| UHMWPE is safe,hygienic and non-toxic and has excellent comprehensive performance.It is widely used in the field of microporous materials.At present,the powder sintering method for UHMWPE microporous materials has many disadvantages,such as long process and low efficiency.Therefore,it is necessary to study a new method with high efficiency,low energy consumption and high degree of automation.In this paper,the injection compression process was introduced,and a new method for preparing microporous materials by High Pressure "Jet Flow"Injection Compression Method was proposed.An injection compression mould suitable for UHMWPE microporous materials was designed.An online visual observation platform was set up to observe and record the filling movement state and compression binding accumulation process of "Jet Flow"particles during the molding process of UHMWPE microporous material.The evolution model of filling movement and dynamic compression accumulation of "Jet Flow" particles is established,and the physical and mathematical model of particle movement and contact collision is established.The effects of different mould structure parameters(compression ratio,axial direction of sample,radial direction of sample,gate structure),molecular weight of UHMWPE and different process parameters(screw speed,injection pressure and injection speed)on the properties of microporous samples were studied.The main work and conclusions of this paper are as follows:(1)A visual injection compression experiment platform was established to observe and photograph the filling movement state and compression accumulation process of "Jet Flow" particles in the cavity were.It was found that "Jet Flow" particles showed different movement and accumulation states.(2)A seven stage dynamic evolution model of "Jet Flow" is established by capturing the process of filling,compression and accumulation of particles at high speed:"Jet Flow" injection stage,large slope accumulation stage,gentle slope accumulation stage,vertical accumulation stage,collision accumulation stage,tight accumulation stage,and stable micropore stage.(3)The Hertz Mindlin contact model is used to establish a soft-ball model of collision between particles,and the movement and force of particle contact extrusion in the process of compression are analyzed.(4)By studying the influence of mold structure parameters on the properties of the sample,it was found that under a certain injection volume,the larger the compression ratio is,that is,the greater the compression degree of initial cavity volume is,the smaller the influence of pressure gradient on the properties of the samples is.By comparing the difference of the axial and radial microstructures and pore parameters of the sample,it is found that the difference of the properties of the samples is lower than that of the fixed cavity type Non-dense Injection Molding method,indicating that the High Pressure"Jet Flow" Injection Compression Method can effectively reduce difference of pore diameter and porosity caused by pressure gradient.The optimal gate structure is the multiple runner point gates,which can not only ensure the secondary high shear,but also reduce the flow resistance of "Jet Flow" during the filling process.(5)By studying the influence of materials and process parameters on the properties of the sample,the better molding parameters are obtained.When the molecular weight of UHMWPE is SLL-8,screw speed is 100%,injection pressure is 106.3MPa and injection speed is 60%,the microporous samples with average pore diameter of 14.81 ? m,porosity of 37.02%and bulk density of 0.617g/cm3 can be prepared by High Pressure "Jet Flow" Injection Compression Method.Compared with commercial sintered UHMWPE microporous products(average pore size 28.06 ?m,porosity 39.25%)and fixed cavity Non Dense Injection Molding microporous samples(average pore size 38.92 ?m,porosity 38.34%),the average pore size is smaller and the porosity is close,which indicates that the microporous sample formed by High Pressure "Jet Flow" Injection Compression Method has better performance. |
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