The dual screw extruder processes the material by conveying, mixing, and pumping within the barrel. The modularity of the barrel facilitates the staging of individual unit operations along the barrel length. The barrel is electronically heated and liquid-cooled and acts as an independent temperature control zone. Segmented elements are combined on high torque shafts to optimize screw configuration according to process requirements. Length-to-diameter (L/D) ratios available for reactive extrusion or multi-stage devolatilization, ranging from 32 to 48:1, up to 60 L/D (or longer). The electrical energy is converted into mechanical energy by a transmission system (motor-gearbox), and the material is sheared by a rotating screw.
Modular barrels and segmented screws with controlled wiping and pumping characteristics allow one to adjust the screw and barrel geometry to match the requirements of the process task. Solids transport and plasticization typically take place during this manufacturing process. Compounding, downstream feeding, liquid injection, and ventilation are commonly used, and their principles are determined by the process. Screw configurations range from shear sensitive to shear passive.
The screw extruder is a lack of material-feeding equipment, and its feeding rate is determined by the metering equipment, which can be a solid feeder or a liquid feeder. The independence of the screw output speed makes it possible to optimize the mixing efficiency by adjusting the shear strength of the twin-screw extruder.
Furthermore, due to the control of the pressure gradient in the dual screw extruder and the fractional zero during the process, material can be introduced into the downstream section of the barrel. This is beneficial, for example, they will decrease if processed over the entire barrel length in high loading starch mixes where all feeds cannot be in one place or at the same feed temperature or shear-sensitive additives (such as natural fibers).
Solids transport melt pressurization and pump mixed gas and devolatilization, but not simply. The research on twin screw extrusion theory started late, coupled with its many types, complex screw geometry, and complex extrusion process, which brought many difficulties to the study of twin screw extruder.
On the whole, the research on twin screw extrusion theory is still in its initial stage, which is called "more skill than science". It is roughly divided into three links from the research of its extrusion process:
1. The law of physical state change of polymer in extrusion process, the truth and law of conveying and exhausting of solid melt. Based on this, a mathematical physical model is established to guide the design of the dual screw extruder and the optimization of the extrusion process.
2. It is necessary to find out the real state of the physical state change of two or more polymers and materials during the extrusion process, the process of mixing form and structure change, and the relationship between the final mixture and performance.
3. The model is established through the internal connection between the reaction process, speed, performance, screw configuration and operating conditions during extrusion reaction molding by dual screw extruder, so as to guide the reaction molding extrusion.
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