| As a complicated mine phenomenon, coal and rock outburst is featured by high risk and frequency, seriously restricting the efficient production of coal mine safety. Gas drainage holes pre-drilled drainage is one of the most effective methods to avoid the outburst.Most coal seams are soft coal in the Southwest. The seam permeability is poor and has greater stress. It seriously affects the efficiency of gas drainage that the hole is easily collapsed after the drill pipe exit in borehole drilling. It is difficult to go back to the original position if the drill has moved. That means the failure hole cannot be repaired. There is no effective way to repair the failure hole except to drill a new one in the present case. Self-propelling and rotating drill has the characteristics that can drill in the formed hole automatically change direction along the original hole. That means the self-propelling and rotating drill is ideal for repair the failure hole.Referring to Science Fund for Creative Research Groups (50621403), a series of experiments related to coal drilling by high pressure water jets were carried out. Through the mechanism of water jet and jet recoil coal calculate the theoretical research, design a set of down hole drilling can be used to clear one's self into the hole and rotary drill, and the use of numerical simulation software Fluent for optimized layout of the bit nozzles. According to the theoretical analysis and numerical simulation results, several processing and manufacturing of self into a more reasonable arrangement of rotary drill bit broke through the coal and rock experiments, analyzed the pros and cons of several nozzle layout to select the optimal nozzle layout. Obtain the best work of the drill bit broke coal drilling parameters and characteristics by experiments.The main contents and conclusion are as follows:①Obtained the motion equations of self-propelling and rotating drill by the rotary drill bit into the equation of motion, while the reverse nozzle and forward by analyze the system with the generation of power and get the best diameter ratio is 1.32.②Developed a new system realize rotary seal ring. The sealing device has been tested no leakage under 25MPa. The speed limit system is reliable which is formed by the resistance ring and this new system.③Establish the drill model with SolidWorks and simulate the experiment with Fluent. Obtained the pressure and velocity distribution by different target distances. According to the simulation results with experimental conditions selected the optimal layout, the forward nozzles has a lmm center nozzle, two angle 15°, lmm in diameter nozzles and two angle 15°, opening angle 20°,1.4mm in diameter nozzles. Reverse nozzles has three 12°,2mm in diameter nozzles.④By modeling experiment, get the effect by pumping and coal particle size of the hardness. With the increase of pump pressure, flow and penetration rate soared; drilling speed and the hole diameter increased with the strength of coal decreased; coal particle size is less impact to the drilling speed. In the clearance experiments, use coal slag to fill the holes have been drilled to simulate the collapse hole, the results shows that the self-rotating drill bit into the little effect on the aperture, means this kind of drill suited for the work of repair the failure hole. |
