Design And Research On Properties Of Intermeshing Co-Rotating Twin Screw High-Distribution Mixing Elements And Pressure Control Element

Co-rotating twin screw extruders were widely used in polymer modification and processing. According to mixing mechanism and meshing theory of co-rotating twin screw extruder, two kinds of high-distribution mixing elements and one pressure control element were designed. The flow fields of these srew elements were numerically simulated by POLYFLOW, and it was investigated by interrelated experiments.For slotted-type split-flow element, an optimal solution was selected by orthogonal design using backflow coefficient as the evaluation index. The major strucure of the optimal solution was two-head reversed screw element with U-type grooves in one flight, and it was compared with reversed kneading blocks. The results showed that its distributive mixing property was good.The simulation results of pin-type split-flow elements suggested that the number of pin has little influence on backflow coefficient, but has relatively obvious influence on residence time distribution and average accumulated strain. The final choice was the element with the maximum pin number in this paper.The pressure control element is made up of forward single-head screw-thread element in the upstream, reversed two-headed screw element in the downstream and transition section. The flow fields of elements with different numbers of grooves in the flight of reversed screw in the downstream were simulated. Two solutions whose pressure drop per barrel inner diameter was greater than 2 MPa and conveying resistance was smaller were selected.Results were presented on mixing characteristics of different screw configuration by experimental research, and it was compared with the simulation results. The comparison showed that the distributive mixing property can be improved by setting reversed screw elements in the downstream of split-flow type distributive mixing elements, and the greater the backflow coefficient is, the smaller the inhomogenous coefficient will be, the stronger the distributive mixing ability will be. According to the backflow coefficient of slotted-type split-flow element and pin-type split-flow element, the inhomofenous coefficient of their corresponding samples was predicted.With the comparison of simulation and experiment for the pressure differential of reversed screw element and revered kneading block, the experimental data were in agreements with the simulation results. The pressure drop per inner barrel diameter of the pressure control elemnets was forcasted based on the experimental results.