Roof Control Technology of Mining Roadway under the Influence of Advanced Supporting Pressure

In order to solve the problem of controlling the roof of the stoping roadway in 1204 fully mechanized face under the influence of advanced support pressure, according to the characteristics of the stoping roadway section, the single hydraulic prop and π-shaped steel beam were selected to verify the shrinkage of the single hydraulic support and establish mechanics. The model calculates that at least 3 single hydraulic props and at least 2 material lanes are required for the transportation lane; through the numerical simulation method, a reasonable roof control plan for the stoping roadway in the advance support section is determined, that is, 0∼ in front of the material lane. The one-beam three-column method is adopted within 30 m, and the row spacing is 0.8 m; the one-beam four-pillar method is adopted within 0–20 m of the working front of the transportation lane; and the one-beam three-pillar method is adopted within 20–30 m, and the row spacing is 0.8 m. On-site industrial test practice proved that the proposed roof control scheme is reasonable, and the roadway section can meet the actual production requirements.

Study on Anchor Cable instead of Single Hydraulic Prop Support in Advance Support of Deep Roadway

In order to solve the problems of complicated advanced support process, high labor intensity, affecting the rapid advance of working face and the destruction of roof bolt (cable) by advance single hydraulic prop in ultra kilometer deep mine roadway, the deformation characteristics of roadway surrounding rock is analyzed. Taking the 27304 working face of Wanglou coal mine as the engineering background, numerical simulation, field monitoring, and theoretical calculation were used to analyze the deformation characteristics of roadway surrounding rock within the advanced influence range of 27304 working face. This paper puts forward the active advance support technology scheme, in which grouting anchor cable replaces the existing single hydraulic prop in the advance influence range of the working face in the ultra-kilometer deep mine, and observes and analyzes the deformation and failure characteristics of the surrounding rock of the working face advance roadway. The numerical simulation results show that in the advanced influence range of deep roadway, grouting anchor cable was used to replace the previous single hydraulic prop, and the vertical stress at both ends of the working face decreased by 15 MPa, with a decrease rate of 33.3%; the displacement of roadway roof, floor, and two sides decreased by 10 mm, 55 mm, and 20 mm, with a decrease rate of 40%, 68.75%, and 47.6%, respectively. The field monitoring results show that the roof separation is obviously improved after using grouting anchor cable as the active advance support scheme. It solves the problem of safe and efficient production faced by the ultra-kilometer deep shaft in Wanglou coal mine and provides theoretical and technical support for unmanned double roadway advance support under the condition of safe and efficient mining.

Effect of Uncertainty in Basing Hydraulic Prop Rod on Dimensional Wear of its Basic Surfaces

Hydraulic power cylinders are the main bearing elements of powered supports at mining enterprises, ensuring reliable fixation of the roof in the required working position, as well as providing advancement of the support in the face. Thus, hydraulic power cylinders ensure stoping safety, so strict requirements are im-posed on them both in terms of workmanship and operational reliability. To ensure reliability and efficiency of powered support operation in faces, it is necessary to ensure stable service life of their hydraulic props, which mainly depends on the quality of manufacturing of mating surfaces and the accuracy of assembling functional joints. The required accuracy of hydraulic prop joints is achieved by selective assembly, which allows ensuring the specified technical requirements and service life of the joints. At the same time, along with the issues of ensuring the accuracy of assembling the props to provide proper safety of the face operation, it is extremely important to identify and analyze the causes of dimensional wear of critical parts of the joints, leading to decreasing service life of the hydraulic props in the course of exploitation. In the paper, using the methods of the analytical theory of bases, the reasons for formation of positional variations of the parts of the powered support hydraulic prop joints in the course of assembling and operation of the unit are identified and described. It was found that arising mismatches and formation of local stress zones on the cylinders, pistons and rods, characterized by intense wear, occurs due to the uncertainty of basing (positioning) of rod and piston in hydraulic cylinder. The dependencies allowing calculating deviation of the rod axis from the required position, taking into account the initial clearance gap in the joints and the adopted design parameters of the hydraulic cylinder, have been obtained.

Modeling and Analysis of Single Hydraulic Props in Coal Mines

This research is focused on dynamic performance of water hydraulic single hydraulic prop, the mathematical and AMESim model of single hydraulic prop are established. And the drop hammer is introduced to simulate the impact load of the surrounding rock acting on the prop. The performance parameters of prop retract displacement and cavity pressure are used as the research objects. The working process of single hydraulic prop is reproduced by the simulation. And the influence of safety valve parameters on the support system is analyzed. The results show that: increasing maximal valve core stroke and dead volume or reducing valve damping hole diameter can improve the support performance of the single hydraulic prop. But the influence of equivalent damping has two sides. For support system, decrease damping can improve the support performance, but for the safety valve, reduce the damping make the valve core stability decline. In addition, the pressure overshoot of the optimized system is 18.3%, adjusting time is 0.5s and the retract displacement is 10mm. The dynamic performances meet the technology requirements of the coal mine safety production of China.

Analysis of Hydraulic Prop High Frequency Induction Cladding Temperature Field

The temperature field of mobile column is simulated, with the theory of high frequency induction heating and fourier heat conduction law , to analyze the change law of the temperature field with time, with different cladding parameters. The results show that the induction heating speed is mainly affected by power frequency of high frequency induction heating and cladding current. The higher frequency induction heating power is or the larger the cladding current is, the the faster the surface temperature of hydraulic prop is rising, the lower the inside-wall termperature and the less influenced the matrix is. The effect and the efficiency of cladding is comparatively superior when cladding frequency is 250KHz and current is 1160A.

Research on the Ni-Cr Alloy Coatings on the Hydraulic Prop by High-Frequency Induction Cladding

Ni-based cladding coatings are prepared on the surface of hydraulic prop mobile column by high-frequency induction cladding with different current. Microstructures of coatings are analyzed by metallographic microscope as well as SEM, while coatings and matrix elements are analyzed by EDS. The results show that metallurgical bonding is formed among transition regions of matrix and coatings with obvious white band, when cladding frequency is 250KHz and current is 1160A. The microstructures of coatings are eutectics of austenite + carbide, relatively uniform. During the process of cladding, Fe as well as Mn in matrix permeats to coatings; while Si element in coatings permeats to matrix. As a result, the Fe content of trasition regions is raised, and the contents of Ni and Cr is comparatively reduced.