Experimental Study On The Micro Mechanism Of Thermal-particle Coupling Clamping Of Hydraulic Spool Valve

The development of intelligent,unmanned and electric hydraulic equipment puts forward higher requirements for the reliability of the hydraulic system.Spool valve is the most widely used precision control element in hydraulic system,and the fit clearance is generally 5~20?m.In practical work,the spool always bear a “Clamping force” under the influence of microscopic factors such as thermal deformation and particle pollution,which is far greater than the “viscous friction”,and leads to deterioration and failure of system performance,even serious consequences of machine destruction.So,the hydraulic reliability problem is the clamping problem of the spool valve in a certain level.The phenomenon of spool clamping is random.At present,there is still a lack of in-depth understanding of its microscopic mechanism and internal law,especially lack of experimental research and systematic data support at the deep and microscopic level.This study is on the basis of the embedded spool valve temperature distribution measurement method and spool valve clamping force measurement device,as well as theoretical analysis and joint simulation technology.The internal temperature distribution and thermal deformation characteristics of the spool valve were obtained,and the clamping forces under the single factor of thermal deformation or solid particles as well as the combined action of thermal deformation and solid particles were measured.After that,the understanding of the microcosmic mechanism of spool valve clamping was advanced,which can provide theoretical guidance for the design and manufacture of high reliability spool valve.The main research contents are as follows:(1)Embedded measurement method and simulation analysis of temperature distribution of spool.An embedded temperature distribution in-situ measurement method was proposed,an experimental system with thermal imaging function was built,and the ANSYS-Fluent & Workbench joint simulation was combined.The effects of valve opening,pressure drop,throttling groove form(K,U,V-shaped throttling grooves)and flow direction on the temperature gradient,temperature distribution and local thermal strain characteristics of spool were studied.Thus,the clamping mechanism of non-annular-orifice spool valve under different conditions was analyzed.The results of temperature measurement and fluid-solid-thermal coupling simulation are in good agreement,which can provide reference for similar research.(2)Temperature distribution measurement and thermal deformation calculation of valve orifice.The temperature distribution of the plane valve orifice was measured,and the effects of the valve opening and pressure drop on the temperature distribution were analyzed combined with the multiphase flow simulation.The discrete temperature measurement data were fitted and the thermal deformation of the sharp edge was calculated.The results show: the temperature gradient seems more sensitive to pressure drop under a small orifice;the higher temperature on the sharp edge diffuses because of the change of wake flow under large valve opening or production of cavitation under large pressure drop;the radial thermal deformation of sharp edge can reach 8.3?m,which reaches or even exceeds the clearance size of the cylindrical spool valve with the same size,and become a non-negligible factor of spool clamping.(3)Development of measuring device and quantitative analysis for clamping force of spool valve.A measuring device for thermal deformation and clamping force of spool valve was established,the clamping force of spool and valve body at different temperature difference were measured,the correlation among temperature,thermal shape variable,and clamping force of spool valve was obtained.The results show: clamping force caused by thermal deformation of spool valve presents obvious non-periodic pulsation characteristics;the longer the fitting length between the spool and the valve hole,the greater the clamping force;the larger the temperature difference between the spool and the valve body,the longer the clamping time,the greater the peak value of clamping force;when the temperature of the spool with the diameter of 20 mm rising 70?,the diameter increase 9.9?m,and the clamping force reaches 27.41 N,which will seriously affect the stability of the spool valve.(4)The clamping mechanism of spool valve under the action of solid particles.Considering the material,size and concentration of particles,as well as the "radial fretting" of spool,the mechanical model of spool valve clamping under the action of solid particles was established,and the curves of spool clamping force under the action of solid particles were obtained through the clearance amplification model experiment.The results show: when the proportion of particle size to clearance size is greater than the "sensitive scale" of 0.7,or the volume concentration of particles is higher than the "sensitive concentration" of 5%,the clamping force of the spool will increase rapidly.(5)Clamping force measurement and mechanism analysis of spool valve under combined action between thermal deformation and particles.The clamping force of the spool valve under combined action between thermal deformation and particles is obviously greater than that under the single factor,which makes the smaller thermal deformation and non-sensitive particles which are not sufficient to cause the clamping become the clamping factor and greatly increases the risk of the spool clamping.The results show: the peak values of clamping force produced under the four conditions of normal temperature(25?)+ pure oil,normal temperature + solid particle pollution(the pollution level is 14),thermal deformation(the temperature of valve body is50?)+ pure oil and thermal deformation + solid particle pollution increase sharply in turn,the clamping force under the four conditions are 0.22,1.34,4.56,12.63 N respectively,the spool may even be stuck under the combined action of thermal deformation and solid particles.In addition,the mechanical model of spool valve clamping triggered by solid sensitive particles was established,a remote sensing system for temperature monitoring of spool valve was developed based on the thermal couple embedded temperature measurement method combined with wireless communication technology,the design method of high reliability spool valve were summarized based on the study of microcosmic mechanism of spool clamping.