Optimum Design And Experimental Study Of Nozzle Used For Half Wet Shotcrete In Jetting Cement Support Technology

According to the engineering background of coal mine roadways,the demands for machine reform, material optimization and process improvement are increasing. Therefore, it is necessary to develop the scientific, safe and efficient mining technology for mine shotcrete support system that could meet the requirements of industry standards and specifications. By means of field investigation, numerical analysis,experimental determination and engineering application, such a system was studied in this dissertation.In order to improve the machines and tools of half wet spraying technology, this study explored the development condition and current situation of the jet concrete supports technology, and proposed a PTS-7 pusher-chain type concrete sprayer based on the working principle of pusher-chain type concrete sprayer. It successfully improved the operating environment and support strength.The design of nozzle influenced the performance. Based on the core issues of high rebound and high dust concentration in shotcrete, this study determined three structural factors that could influence the spraying performance, which are, the number of inlet, the inlet angle and the length of the mixing section. Nine types of new nozzles were designed based on a series of orthogonal experiments. In order to explore the effects of these three factors on the spraying performance, the numerical simulation of the flow field in the nine new nozzles was carried out by using FLUENT software. The volume fraction, velocity and pressure of the gas-liquid-solid phase flow in the nozzle were analyzed, and the movement of air, water and mixture were obtained.According to the relevant standard requirements, coal mine conditions and the characteristics of push-type concrete spray machine,this study determined the mine jet mix concrete ratio from the perspective of material selection and the proportion of quality. Through the new effect tests, the performance of rebound and compressive strength of new nozzles were compared with the regular ones in domestic wetting jet, the results show that the performance of the new nozzles is better at reducing ducks and rebounds.In addition, based on the orthogonal experiment and synthesis analysis, the measurement of rebound based on real working conditions was used to describe the spraying performance. Effects of diverse technological parameters including the working wind pressure, working water pressure, jet distance, spray angle and initial spray thickness on the rebound during spraying process were determined, and based on which the optimal parameters of the shotcrete construction process were obtained. These findings provide theoretical basis for the popularization of half wet shotcreting technology in the mining industry.Through the on-the-spot measurement of the half wet shotcreting technology effects on the construction technology, it is proved that the technology and process of the half wet shotcreting technology are in line with the actual needs of the coal mine. The coal mine roadway is divided into Three zones according to the stability of the surrounding rock. Five different concrete compartments are designed for jet support, and the construction effect is tested. It is found that the new nozzle reduces the material rebound and improves the spray quality. Therefore, the half wet shotcreting technology creates a good working environment for the miners and has the potential to be widely applied in coal mine industry.