Crushing properties of hard coal under auxiliary impact by picks

The proportion of hard coal seams has been increasing in recent years. The low efficiency of traditional mechanical cutting methods under hard coal has always been a problem for the China’s coal industry. Therefore, a crushing method with strong applicability to hard coal is required, which has become an important scientific issue for the intelligent modernization of coal mines. Impacting cutting technique is a new type of hard coal mining method. The reciprocating impact of picks in the tangential direction of movement is used for the destruction of coal, and the difficulty of hard coal mining is reduced. However, the coal crushing performance may be affected by the time and space difference of picks impact. In this study, the impact picks were applied to the shearer drum, and the modified structure of the shearer with picks impact function was designed. The different motion models of the impact time and space of picks were established based on the drum structure. Also the coal crushing properties of the drum with different impact time and space relationships were analyzed using discrete element method. The simulation results show that the coal crushing efficiency of the synchronous impact method is better than that of the asynchronous impact under each scheme. The average and peak force of the drum are lower than that of the asynchronous impact, and it is more stable than the asynchronous impact. In addition, the coal crushing performance of synchronous impact under each scheme has been improved compared with traditional drum. The maximum difference in coal crushing efficiency between the two methods is close to 24%, and the maximum difference in drum force is up to 60 kN. In order to test the actual performance of the coal crushing in conjunction with impacting cutting technique, a simplified test device was designed, and the coal crushing test was carried out. The test results show that the average cutting resistance of the picks under impact and un impacted states are 4 473 N and 5 390 N. The impact of picks can reduce the cutting resistance by more than 17.22% compared with the un impacted state. Although the results obtained were deviated from the simulation results, the reduction of the comprehensive cutting mechanism and the reduction of hardness of coal could still be considered as that the actual performance of coal breaking by impact and cutting synergistic had achieved an ideal effect. The effectiveness of coal crushing with impacting cutting technique on hard coal seams was reflected. Meanwhile, it could be considered that the change law of cutting load reduction was similar to the change law obtained by simulation, which verified the conclusion that the time space relationship of synchronous shock had higher applicability to hard coal.