Abstract
Single-screw extruders are usually operated with the screw fully filled (flood-fed mode) and not partially filled (starve-fed mode). These modes result in completely different processing characteristics, and although starve-fed mode has been shown to have significant advantages, such as improved mixing and melting performance, it is rarely used, and experimental studies are scarce. Here, we present extensive experimental research into starve-fed extrusion at feeding rates as low as 25%. We compared various operating parameters (e.g., residence time, pressure build-up, and melting performance) at various feeding rates and screw speeds. The results show a first insight into the performance of starve-fed extruders compared to flood-fed extruders. We explored starve-fed extrusion of a polyethylene material which contains a Very High Molecular Weight Polyethylene fraction (VHMWPE). VHMWPE offers several advantages in terms of mechanical properties, but its high viscosity renders common continuous melt processes, such as compression molding, ram extrusion and sintering, ineffective. This work shows that operating single-screw extruders in extreme starve-fed mode significantly increases residence time, melt temperature, and improves melting and that-in combination—this results in significant elongation of VHMWPE particles.
Highlights
Accepted: 17 March 2021Single-screw extruders are among the most important machinery in polymer processing
As its output depends on the feeding rate and not on the screw speed, a partially filled screw exhibits processing characteristics that differ completely from those of a screw operated in flood-fed mode [1]
We aimed to discover the effect of starve-fed extrusion on different processing parameters like melt temperature, residence time, degradation of the material, specific energy input and melting performance
Summary
Single-screw extruders are among the most important machinery in polymer processing. They are usually operated in flood-fed mode, where the screw beneath the hopper is fully filled and takes in as much material as possible. Single-screw extruders can be operated in starve-fed mode, where the screw is not fully filled. As its output depends on the feeding rate and not on the screw speed, a partially filled screw exhibits processing characteristics (e.g., axial pressure profile and melting) that differ completely from those of a screw operated in flood-fed mode [1]. The starve-fed mode is rarely used in single-screw extrusion, significant benefits in terms of improved melting and mixing have been observed for twin-screw extruders operated in this mode. Only a few studies that concentrate on starve-fed single-screw extrusion have been published
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