In order to solve the key problem of blockage in the borehole slag discharge channel during the drilling in soft coal seams,based on the concept of optimizing the cross-sectional shape of drill rod to increase slag discharge space and prevent borehole blockage,a geometric design conception of the four-wing concave groove drill rod was proposed.Through the calcula-tion of the mechanical equation of slag discharge resistance in the borehole and the numerical simulation of the slag discharge effect of drill rod,the influence of the structural parameters of drill rod on the slag discharge performance was analyzed.The four-wing concave groove drill rod was developed,and the industrial tests were conducted in a mine.The results show that compared to the traditional circular groove drilling rod,the four-wing concave groove drill rod has a larger slag discharge space during the construction process.Through the calculation and comparison of the on-way frictional resistance in the borehole,the on-way frictional resistance of the four-wing concave groove drill rod is 13％lower than that of the circular groove drill rod.The numerical simulation results show that when the central angle of the arc-shaped concave groove on the drill rod is 35 de-grees and the cutting depth is 4 mm,the slag transportation distance and the average transportation speed are the greatest,and the slag discharge performance is the optimal.The industrial tests show that the use of four-wing concave groove drill rod for drilling significantly improves the length of per-shift drilling depth and the depth of final hole.The research results can pro-vide reference for the design of drilling tools for gas drainage in coal mines.
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