Evaluation of Flow Resistance Increase Due to Fouling in Cooling Channels: A Case Study for Rapid Injection Molding

Abstract

Abstract After certain time of operation, the cross-section of cooling channels in injection molds may decrease due to fouling, i.e. the formation and growth of a layer of sediment on the walls of the channels. This phenomenon can decrease heat transfer or ultimately completely block the flow of coolant in the channel. The build-up of the sediment layer increases the temperature of the mold, which may consequently reduce the quality of the plastic products. In the paper, the pressure drop in a typical cooling channel of an injection mold is investigated, as well as the effect of the sediment layer on the coolant flow in an example channel with a diameter of 10 mm. A novelty is the developed analytical model that allows determining the pressure drop in the case when two perpendicular channels do not intersect centrally due to manufacturing inaccuracies that often happen when drilling long channels in hard materials. The proposed hydraulic model allows for calculation of the coolant pressure drop in real injection molds and can be an alternative to time-consuming CFD simulations. The presented results of measurements and the hydraulic model calculations show that the thickness of the sediment layer in the tested channel of the actual injection mold can be up to 1.7 mm. The hydraulic model proposed in this work allows for the estimation of the thickness of the sediment layer and the identification of places of local increase in the coolant velocity, where self-cleaning of the channels in injection molds may take place.