Study On Thin Wall Phenolic Hollow Microsphere/Epoxy Resin Composites Low Shear Mixing Techmology

Phenolic hollow microspheres/epoxy resin composite is a kind of special composite with excellent thermal damping properties, ablation resistance, low density and good mechanical strength performance, especially, the excellent design property of its performance, makes it very extensively used in the aerospace. But because of the limitation of processing performance of hollow phenolic microsphere, the production of composites with high microspheres filling ratio is still by manual mixing, which is difficult to be large-scale produced.In view of the characteristics of the composites, this paper introduces a device for processing the material. Based on the researches of spherical powder packing model, the composites model has been developed. The result says the density change rate of the composites and the hollow phenolic microspheres breakage rate is completely linear correlated, so the density can be used as a rapid method to evaluate the quality of the composite, and then determining the theoretical basis for the reason why bottle pycnometer method is chosen for testing density of the composites. Based on the study of the mechanical behavior of resin and microspheres, the low-shear experimental device has been developed. The movement of the mixer element was along the axial line. Comparative experiments were carried out to improve the structure of experimental machine, the shape of material mixing barrel was changed from the initial closed cylindrical to open "U"-type structure, because the latter can provide more material movement space, thereby reducing the phenolic hollow microspheres brakeage in the mixing process and improving the homogeneity of composites. Coefficient of variation is introduced to evaluate the discrete degree of experimental data among different groups. The influence of the mixer elements’structure on mixing effect has been compared by experiments, results show that when the structure is more suitable for the material axial movement, the microsphere breakage rate can be greatly decreased. It does good to material mixing, the four-blade element mixer with cylindrical guide performed best mixing effect among experiments. The process parameters of the machine were further studied, results show that, the mixing cylinder filling rate and microsphere breakage rate is positively correlation, and the degree of homogeneity is first increased and then decreased with the filling rate increasing, when the filling rate of barrel between40%to50%, the homogeneity of the mixing comes to the best. At the same time, in the preparation of composite material, prolong mixing time cannot improve the mixing uniformity degree, while the breakage rate of microspheres increases. In the material mixing barrel swing condition, material mixing uniformity is improved, at the same time the increasing velocity of microsphere breakage rate is greatly reduced, it indicates that material exchanging at the end of the barrel will greatly improve the mixing quality. Based on the experimental results, a small batch production machine with low shear method has been developed and experiments have been done. The results show that the equipment can be well achieved the requirement of the composite material processing.The successfully development of small batch production equipment marks that the feasibility of low shear mixing theory is applicable to the phenolic hollow microspheres/epoxy resin composite materials processing. This laid the theoretical foundation for the development of large batch production of this material and had the extremely vital significance to the popularization and application of the material.