Pressure Control And Numerical Simulation Of The Microcapillary Formation Within Extruded Plastic Films

The extrusion process equipment of Microcapillary film (MCF) were designed and built, as well as the air supply apparatus. This paper reports the experimental observation and numerical simulation of microcapillary formation of both single-and28-capillary films, which was manipulated by the injection air pressure. It was demonstrated to be an effective and easy method to control both the capillary size and voidage of MCFs through adjusting injection air pressure. The relationships between the microcapillary size and voidage of both single-and28-capillary films and the injection air pressure were investigated. Empirical equations for predicting the capillary diameter and voidage have been established. The pumping effect of the microcapillary formation process was also found.Initial numerical simulations of processing of both single-and28-capillary films using Polyflow(?) were carried out, and the influence of injection air pressure on the microcapillary formation was confirmed which was analyzed to be related to the extrusion swell phenomenon. The simulation results provided an insight of capillary formation. The microcapillary size error of the numerical simulations increased with the increase of the injection air pressure, and the velocity distribution on the surface on the melt drawing stage was found to inconsistent with the experimental result.Based on the experimental and numerical simulation results, the mechanisms of some special processing phenomena were analyzed and discussed. Due to the scale effect, outside air can only enter through the injection needles. Microcapillary pumping effect is a result of the mechanical properties of the plastic melt before fully solidified. The reason of the inconsistent increase among the28capillaries within28-capillary film with the injection air pressure was analyzed. The research will facilitate the application of microcapillary films.