OPERATING EXPERIENCE WITH A BUCKET WHEEL EXCAVATOR FOR DIGGING MARL

A lightly fissured lime marl with a moisture content of 10 to 12 % and an average compressive strength of IO to 20 MPa is mined in the quarr y at the Teutonia Zementwerk AG. The range of fluctuation in the lime standard from 65 to 150 means that selective digging is needed. Since 1991 one third of the annual requirement of about 1.5 million tonnes o f lime marl has been dug with a bucket wheel excavator which has an el ectrical power consumption of 560 kW. The excavator's output of 800 t/ h is governed to a crucial extent by the design of the bucket wheel an d its cutting elements. In 1991 to 1996 the average operating costs fo r personnel, power maintenance and repairs came to 1.72 DM/t. Dispensi ng with large-diameter hole blasting has reduced the nuisance caused b y blasting vibrations and noise and has contributed to making the ceme nt works more acceptable to the local residents. It is necessary to di g at 3 to 4 working positions in order to produce the required quality of lime marl. The lime standard of the individual working positions i s determined with the aid of a computer-assisted digging program to ma ximize the output of the bucket wheel excavator. The intention is that in the future the excavation at the other working positions should al so be carried out with a small bucket wheel excavator with an output o f 300 t/h which can be used very flexibly. The new working scheme woul d permit flexible and environmentally compatible mining of the lime ma rl at even lower costs.