Scale‐up of single screw extruders

Abstract

AbstractScale‐up from small laboratory size extruders to large production size extruders is a procedure of great practical importance. Many scale‐up rules and theories have been proposed in the past, however it is not always clear how the different scale‐up methods will affect extruder performance. A basic analysis of scale‐up in plasticating single screw extruders is developed from which the effect of a certain scale‐up strategy on extrusion performance can be evaluated in terms of solids conveying, melting, melt conveying, mixing, residence time, heat transfer, power consumption, and specific energy consumption. Various existing scale‐up theories are evaluated and compared using the basic analysis. A number of existing scale‐up theories have some significant drawbacks, in particular with non‐constant specific energy consumption and imbalance between melting rate and pumping rate. Conditions that are desirable to achieve in scale‐up are enumerated and ranked in terms of importance. This leads to two new scale‐up methods that result in constant mechanical specific energy consumption and high throughput rates. The first scale‐up method keeps the specific surface area constant. This scale‐up should work well for high values of the Brinkman number. However, at low values of the Brinkman number, the melting rate may be insufficient. The second scale‐up method keeps the melting rate at low Brinkman number equal to the pumping rate and, thus, should be useful in cases where the first scale‐up method cannot be used.