Design And Experimental Study Of Screw-type Atomization Coating Valve

As the electronics industry is accelerating its transformation and upgrading towards intelligence,flexibility,and comprehensiveness,traditional coating equipment can no longer meet increasingly stringent process requirements,and the development of high-precision coating equipment is imperative.Compared with other coating valves,the screw-type atomization coating valve has obvious coating advantages: high coating accuracy,precise spray width and thickness control.Although the metering type atomized coating valve has also been introduced by domestic companies,they are all applied to the low-end coating process.The coating technology that is truly suitable for high-precision processes is not mature in China.The core components of this product abroad are Design and manufacturing are still in a monopoly position.In order to solve the application problem of the existing coating technology in the high-precision process,a coating valve based on the principle of screw metering and gas-liquid two-phase mixed atomization was developed,the structural size parameters of the atomizing nozzles of the core components were optimized and the effects of four parameters,such as atomizing air pressure,liquid flow rate,liquid viscosity,and spraying height,on the spraying effect were studied through prototype experiments.The paper mainly includes five parts:1.Research on the working principle of screw pumpThrough the analysis of screw pump metering process,the main characteristics and advantages of screw pump metering feed are understood.Through the kinematic analysis of screw and stator of screw pump,the profile equation,meshing relationship and the movement law of screw in stator are obtained.Through the dynamic analysis of screw pump,the stress state of screw is analyzed.The sealing characteristics and leakage principle of screw pump are studied.The cross-section structure of screw and stator is taken as the theoretical model to study the flow field distribution in the cavity when screw pump works.2.Research on the basic theory of liquid atomizationBased on the study of the basic theory of liquid atomization,this paper introduces the process and mode of the splitting and breaking in the mixing process of gas and liquid.The breaking of liquid into smaller droplets requires one-time atomization and two-time atomization.When the liquid is affected by the external aerodynamic force,the internal viscous force and the surface tension,the unstable surface wave will be generated on the surface of the liquid.With the increase of the aerodynamic force,the amplitude of the surface wave will increase,and the liquid will be broken and atomized into tiny droplets.According to the principle of liquid atomization,the structure of atomizing nozzle,the relative velocity of gas and liquid,and the physical properties of gas and liquid are all important factors affecting the effect of liquid atomization.This paper establishes three indexes for evaluating the atomization performance of liquids: atomized droplet fineness,atomization angle,and atomization uniformity,and concludes that the diameter distribution of atomized droplets conforms to the normal distribution.A theoretical model that affects the effect of liquid atomization was established,and the relationship curves between liquid velocity,gas velocity,gas-liquid volume flow ratio,liquid viscosity,and droplet diameter were obtained.3.Structural design of screw-type atomization coating valveThe structure of the screw-type atomizing coating valve is optimized.The structure size of the screw and the stator is designed based on the given flow rate and speed.The axial force analysis of the transmission of the screw was performed to select the appropriate bearing and flexible shaft.The liquid flow path and gas flow path of the atomizing nozzle of the coating valve are simulated and optimized to obtain the structural parameters for achieving the optimal atomizing effect.Simulation and optimization of the gas homogeneous plate on the gas flow channel were selected,and 8 holes were uniformly arranged as the structural design parameters of the gas homogeneous plate.The two-phase flow simulation of gas-liquid two-phase mixed fluid at the atomizing nozzle was performed,and the influence of gas outlet diameter,liquid flow rate and atomizing pressure on gas-liquid mixed atomization are obtained.The results show that as the diameter of the gas outlet increases,the flow velocity of the gas-liquid mixed fluid at the outlet gradually decreases;as the liquid flow rate increases,the flow velocity and spray width of the gas-liquid mixed fluid remain almost unchanged;as the atomizing pressure increases,the flow rate and spray width of the gas-liquid mixed fluid increase.4.Design of control system for screw-type atomization coating valveA screw-type atomizing coating valve control system is designed,and the components and working principles of the control system are analyzed.A single-chip microcomputer and a DC motor driver are used as the core to design a complete control system.Aiming at the functions commonly used in the atomization coating operation,two working modes of jog and line drawing are set to adapt to different coating processes.5.Experimental research and result analysis of screw-type atomization coating valveA screw-type atomization coating valve test platform was set up,and the effects of four parameters,such as atomization pressure,liquid flow rate,liquid viscosity,and spray height,on the spraying effect were experimentally analyzed.The results show that with the increase of the atomizing pressure,the spraying width of the atomized spray changes irregularly,generally increasing first and then decreasing,and then increasing after stable,while the thickness of the spraying gradually decreases;with the increase of the liquid flow,the spraying width of the atomized spray increases first and then decreases,and the thickness of the spraying gradually increases;with the increase of the viscosity of the liquid,the spraying width of the atomized spray decreases,and the decreasing trend gradually decreases,while the weight of the spraying gradually decreases;as the spraying height rises,the spray width of the atomized spray rises first and gradually stabilizes.Using the PDPA test platform,the particle size of the atomized liquid is used as a performance evaluation index of the atomization effect,and the influence of the atomization pressure,liquid flow rate,and liquid viscosity on the atomization particle size is analyzed.The results show that: as the atomizing pressure increases,the particle size of the atomized particles appears to decrease;as the flow rate of the liquid increases,the particle size of the atomized particles tends to increase;as the viscosity of the liquid increases,the uniformity of the liquid atomization tends to deteriorate.The screw-type atomization coating valve developed in this paper can easily obtain atomized particles with a smaller particle size(less than 100 μm)under different operating parameters,and performs well on the two evaluation indexes of atomized droplet fineness and atomization uniformity.