Signal devices reliably guide through open-cast mining
In the Europe’s largest brown coal open-cast mining region at the RWE Hambach mining location, in excess of 300 million m³ of earth is quarried every year to be able to source the valuable brown coal. The world’s biggest crawler excavators are used, and with their enormous dimensions of 240 m in length and 96 m in height the rotating crawlers dig into the earth at a depth of 400 m. In order to access this depth, excavators, people, conveyors and vehicles force their way down towards the mining surface. Everything is exposed to the elements. Downpours of rain, storms, baking heat and temperatures well below freezing point daily challenge the inter-play of work and technology in open-cast mining. Earth and coal collect everywhere and blow ‘sand in the works’. Knocks and constant shaking mean a constant endurance test for equipment. Large-sized equipment swings out wide, and excavators operate where employees are working. Information has to flow clearly and quickly so that people and machines do not hamper each other. This is ensured by the use of optical signals.
1 Signal devices fit for mining
Only very few signal devices are tough enough for the challenging environmental conditions prevalent in open-cast mining. Recently it was a case of new beacons. Spreaders that shake earth residues out onto slag heaps are exposed to strong vibration. Halogen beacons on these spreader machines often failed. And each signal device failure meant idle machine times that cost the company valuable time and money.
WERMA offered the LED permanent beacon 829 as a replacement for the incandescent bulb beacons used by RWE. LED technology solves two problems at the same time: LEDs with 50 000 hours light ten times longer than conventional incandescent bulbs, and at the same time even major vibrations can do light emitting diodes next to no harm. With its robust, lightweight housing of polycarbonate and PC/ABS blend the device is both temperature-resistant, highly UV-resistant and colour-fast from -30 to +50 °C. Extra casting compound in the housing base and stabilised PC boards further protect the device from strong vibrations in open-cast mining.
The RWE technicians initially had very little faith in the robustness of the device. The RWE technicians grabbed the beacon and simply threw it out of the window. A few tense moments later it was obvious. The device remained intact. The next test was even tougher. The beacon was subjected to constant shaking and vibration in permanent deployment on the largest crawler excavator in the world. Following various improvements, the LED permanent beacon 829 reliably operated for more than one year on the over 13 000 t-heavy and 240 m-long excavator. Since that time it is used as standard equipment on the emergency stop switches and traffic lights (Fig. 1) throughout the Hambach open-cast mining location. The LED permanent beacons signal reliably on spreaders (Fig. 2), trippers, conveyor belts and the crawler excavator. And up to 100 of these are distributed over the equipment.
A similar case was found with the traffic lights in Hambach. These signal at strategic locations, for example at the belt collection point. Here conveying belts transport coal and earth, and below these belts are traffic paths for people and vehicles. To prevent material falling down onto these, the traffic light switches to red when the transport belts are in operation and to green when the paths can be crossed without danger (Fig. 3). Halogen traffic lights were previously used that often failed.
The energy provider changed over to LED technology with the 890 traffic lights from WERMA Signaltechnik. For open-cast mining applications the signal technology manufacturer additionally strengthened the housing and stabilised the PC boards. And here as well the vibration-resistant, long-life and bright LED technology really convinces, because shaking of the machines and conveyors has no effect on the robust LEDs.
WERMA has developed a further beacon version for RWE suitable for open-cast mining. Levelers on caterpillars working around crawler excavators must always know whether the crawler is moving to or away from them. This is signalled by the red and green colours of the rotating beacons 280. Once again RWE replaced its signal devices featuring conventional light sources with LED beacons in order to benefit from freedom of maintenance. WERMA fixed the new beacons with a supplementary PC board ring, thus ensuring that the inner electronics can reliably withstand shaking.
The LED signal devices from WERMA suitable for open-cast mining make the Hambach coal location more economic and safer. At the same time raises productivity and safety for employees and machines are increased.
WERMA Signaltechnik GmbH + Co. KG, Rietheim-Weilheim (D), www.werma.com
