Numerical Discrete Element Analyses for Rock-Breaking Effects of Inserted-Tooth Hob and Cooperative Mechanism Between the Inserted Tooth

The Inserted-tooth Hob has been widely used in underground engineering when the mechanical rock drilling direction downward. Based on the mechanical parameters of the sandstone, the high precision fitting discrete element numerical model is obtained to research the influence of rolling mode on rock-breaking effect. The results show that, under the condition of no confining pressure, the crack propagation will deviate from the central axis of the cutters, and the damage and fragmentation caused by the front inserted-tooth will increase the rock-breaking efficiency of the adjacent rear inserted-tooth. The maximum normal thrusting force (NTF) of both front and rear teeth increases under confining pressure. However, the vibration of the tangential rolling force (TRF) in the rock-breaking process of a single ring inserted-tooth hob is more sensitive to the adjacent tooth spacing than that of NTF. When the hob slips forward, the NTF and TRF all increase obviously under 10 MPa confining pressure, but the fluctuation of NTF becomes larger and the fluctuation of TRF decreases. When the hob slips backward, the NTF decreases and the fluctuation increases slightly under 10 MPa confining pressure, but the average of TRF increases twice and the coefficient of variation of TRF decreases by 55.18%, and the fluctuation decreases obviously. This research is of great significance to the design of inserted-tooth hob and to improve the drilling efficiency of mechanical rock-breaking.