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Abstract̅Fractal expression of the size distribution of impact crusher of coal is built according to fractal theory. Orthogonal experiment is carried out by impactive crush equipment and size distribution of the crusher of coal is linear fitted and analyzed in double logarithmic coordinates. The results indicate that regression curve in double logarithmic coordinates is straight and linear regression is favorable. The fractal theory is suitable for the distribution discipline of the impact crusher of coal. Among the factors which affect the fractal dimension of coal, the speed of impact is notable, hardness of materiel is secondly and impact frequency is very little; fractal dimension decreases with the increases of hardness of coal and increases with the increases of impact speed. Key words̅impact crusher; fractal properties; orthogonal experiment; size distribution 35844
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I. INTRODUCTION With the increasing mechanization of mining and the exploitation of coal seam with dirt band, the quality of raw coal decreases as the increases of the content of large gangue mixed in the coal. The large number of gangue goes into the coal preparation that affects the efficiency of coal preparation and increase the cost of preparation. Meanwhile the gangue is stacked on the ground after preparation, which becomes the hazard sources of environmental Pollution. The separation of gangue from coal underground can not only improve the quality of raw coal, decrease the cost of preparation, but also provide materials to the gangue filling underground[1̚2]. The impactive crash of coal and gangue is a effective way to separate gangue from coal underground and the statistical characteristics of rock crash can described by fractal dimension[3̚4]. Therefore the research of fractal fragmentation distribution of coal and gangue can provide the gangue separation with theoretical support. Scholars at home and abroad mainly probe into the fragments fractal character of rock material damaged under Blast loading for the research of size distribution of particle, fractal character of rock material damaged under general mechanical disruption has not be discussed adequately. The fractal character of rock fragment loading on uiaxial compressive test was studied in reference [5, 6], fractal model for consuming energy on rock fragmentation is provided in rotary drilling in reference [7], fractal character of the distribution law of the cutting coal size was studied in reference [8]. Research of the fractal character of the impact crusher of coal and gangue is rare in contrast. Therefore, fractal character of the impact crusher of coal is researched according to impactive experimentation in this paper.
II. FRACTAL MODEL OF SIZE DISTRIBUTION There are many models which study on the distribution law of particle size, Rosin-Rammler (R-R) and Gates-Gaudin-Schuhmann model and Weibull distribution are in common use[9-10]. Using fractal dimension to describe the seemingly haphazard size distribution is a significant progress in the field of research on size distribution of rock in the last decades[11,12]. Fractal dimension was defined the as follows[13] DFcx−=−
(1) Were x is characteristic scale of crashed coal; F is amount of crashed coal that characteristic scale is greater than or equal to x; c is constant of proportionality; D is fractal dimension. Density distribution function of coal particles can be got by the derivation of fractal dimension 1()Dfx cDx−−=
(2) Mass of particle whose size is greater than x was obtained from Eq.2 max 31 3 3max ()3xDDDxv vxD MkxcDxdxkcxxDρρ −− − −> ==−− ³