Xiaohui Liu's research while affiliated with Xi’an International Studies University and other places

During the excavation of a roadway, the drilling speed of a cutting head is low and the cutting load is excessive. To solve these problems, a spatial mechanical model of a pick was established. Then, the drilling process and rock breaking mechanism of the pick were analyzed using the numerical simulation software LS-DYNA. By investigating the relationship between the pick working angle and the cutting load, a reasonable range for the working angle was obtained. Based on this range, the pick lacing arrangements and working angle of the cutting head were optimized, and a cutting experiment was carried out to assess that optimization. The results show that the cutting force of the pick and the cutting force change value both increase with increasing elevation and inclination angles. In contrast, the feeding force of the pick and the feeding change value increase with increasing elevation angle, but decrease with the increasing inclination angle. It can be concluded that the reasonable choice ranges for the elevation and inclination angle are 40–50° and 20–40°, respectively. Meanwhile, a contrastive analysis was performed for the cutting load of the cutting head with un-optimized and optimized pick working angles. The cutting torque and feeding force for the optimized cutting head were reduced by 8.2 and 16.08%, respectively, and the wear on the pick was significantly reduced.

A new self-controlling hydro-pick, which can control water flow automatically, was designed based on hydrodynamic theory. Firstly, the balance of forces acting on the pick was shown to present the operating principle of it, specifically, the force exerted by the water pressure acting over an annual area of the pick. A rock-breaking test bed was developed to study the frictional resistance, dynamic response, flow and rock-breaking characteristics of the self-controlling hydro-pick. The results indicate that, the external and internal diameter of the annual area on the pick should be 40.6. mm and 40. mm, respectively to ensure normal shutdown of the self-controlling hydro-pick at a jet pressure 40. MPa. The opening times (time taken to open the valve) increased with jet pressure and decreased with the cutting depth. For a jet pressure and cutting depth of 40. MPa and 12. mm, respectively, the opening time was 0.035. s. The water flow of the self-controlling hydro-pick was less than that of the common hydro-pick when the diameter of the damping hole was 0.5. mm. The percentage water flow reduction increased with the jet pressure and cutting depth. When the jet pressure and cutting depth are 40. MPa and 12. mm, respectively, the percentage cutting force reduction was 22.6%, the depth of the cutting slot increased by 24.2%, and the volume of rock breakage increased by 29.3%.

In the rock breaking progress, the resistant force results in tools failure and the low cutting efficiency, thus, it is necessary to reduce the failure of tools and enhance the efficiency of cutting and drilling. In this paper, different configuration modes of water jet were presented to solve this issue. Moreover, the symmetrical pre-split finite element models for rock breaking by pick without water jet and picks assisted with different configuration modes of water jet were established to analyze the effect of different configuration modes on rock stress distribution and pick cutting forces. Finally, the experiments were conducted to validate the theory analysis. The results indicate that the cutting force decreasing rate of JCP is maximum all the time under the same conditions compared with the decreasing rate of JSP and JFP; and the numerical results were consistent with the numerical, which verifies the correctness of theory analysis. © 2015, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.

Conical picks are one kind of cutting tools widely used in engineering machinery. In the process of rock breaking, the conical pick bears great cutting force and wear. To solve the problem, a new method, conical pick assisted with high pressure water jet, could break rock effectively, and four different configuration modes of water jet were presented. In this paper, based on the analysis of the different water jet configuration's advantages and disadvantages, experiments on front water jet, new typed rear water jet, and the combination of those two water jet configuration modes were conducted to study the assisting cutting performance and obtain the quantitative results.

The numerical model of rock breaking by water jet was established based on finite element method (FEM) and smoothed particle hydrodynamics (SPH) to research the efficiency of rock breaking by water jet. Firstly, the research on the impact pressure of water jet was conducted under different diameters and velocities. Then, the effect of water jet diameter, jet angle and jet velocity on the efficiency of rock breaking was studied and the reasons were shown through analyzing the impact rock momentum, rock energy, mean cutting depth and mean cutting width. The results indicated that, the efficiency of rock breaking increased with the jet angle firstly and then decreased, and the jet angle about 10° was the most optimal to break rock; meanwhile, it can be concluded in terms of energy that more micro-damages formed when the jet angle was 0°. The efficiency of rock breaking, expressed as the relative rock eroded element number, mostly increased with the diameter of water jet in a trend of stair-step and there was no difference under different rock strength. Moreover, rock breaking efficiency increased with the velocity of water jet in a trend of straight line and the trend varied not with rock strength yet. However, the trend slowed down with the increase of rock strength, which showed that efficiency of rock breaking could be enhanced greatly by increasing velocity of water jet, and the smaller the rock strength, the more obvious the efficiency.

In the process of rock breaking, the conical pick bears great cutting force and wear, as a result, high-pressure water jet technology is used to assist with cutting. However, the effect of the water jet position has not been studied for rock breaking using a pick. Therefore, the models of rock breaking with different configuration modes of the water jet are established based on SPH combined with FEM. The effect of the water jet pressure, distance between the jet and the pick bit, and cutting depth on the rock breaking performance as well as a comparison of the tension and compression stress are studied via simulation; the simulation results are verified by experiments. The numerical and experimental results indicate that the decrease in the rates of the pick force obviously increases from 25 MPa to 40 MPa, but slowly after 40 MPa, and the optimal distance between the jet and the pick bit is 2 mm under the JFP and JSP modes. The JCP mode is proved the best, followed by the modes of JRP and JFP, and the worst mode is JSP. The decrease in the rates of the pick force of the JCP, JRP, JFP, and JSP modes are up to 30.96%, 28.96%, 33.46%, 28.17%, and 25.42%, respectively, in experiment. Moreover, the JSP mode can be regarded as a special JFP model when the distance between the pick-tip and the jet impact point is 0 mm. This paper has a dominant capability in introducing new numerical and experimental method for the study of rock breaking assisted by water jet and electing the best water jet position from four different configuration modes.

The size of coal fragment cutoffs by cutting mechanisms is an important index of coal mining. The larger the coal fragments, the less the dust, the lower the specific energy consumption and the higher the benefit. Therefore, a coal fragment size model was formulated in order to obtain large coal fragments in the cutting process, which considered the effect of pick arrangements (sequence and Punnett-square), helix angle, advancing velocity and the cutting line space of cutting mechanisms. Moreover, the effect of the above parameters on the size of coal fragments was analyzed in theory, which was validated by the cutting experiments correspondingly conducted using 8 different helix drums. The theoretical and experimental results indicate that the coal fragment cutoffs by Punnett-square drums are larger in size and more uniform in size distribution than by sequence drums; the size of coal fragments, increasing with the advancing velocity and the cutting line space, is almost unaffected by helix angle; the effect of advancing velocity and the cutting line space for Punnett-square arrangement is greater; the effect of cutting line space on coal fragment mass percentage below 1 cm is greater than that of advancing velocity.

In the process of drilling coal, the kinematics of drill-rod is quite complicated. The drill-rod not only vibrates in longitudinal, transverse and torsional direction, but also random impacts and contacts coal wall. Considering the drilling load of drill-bit and coal, contact impact of the drill-rod and coal wall, the drill-rods are dispersed into a number of finite elements. At the same time, the nonlinear dynamic model of drill-rod system coupling longitudinal, transverse and torsional vibration is set up. The simulations of the dynamic model are researched under the conditions of different hardness coal (2.7, 3.7, 4.65). In order to decrease the vibration of auger drill, the stabilizer is added onto the drilling mechanism. And the underground experiments are done at 2404 working face of Xie-Zhang Coal Mine in Shan-Dong Province of China. The results indicate that the transverse vibration radius, the longitudinal vibration frequency and amplitude all decrease with the rock hardness. The maximum transverse vibration radius shows an exponential relation with the drilling depth under the condition of the same rock. Under the same condition, the drilling depth of auger drill with stabilizer is 1.39 times that with no stabilizer, and the drilling pressure decreases about 2/3.