| In the coal industry,pneumoconiosis,an invisible killer in the mine,is a multiple occupational disease.In China’s coal industry,the concept with "safe,efficient and green" has greatly taken root in the hearts of the people,and the state has paid more and more attention to the prevention and control of occupational diseases.Although most of the dust reduction technologies can reduce the dust concentration in the underground production process,these technologies often have hysteresis and lack of corresponding inspection standards,which makes these technologies have certain blindness in the implementation process.In order to solve this engineering bottleneck problem,it is necessary to grasp the crushing mechanism of coal seam in the mining process,clarify the main control factors affecting dust production,and master the dust production law,and implement targeted dust prevention technology from the root.Therefore,in view of the current shortcoming for cutting dust production mechanism,this paper established the damage model of cutting teeth invading coal body and analyzed the key factors affecting coal body damage based on the cutting mechanics.Then,the cutting experiments under different cutting key factors were carried out to investigate the influence law of different main control factors on the cutting dust production.At the same time,combined with the dust emission characteristics of cutting dust in roadway,this paper analyzed the influence weight of main control factors affecting cutting dust production on the roadway dust concentration,and then provided the key evaluation indexes for coal cutting dust production ability.The main research contents and conclusions are as follows:(1)The coal cutting process of the pick of the comprehensive roadheader was analyzed.Based on the elastic mechanics,plastic mechanics,rock mechanics and cavity expansion theory,the control equation of the plastic damage zone of the pick invading the coal body was established,and then the sensitivity analysis of the relevant influencing factors is carried out.Results showed that,the uniaxial compressive strength,pick cone angle and confining pressure are the main controlling factors affecting the damage range of pick after invading coal body,while the elastic modulus,Poisson’s ratio,internal friction angle and dilatancy angle are the secondary factors.(2)Based on the industrial CT technology,an experimental platform for the intrusion of picks was established,and the damage area after the picks invading into the coal was analyzed qualitatively and quantitatively by using the CT scanning technology.Results showed that the range of damage zone decreases with the increase of uniaxial compressive strength and cutting confining pressure of coal.When the contact radius between the coal body and the pick is the same,the damage area after the pick invades the coal body decreases with the increase of the cone angle of the pick.(3)By using the experimental system of pick intrusion into coal body,the experiment of pick intrusion and crushing under different main control factors was carried out.The results showed that the greater uniaxial compressive strength of coal body and cutting numbers of pick making the 4,the more fully broken coal and thus the higher the dust production.The high confining pressure increases the number of cutting cycles and cutting load,resulting in the growing dust production.The smaller cone angle of the pick and cutting numbers making a poor broken effect of coal,and thus a lower dust production.(4)The PFC-2D discrete element numerical simulation software was used to calibrate the meso-parameters of different coal,and the calibration error was less than 1.5 %.The discrete element model of linear cutting of picks under different main control factors was established.Results showed that the confining pressure had a suppression effect on the propagation of internal cracks in coal bodies,but it would aggravate the damage degree of the cutting area of picks,resulting in the reducing average particle size of cutting dust and the growing dust production.The change of truncated cone angle has few effect on the crack propagation direction,but the increase of truncated cone angle will cause the increase of cutting load,resulting in the increase of coal fragmentation,the decrease of average particle size and the increase of dust production.The overall damage range of coal decreases with the increase of uniaxial compressive strength,but the damage degree of pick cutting area increases with the increase of uniaxial compressive strength,resulting in the decrease of average particle size of cutting dust and the increase of dust production.(5)The experimental platform for cutting dust production in tunneling roadway was designed and built,and the cutting dust production and dust emission experiments in roadway under different main control factors were carried out.The total dust concentration and respiratory dust concentration in roadway increased with the increase of main control factors.The normalized analysis was used to carry out the dimensionless analysis on the influence degree of each main control factor on the dust concentration in the roadway.The results showed that the truncated cone angle has the greatest influence on the dust concentration in the roadway,followed by confining pressure and uniaxial compressive strength of coal.There are 201 figures,75 tables and 146 references in this paper. |
