Coal Age

JUL-AUG 2017

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26 July/August 2017 surface mining continued Apart from reducing machinery and personnel costs, the process is also much more time-saving than conven- tional methods. What is more, surface miners produce level, stable surfaces — a great advantage for mine logistics as it means that ordinary trucks can travel over the routed access roads. Not only can they transport the material more quickly, but they are also more cost- effective to acquire and maintain than dumpers. Efficient Material Extraction Surface miners operate in a similar way to road milling machines working on as- phalt or concrete. A special cutting drum cuts and crushes the material. Robust loading conveyor systems then load the material onto haul trucks or they can stack the material in windrows behind the machine. Alternatively, the material can also be side-cast. A high-precision, automated leveling system ensures a constant cutting depth. This extremely precise method supports selective mining of a wide range of mate- rials — for instance, coal, limestone, gyp- sum, salt, bauxite, iron ore, etc. The mechanically driven cutting drum on which the cutting tools are arranged in a helical pattern, work against the di- rection of travel, cutting the material and crushing it. Ejectors on the milling drum help to transfer the material to the loading conveyor system. The main loading conveyor takes the material from the drum housing and transports it to the rear of the ma- chine, where it is then transferred to the slewing, height-adjustable discharge conveyor. The discharge conveyor loads the material onto trucks or dumpers or side-casts it alongside the machine. The height of the discharge conveyor can be adapted flexibly to the height of any transport truck. This article was submitted by Wirtgen. The driver loads a tandem coal train within minutes in the mine in south Texas. This then drives some 26 km to unload the material at the power plant. The Wirtgen 4200 SM cuts lignite 30 cm deep. It also pre-crushes the coal prior to loading.

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