| Screw extruder is one of the most important equipment in the polymer processing industry,and widely used in polymer mixing granulation,extrusion molding and so on.Screw is the core part of the extruder,the role of the screw shear,extrusion,stretching,etc.,to complete the polymer compounding work.The screw structure directly affects the structure and properties of the composites.If the screw assembly configuration is unreasonable,it will cause the flow field,temperature,pressure fluctuation,which in turn affects the mechanical properties of the product.In particular,for the preparation of fiber reinforced composites,the screw element structure and the screw combination configuration have an important effect on the retention length of the fibers and the distribution of the fibers in the polymer.Therefore,in order to improve the performance of fiber reinforced composite materials,the design of new screw components and optimize the screw assemblies is quite meaningful.In this paper,the optimization experiment of fiber reinforced composite extrusion process was carried out by means of DOE experimental design.The influence of process parameters such as processing temperature,screw speed and feed volume on the retention length of the fiber and the properties of the composites were analyzed,and the model was established to predict and control the performance of the composites.The results show that when the three processes increase,the fiber retention length changes linearly,while the mechanical strength tends to increase first and then decrease.And The optimized process conditions were as follows:when the temperature was 274 ℃,the screw speed was 162 r/min,and the feeding speed was 12 Kg/h,the tensile strength of the blend was 105.6 MPa.Some new mixing elements(SME and TKD)with low shear rate and high mixing performance were designed for the TRISE by UG 8.0 software.The flow field of the mixing element was simulated by Polyflow software.Studying the influence of the structural parameters of the mixing element on the pressure field,the shear rate field and the mixing index of the component,and the reliability of the simulation were verified by the experimental study.The results show that the number,pitch and structure size of slots can make some changes in the length of the ribs,the thrust surface and the drag surface area to a certain extent.The increase of which could lead to the reduction of the length of the ribs,the thrust surface and the drag surface area,contributing to the decrease of the pressure and the average local shear rate,and the increasing mixing index.A number of screw assembles with different mixing performance were designed to prepare GF/PPO/HIPS and CF/PA66 composites.The relationship between residual fiber length,product performance and screw assembles were systematically analysised.It was found that the No.7#(TKD + SME)was the most suitable screw combination for preparing GF/PPO/HIPS composite,and Compared with the traditional screw combination(No.1#),the fiber length,tensile,bending and impact properties of the composites were 26.60%,8.45%,11.45%and 13.75%respectively.The No.6#screw combination(SME × 2)with minimum shear rate was confirmed to be benifit for the processing CF/PA66,and the fiber length,tensile,bending and impact properties of the composites were 55.55%、14.82%、8.10%and 20.22%respectively.It’s obvious that the fiber with different properties should be processed by suitable flow field.In order to prepare high-performance fiber reforced composites,the special screw combination with weakened shear field,and strengthen extensional field was essential to enhance the length of residual fiber,and promot product performance.The optimization results of this work have a certain effect on the application of the TRISE,and also have some guiding significance to the actual production. |
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