| The electro-hydraulic reversing valve of the hydraulic support is used to control the movement of the hydraulic support,and is the key control element for realizing automation of the fully mechanized coal mining face.Since the pump source in the downhole support hydraulic system needs remote fluid supply,the emulsion has lower viscosity than oil and less pressure loss along the way,which can meet the requirements of remote fluid supply for the support hydraulic system.Compared with the oil pressure system,the emulsion can not only meet the requirements of explosion-proof and flameproof in coal mines,but also be more environmentally friendly and cheaper.Therefore,the hydraulic support uses high water base emulsion as the transmission medium.Through the flow of emulsion in the pipeline and control components,energy conversion and transmission are realized.Compared with oil,emulsion has low viscosity and poor lubricity,which is easy to cause problems such as wear,corrosion and leakage of reversing valve.In this thesis,the short carbon fiber filled polyetheretherketone(CF/PEEK)composite with strong wear resistance,corrosion resistance and mechanical properties is proposed to replace the metal material to design the valve body of the pilot valve in the directional valve,and the CF/PEEK composite-metal"soft-hard"paired conical sealing pair structure is proposed to improve the sealing performance of the directional valve.The tensile,compression and bending mechanical properties of PEEK and CF/PEEK composite materials were tested to get the material mechanical parameters.The method of unidirectional fluid-structure interaction was used to simulate and analyze the force and deformation of the CF/PEEK composite valve body under the flow field of 31.5MPa.Using method of computational fluid dynamics(CFD)to simulate and analyze the velocity and pressure of the pilot valve’s flow field with different openings.Under the single effect of erosion and the combined effects of erosion and cavitation,the influence of erosion particle size,erosion rate and erosion time on the erosion rate of CF/PEEK composites was studied respectively,and the erosion and wear mechanism of CF/PEEK composites were analyzed.Aiming at the sealing problem of the poppet valve port,the CF/PEEK composite material-metal"soft-hard"sealing structure is adopted.The leakage model of the poppet valve port,the leakage fractal model of the rough surface and the micro convex contact fractal model were established.Through theoretical derivation,it is concluded that the leakage of the reversing valve is proportional to the pressure difference,the fractal parameter G and the surface roughness of the sealing pair,and inversely proportional to the fractal parameter D.CF/PEEK composite material-metal pair sealing performance was tested.It was found that the leakage rate decreased significantly when the sealing contact force increased.Under the same sealing contact force,the leakage rate increases with the increase of surface roughness,and the smaller the sealing contact force,the more obvious the increasing trend.Under the same seal contact force,the smaller the seal contact area,the smaller the leakage rate.With the increase of the sealing contact force,the sensitivity of the leakage rate to the contact area decreases gradually.LS-DYNA software was used to solve the mass loss caused by erosion when the half cone angles of CF/PEEK composite valve seats are 30°,45°and 60°.The simulation results show that when the half cone angle is 30°,the mass loss caused by erosion is the smallest.Appropriately reduce the half cone angle of the valve seat to reduce the erosion angle of the valve seat by the high-speed liquid flow,and the impact force is correspondingly reduced,which can effectively reduce the erosion and wear of the valve seat.The dynamic response mathematical models of the pilot valve and the main valve in the electro-hydraulic directional valve were established.The pilot valve and the main valve are modeled at the component level in the hydraulic simulation software AMESim.A simulation model of the electro-hydraulic reversing valve system was built,the dynamic response characteristic curve of the reversing valve was obtained by simulation,and the dynamic characteristics of the reversing valve were analyzed.Based on the method of AMESim batch processing,the orifice diameter of main valve core control cavity,the shoulder diameter of main valve core and the outer diameter of main valve core are optimized for dynamic response.After optimization,the response time of the reversing valve is shortened and the response is more sensitive.For the high surface quality requirements of the key assembly surface of CF/PEEK composite pilot valve body,but the milling surface quality of CF/PEEK composite is difficult to control.The milling performance of CF/PEEK composite material was studied.By comparing the quality of surface milled by tools of polycrystalline diamond(PCD),cubic boron nitride(CBN)and cemented carbide.It was found that it is easier to obtain higher surface quality by using PCD tool to mill CF/PEEK composite material.The milling test of CF/PEEK composites with different carbon fiber content shows that:the more fiber content,the greater the milling surface roughness.Taking the minimum surface roughness as the goal,the response surface method was used to optimize the spindle speed,feed rate and the cutting depth,obtaining the optimal milling parameters:n=4102r/min,v_f=303mm/min,a_p=0.2mm.Using gray correlation analysis,combined with principal component analysis and response surface analysis to optimize the milling parameters with the goal of minimizing surface roughness and maximizing material removal rate.The milling parameters obtained are:n=4966r/min,v_f=466mm/min,a_p=1.8mm.After optimization,the surface roughness was reduced by 9.7%,and the material removal rate was increased by about 10 times.The prototype of the CF/PEEK composite directional valve was manufactured and the assembly research was carried out.According to the national standard of the reversing valve for coal mines,the performance test and durability test of the reversing valve are carried out.The comprehensive performance test system platform of the reversing valve was built and verified by AMESim software.Testing the reversing performance of the reversing valve at 10MPa and 31.5MPa respectively.The strength and sealing performance of the CF/PEEK composite electromagnetic directional valve meet the requirements,ant it can be opened and reset normally,having good opening and closing performance.It can be closed reliably under back pressure.The durability test of the CF/PEEK composite pilot valve has been completed 22,680 cycles,which meets the requirements of the national standard. |
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