The Process of Melt Homogenization in a Metered-Discharge Disk Extruder
Keywords:extrusion, disk extruder, melt quality, temperature homogeneity, homogenization
Purpose. This paper aims to develop a physical model of the homogenization process in a metered-discharge disk extruder, as well as to select and justify the variable parameters that can be used to evaluate the efficiency of mixing and process control. Methodology. With the advent of a large number of alloying additives, filled and composite materials, there is a need for continuous monitoring and control of the melt homogenization process. In classical worm extruders, the processes of feeding, melting, homogenization, and pressure generation are interconnected and are triggered simultaneously by a single working body, the worm, which makes it impossible to control each process separately to optimize them. In such cases, cascade extrusion schemes are used, where the process is divided into separate subprocesses or groups of them with the ability to control them independently. Findings. The scheme of a cascade disk-gear extruder is described, where a metered-powered disk extruder is used as a melt-homogenizer, and a gear pump is used to create pressure and dosing. The variable parameters of the disk extruder for adjusting the mixing efficiency are selected and substantiated. The speed components and their ratios for different parts of the homogenization zone are analyzed. The expediency of using a disk extruder as a melt-homogenizer in cascade extrusion schemes is substantiated. The adequacy of using the mixing index in the form of temperature inhomogeneity is emphasized. The homogenization zone in the form of four separate subzones and changes in the accumulated shear strain along each subzone, as well as the possibility of their regulation, are described. Originality. For the first time, a hydrodynamic model of processes in the homogenization zone of a metered-discharge disk extruder was developed and described. Practical value. The possibility of adjusting the velocity field in the homogenization zone of a disk extruder has been substantiated, which allows controlling the mixing effect directly during the extrusion process. The possibility of selecting the optimal mode of operation of the homogenization zone makes it possible to obtain a melt of a given quality with minimal energy consumption.
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