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

Mechanical Properties of Nanocrystalline Tetragonal Zirconia Stabilized with CaO, MgO and Y2O3Y_2O_3

The citrate gel method, similar to the polymerized complex method, was used to synthesize homogeneous tetragonal zirconia at 1000°C. Nanocrystalline tetragonal phase has been fully stabilized at wide temperature range with 10 mol.% CaO, MgO, and $Y_2O_3$ addition. Scanning electron microscopy, X-ray diffraction, and microhardness tests are used to characterize synthesized materials. The grain size and dislocation density were calculated from X-ray diffraction data. The examined material exhibits indentation size effect behavior. Results revealed that the Vickers and Knoop microhardness are dependent on indentation test load. Geometrically necessary dislocation model and modified proportional resistance model are used to analyze the load dependence of the microhardness. The highest hardness values were obtained for the samples with CaO addition; however the lowest values were acquired for sample stabilized with $Y_2O_3$ by using both Knoop and Vickers techniques. This situation might be explained using the Hall-Petch relation

Hardness Behavior of Alumina-Zirconia Nanocomposites Synthesized by Gel Process

The alumina-zirconia composites are one of the relatively good and promising candidates for biomaterials application, due to biocompatibility and their mechanical properties that combines high flexural strength with a high toughness. The aim of the present work is to analyze the mechanical properties of these composites, where zirconia content was varied from 5 to 50 wt%. The citrate gel method, similar to the polymerized complex method, was used to synthesize these ceramics. Scanning electron microscopy, X-ray diffraction and microhardness tests are used to characterize synthesized materials. The examined material exhibits the behaviour of indentation size effect. Modified proportional resistance model are used to analyze the load dependence of the microhardness. X-ray diffraction analysis was used to calculation of the grain size and dislocation density. It is found that hardness is decreased when the zirconia content increases with enlargement of grain size