E.U. Conrad, of Eickhoff Bergbautechnik, addressed the development and design process of the SL 500 shearer for the Eyesizwe Coal owned Matla mine in his paper recently presented at the Aachen International Mining Symposia last month.
Conrad said in April 2000 when Matla Coal lodged an inquiry for a shearer loader it was met with lively approval by Eikhoff engineers. Matla specified the shearer for their No 2 mine was to service a face length of 121 metres and height of 5.5 metres, a compressive strength of coal to be cut 35-55Mpa, a specific cutting power requirement at 0.45kWh/t, an annual output of 5Mt and production rate of 4500t/hr. The shearer was required to be ready for delivery by December 2001.
“The comparison between the Matla inquiry and the key figures of the biggest shearer loader type SL 500 delivered so far revealed deficiencies not only in the cutting power, but also in the haulage drive power,” Conrad said.
“The machines manufactured until 1999 had a cutting power of 2 x 500kW and a haulage drive power of up to 2 x 60kW. The maximum seam thickness which could be cut amounted to 5.1 metres.”
With the specification of 4500t/hr production it was decided the Matla machine needed a cutting power of 2 x 825kW and a haulage drive power of 2 x 90kW (AC). Consequently, it was necessary to re-design major units of the existing version of the SL 500.
Before starting the design of separate components, Eikhoff developed a Finite Element Model of the machine to simulate any conceivable working load to analyse how loads would act on the machines components.
When designing the ranging arm the capacity had to be increased by 65% compared to the existing SL 500, paying careful attention to a range of marginal conditions.
A Failure Mode and Effect Analysis was carried out on the design of the entire machine to prevent constructional errors. Next, Finite Elemente Method was also developed for dimensioning highly stressed machine elements in compliance with the loads acting on them.
Due to the high tactive force of 950kN installed in the machine, the ranging arms had to withstand very high bending and torsional moments during operation. Conrad said the bending and torsional behaviour and dimensional stability of the ranging arm were controlled during tests using strain gauges for measuring stresses and deformations.
In loading tests on the empty ranging arm casing emphasis was placed on performance tests (r.h./l.h. trial runs) at no-load, heat runs and measurements of efficiency at nominal load 825 kW for six hours and overload 1230 kW for half an hour, torque measurements and determination of oil quantities required for an optimum operation.
All other major units of the shearer loader were submitted to a development process similar to those demonstrated by the ranging arm.
An acceptance test was then run which looked at dimensions, kinematics and geometry of the machine, the performance in service and pressures of the hydraulic system, the control, protective circuits, diagnostics of the electrical system and 24 hours endurance test trialing temperature rise of hydraulic and electrical systems.
With all the tests successfully completed the system was installed underground and commissioned in August 2002 with 'triumphant results.' The record reached with the machine was 12 cuts per shift, corresponding to an output of 10.000 tonnes per shift.
“With regard to future prospects, it should be mentioned that, based on these developments, four shearer loaders type SL 500 with a reduced cutting capacity of 2 x 750 kW have meanwhile been delivered to China,” Conrad said.
“The peak performances achieved so far in three shifts a day amount to 36.000 tonnes per day representing 900.000 tonnes per month. The machine availability is more than 98%.”