Study On Extrusion Swelling And Cooling Of Polymer Five-lumen Micro Tube

With the continuous development of plastic products, plastic micro tubes have been applied increasingly in the areas such as medical treatment, communication and automotive industry in recent years. Therefore, miniaturization has also been a development trend of the polymer extrusion technology, and micro extrusion technology appeared. During the micro extrusion process, extrudate swell will happen after the polymer melt leaving the extrusion die and before getting into the water cooling tank. Moreover, the polymer par ison will shrink in the cooling process. These phenomenon have been a research ho tspot for many scholars in the field. Because of the characteristics of the multi-lumen micro tube such as complex cross section, small size, high accuracy, there are still problems and challenges to be further studied before high quality micro tubes can be produced in mass production. Therefore, aiming at this problem, a typical five-lumen micro tube with uneven wall thicknesses is taken as the research object in this study. The primary items in this work are as follows:Firstly, the mathematical model was proposed for the polymer extrusion flow of the five-lumen micro tube. According to the flow characteristics of polymer, the basic control equations of polymer micro extrusion flow were established after reasonable simplifications and assumptions in the process of polymer micro extrusion flow. Based on the size characteristics of the mould flow channel for five-lumen micro tube, the micro scale viscosity model was chosen which could represent the law of the viscosity variation with the flow channel characteristic size change. The capillary rheometer was used in the measurement for the shear viscosity of polymer melt under different characteristic sizes, and the model coefficients of the microscale viscosity model were determined.Secondly, based on the above-mentioned mathematical model of the polymer extrusion flow of five-lumen micro tube, the extrusion swell phenomenon of the five-lumen micro tube and the laws of extrusion deformation were researched by numerical simulation method. By the analysis of a variety of field distributions for polymer melt inside and outside the flow channel during extrusion, such as velocity, shear rate, shear stress, the essence of the extrusion swell and the varying patterns of the extrusion swell were revealed. And the influence of process parameters, such as extrusion flow rate, inner cavity ventilation in the extrudate swell and its shape and size deformation were studied, which will provide a certain theoretical basis for producing high quality five-lumen micro tubes.Then, based on heat transfer theory, the section temperature variation laws and the section shrinkage laws of five-lumen micro tube during the cooling and calibrating process were studied by numerical simulation. By the heat transfer analysis during parison cooling stage, the mathematical model of the cooling process of the five-lumen micro tube was established, and the convective heat transfer coefficient between parison outside surface and cooling water was determined. On the basis, the thermal-stress coupling analysis method was adopted to obtain the transient temperature distribution on the parison section and temperature variation of the key points in the cooling process. Simultaneously, the law of the parison section shrinkage in the cooling and calibrating process was revealed, which has a certain guiding significance to formulate technological parameters in the cooling and calibrating process of micro extrusion.Finally, the polymer extrusion experiments of five-lumen micro tube were carried out. The experimental results showed:in the process of micro extrusion molding process, the polymer extrudate swell and the cooling shrinkage have a significant impact on size precision and shape of polymer products. The ventilation in cavities and cooling time are critical factors for the quality of micro extrusion compared to other factors. In experiments, adjusting the process parameters to the optimum parameters obtained by numerical simulations, polymer five-lumen micro tube can be obtained which meets the design requirements.