Belts

    I agree with Mr Nordells comments regarding the importance of steel cord placement in the rubber matrix for steel cord belts.

    We have seen this problem show itself time and again in the Pilbara especially on belts with thick top covers and running over HT Bend pulleys.

    I have however come acros a few cases recently where this problem has occured on systems running fabric plied belting typically PN800/4 or PN1000/4. In both cases the manufacturer was Apex Belting (whether this is of importance or not I am unsure)

    Another interesting point was in all cases the pulley diameters were very close to minimum recommended as were the transition distances.

    The pattern shown on the pulley, and the belt in short cycle systems was an 'erosion' style pattern. And it presented itself in an almost zig zag pattern where the zigzag angle was at approx 45-60 degrees to the belt edge.

    Any comments on this occurance and a possible solution would be greatly appreciated.

    Regards Dan

  9. #9
    David Beckley Guest
    Hello Paul,

    The problem that you refer to of lagging wear on the edges of pulleys usually occurs at head drive pulleys on conveyors that are fitted with multi-ply textile reinforced belts. At the drive pulley there will be a change in the belt tension from the tight side T1 to the slack side T2. This change in tension will result in a reduction in the belt length at the drive pulley. With low modulus belts such as NN and PN construction, where the change in length will be significant, there is likely to be some creep or slippage between the belt and the pulley lagging. In addition, if the head end transition is short, a significant increase in edge tension will occur in the transition zone and this will flow on to the pulley. The extra tension in the belt edges will result in a larger tension change around the pulley and hence more slip and more wear will be noticed at the edges. If you are experiencing this problem, you could try increasing the transition length.

    The propblem of lagging wear in the centre of high tension bend pulleys that are in contact with the carry or dirty side of the belt that Dan Owbridge referrs to above, is very common in the hard rock mining industry where belt top covers are usually quite thick and the problem is usually worse with steel cord belting. When the worn surface of the belt comes into contact with the bend pulley, the radial distance to the cords at the centre will be less than at the belt edges and some slippage must occur to compensate for the differential path lengths of the cords. The distortion of the outer cords will increase the edge tension and reduce the centre tension, in this case the slippage will occur at the centre of the pulley, where the tension and hence pressure between the belt and the pulley is at its lowest value.

    Regards,

    Dave Beckley
    Conveyor Design Consultants of WA
    Perth, Western Australia.

  10. #10
    Owbridge - Sandvik Guest
    Dave,

    Thanks for your reply, I have a recently seen systems with tail and bend pulleys running a fabric belt with a 'creep' style pattern on their edges . Have you ever struck this before? Pattern is also present on top cover of belt.

    Regards

    Dan

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