Application and development on drill rod matched for large diameter and directional long borehole in underground coal mine

For solving drill rod joint fracture frequently while drilling large diameter and long directional borehole，ø89mm drill rod with high strength and high toughness is developed after improving joint structure，optimizing thread type，testing new material and its matched heat treatment process.The paper introduced design scheme and key control point on processing techniques of drill rod briefly.In field trial of Guqiao Coal Mine，it drills 7 boreholes.When reams holes to ø153 mm,it drills 2 309.5 m in total of which the maximum drilling depth of single hole is 530 m; when reams holes to ø220 mm，it drills 651 m in total of which the maximum drilling depth of single hole is 506 m; when reams holes to ø248 mm,it drills 208 m in total of which the maximum drilling depth of single hole is 158 m.It shows the drill rod has good value for popularization and application in large diameter and directional long borehole construction at roof high-level of coal layer.Finally，it provides corresponding proposal for open questions of reaming construction.