At Matla, the best results are achieved by equipment utilisation at constantly high, but not maximum production levels. This is now being demonstrated by the “Opti Shearer Cycle”, the current method of shearer operation. Web cycle time is minimised, as this determines the system output capacity for a given system utilisation. This is achieved by eliminating the double shuffle process as used in the bi-di cycle, and regulating the coal output over the cycle to eliminate peaks.

The OPTI cycle utilises the principle that the web is extracted in two passes of the face with a bottom bench left to be extracted on the second pass. With an anti-clockwise tail gate drum rotation the leading drum cuts from roof to floor, the reaction forces on the drum try to lift the leading drum side of the machine. However, the leading drum leaves the upper portion of the top bench to be cut by the trailing drum. This limits the angle of the leading ranging arm which has contributed to smoother cutting performance.

Studies have found the OPTI cycle to be approximately 15% more productive, for a seam height of 4 m in the 4 seam at Matla, however the productivity differential is expected to increase to approximately 30% for a seam height of 5.5m on Matla’s 2 seam shortwall.

Using the Opti Cycle in the No. 2 seam shortwall will make it possible to retain the roller curve principle to combine AFC and stage loader. The new system will feature a 48 mm chain, 2 x 630 KW drives and 2.2 m dia roller discs to guide chain and flights around the 90 degree corner from face to head gate.

The PF-5 line pans are the heaviest supplied by DBT. These super heavy duty conveyor pans are ideally suited not only to convey millions of tons of coal but also will carry the 100 t Eickhoff double drum shearer fitted 2.5m diameter drums. The drums cut 1 m deep. When cutting 5.5m high approx 900 tons are mined in one cycle in one pass in 15 to 20 minutes.

A DBT Minpro 350 KW crusher is integrated into the conveyor chain between roller curve and AFC discharge. This equipment configuration is able to handle the uniform flow of 2500t/h coal as is produced by the Opti Shearer cycle. Short, peak coal discharges as may be produced with the bi-di cycle would require higher powered drive trains and a larger than 48 mm link chain. This would rule out a roller curve as the disc diameter must be larger as chain link increases. This in turn would exceed dimensional limitations of Matla’s gate entries.

Shield and longwall system automation were placed high on the list of requirements specified by Matla. DBT’s acclaimed PM – 4 electro-hydraulic controls are the heart of the automation system. The Matla PM 4 configuration includes 12 solenoid circuits to control a total of 13 hydraulic cylinders in each shield. This includes two 400 mm bore leg cylinders each having a capacity of 5300 Kn at 420 bar pressure. Most cylinders are fitted with either stroke or pressure sensors to constantly monitor actual conditions and provide feedback to the automation loops. A typical automated mode of operation runs as follows.

· Shearer cuts top bench of seam, continuously sending position signal to infra red receivers placed in each shield.

· Shields advance automatically approximately 5 m (distance is on face programmable) behind shearer by lowering support legs and energising advance ram anchored to the face conveyor.

· At end of advance stroke shield legs are automatically reset (set pressure is programmable) to support expose roof and to let roof cave behind the shields.

· On return trip to head gate shearer cuts bottom bench of seam, AFC is automatically advanced behind shearer by means of the advance ram now anchored in each shield.

Monitoring functions serve to maintain alignment of shields and AFC to prevent shearer drum to shield flipper collision and to maintain optimum support cylinder pressure levels. Longwall system automation includes condition monitoring of all drive motors, gear boxes, temperatures, currents and voltages. All information is transmitted to a surface control room for screen display and data accumulation for various management actions such as triggering preventative maintenance and optimisation tasks.

In addition to design and supply of the equipment the project involves for DBT a large spectrum of services, all with the objective of ensuring a smooth and trouble free start up and to achieve rated production in the shortest possible time. DBT’s South African subsidiary in Germiston is taking the lead function within the DBT Group.

While manufacturing was in progress, the main emphasis in South Africa were weekly project meetings with the customer and other equipment suppliers, such as Eickhoff. Extensive equipment documentation and a computer-based training program has been finalised. A parts inventory will be available to the customer for immediate delivery of spares.

Last year a Matla delegation visited DBT’s test center in Germany to witness prototype and compatibility tests. This involved a plant set up of 40m of face equipment, including the shearer, with all electric motors wired and powered up. Realistic underground situations were simulated to ensure system compatibility under extreme conditions. Installation and start up underground is planned for the second quarter of 2002.