Effect of shear rate on purging of hot runners

Purging issues (which encompass changes in color and or resin type and the removal of contamination from equipment) have received little attention from engineering and production management. Purging in an injection-molding machine is a vital procedure for every molder when switching from one resin formulation to another or when simply shutting down the machine. Complete removal of primary resin and hang-up of degraded material is necessary to achieve a good production run.; The purpose of this study was to examine the purging behavior of two materials High-density polyethylene (HDPE) and Polycarbonate (PC) using a Hot-Runner manifold. The research investigated the purging efficiency in how different rheological behavior of the plastic material and process parameter settings affect efficiency.; The result of the study showed that purging efficiency depends on the process parameter settings and purging the manifold and screw separately. Purging of the screw/barrel depends on the viscosity and processing temperature of the materials used as well as on the break-up of the solid bed in the screw. The purging manifold efficiency is increased with an increase in injection velocity/injection rate.