The belt has been built with the anomolies in it.

We designed the Channar 20km overland in Australia. It had 77 splices. The belt had four 600m sections installed with the factory construction ends reversed. These 600m sections all tracked off about 150mm from the rest. This was corrected by cutting out the four sections and reversing them end for end. Expensive, but no more offset. ■

Yes, the supplier was very much aware. He had guaranteed the edge tracking error to less than +/- 25mm with reference to the belt's center over 95 % of the belt supply.

Production errors in field tracking of first loop, second loop through eigth loop could be easily seen. Each successive production roll was a little better than the one before. All were within spec. Then the mfgr changed to producing two belt widths in the same press. The wheels fell off the trolley. The belts went well out of spec. (>100mm) This only became known when we took digital records of the belt edge tracking configuration. Our Vendor belt specs strictly forbade producing multiple belt widths per pressing.

We measured edge travel for each 40km belt loop 3 successive times on each conveyor. Measurements were repeatable to within 0.8mm over the entire length of each belt. Samples were taken every 0.5 meter on both sides simutaneously. About 82000 sample points per side of each belt agreed for all three rotations.

We also determined that 4 loops were installed backwards and had to be reversed. At 600m per loop, this was some expensive to someone who go the reeling reversed. The belts came in cassettes that had to be reeled onto one roll for insallation.

Client contemplated calling the warranty for free replacement belt, but took no action when production commenced. The belts lasted about 14 years. Nonetheless, it was a bad lesson. ■

Per your question:

Conveyor Dynamics, Inc. (CDI) designed the apparatus and recorded the anomolies on Channar, during commissioning in 1989. The measurements were presented to the supplier. He was free to make his own measurements, but did not do so.

We had the supplier mark every roll direction through his plant press. The outside of every roll shipping carton was also marked for its installation direction.

However, as I stated above, the belts were shipped in dual rolls or cassette configurations. The cassettes were mounted onto a special reel system that could accept 600m from two 300 m reel ends in cassette format. In four instances, the handlers reversed the reeling installation pattern. The rolls were installed backward to the production direction. This caused a +150mm tracking offset to all other reels.

A few glaring plant construction errors, in cable alignment/pretension could be clearly seen. Many splice construction errors could also be seen. All splices were x-rayed. The patterns were examined, based on the field measurements. Clear correleation of cable position with tracking events were evident. In no case were these seen a cause for correction.

The errors beg questions about longevity. Plant and field construction errors that are observable as tracking offsets, do cause local stress anomolies in cables and in rubber between cables in splices. The potential for failure should be examined where the belt undergoes its highest stress. This is usually at the head/drive station transition or in a convex curve near the head end. ■

Please see a papers on this subject :

1. "Predicting the Tracking Characteristics of Steel Cord Belts", Bulk Solids Handling Vol 10, Nr. 1 1990, pp47-53

2. "Stress Distributions in Steel Cord Belts with Cord Plane Defects and Inlaid repair", Bulk Solids handling Vol8, Nr. 4, 1988, pp443 - 446

There are also other refernces there you can track down.

Note that many countries have manufacturing Standards such as DIN 22131, AS1333/4 etc that specify tolerances and tracking is included but not often specifically called for in a bid.

We have been testing steel cord belts since 1979 and there are a host of causes for tracking problems which are related to quality of the cord plane, user set-up and idler alignment and splice straightness. ■

Alex,

TWO POSTING!

I hope you can drop a note on how to make contact to the undersigned. ■