Influence mechanism of polycrystalline diamond compact bit temperature rise based on thermo-fluid-solid coupling.

In order to improve the drilling performance of polycrystalline diamond compact bit and prolong its service life during drilling in coal rock under the action of wind cycle, the theoretical calculation model of polycrystalline diamond compact bit cutting teeth temperature was derived based on the theory of tribology and heat transfer. The theoretical temperature field of polycrystalline diamond compact bit-cutting teeth was analyzed. Using the joint simulation of EDEM-FLUENT, the temperature variation law of polycrystalline diamond compact bit cutting teeth under the thermo-fluid-solid coupling was analyzed to verify the validity of the theoretical calculation model of polycrystalline diamond compact bit cutting teeth temperature. By building a rotary drilling test platform and conducting drilling experiments on polycrystalline diamond compact bit under different drilling parameters respectively, the correctness of the theoretical model and the simulation data were verified. In addition, a response surface analysis model was established to study the influence of different drilling parameters on the polycrystalline diamond compact bit cutting teeth temperature during drilling in coal rock. The analysis results show that the influence degree of various drilling parameters on the polycrystalline diamond compact bit cutting teeth temperature from large to small is drilling pressure, drilling speed, coal rock properties, and wind speed. Compared with the working condition without wind cycle, the drilling efficiency of polycrystalline diamond compact bit can be increased by 14.38% and the temperature is reduced by 8% when it drills in coal. The drilling efficiency of polycrystalline diamond compact bit can be increased by 17.79% and the temperature is reduced by 10.5% when it drills in coal gangue.

Stick-slip vibration characteristics of drilling tool during drilling in coal seam with gangue.

Aiming at the problem of stick-slip vibration caused by sudden drilling resistance torque during drilling in coal seam with gangue, the drilling tool dynamic model with two degree of freedom was established based on the interaction between the bit cutting teeth and the coal seam with gangue. So, the motion differential equation of torsional vibration of drilling tool was derived, and the torsional vibration response of drilling tool was analyzed. Taking the drilling tool with drilling depth of 300 m as an example, the response laws of angular displacement, angular velocity, resistance torque, driving torque, relative motion phase trajectory and torsional vibration of the drill bit were discussed. The results show that the drilling tool has obvious stick-slip vibration under the action of sudden drilling resistance in the process of drilling in coal seam with gangue. The angular velocity of the drill bit moves alternately between the viscous stage and the sliding stage. A stable limit cycle will appear in the phase trajectory curve of the drill bit.