Research On The Processing Of PA11 Micro-tube Precision Extrusion

As the development of science and medicine, medical plastic tubes are applied more and more in various fields of modern medicine. However, the catheter for interventional treatment with high-tech and high value-added, we rely on imports to meet the needs. Therefore, the development of production technology for precise medical catheters is significant to both our health and economy. As the medical pipe such as interventional catheter with small size, the flow state and flow condition in the micro channel is different from the state in the macro channel, so the study of microtubules melt extrusion process has important application value.Firstly the general aspect of extrusion for micro-tubes is introduced. There is a big gap in the extrusion for high-precision and high value-added catheter between home and abord. Summed up the domestic micro-tubes forming technology in materials, molding equipment, measurement and control system and extrusion process. Found that the current domestic research focused on the development of new medical catheter materials and high precision and stability of the extrusion device, but the study of the extrusion process technology and their relationship does not have much. Therefore, it is highly necessary to research the extrusion process.Secondly, researched the rheological properties of PA11 by experiment, including the melting temperature, the flow index under the operating temperature, and the relationship between the PA11 viscosity and temperature and shear rate. Obtained the PA11 dependence and sensitivity of viscosity on temperature, which gives us the basics of barrel and die temperature setting up.A new deformation law of the size change for the melt after leaving the die was deduced. It was found that the size change of melt may be divided into three stages(Extrudate swell, blowing swell, traction shrink). Derived the equations of three stages, analysis the relationship of screw speed, gas injection pressure, traction speed and other parameters effects to the diameter and wall thickness dimensions. All the laws were verified by the experiment of PA11 under different operate condition. And the laws are significantly to the instruction of process control. And provide a mathematic model for closed-loop control system.As to problems occurred in extrusion process, such as intermittent melt fracture, melt-section deformation, analyzed the melt and extrusion die by thermal imaging analysis system. Found that the temperature of die in the circumferential direction was unevenly distributed and the melt cooling rate waw too slow. Then solved them by adjusting the die gap and injecting cold air. The results showed that the analysis and the solution for those problems were effective.After analyzing and comparing with the changes in the diameter and wall thickness under different processes obtained and verified the optimal combination of process parameters. All things show that the orthogonal experimental method is an effective way to optimize the extrusion process parameters for precise micro-tube production.