Single screw extruders and twin screw extuders are the most widely used extruders
Extrusion is the process of forcing ingredients through an orifice or die under controlled conditions (e.g., temperature, feed rate, and pressure) to form a new material (1). More than 90% of the extruders at pharmaceutical companies are twin-screw models, says Charlie Martin, general manager of Leistritz. Twin screw extruders mix materials better than single-screw extruders and are better suited to pharmaceutical processes.
Single screw extruders and twin screw extuders are the most widely used extruders. The screw that is used to push the resin out of the die is the important component of a screw extruder. In the earlier days rubber screw were used but the rubber screw was not able to give enough amount of shear into the polymer. Therefore, screws were designed that would start deeper in the feed and gradually taper shallower in the metering section to apply more work on the polymer as it was going from the feed to the discharge.
Basically speaking, the study of twin screw extruding theory is still at the initial stage, which indicates that the study is still more art than science. There are three links of its operation principles according to the extruding process:
The design of twin screw extruder and optimization of extruding process could be improved by material change laws, conveying theory ,including convey of solid and melt, also gas filling and ejecting characteristics, which can form a mathematics and physical model in the extruding process.