PA11微管精密挤出成型工艺的研究
摘要
随着科学技术与医疗水平的发展,医用塑料导管的越来越多的应用在现代医学的各个领域。但是像介入导管这种高技术含量、高附加值的产品,我国只能依靠进口来满足需要。因此,开发精密医用导管生产技术对我国国民健康水平的提高和经济效益的增加都有重要意义。由于介入导管这种医用管材尺寸微小,在微小流道内的流动状态及成型条件与常规宏观流道中的有较大差异,因此研究微管熔体的挤出成型工艺具有重要应用价值。
本文首先对微管挤出成型的总体情况进行了介绍。分析了国内外在高精度、高附加值导管成型上的差距,总结了国内对微管成型技术在材料、成型设备,测量与控制系统及成型工艺方面的研究进展,发现目前国内研究主要集中在新型医用导管材料的开发及高精度和稳定性的成型设备上,而成型过程中至关重要的工艺及其关系的研究却不多。因此研究微管成型工艺非常必要,这也是本文的研究重点。
其次,研究了实验原料PA11在常用加工温度下的流变性能,得到了PA11材料的熔化区间温度及各工作温度下的流动指数,分析了PA11黏度与温度、剪切速率的关系。通过计算得到了PA11在不同剪切速率下的黏流活化能,从而获取了PA11黏度对温度的敏感性及依赖程度,为料筒和模头温度设置提供了指导和依据。
本文研究分析了微管熔体离开口模后的变形规律,提出了将熔体的尺寸变化过程划分为离模膨胀、注气胀大及牵引变细三个阶段,推导出了三个阶段的尺寸变化方程,分析了管径和壁厚两个尺寸受螺杆转速、注气压力、牵引速度等工艺参数的影响关系。并用PA11在不同工艺参数下的实验数据对三个阶段的尺寸变化方程进行了验证,结果表明理论与实验数据的一致性良好。上述熔体尺寸变形的研究为微管成型工艺的调整,及挤出过程的控制系统研究提供了良好的指导作用。
此外,对挤出模头和挤出熔体进行了热分析,发现了模头周向温度的分布不均及熔体冷却速度的不匹配,据此分析得出了挤出过程中出现的熔体破裂及截面变形等问题产生的原因,并通过调整口模间隙及注入冷压缩空气的方法进行了修正。结果表明,修正后上述问题基本得到解决,微管挤出过程中问题分析及解决办法的有效性得到了验证。
最后,通过正交实验法研究了不同工艺参数下管径和壁厚的变化情况,经分析、比较后得到了本实验平台上的最优工艺参数组合,并对得到的最优工艺参数进行验证,最终确定了螺杆转速6r/min、牵引速度120mm/s、注气压力7KPa、模头温度210℃的工艺组合。上述实验证明了在精密微管挤出成型过程中,通过正交实验法来快速优化工艺参数的设定能起到良好的效果。
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.
本文首先对微管挤出成型的总体情况进行了介绍。分析了国内外在高精度、高附加值导管成型上的差距,总结了国内对微管成型技术在材料、成型设备,测量与控制系统及成型工艺方面的研究进展,发现目前国内研究主要集中在新型医用导管材料的开发及高精度和稳定性的成型设备上,而成型过程中至关重要的工艺及其关系的研究却不多。因此研究微管成型工艺非常必要,这也是本文的研究重点。
其次,研究了实验原料PA11在常用加工温度下的流变性能,得到了PA11材料的熔化区间温度及各工作温度下的流动指数,分析了PA11黏度与温度、剪切速率的关系。通过计算得到了PA11在不同剪切速率下的黏流活化能,从而获取了PA11黏度对温度的敏感性及依赖程度,为料筒和模头温度设置提供了指导和依据。
本文研究分析了微管熔体离开口模后的变形规律,提出了将熔体的尺寸变化过程划分为离模膨胀、注气胀大及牵引变细三个阶段,推导出了三个阶段的尺寸变化方程,分析了管径和壁厚两个尺寸受螺杆转速、注气压力、牵引速度等工艺参数的影响关系。并用PA11在不同工艺参数下的实验数据对三个阶段的尺寸变化方程进行了验证,结果表明理论与实验数据的一致性良好。上述熔体尺寸变形的研究为微管成型工艺的调整,及挤出过程的控制系统研究提供了良好的指导作用。
此外,对挤出模头和挤出熔体进行了热分析,发现了模头周向温度的分布不均及熔体冷却速度的不匹配,据此分析得出了挤出过程中出现的熔体破裂及截面变形等问题产生的原因,并通过调整口模间隙及注入冷压缩空气的方法进行了修正。结果表明,修正后上述问题基本得到解决,微管挤出过程中问题分析及解决办法的有效性得到了验证。
最后,通过正交实验法研究了不同工艺参数下管径和壁厚的变化情况,经分析、比较后得到了本实验平台上的最优工艺参数组合,并对得到的最优工艺参数进行验证,最终确定了螺杆转速6r/min、牵引速度120mm/s、注气压力7KPa、模头温度210℃的工艺组合。上述实验证明了在精密微管挤出成型过程中,通过正交实验法来快速优化工艺参数的设定能起到良好的效果。
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.
引文
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[9]吴大鸣,刘颖,郭奕崇.精密医用塑料导管的应用前景[J].塑料制造, 2006,(06) : 38-44.
[10]张承焱.医用高分子材料的应用研究及发展(二)[J].中国医疗器械信息, 2005, 11 (6): 17-22.
[11]段志泉,张强.实用血管外科[M].沈阳:辽宁科学技术出版社, 1999, 10-15.
[12] John C. Miller, The influence of screw wear on blow molding processability[J]. Plastic Engineering, 1989, (10), 37.
[13] Aaron J, Jeffrey A. Post die extrusion of plastic pipe[J]. Poly-Plastic Technology,2000, 39(1): 23-46.
[14] Riemann D. Innovations for pipe and profile downstream equipment[A]. Extrusion Technology: From Milestone to Milestone[C]. Germany Battenfeld, 2000, 124-129.
[15] BROEL, PLATER. Optimization of the control of polymer extrusion processes[J].Polymer, 1997, 42(6): 386-397.
[16] B.H.Moddock. Measurement and analysis of extruder stability[J]. Society of Polymer Engineering, December, 1964, 1277-1283.
[17]张友根.关于我国医疗塑料制品成型设备科学发展的探讨[J].橡塑技术与装备, 2010,(08) : 4-14.
[18]叶钢,张伟民,严庆,等.医用塑料及其加工[J].国外塑料, 2007, 15(5): 86-91.
[19]吴大鸣,李晓林,刘颖.影响挤出成型精密度的因素[J].塑料, 2003,(01) : 26-30.
[20] Li Xiaolin, Wu Daming, Lin Bingjian. Study and application of precise extrusionexperiment equipment[J]. China Synthetic Rubber Industry, 2001, 24(6):1-8
[21] R.E.Liang, M.R.Maekley. The Gas Assisted Extrusion of Molten Polyethylene[J].Journal of Rheology, 2001, 45(l): 211-216.
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