Theoretical Research On Mechanism Of Extrudate Swell And Numeric Design Of Die For Multi-Lumen Precise Medical Catheter

With the development of the modern science and medical treatment technology, medical plastic products were used widely and deeply in many fields in the modern medicine because of their excellent material property. Today it has become a new high technique and high added value industry in modern instrument. In the past 40 year, China has made a quiet great progress in the medicine plastic product. However, there are still some untouched fields in the high technique and added value medical plastic products such as balloon catheter because of lacking technology and financial resources. Modern medicine in China, especially intervenient medicine, is blocked because almost of balloon catheters are imported from abroad. Therefore, developing medical catheter is very important to improve medicine technology and the medicine standard in China. This thesis is a part of the project named Development and Industrialization of Precise Medical Tubing, which research on the extrusion mechanism, equipment and process conditions. This thesis focuses on the extrusion of multi-lumen precise medical catheter because it is an important role in modern medicine.Firstly the general aspect of extrusion for medical tubing is introduced. There is a big gap in the extrusion for key and high added value multi-lumen precise medical catheter between home and abroad because of lacking the design theory of die. It is also the most difficult problem for the manufactory in China. The extrusion experiment shows it is a difficult task to predict the extrudate swell because there is cross-section profile with multi-lumen, axial asymmetry, high tolerance, small diameter and inhomogeneous thickness. Moreover, a gas injection equipment was introduced in the extrusion process to assist the shape of lumen. It brings more challenge to predict the extrudate swell for the affection of gas. Therefore, it is highly necessary to research, simulate and verify the extrusion process and extrudate swell under the gas injection condition for the multi-lumen precise medical catheter.A new dynamic theory of die swell for entangled polymeric melts in the simple shear flow at steady shear stress was deduced. It was found that the course of extrudate swell may be divided into two recovery regions (Instantaneous and delayed regions) and three growth stages (instantaneous, delayed and ultimate extrudate swell stage). The correlations of instantaneous, delayed, ultimate extrudate swell effects to the molecular parameters and the operational variables in the simple shear flow at steady shear stress were derived. These equations were verified by the experimental of PBD and HDPE under different operational variable such as molecular weight, temperature and different die aspect ratio of length to diameter. An excellent agreement result is obtained. These research effort gave directions and advices for adjusting the operational condition, designing die and simulating of extrudate swell during the extrusion of multi-lumen precise medical catheter.A die with preferable construction and parameters was designed based on the experments and theory research. By simulating of melts flow in the die for two type of multi-lumen precise medical catheter, distribution of velocity and shear rate at the exit of die were obtained. Moreover, distribution of velocity along the most and least thickness at the cross section of die exit was studied, and uniformity of velocity was put forward. Because there is a gas injection during extrusion, a modified die was designed based on the balance of local area flux and the uniformity of vecolity. The result of simulation shows that the modified die is preferable.The model of extrudate swell of multi-lumen precise medical catheter under the free and minim pressure in lumen were established. At the same time the simulation of extrudate swell under the two different conditon was conducted. The correlations between the shape of cross section and extrudate swell and lumen pressure under different temperature and pressure were obtained. They are useful to design the die and determine the operational parameters during the extursion. Furthermore, the simulation of extrudate swell for the modified die were studied and verified by experiments.A new precise and numeric control gas injection equipment was desgined by ourself and successfully used in the extrusion process for the multi-lumen precise medical catheter. According the character of multi-lumen precise medical catheter, The important sizes, ovality and uniformity of the cross section were defined, which can discrible the shape of the cross section. Moreover, experiments were processed to study the correlations between the shape of cross section and the operational conditions such as die temperature, pulling rate and gas flow rate. The experiment shows that the precise gas injection equipment can meet the requirement in the extrusion for multi-lumen precise medical catheter.Moreover, the inverse extrusion was used to solve the die design of two representative multi-lumen medical catheter. The shape of cross section of die for the two type medical catheter under free and minum pressure in lumens were obtained. Furthermore, the shape of cross section of other medical catheters were simulated. The results show that that inverse extrusion method can more quickly get a desired cross section of die. It is important to design die and is an interesting research field.The mechanism and theory of the extrusion for the precise multi-lumen medical catheter is a widely and deeply problem because of its complexity, there is still a lot of content need to be study, some advice for further research were listed at the last chapter.