On the Correlation of Cutting Resistance and Physical-mechanical Properties of Lignite and Overburden Rocks from Oltenia Coalfield

The performance of the excavation machines depends largely on the tool and overall machine characteristics, and on the other hand on physical mechanical characteristics of the excavated rock. There were more theories based on heuristic approach aiming to explain the main cutting parameters on the basis of basic physical mechanical properties of the excavated rock . The classical widespread parameters used by many researchers (mainly coming from rock mechanics community) are the unconfined compressive strength UCS, internal friction angle, cohesion, Brazilian test, hammer rebound, scratch test and point load indexes. In our opinion, all these parameters are intrinsic rock properties, ignoring the second element – cutting tool geometry, kinematics, shape, operating status a.s.o. so they are hard to characterize the main features related to excavation behavior of the given rock. Despite this huge intellectual effort, spent to characterize intrinsic “cuttability” of rocks, the best results were obtained based on experimental data obtained on test rigs with as close as possible to real excavation conditions or in situ measurements performed on real working conditions. The argument that these measurements are more equipment and technology specific than excavated material specific remain a subject to debate. Each manufacturer, for each particular coalfield has developed proper methodologies for data gathering and tricks for transferring these results towards excavating tool design and excavation process governing recommendations. The most relevant source of information, i.e. the measurements preformed in order to assess the forces acting on teeth of the bucket wheel excavator during the excavation process in real working conditions is difficult and expensive. The laboratory tests performed on the testing rig eliminates these disadvantages, even if they cannot reproduce all the conditions from the working place. Using full scale teeth for the laboratory tests is not possible, because that requires samples of large size impossible to be collected and manipulated. On the other hand, in order to satisfy the statistically reasonable number of samples, the amount of material used as samples would be very high and impossible to be collected. By these reasons , both worldwide and in Romania the laboratory tests are performed using assay teeth at reduced scale, rationally selected, such as the results could be translated into reality. An important problem is the transposition in reality of the measured forces in MultiScience XXX. microCAD International Multidisciplinary Scientific Conference University of Miskolc, Hungary, 21-22 April 2016, ISBN 978-963-358-113-1