Cable-Safe System for Shuttle Cars

Underground » Roadway Development

Published: August 00Project Number: C9004

Get ReportAuthor: Bob Ifield | Hyden Engineering

The objective of the project was to improve safety and to reduce the costs associated with failures of trailing cables, through the application of a new product that may be retrofitted to existing fleets. This product: (1) increases the minimum tension to reduce failures resulting from the formation of 'loops' in the cable and failures from the car crushing its own cable, and (2) decreases the maximum tension to reduce failures from tension overload.

Cable tension decreases as the cable reel fills and is therefore at a minimum at the anchor. It also decreases as the vehicle accelerates towards the anchor and, with several build standards, this is compounded at the boot end by the actuation of the conveyor cylinder. Thus cable failures due to 'loops', and from the car crushing its own cable, will predominantly occur near the anchor and probably during the pay-out process that immediately follows reeling-in under low tension.

Low tension may also occur due to losses at the Archimedes and guide rollers, since these losses subtract from the torque available to the reel. These losses are particularly high when the car is cornering, as demonstrated during earlier underground tests at Myuna.

Highest tension occurs during pay-out with a near empty reel and since this is where the bend radius is minimum, the condition for the cable is severe. Resulting elongation travels along the cable to the loose end causing 'knuckling' at the anchor.

The design achieved the constant tension objective and should provide relief to the cable problem. One component of the design is already proven through underground use at Appin, Myuna and Southland mines.

The CT (constant tension) design provides 90-kg tension for both the reel-in and pay-out modes. It reduces tension during pay-out, with a near empty reel, by a factor of 2 and increases tension during reel-in, with a full reel, by a factor of 1.8. 4

Tests at Appin mine, midway through the project, indicated that extreme transient loads occurred when 'bumps' in the road are encountered and that these were higher than targeted by the project and by the devices developed. While tensions in excess of 400 kg frequently occurred, some tests produced loads in excess of 1000 kg. The recommended maximum tension is 150 kg for 25mm cables and 210 kg for 35mm cables.

Industry representatives, invited to review the project, recommended an expansion to the 'bump' studies and this decision postponed the completion of development and underground testing of the CT system. These representatives also concluded that the 'Appin' test track may not be representative and proposed a different 'bump' test (refer appendix).

The new test track produced less violent 'pitching' of the vehicle and generally the shock loads to the cable were less than 400kg. A key finding, from the additional 'bump' tests, was that the shocks to the cable were not directly related to the proximity of the bump to the anchor but were related to the amount of cable on the reel at the time.

A new anchor device improved the protection against shock for bumps in close proximity, but this had a reducing benefit as the distance between the bump and anchor increased. The decision to vary the project was validated since the additional study determined other causes of failure, providing direction for further study and a need to consider interim operational restrictions. Given the assessment that the 'Appin' tests were extreme, this study has provided solutions to the majority of problems concerning cables and has identified means of dealing with the remainder. However, some engineers have questioned the assessment made regarding 'bumps' and further input is now sought.


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