Abstract
The diameter of a micro-tube is very small and its wall thickness is very thin. Thus, when applying double-layer gas-assisted extrusion technology to process a micro-tube, it is necessary to find the suitable inlet gas pressure and a method for forming a stable double gas layer. In this study, a double-layer gas-assisted extrusion experiment is conducted and combined with a numerical simulation made by POLYFLOW to analyze the effect of inlet gas pressure on micro-tube extrusion molding and the rheological properties of the melt under different inlet gas pressures. A method of forming a stable double gas layer is proposed, and its formation mechanism is analyzed. The research shows that when the inlet gas pressure is large, the viscosity on the inner and outer wall surfaces of the melt is very low due to the effects of shear thinning, viscous dissipation, and the compression effect of the melt, so the melt does not easily adhere to the wall surface of the die, and a double gas layer can be formed. When the inlet gas pressure slowly decreases, the effects of shear thinning and viscous dissipation are weakened, but the gas and the melt were constantly displacing each other and reaching a new balanced state and the gas and melt changed rapidly and steadily in the process without sudden changes, so the melt still does not easily adhere to the wall of the die. Thus, in this experiment, we adjusted the inlet gas pressure to 5000 Pa first to ensure that the melt do not adhere to the wall surface and then slowly increased the inlet gas pressure to 10,000 Pa to reduce the viscosity of the melt. Lastly, we slowly decreased the inlet gas pressure to 1000 Pa to form a stable double gas layer. Using this method will not only facilitate the formation of a stable double gas layer, but can also accurately control the diameter of the micro-tube.
Highlights
Plastic micro-tubes are widely used in medicine, communication, automotive and other fields and they have high added value
Distribution has an important influence on the formation of the stable double gas layer when the inlet gas pressure is 1000 and 5000 Pa, so we focused on the analysis of the two inlet gas pressures
We focused on the analysis stable double layerinwhen the6.inlet gas pressure and 5000influence
Summary
Plastic micro-tubes are widely used in medicine, communication, automotive and other fields and they have high added value. The micro-tubes were extruded mainly using experimental methods and numerical simulation methods to analyze the melt flow behavior and extrusion swell in the micro-channel, and to analyze the influence of various factors on the melt flow stability and extrusion swell [1–13] in small-section flow channels. The numerical simulation of plastic micro-tube extrusion molding was carried out by Fu [14]. The influence of gas injection pressure on micro-tube cross-section size, pressure field, and velocity field were analyzed, and a reasonable gas injection pressure range was determined. Some scholars [15–23] analyzed micro-tube extrusion dies while researching micro-tube extrusion, but they have not solved the problem of extrusion swelling [24–35], melt fractures, and the distortion of micro-tube extrusion.
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