Effect of Pressure Difference between Inner and Outer Gas Layer on Micro-Tube Deformation during Gas-Assisted Extrusion

Abstract

In the process of double-layer gas-assiste extrusion of a plastic micro-tube, the tugging effect caused by the pressure difference of the gas cushion layer inside the die has a great influence on the external dimensions of the micro-tube. Therefore, this study establishes a two-phase extrusion model based on compressible gas and incompressible melt. Ansys Polyflow finite element software was used to numerically simulate the extrusion process of the melt to analyze the effect of the gas cushion layer pressure difference on the micro-tube deformation. The research shows that the shrinkage rate of the micro-tube increases with increasing pressure of the outer cushion layer, and the degree of tube wall migration increases, too. In the process of extrusion, the first normal stress difference at the entrance of the gas cushion layer shows a significant effect on the melt velocity field distribution and the extruded micro-tube cross-sectional deformation.

Numerical and Experimental Studies on the Improvement of Gas Chamber Structure during Gas-Assisted Extrusion

“…The gas-assisted extrusion experimental equipment [ 37 ] is shown in Figure 9 . It includes a gas generation system, a gas heating control system, an extruder, cooling equipment, and pulling equipment.…”

Study on the Melt Rheological Characterization of Micro-Tube Gas-Assisted Extrusion Based on the Cross-Scale Viscoelastic Model

“…Therefore, in the numerical simulation, the gas inlet is set as the pressure inlet boundary conditions. Since the inner gas pressure needs to be greater than the outer gas pressure [13], we set the inner gas pressure to 6000 Pa and the outer gas pressure to 5000 Pa initially. (3) Wall boundary: In the gas-assisted extrusion process, the gas forms a stable gas cushion layer, so the melt is not in contact with the die wall but with the gas.…”

“…To improve the extrusion quality of micro-tubes, the current prevailing approach involves combining numerical simulation with experimental studies to investigate the melt flow behavior and extrudate swell and then analyzing the impact of process parameters on the extrusion quality of the micro-tubes [10][11][12]. Liu B. et al [13] simplified the physical model of the micro-tube extrusion process and subsequently established a 2D two-phase flow model based on a compressible gas and an incompressible melt. Then, the mechanism of the pressure difference between the inner and outer gas on the micro-tube extrusion quality was clarified by analyzing the distribution of the melt pressure, velocity, and stress.…”

Influence of Gas Inlet Slit Width on Gas-Assisted Plastic Micro-Tube Extrusion

“…The equation parameters of the auxiliary gas and polypropylene (PP) are shown in Table 1. These represent the physical properties of the auxiliary gas and polypropylene melt at a reference temperature of 200 degrees Celsius and are taken from Liu [3].…”

“…Nevertheless, owing to the viscoelastic properties of their materials, micro-tubes are susceptible to dimensional fluctuations throughout production. To enhance product excellence and minimize wastage, it is imperative to address the treatment methodology for polymer micro-tubes [3]. Die configuration is crucial for ensuring the quality of polymer tubes.…”