Purging 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 good production runs.; The purpose of this study was to examine the dependence of rheology of a commercial purging compound on parameter settings during plastication. The results have been used to research the purging efficiency when purging materials as polycarbonate and polyamide-6,6 which are immiscible with the base resin of the purging compound.; The results of the study showed that the purging efficiency depends on the flow induced morphology of the multi-phase systems in the nozzle and on the content of undissolved gas in each purge shot. The latter proved to be controllable by the parameter settings during shot build-up. Purging of the screw depends on the viscosity and melting point of the materials used as well as on the break-up of the solid bed in the screw flights.; Calculations of cost per purge showed that using a commercial purging compound with a rheologically based purging strategy can lead to the fastest switch-over and lowest purging cost.
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