Tenova TAKRAF developed and supplied a new type of compact bucket wheel excavator for the Brod Gneotino open-cast mine in Macedonia and the special working conditions encountered in the coalfields there.
The Brod Gneotino coalmine is located close to the city of Bitola in the Pelagonian coal basin south of the Suvodol open-cast mine. In future the mine will extend almost to Macedonia’s frontier with Greece. With one coal and three overburden lines, the open-cast mine will supply up to 6.5 million tonnes of coal per annum to the power station in Bitola in its final development stage.
Tenova TAKRAF already supplied equipment at the beginning of the 1980’s for Macedonia’s state energy company ELEM (A.D. Elektrani na Makedonija), including two SRs 2000 bucket wheel excavators operating in the Suvodol open-cast mine. These units are still in operation and have, in part, been modernised by Tenova TAKRAF.
As coal reserves are now extremely limited in the Suvodol open-cast mine, the Brod Gneotino field will, in the long-run, develop to become the most important source of coal in Macedonia. In order to equip the Brod Gneotino open-cast mine, ELEM assigned Tenova TAKRAF with the delivery of a compact bucket wheel excavator and a spreader. The SRs(H) 1050.23/2.0 (900kW) bucket wheel excavator will be employed in the initial expansion stage of the mine on the 2nd overburden bench and work directly above the coal seam. The A2Rs-B 5500.60 spreader is intended for the operation on the internal dump.
The overburden to be conveyed mainly consists of sand and gravel with at times soft and sticky clay deposits. Harder clays also need to be excavated. Both sticky materials and solid areas had to be taken into consideration when designing the excavator.
In the Brod Gneotino open-cast mine further geological characteristics exists.
The coal seams are longitudinally inclined by up to max. 117#37; in the direction of removal and interspersed with several interburden layers (overburden layers). It was therefore necessary when designing the excavator to ensure that the excavator can operate in block mode on a working level with an 11% longitudinal slope, and that thin coal layers can also be selectively exploited under these conditions and interburden layers excluded.
The compact SRs (H) 1050 bucket wheel excavator is equipped with a levelling device for this purpose which can longitudinally level the superstructure. This is achieved with four hydraulic cylinders in the undercarriage which can raise and lower the undercarriage ring carrier relative to the position of the two oscillating crawler tracks. The statically-determined four-point support of the two-crawler chassis is a prerequisite for the installation of the levelling device.
Digging the first terrace the excavator technology on a slanted plane requires uniform raising and lowering of the wheel boom when pivoting the superstructure in the block. The bucket wheel boom hoisting gear was adapted to suit these circumstances and the changing operating conditions to be expected. The spreader is supported by two large lifting cylinders hydraulically connected to each other. Initial operating experience indicated that vibration-free work can be achieved with the unit, even where continuously-changing material hardnesses are encountered in the block.
In connection with a mobile transfer conveyor a maximum block width of up to 43m can be attained. The excavator can work in a high step of maximum 23m. The bucket wheel excavator achieves a theoretical output of 4800lm3/h. The belt width is 1.8m, the bucket wheel outreach 27m and the bucket wheel is powered by a driving power of 900kW.
The block effectiveness of the excavator is approx. 0.8 and therefore approaches the block effectiveness of large bucket wheel excavators. However, given practically the same block effectiveness, the service weight of the compact excavator is much lower.
An important reason for the excellent block work factor are the two short, extremely compact tracks of the excavator which permit a unit advance of over 10m per terrace.
The compact character of the excavator, innovative bearing mounts for the wheel boom and the special design of the undercarriage and the track chassis distinguish the SRs(H)1050 bucket wheel excavator as a particularly versatile and flexible unit for use on the mining bench.
Another advantage of the SRs (H) 1050 when compared to other designs is its maintenance-friendliness, characterized by excellent access for the installation and removal of components, a reduced number of wear parts and more extensive use of components lubricated for life. Hardened teeth, an open swivelling turntable joint between the superstructure and substructure and hardened pairing between crawler chain shackles and the bogie increase the service life of important individual excavator components.
Key components of the compact bucket wheel excavator (e.g. the bucket wheel, buckets and bucket wheel gears, slew bearings, gear rims, belt pulleys, the track chassis and heavy portal structures, including machining for the boom mounts) were manufactured in Tenova TAKRAF’s own factory in Lauchhammer.