Study On Friction Characteristics Of High-speed Variable Gap Seal Hydraulic Cylinder Based On Texture Technology

High-speed servo hydraulic cylinder,the last link of the whole control system and the lowest dynamic response in the system,is the core component of metallurgical production automation equipment and the actuator of hydraulic servo control system.Its performance directly affects the control precision and the response speed of the whole system.Friction and leakage are important parameters for measuring the performance of high-speed servo cylinders.Therefore,reducing the friction of the hydraulic cylinder and improving its response speed,as well as optimizing the sealing performance are keypoint of the servo hydraulic system with high-power,high-precision control and low leakage.This dissertation,based on improving the dynamic response performance of high-speed variable gap seal hydraulic cylinder,introduces the bionic texture technology.the bionic micro-texture morphology is constructed on the inner surface of the cylinder and the friction characteristics of the variable gap seal hydraulic cylinder is analyzed under the deformation lip of the piston to achieve low leakage,which will ensure the performance of low friction,high speed and high frequency response.Firstly,the dynamic pressure lubrication model of bionic micro-texture morphology is proposed and designed on the inner surface of cylinder.Taking the gap flow field between the cylinder and the piston of the hydraulic cylinder as the research object,the pressure in the flow field is analyzed and the pressure equation is established.Meanwhile,the bionic elliptical texture and rhomboid texture are constructed on the inner surface of the cylinder.The length of the horizontal and vertical half-axis of the texture is taken as the target parameter in the dynamic pressure lubrication control equation.The numerical optimization and analysis of multi-parameter changes are carried out by mathematical methods such as five-point difference method,cyclic iteration method and Simpson integral formula.The results show that the optimal surface bionic micro-texture morphology is a diamond-shaped texture.The oil film bearing capacity is 9 times higher than that of the untextured,and is nearly doubled compared with the elliptical texture.The coefficient of friction of the inner surface of the cylinder is also reduced to one eighth of the untextured.Secondly,the coupling effect of surface roughness and surface texture on the dynamic friction characteristics of hydraulic cylinders is proposed.Based on the equivalent flow method proposed by Patir and Cheng,the mathematical model of coupled lubrication with surface roughness and texture is deduced and established,and the flow factors such as pressure flow factor,shear flow factor and surface factor in the lubrication model are determined and lubricated.The equation is numerically solved and the coupling effects between surface roughness and rhombohedral texture has a great influence on the lubrication friction performance of the inner surface of the cylinder.The roughness of the inner surface of the cylinder is not as smooth as possible,but exists an optimal comprehensive roughness which makes the largest the oil film bearing capacity of the inner surface of the cylinder barrel and the smallest the friction coefficient.At the same time,the rough peak direction of the friction pair surface also has a significant influence on the friction performance,that is,the trend of the rough peak and the flow of the liquid.When the direction is the same,the lubrication characteristics of the inner surface of the cylinder will be greatly improved.Thirdly,starting from the variable gap sealing mechanism of high-speed variable gap sealing hydraulic cylinder,the variable gap sealing principle of hydraulic cylinder and the eccentricity of the piston generated during operation are analyzed.The influence of piston eccentricity on the leakage of the hydraulic cylinder and the lubrication performance of the inner surface of the cylinder is importantly analyzed.At the same time,the relative movement speed of the piston and the hydraulic cylinder and the influence of the change in the texture depth on the lubrication performance of the inner surface of the cylinder are analyzed.Finally,a laser preparation method for bionic texture of 45# steel surface of the hydraulic cylinders is proposed.The test piece is made of 45 steel,which is commonly used in hydraulic cylinders.The base of the test piece is obtained by numerical control machining,grinding and polishing.The diamond texture of different shape parameters is prepared on the surface by nanosecond laser processing.At the same time,considering the actual operating conditions of the hydraulic cylinder,the experiments of friction gap change,texture wear depth change and friction pair relative motion speed were designed and analyzed.Through the mutual verification between the numerical simulation results and the experimental results,the foundation for the wide application of bionic texture technology in the hydraulic field is laid.