Since August 2015, a Bell B25E has been operating as a versatile production machine in the production chain of Knüllwalder Tagebau GmbH, an open-cast mine in North Hesse. In addition to sands and high-quality clay materials, the company extracts basalt all year round. It rounds off its varied product range with products obtained from qualified concrete and construction waste recycling. The smallest model from Bell Equipment’s range of articulated dump trucks is equipped with state-of-the-art EU-IV exhaust gas technology and replaces a Bell B25D in Knüllwald after a good three years.
A total of around 200 000 t raw materials are extracted per year in Knüllwald – consisting of 45 % sands and 45 % clays as well as 10 % basalt. Defined material grades and blends are produced with semi-stationary and mobile processing technology. On the around 70-hectare-large site, materials are extracted and handled by a total of seven large machines, which are also used in filling of the uncontaminated residual materials. On the account of the limited width of the 22-m³ secondary crusher bin, the company uses a 25-t articulated dumper as the only transport machine. Since 2012, the company owner Karl-Hans Krug has relied on dump truck technology from Bell Equipment, supplied and serviced by the responsible Bell regional partner König Baumaschinen.
The existing Bell B25D with the successor model B25E was replaced as scheduled in August last year after a total of 4000 operating hours. With the selective extraction of the different raw material types on a total of four levels, the 6 x 6 transport roadways in the Knüllwald open mine reach up to 300 m and include ascending slopes of max. 30 %. “Although our roadways dry faster than those at other clay pits, the Bell dump trucks impress with very good retarder performance especially when driving downhill under load,” says Karl-Hans Krug, explaining an important plus point that was a crucial factor in the decision to acquire the Bell B25E. Also in the current EU-IV-compliant version, the 25-tonne truck features a highly effective combination of engine valve brake and variable transmission retarder, which in six well-applied stages automatically ensures gentle, but effective retardation.
Since the end of 2014, the E-series models presented by Bell Equipment in 2013 have been supplied with EU-IV/tier4 final emissions control. The most important new feature of the new models is the Mercedes-Benz OM936LA engines. As EGR engines with minimal post-combustion of cooled exhaust gases, the 7.7-l six cylinders enable EU-IV-compliant exhaust gas control without a diesel particulate filter, but solely with the SCR process on the basis of urea, which has been proven effective a thousand times over. Besides better availability as a result of the elimination of filter regeneration and lower risk of failure, the new MB engines in combination with Allison six-speed automatic transmission are designed for high economic efficiency. The Bell B25E has a gross power of 210 kW, the maximum torque of 1150 Nm lies in a broad speed range from 1200 to 1600 rpm.
These engine characteristics guarantee superior driving performance on the surfaced drive ways and on heavy terrain, the “little” Bell benefiting from a new front suspension and electronically activated traction control. Also in a class comparison of operating weights, which can be a particularly sensitive issue for 25-tonne machines, the B25E Bell-is typically well ahead: with 19.7 t empty operating weight, it undercuts its direct competitors by up to 3.5 t – with identical nominal payloads or dump volumes (24.0 t/15.0 m³). For operation in the field, appreciable saving potential results for fuel consumption and other wear-critical operating costs (e.g. tyres).
This is also shown at the Knüllwald Mine, where the truck has to perform varied transport duties. While for the predecessor model B25D, an average consumption of 9-12 l/h was documented in daily use, the satellite-supported management system Fleetm@tic reports a three-month average below 8 l/h for the new Bell B25E.