Dear Dale Coward,

From the description of your problem there are only three possibilities which can cause the problem.

1) The gap between central roller and side roller is more than permitted limit, i.e. link connection is not of proper design / arrangement. I can give you suggestion if you inform about this connection.

2) Belt is not stiff enough, i.e. belt fabric and thickness are not of adequate lateral stiffness. This you should take care when you are replacing the belt ( as and when arises).

3) Idlers vertical alignment has too much of misalignment, i.e. consecutive idlers in vertical plane are not at proper level. This results into excessive pressing of belt on central roller where the idler is up relative to neighbouring idlers and it can cause pinching. This may be ocurring at many points along conveyor length.

Possibly the main reason could be as per serial no. 1 and 2. However serial number 3 needs to be also examines at your end.

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 ■

Dale,

Suggest that you contact Bruce Baker to take a look at your system. He has a wealth of experience with belt related problems such as you dscribed and I believe he lives in your area.

Bruce can be contacted via e-mail at minesite@mining-services.com.

The three probabilities that Dr. Mulani suggested are the most likely -- but there are other possibilities. A site visit could solve your problem.

Best of luck! ■

Dear Mr. Coward,

Your question and observations suggests an improper design. To the above response I add the following.

There may be a simple solution to some of the problem causes, or the solution may require a more costly correction depending on the existing design and its fix.

CDI has experience with belts that can fail due to idler junction stress/strain failure. For long spaced idlers, high trough angles, large widths and tonnage, convex curves, idler transiton zones, existing alignment dimensions, high ore density in combinations with the above, the belt's structural integrity, such as transverse stiffness and worn belt profile, the junction strength may be insufficient to provide infinite or long life at the junction point.

Belt degradation can occur as you suggest with working the joint area. This can produce many of the characteristics you note from rubber strain work hardening.

This problem is more pronounced on some equipment such as trippers, stackers, and reclaimers. Here, long belt free spans and deep trough idlers can more frequently work the joint to failure more. In case of these junction conditions, the fix may only require the addition of adding idlers in the junction areas cutting the sharp angle and improvng the belt's support. This type of equipment normally has strucurally stiff belts to overcome this type of problem. However, the belt wears in the center region altering the structural capacity.

Belt cycle time may increase the failure rate.

Some load station impact zone designs can cause premature failure.

We make it a habit to analyze the idler junction for new and worn belts for large and log overlands. We have developed special in-house procedures for this analysis and limiting criteria.

Giving more information on the belt's construction would allow a more meaningful response such as:

1. fabric or steel construction (if fabric give details on plies, matl.)

2. top and bottom cover thickness

3. strength rating

4. speed

5. idler spacing and specified installation accuracy; setttlements

6. roll diameters

7. idler transitions and vertical convex curve details

8. material density

9. rock size

10. load impact zone configuration

11. other apropriate information as suggested from above comments.

Lawrence Nordell

Conveyor Dynamics, Inc.

website: www.conveyor-dynamics.com

email: nordell@conveyor-dynamics.com ■

Another comment:

The idler roll configuration can contribute to the junction failure as suggested above from an excessive gap and, excessive offset distance between wing and center rolls.

Some designers have used two rolls Vees on the carry side after the stacker/reclaimer travel limit. The junction force becomes excessive as the belt transitions to the head pulley in some cases.

This caused a recent belt failure, on a high strength steel cord belt with six years of service.

LKN ■