The Injection Process Optimization And Property Study Of A Fixed Plate Made By Glass Fibers Reinforced Polyamide66 Composite Filled With Red Phosphorus Used In Medium Voltage Switch

Glass fiber reinforced nylon 66(PA66)is thermoplastic engineering composite material with excellent performance.For its high mechanical strength,good impact resistance,stable chemical performance and good insulation performance,it has been widely used in electronic,mechanical,automotive industry and so on.The research object of this paper is the fixed plate of medium voltage switch,which comes from the task entrusted by the enterprise.The material is red phosphorus flame retardant glass fiber reinforced nylon 66(PA66-GF25 FR(RP))filled with red phosphorus used in medium voltage switch whose flame retardant level is up to V-0.Because it needs to play the role of isolating the upper and lower high-voltage currents in the medium-voltage switch,in order,it is required that there are no pores inside the fixed plate,no burrs on the surface to prevent high-voltage breakdown and tip discharge.And it has high requirements in the dimensional accuracy of the board and aging resistance.The PA66-GF25 composite itself has anisotropy due to the orientation of glass fiber,resulting in a large difference in the horizontal and vertical shrinkage of the material surface(the lateral shrinkage can be 1.5 times of the longitudinal shrinkage).Therefore,according to the requirements of dimensional accuracy and performance in the injection mold design,a push plate without push marks is used to push out the plate,the gate is located at the lateral edge of the plate,away from the center hole with high accuracy requirements;Numerical simulation method was used to optimize the injection molding parameters,which is used to guide the trial;"Supporting mold" was used to compensate the difference of horizontal and vertical shrinkage rate;water boiling at 90～100℃ and secondary drying were used to improve the mechanical properties of the plates.Based on the different order of"supporting mold" and the boiled water,three routes were proposed to optimize the process.The research results show that,for PA66-GF25 FR(RP),the position of the injection gate determines the direction of the glass fiber,which in turn determines the difference between the horizontal and vertical shrinkage of the injection molded product;To a certain extent,the existence of this difference is sustained,but the external force because of the "supporting mold" increases the residual internal stress of the product,causing a decrease in the mechanical properties.The boiling water heat treatment can eliminate the residual internal stress of the product and improve its mechanical properties.Comparing the dimensional accuracy,mechanical properties and the fracture morphology of the products with the three routes,it was found that the route of "supporting mold"+boiling water(route Ⅱ)after injection can improve the mechanical properties of the plate and guarantees its dimensional accuracy.Because the mechanical properties,density,and dimensional stability of the composite are closely related to the crystalline properties of it.In order to analyze the effect of boiling water heat treatment on the performance of the PA66-GF25 FR(RP),The crystallization kinetics of the PA66-GF25 FR(RP)before and after the three routes of the composite were analyzed by using differential scanning calorimeter(DSC)method,exploring the essence of the effect of heat treatment on its performance.Because PA66 is a semi-crystalline polymer,the isothermal crystallization kinetics of PA66-GF25 FR(RP)were studied by the Avrami equation.The results showed that the crystalline form of PA66-GF25 FR(RP)may be the mixture with two-dimensional and three-dimensional growth;At the same temperature,the crystallization rate of route Ⅱ is higher than the other two.Secondly,the non-isothermal crystallization kinetics of PA66-GF25 FR(RP)were studied by the Jeziorny method and Mo’s method.The results show that the Mo’s method can better handle the non-isothermal crystallization kinetics of PA66-GF25 FR(RP)composites.After comparison,it is found that,at 50%relative crystallinity,the F(T)value of routeⅡ is the lowest,which shows that the crystallization rate of route Ⅱ is highest.