The single operating variable that most directly influences chain failure is the tension in the chain. Chain tension derives from the chain pretension, friction in the upper and the lower pans, sidewall friction, the conveyor inclination, as well as the jamming of large pieces of coal slabbing off the face. The type of the material being carried influences the load levels as well as the type of operation, eg snaking or straight runs. When the operating loads exceed the break-out torque capacity of the electrical drives, the motors stall and the conveyor stops.

This is accompanied by a high spike in the chain tension before the AFC stops. The magnitude of the spike depends on the location and the suddenness of the stoppage. In addition to such discrete events, significant dynamics may be present in the chain tension, even during normal operation, due to the inherently discrete nature of the loading at the chain-sprocket interface (sprocket continuously engaging and disengaging with the chain links).

The CMTE (Co-operative Research Centre for Mining Technology and Equipment) is working to build an AFC tensionmeter, comprising an instrumented flight bar, to directly measure the dynamic in situ chain tension in operation. The tensionmeter will be installed on the chain and will be able to move with the chain along the face and over the sprockets.

The on-board data storage capacity will be large enough to store data for up to a week. There will be in-built telemetry capacity so that the data can also be transmitted to a nearby receiver by a radio link. This would be done in bursts when the tensionmeter is near the maingate where radio transmission should be feasible.

The principal aim is to capture data under different operating conditions, including straight runs, during snaking, as well as motor stalls and recoveries. The motor currents and voltages will be recorded on a parallel system during the tests and correlations will be sought between the chain tension and the electrical motor parameters.

Up to the design and construction of the first prototype, the project is being funded by the CMTE. A proposal has been submitted to ACARP with a field testing program which will use this tensionmeter to measure and compare chain tensions at a number of sites.

Future applications of the technology could allow the continual measurement of growing resistance and a subsequent control of motor output to manage load variations.

For more information about this work please contact Professor Hal Gurgenci, Program Leader — Reliability&Maintenance, CRC for Mining Technology and Equipment (CMTE). Tel: (07) 3365 3607; e-mail: h.gurgenci@cmte.org.au; URL: www.cmte.org.au.