Numerical Study And Process Optimization On The Resin Sand Shooting Process Based On Gas-Solid Two-Phase Fluid Model

With the rapid development of aerospace,automobile and railway industry,the demand of high-end equipments is continuously increased.Therefore,castings are developed toward to complication and thin wall which lead to an increasing complex structures in their cavity.For example,complex cavity such as oil pass,water pass and air pass are located in engine cylinder head castings,so it need several complex sand cores with multiple curved surfaces for casting.The sand shooting process which shoot core sand by high-pressure gas is the most widely used technology for coremaking.The sand used in sand shooting process ofen covered with binder which lead to a bad flowability in high-pressure gas.Therefore,the sand shooting process is a complex gas-solid two-phase flow system and the design of sand shooting process is difficult.The trial and error method which is still the most widely used method to optimize the sand shooting process is hard to design complex sand shooting process.In order to solve this problem,a gas-solid two-phase fluid model is established for sand shooting process design in this paper.A simulation system for process parameters of sand shooting process is developed.It can be used for sand shooting simulation and process optimization of complex sand cores.An digital solution technology is proposed for the process design of sand shooting forming by this method.The main research work is as follows.(1)A heterogeneious structure drag coefficient correlation for gas-solid flow based on EMMS theory is established.With two-fluid model based on KTGF theory,a precise simulation of sand shooting process coupling with macroscale and particle scale is achieved.In EMMS drag model,the gas-solid flow is resolved into a dense phase,a dilute phase and an interaction phase.With specified material properties(density et al.)and operating conditions of sand shooting process(sand shooting velocity et al),a heterogeneious drag coefficient for sand shooting process is obtained by minimizing the energy consumption.A more precise prediction of particle flow structure is achieved by comparison between other models.A visual mould based on high-speed camera recording system is designed for sand shooting process and a great agreement is achieved by comparison between experimental results and simulation results with this model.Moreover,a great accuracy on sand shooting process simulation by our model is validated by comparison with discrete element coupling model.(2)An energy dissipation model during particle collision is established.A novel approach to determine energy dissipation in particle flow through wet restitution coefficients quantificationally is introduced.A fitting function with resin viscosity,thickness,density and particle diameter for wet restitution coefficients is obtained.A quantitative measurement of resin sand particle restitution coefficient is achieved.The problem that estimating the influence of resin binder ratio in sand shooting process simulaiton is solved.The roughness of dry particles has a great effect on energy dissipation during particle collisions.The interaction between particles tend to elastic collision when the particle radius decreasing.The liquid coating thickness and viscosity has a great influence on the restitution coefficient of wet particles by affecting collision energy loss.The more thickness and viscosity of the liquid coating,the more energy loss will occur in collision,the restitution coefficient is decreased.Then,a study for the flow behavior of sand particles with furan resin is proposed.The results suggest that the fluidity of sand particles and the speed of sand filling increased with resin binder decreasing.The distribution of sand particles in cores became more homogeneous with a lower resin percentage.However,the packing degree will decrease with a low resin percentage.When resin increased,the fluidity and filling speed decreased,the difference bewtwen wall and center and the packing degree is increaseing.(3)The optimum technological parameters of quantity and proportion for two resin binders is acquired.Based on the compressive strength test and SEM analysis of fractures,the influence of resin binder properties on the strength of sand cores is researched.The results showed that the furan resin has a great ablity of infiltrating,so cohesive fracture is easily happened in furan resin sand.The micro pore in liquid bridge have a great influence on sand core strength and the best furan resin adding quantity is 1.25%?1.75%.The strength of phenolic urethane resin sand is influenced by ingredient proportion of resin.The best phenolic urethane resin adding quantity is 1.6%?2.0%,and the ingredient proportion is 50:50.(4)The influence of process parameters on sand shooting are analyzed.The shooting pressure,the number and distribution of vents and nozzle diameter are researched based on the gas-solid two-phase fluid model established in this paper.The results suggest that,with increasing of shooting pressure,the sand filling speed increasing and the dead zone in sand bin decreasing.However,a higher pressure will lead to a drastic fluctuation of sand flow,the distribution of sand particles in cores became more heterogeneous.The vents which located in the direction of sand flow will be more efficient for sand filling.In order to get a efficient filling process,the total area of vents must be 50%?60%of nozzle area.The nozzle diameter has a significant influence on sand mass flux,the relation between nozzle diameter and sand mass flux is Q=D^2.2.The nozzle diameter also has effect on sand filling fluctuation,the filling will be more stable with a bigger nozzle.(5)The praticability and reliability of the sand shooting process simulation system established in this study are validated.A crank core and a rear axle core are taken as example for sand shooting process simulation and optimization.The defect of crank core is related to short shot.The nozzle has been blocked before sand filling finished,so sand particles are unable to fill the sand box.With optimization on the sand filling velocity,the core box will fill in clockwise order which can avoid blocking in the nozzle,and the short shot is dissapeared.The defect of rear axle core is due to the inefficiency of gas exhausting and unreasonable structure of sand box.By increasing some part of nozzle diameter and decreasing shooting pressure,the sand filling process became more steady.The defect of nozzle blocking and plume can be avoid by optimized sand shooting process.With the improved and optimized process program,high quality sand cores without defects can be manufactured.