Abstract
We developed a mathematical model of the process of polymer processing in co- and counter-rotating twin-screw extruders. The model takes into account a heat transfer of a polymer with screws and a barrel, as well as real boundary conditions (screws rotate, a barrel is stationary).We used the model of the allocated C-shaped volume, which is limited by one turn of cutting of each of screws and in which contains a volume of the processed polymer is located, for the analysis of the process. The model gives possibility to describe the process of processing both in the case of complete and partial filling of an operation channel with processed material. This is especially important in the case of dosed feeding of an extruder with a polymer, which is typical for modern extrusion equipment.We studied a temperature field of a polymer in operation channels of co- and counter-rotating twin-screw extruders and compared the results of the calculation with experimental data. We substantiated theoretically and confirmed experimentally, that, unlike in a single-screw extruder, it is necessary to heat operation elements firstly and to cool them then (in the direction from a loading funnel to an extrusion head) in a twin-screw extruder.We used the developed technique successfully at the development of modes of processing of various polymeric materials on co- and counter-rotating twin-screw extruders with screws of a diameter of 125 and 83 mm, respectively.The discrepancy between the calculated values and the experimental values of temperature at the outlet of a twin-screw extruder with co-rotation screws O83×30D does not exceed 10 %. The experimental value of the temperature somewhat exceeded the given value. We explain this by the fact that the system of thermal stabilization of working elements for the studied processing modes could not remove released heat of dissipation effectively.Application of the developed mathematical model will give possibility to forecast effective modes of operation of twin-screw extruders better, especially at processing of materials with low thermal stability.
Highlights
Manufacturers use single-screw extruders for continuous fabrication of products from thermoplastic polymers
We proposed a model of the separated volume limited by one turn of a screw [5, 25] for the analysis of the process of twin-screw extrusion taking into account the above
We developed models for the processing of polymers in co- and counter-rotating twin-screw extruders based on the generalized mathematical model of screw extrusion
Summary
Manufacturers use single-screw extruders for continuous fabrication of products from thermoplastic polymers. They have started to use twin-screw extruders. Producers of equipment for processing of polymers offer many twin-screw extruders with various geometries, which significantly complicates the selection of necessary equipment. That is why mathematical modeling of the process of twin-screw extrusion acquires great importance. That makes it possible to select the most efficient equipment quickly. Authors made various assumptions to simplify a mathematical description of the process Such an approach was acceptable for a long time, but as the productivity of extruders has increased significantly over time, many processing models became unacceptable for practical use. Modeling the process of polymer processing in twin-screw extruders, taking into account actual boundary conditions, as well as a heat exchange of a polymer with screws and an extruder barrel, is relevant
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