【作者】 董维煜；

【导师】 吴大鸣；

【作者基本信息】 北京化工大学 ， 机械设计及理论， 2009， 博士

【摘要】 高弹态聚合物在外力作用下会产生大变形,引发分子链取向,使得材料在取向方向上的宏观力学性能大幅增加。由于双向拉伸自增强管材在强度、耐热性、模量以及抗冲击性等方面得到显著提高,使其具有广阔的开发应用前景。本课题中采用布管扩胀的方法,以硬聚氯乙烯(PVC-U)管材为原料,采用专门设计的连续扩胀设备(包括加热器、行程控制装置、扩胀装置、牵引装置和冷却装置),能够比较精确地控制各工艺参数,实现管材的连续扩胀;通过大量实验确定了最佳扩胀条件。主要工作总结如下:1.研究了塑料管材的取向机理,对比国内外拉伸增强管材的生产工艺,通过一系列可行性实验,借鉴热缩管生产中的布管扩胀法,提出了双向拉伸增强管材的新方法。2.建立数学模型深入地研究了管材扩胀过程中的加热、充气扩胀和冷却等关键环节。按照弹性理论计算,扩胀时管壁内的应力近似为线性分布,其中,环向应力近似为均匀分布;通过传热理论计算,可以得到在PVC管坯的加热效率曲线。通过建立数学模型分析充气冷却过程,得到了管壁温度在不同换热系数下随时间的变化规律。3.设计并改进一套新型的双向拉伸自增强管材连续生产装置。此装置具有扩胀摩擦阻力小、环向扩胀率高、生产装置简单、生产线启动容易等优点。4.应用布管内压扩胀方法,在不同参数条件下,对PVC-U管进行间歇式和连续式扩胀,获得一系列扩胀管。对这些扩胀管进行几何测试和力学性能测试,证明采用布管内压扩胀法可以得到外观均匀、管径稳定的扩胀管,而且由于材料的取向作用,管材的环向拉伸强度和拉伸弹性模量都有大幅提高;但是作为代价,扩胀管的断裂伸长率有一定程度的降低。说明取向后管材的强度增加很大但是韧性略有降低。5.为了实现定量表征自增强管材的取向度,本文探索了用超声波测材料取向度的方法。随着材料拉伸比增加,超声波沿材料拉伸方向的速度增加,沿拉伸法线方向(同平面上)的速度逐渐降低。由取向度计算公式得,随材料拉伸比增加,取向度值相应增加。从超声波的数据来看,与单轴拉伸相比,若环向扩胀比保持不变,双向拉伸时的取向度有所降低。更多还原

【Abstract】 Mechanical properties of a polymer may be considerably enhanced by deforming the polymer in the elastomeric state and thereby achieving orientation of the molecular chains. Plastic Pipes had considerably enhanced hoop strength, impact strength and resistance to fatigue from cyclic pressure by biaxially orientation.In this paper, the principle of inner-pressing expansion of PVC-U pipes with cloth tube filled with compressed air was studied, a hop-pocket expansion technique was introduced and a new industrial processing equipment of biaxially drawing plastic pipes (including reheat equipment, control unit, expansion equipment, draught equipment and so on) was designed. The main controlling technological parameters were studied. The continuously expansion process was achieved by inner-pressing expansion method. The process of the preparation consisted of :1. By the comparison of these orientation techniques of plastic pipe inside and outside, the author did biaxially oriented experiments to research the feasibility of the technique. The biaxially oriented self-reinforcement mechanism of polymer material was studied. A new producing method of biaxially oriented self-reinforcement plastic pipes was designed from the hop-pocket technique of the pyrocondensation tubes production.2. The processes of reheating, expansion and cooling were studied by theoretical models. According to elastic theory, the hoop stress and radial stress in pipe wall are near-linearly nearly distributed, and the hoop stress is nearly constant when the expansion pressure is small. The heating efficiency is got by heat transfer calculation in different oil bath temperature and heating time. It would guide experiment and production of PVC-0 pipe that compute the stress distribution in expansion process and thermal distribution in heating process.3. The biaxially drawing experiment contained ballscrew and glide tracks which could drive the mould reciprocating and realize the continuous manufacture. The technique have many advantages, such as low friction, high draw ratio, simple structure and easy to start.4. The experiments of both batch inner-pressing expansion and continuously expansion of PVC-U pipes with cloth tube filled with compressed air were done to get series of expanded pipes. The performance testing shows that the expanded pipes have uniform appearance with larger diameter and considerably higher tensile strength and elastic modulus with a little bit lower rupture elongation ratio.5. In order to determine the orientation ratio of a material, the paper studied a new method by using ultrasound method.更多还原