Cuttability characteristics of some high strength rocks for roadheader selection in Zonguldak Coalfield

10th International Symposium on Mine Planning and Equipment Selection (MPES) -- NOV 19-21, 2001 -- NEW DELHI, INDIAWOS: 000176775500109Hard coal is only exploited in Turkey in Zonguldak Coalfield and mining activities are carried out since 1848. The expected coal reserves are 1.3 billion tons, The annual production of the coal decreased dramatically for the last ten years due to the geological difficulties. However, many research works were carried out in the last years to increase the annual production and to decrease the production cost. The roadways are mainly driven in high strengths rocks with drill and blast methods, The research results discussed in this paper is a summary of a research work sponsored by The Research Fund of the Karaelmas University with the support of the Mining Engineering Department of The Technical University of Istanbul. Systematic rock samples from the rock strata were collected from the mine and these samples were subjected to the various mechanical and physical tests. These are sandstone, mudstone, shale and limestone, having compressive strength values up to 170 MPa. In the later stage, samples having size of 0.7x0.7x0.5m were subjected to the full-scale cutting tests in the laboratories of Mining Engineering Department of The Technical University of Istanbul within the facilities provided by NATO-TU Excavation Project. The cutter forces and specific energy values for different depth of cut and cutter spacing were recorded. Later, the results were discussed for the application of roadheaders equipped with conical bits and mini discs within the light of present and other ongoing research projects

Dominant rock properties affecting the performance of conical picks and the comparison of some experimental and theoretical results

Conical picks are the essential cutting tools used especially on roadheaders, continuous miners and shearers and their cutting performance affects directly the efficiency and the cost of rock/mineral excavation. In this study, in order to better understand the effects of dominant rock properties on cutter performance, 22 different rock specimens having compressive strength values varying from 10 to 170 MPa are first subjected to a wide range of mechanical tests. Then, laboratory full-scale linear cutting tests with different depth of cut and cutter spacing values are realized on large blocks of rock specimens using one type of conical pick. Specific energy, cutting and normal force values for relieved and unrelieved cutting modes are recorded using a triaxial force dynamometer with capacity of 50 tonnes and a data acquisition system. Cutter force and specific energy values are correlated with rock properties and theoretical force and specific energy values obtained from widely used theoretical approaches. The results indicate that uniaxial compressive strength among the rock properties investigated is best correlated with the measured cutter performance values, which is in good agreement with previous studies. However, it is also emphasized in this study that Brazilian tensile strength, Schmidt hammer rebound values, static and dynamic elasticity modulus are also dominant rock properties affecting cutter performance. Theoretical specific energy defined by different researchers has a mean ingful relationship with the experimental specific energy, which is an essential parameter for predicting the instantaneous cutting rates of mechanical excavation systems. It is also demonstrated that the experimental cutter forces obtained for 5 mm depth of cut are in good agreement with theoretical force values, if the friction angle between rock and cutting tool is included in the theoretical formulation. It is emphasized that, to some extend, laboratory tests can help to minimize high cost of a trial-error approach in the field. © 2005 Elsevier Ltd. All rights reserved.North Atlantic Treaty Organization Devlet Planlama Örgütü Magyar Tudományos AkadémiaThis paper is a summary of a research programme carried out in Istanbul Technical University, Mining Engineering Department during the last 8 years. The research was sponsored by NATO Sfs programme, the Turkey Republic Prime Ministry State Planning Organization (DPT), Istanbul Technical University Research Fund, Karaelmas University Research Fund and General Directorate of Mineral Research and Exploration (MTA). The authors acknowledge Prof. Dr. Levent Ozdemir from the Earth Mechanics Institute of Colorado School of Mines and all the research staff involved without their help and work, this contribution to rock cutting mechanics could not be possible