Search

Purpose. To determine an influence exerted by the cutting mode and by geometry of cutters on the impact loads in various scenarios of cuttersolid inclusion interaction. Methodology. Mathematical simulation, statistical analysis Findings. Fracture of coal seams of a complex structure which contain solid discontinuities (solid inclusions and hard dirt bands) is associated with generation of impact loads on cutters and cutting heads of mining machines which cause a decrease in the productivity of the coal extraction process and premature failure of their components and elements. This impairs efficiency of coal cutting and causes premature failure of different components and parts. It is found that when a cutter cuts an inclusion or touches it, the size of the inclusion has no influence on the value of the peak load. On the contrary, in case of tear-out of an inclusion, the peak cutting force value essentially depends on the size and shape of the inclusion, as well as on the brittleness and plasticity of coal as these properties govern coal-inclusion cohesion. It is found that out of all modes of cutter-solid inclusion interaction, the highest loads arise in the mode of central cutting of inclusions. The mechanisms and behavior of occurrence of loads in short-term cutting of large (unbroken) solid inclusions by a group of cutters are discussed. The maximal loads on groups of cutters on cutting heads can also arise in gradual stalling when the average loading level approaches the tractive effort torque of electric motor when a group of cutters cuts many solid inclusions simultaneously, or in undermining of roof rocks, or in cutting hard dirt bands. Originality. The probabilities of solid inclusion cutting by a cutter are determined for different outputs of a cutting head, and the action times of the maximal peak load in cutting a coal strip 100 m long are assessed. The relations are proposed to calculate the levels and action times of maximal loads on a group of cutters in cutting solid inclusions, as well as the coefficients of variation in the loads and the loading inequality of a cutting head. Practical value. The results obtained by the authors should be taken as a basis in determination of the maximal instantaneous torque in the cutting head transmission to be used later on in calculation of the long-term strength of the transmission components.

The article analyzes indexes that characterize properties of coal seams and are used in calculation of loads on cutting tools of mining machines, or in selection of drives. Determination of geological structure complexity of coal seams takes into account hard inclusions and dirt bands in coal, as well as their size and lithology type. The notion of coal cuttability in spalled and unspalled face zones is explained using the coefficient of coal spalling. For strength estimation of complex structure coal seams with dirt bands and hard inclusions, it is proposed to use the index of integral cuttability which is the sum of coal cuttability and generalized index of densities and properties of inhomogeneities in the seam. In geological documentation, strength characteristics of inhomogeneities are described using the ultimate compression strength or Protodyakonov factor of hardness (in Russia). For this reason, the authors propose an empirical expression to recalculate cuttability of inhomogeneities in terms of uniaxial compression strength or hardness factor. The estimation algorithms of brittleness, grindability and breakability of coal seams are presented. The formula of coal abrasiveness is given. Systematization of data on breakability of coal seams has made a framework for classification of coal seams as media disintegrated by cutting tools of mining machines.