Research On Vibration Characteristics Of Auger Drilling System

Coal auger, the key equipment for coal mining on thin and extremely thin coal seam, hasbeen developed for the thin coal seam of0.4~0.8m. It is advanced in mechanization, coalrecovery and can really realize the unmanned coal mining face. It is significant to enhance thereliability of mechanical mining, the coal productivity and the economic benefit of enterprises.Thus, the theoretical analysis, simulation and experiment are combined to investigate thecoupled vibration characteristic of coal auger drilling system follow the study path ofpick—drill--single drill-rod--three drill-rods system.Based on the coal&rock cutting theory, the contact model of pick-coal is established todecrease the cutting force of single pick, the interference between pick and coal, the wear ofpick. With this based on, the theory mechanical model for coal is established according to theelastoplastic-brittle theory. Moreover, the numerical model of interaction between picks andcoal is established. The load of pick on different installing parameters is analyzed and grasped,which points out that the cutting resistance increases with cutting angle and inclination angle;the feed resistance increases with cutting angle and decreases with inclination angle.To carry out the research of coupled vibration characteristic of coal auger drilling system,the single drill-rod and three drill-rod test-bed for coal auger are developed by modifying thedeveloped cutting test-bed for coal&rock, which contains drilling system of coal auger, themain transmission system and the measurement system. The drills and picks used inexperiments are developed and the coal specimens of four different compressive strengths areconfigured according to the similarity theory and the compressive strength of natural coal.The configured coal specimens can inmates coal of hardness coefficient of3.6,2.88,2.07and1.43. All mentioned above provides experimental foundation for the research of vibrationcharacteristic of coal auger drilling system.In order to research the vibration characteristic of drilling system to decrease and restrainthe vibration and shock of coal auger due to the external factor, the numerical model for drilldrilling coal is established based on finite element method, and the process of opening andboring hole and three-direction cutting forces of drill are analyzed. With this based on, thenatural frequencies and mode shapes of single drill drilling mechanism are obtained accordingto the basis vibration theory and modal analysis method. The results indicate that the verticalnatural frequency of single drill drilling mechanism is greater than the torsional one,moreover, the vertical and torsional natural frequency decreases greatly with the drilling depth.Based on the multi-body dynamic theory, the nonlinear dynamic model of interactionbetween coal and the one, three drills drilling system is established to analyze the vibrationcharacteristic of drilling mechanism under different coal rock hardness, different drillingdepth and different motion parameters. And the experiments are conducted on the establisheddrilling test-bed for coal auger to compare with theory study. The results indicate that thevibration rule of one, three drills drilling system are consistent with each other. However, thevibration of three drills drilling system is greater than the single drill. Moreover, the cuttingtorque and feed resistance of the one, three drills drilling mechanism increase with the drillingdepth and decrease with the rotational speed.In order to study the internal relation between coal breaking and drilling drill torque,drilling rod amplitude varying with time, the nonlinear characteristic of drilling load isresearched. Based on chaos theory, the phase space and the maximum Lyapunov exponent arecalculated and analyzed under different coal rock hardness, different drilling depth anddifferent rotational speeds, which indicates that the load of drilling system is obvious chaotic.Based on fractal theory, scaleless property and self-similarity analysis are carried out on thedrilling load under different working conditions, which shows that the load of drilling systemis obvious fractal. Moreover, the relation between the fractal dimension, maximum Lyapunovexponent and coal rock hardness, drilling depth, rotational speeds is obtained. And it isanalyzed that the reason why the load of drilling system is chaotic and fractal.Based on variational principle, equivalent nonlinear dynamic differential equation ofdrilling rod is established which is in dimensionless treatment to obtain the bendingdeformation equation. Then, the buckling vibration of drilling rod is analyzed and the criticalbending load and its mode shape are calculated under the axial load. The results indicates thatthe stability of drilling rod buckling shape can be judged by calculated the variation ofvibration frequency with axial load.