Functionally integrative extruder concept with freely rotating screw sleeve and dynamic mixer to achieve high melt quality in high speed operation

• Applicant: Professor Dr.-Ing. Johannes Karl Wortberg
• Subject Area: Plastics Engineering
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 288888720

The increase in throughput for a improved performance of extruders can be realized among others by increasing the screw speed. Accordingly, the number of high-speed industrial applications is steadily increasing. The high-speed extrusion is still an interesting field of research.Critical to the increase in speed is maintenance of the required melt temperature while keeping a high melt quality. It is known, however, that the spec. throughput decreases with increasing speed, whereby the permissible material temperature is reached quickly. Also the increasing shearing of the material causes a rapid rise in temperature. Therefore, the high-speed extrusion is enforced by alternative extrusion techniques such as the high-speed S-Truder (HSST).The concept is based on the separation of solid and melt. It uses a freely rotating screw sleeve with radial bores to remove the melt from the channel of the rapidly rotating screw. A Dynamic Mixing Ring (DMR) is used for homogenization.Plasticization experiments with the HSST were positive. Nevertheless, some improvement approaches have been demonstrated. In particular, the use of a dynamic mixer under high-speed conditions and uneven removal of the melt along the screw sleeve inhibit the achievable speeds and throughputs. Design measures for an improved melt removal and conveying as well as to reduce the shear heating are therefore of primary interest. If it is possible to solve the above mentioned problems, the efficiency and functionality could further increase.Using a custom developed material model for CFD simulation of melting processes extensive simulations and analysis of the plasticization in the HSST will be carried out to gain further understanding of the process and to develop optimization measures. The simulations are used to design a suitable screw design to homogenize the melt removal over the length of the screw sleeve as well as to improve of the screw sleeve design. This primarily includes a revision of the length ratio between the feed zone and the screw sleeve. The used DMR is a major cause of the heating of the material and is adapted to the conditions of the high-speed operation.Parallel to the above operations a software for the pre-design of the S-Truder will be developed which calculates the plasticizing and the melt flows occurring in the HSST for a given design of the screw and screw sleeve largely analytical. By this the number of complex, numerical CFD calculations can be reduced to a minimum in future works. The optimized HSST is transposed to a laboratory scale. Plasticization experiments are performed to determine its functionality and performance, this means the maximum achievable throughput, the temperature development and the melt quality.

• DFG Programme: Research Grants