Heat Transfer Behavior in Solids Conveying Step of an Intermeshing Twin Screw Extruder

Abstract

Particulate solids handling is the first polymer processing step taking place in twin screw extrusion, and more emphasis must be placed on understanding solids conveying and pre-heating mechanisms. Solids conveying and pre-heating of particulate resin in an extruder by heating from screws and barrel are very effective for reduction of power consumption, favorable plasticization and mixing as well as for achieving higher production rates and uniform melt temperature distribution. Hence, quantitative analysis regarding solids conveying and heat transfer behavior plays an important role in the evaluation of screw design. This study is conducted both experimentally and theoretically to obtain the solids conveying efficiency and the temperature rise characteristics in a solids conveying step of an intermeshing counter-rotating twin scerw extruder by using rigid PVC resin.As a result, the followings have become elucidated:1) The solids conveying efficiency ηe is determined by the amount of backwards leakage flow through the intermeshing sections.2) A general theoretical formula for estimating temperature increment has been induced and the temperature rise characteristics can be expressed with the heat transfer coefficient hw=70-230W/m2K depending on the filling fraction φ.3) Heat transfer between the particulate resin and barrel, screw surfaces can be grasped in a way similar to the case of the stationary packed bed and the fluidized bed.