Study On Injection Molding Of Long Glass Fiber Reinforced Polypropylene

Long-Fiber Reinforce Polypropylene(LFT-PP)composites are superior in performance compared to short-fiber Reinforce Polypropylene(SFT-PP)composites.Gradually replace the SFT-PP applied to the car parts.However,during the injection molding process of LFT-PP,due to the influence of equipment structure and molding process parameters,the fiber is subjected to more serious fracture during the molding process,which affects the mechanical properties of the fmal product.In this paper,the effects of process parameters,equipment structure and injection molding process on fiber fracture and mechanical properties were studied in the process of fiber fracture during LFT-PP injection molding.The main conclusions are as follows:1.The length of fiber in the screw tip,nozzle and die in the injection molding process of LFT-PP was calculated to study the amplitude of fiber fracture at each stage of injection molding.It was concluded that the fracture rate of fiber reached 73.48%in the screw fracture sharpest plasticizing phase,followed by the melt filling stage,46.32%.Increasing the temperature of the barrel can reduce the degree of fiber fracture,LFT-PP strength also increases.Increasing the screw speed will increase the friction of the screw to the fiber,and the fiber fracture will increase.The strength of the LFT-PP will increase first and then decrease with the increase of the screw speed,and the maximum value will be obtained at 35r/min.The 5mm diameter straight-through nozzle is more conducive to the maintenance of the fiber length and the improvement of mechanical properties.2.The fracture length of the fiber in the flow channel was studied by comparing the fiber length at the nozzle and the inlet.The fracture rate of the fiber in the conventional injection mold was 38.53%.Respectively,the design of curved flow channel mold and straight channel mold and for LFT-PP injection molding,the statistics of the fiber in the flow path of the fracture found that:The fracture rate of the fiber in the curved flow channel is 25.767%,and the fracture width of the fiber in the straight channel is 10.525%.Compared with the conventional injection molds,the bending strength and notched impact strength of the bending runner mold samples were increased by 21.72%and 43.70%respectively.The flexural strength and notched impact strength of the straight channel mold samples increased by 27.53%and 81.08%.3.The mechanism of fiber fracture in LFT-PP filling process was studied by injection compression molding of LFT-PP by self-designed injection compression mold.The effects of different compression distance,compression rate and compressive force on the fiber residual length and mechanical properties were studied.The results show that the shearing force produced by the melt flow process and the pressure produced by the mold compression will have different effects on the fracture of the fiber.The mechanical properties of LFT-PP fiber are increased and then decreased with the increase of compression distance,compression rate and compressive force.The optimum compression parameters are:4mm compression distance,30%compression speed and 50MPa compression force.4.Compared with the conventional injection mold samples under the same plasticizing process parameters,the fiber residual length of the compressed compressed sample is longer.The fibers are arranged more closely in the sample.Compared with the mechanical properties,the tensile strength increased by 12.86%,the bending strength increased by 20.62%,and the notched impact strength increased by 212.57%.