膨体聚四氟乙烯（ePTFE）密封材料的力学行为与密封性能研究

发布时间：2018-05-29 11:14

本文选题：膨体聚四氟乙烯(ePTFE) + 垫片　；参考：《华东理工大学》2014年硕士论文

【摘要】：聚四氟乙烯(PTFE)具有高熔点、抗腐蚀、耐高温、低摩擦等优异的物理性能,广泛应用于电子、机械和化工等领域。作为密封材料,较差的抗蠕变性能限制了其广泛应用。膨体聚四氟乙烯(ePTFE)作为PTFE的改性材料,具有PTFE所有优良性能,同时大大改善了易蠕变、强度低等不足,在密封领域获得了越来越广泛的应用。本文以ePTFE为研究对象,对其力学行为、蠕变性能与密封性能进行系统研究,探讨了力学行为、蠕变性能和厚度对密封性能的影响规律；并在考虑ePTFE垫片蠕变的基础上,进行了螺栓法兰系统的有限元模拟,探讨了其密封行为的长期变化规律。主要研究内容和结果如下： (1)通过拉伸、压缩回弹和蠕变松弛实验,研究了ePTFE密封材料的力学行为。实验表明：由于多层叠加材料界面的影响,最大拉伸强度和弹性模量随厚度增加而先增加再减小。密度越大压缩率越小,回弹率随厚度的增加而增加。ePTFE的蠕变松弛率随材料厚度的增加而增加。 (2)对不同厚度ePTFE进行拉伸蠕变实验,发现ePTFE的蠕变性能具有厚度的相关性,选用合适的Kohlrausch-Williams-Watts(KWW)方程解释了厚度影响蠕变柔量的机理,并从叠加材料内部结构的角度给予了合理解释。获得了利用拉伸蠕变实验评价螺栓法兰垫片连接系统长期蠕变松弛行为的特征参量△J/J0。 (3)在不同条件下,对不同厚度ePTFE垫片进行气密性试验,探讨ePTFE垫片的泄漏规律,以及密封性能、蠕变、力学行为、厚度的内在关系。结果表明：在小密封比压下,ePTFE垫片的泄漏率随介质压力增加有较大增加,只适合于介质压力波动较小的工况。但在高密封比压下,ePTFE垫片的泄漏率随介质压力增加较化不大,适合于介质压力波动的工况；ePTEF的主要泄漏方式为界面泄漏,且由于ePTFE的回弹率较小,使得抗蠕变性决定了密封性能的好坏。继而成功将材料蠕变试验的研究应用于评价密封材料的性能,可以采用特征松弛时间τ在一定程度上评价密封材料的密封性能。 (4)在考虑ePTFE垫片蠕变的基础上,利用ANSYS有限元软件,模拟了安装ePTFE垫片的螺栓法兰系统的长期机械性能,并和实验值相互验证,模拟值和实验值的相对误差在10%以内。并且通过有限元法模拟,分析了ePTFE垫片厚度、弹性模量对螺栓法兰系统中螺栓力的影响。
[Abstract]:PTFE (PTFE) has high melting point, corrosion resistance, high temperature resistance, low friction and other excellent physical properties, widely used in electronic, mechanical and chemical fields. As a sealing material, its wide application is limited by its poor creep resistance. As a modified material of PTFE, expanded PTFEs have all the excellent properties of PTFE, and have been widely used in the field of sealing due to their disadvantages such as easy creep, low strength and so on. In this paper, the mechanical behavior, creep property and sealing performance of ePTFE are studied systematically, and the effects of mechanical behavior, creep property and thickness on sealing performance are discussed, and the creep of ePTFE gasket is considered. The finite element simulation of bolt flange system is carried out, and the long-term variation of sealing behavior is discussed. The main contents and results are as follows: 1) the mechanical behavior of ePTFE sealing material was studied by tensile, compression springback and creep relaxation experiments. The experimental results show that the maximum tensile strength and elastic modulus increase first and then decrease with the increase of thickness due to the influence of the interface of multilayer superimposed materials. The higher the density is, the smaller the compression ratio is, and the creep-relaxation rate of ePTFE increases with the increase of the thickness of the material, and the creep relaxation rate of ePTFE increases with the increase of the thickness of the material. It is found that the creep properties of ePTFE have thickness correlation. The suitable Kohlrausch-Williams-Wattske equation is used to explain the mechanism of thickness affecting creep compliance, and the reasonable explanation is given from the point of view of the internal structure of superimposed materials. The characteristic parameter J / J _ 0 is obtained to evaluate the long-term creep relaxation behavior of bolt flange gasket connection system by tensile creep test. 3) under different conditions, the airtightness test of ePTFE gasket with different thickness was carried out, and the leakage law of ePTFE gasket and the internal relations of sealing performance, creep, mechanical behavior and thickness were discussed. The results show that the leakage rate of PTFE gasket increases with the increase of medium pressure, and it is only suitable for the condition where the pressure fluctuation is small. However, under high sealing pressure, the leakage rate of ePTFE gasket is relatively small with the increase of medium pressure. The main leakage mode of EPTEF is interface leakage under the condition of medium pressure fluctuation, and the springback rate of ePTFE is small. The creep resistance determines the sealing performance. Then the creep test is successfully applied to evaluate the performance of the sealing material, and the characteristic relaxation time 蟿 can be used to evaluate the sealing performance of the sealing material to a certain extent. On the basis of considering the creep of ePTFE gasket, the long-term mechanical performance of bolted flange system installed with ePTFE gasket is simulated by using ANSYS finite element software, and the relative error between simulation value and experimental value is less than 10%. The influence of ePTFE gasket thickness and elastic modulus on bolt force in bolt flange system is analyzed by finite element method.
【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB42;TQ317

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