本文選題：膨體聚四氟乙烯(ePTFE) + 墊片　； 參考：《華東理工大學(xué)》2014年碩士論文

【摘要】：聚四氟乙烯(PTFE)具有高熔點(diǎn)、抗腐蝕、耐高溫、低摩擦等優(yōu)異的物理性能,廣泛應(yīng)用于電子、機(jī)械和化工等領(lǐng)域。作為密封材料,較差的抗蠕變性能限制了其廣泛應(yīng)用。膨體聚四氟乙烯(ePTFE)作為PTFE的改性材料,具有PTFE所有優(yōu)良性能,同時(shí)大大改善了易蠕變、強(qiáng)度低等不足,在密封領(lǐng)域獲得了越來越廣泛的應(yīng)用。本文以ePTFE為研究對(duì)象,對(duì)其力學(xué)行為、蠕變性能與密封性能進(jìn)行系統(tǒng)研究,探討了力學(xué)行為、蠕變性能和厚度對(duì)密封性能的影響規(guī)律；并在考慮ePTFE墊片蠕變的基礎(chǔ)上,進(jìn)行了螺栓法蘭系統(tǒng)的有限元模擬,探討了其密封行為的長(zhǎng)期變化規(guī)律。主要研究?jī)?nèi)容和結(jié)果如下： (1)通過拉伸、壓縮回彈和蠕變松弛實(shí)驗(yàn),研究了ePTFE密封材料的力學(xué)行為。實(shí)驗(yàn)表明：由于多層疊加材料界面的影響,最大拉伸強(qiáng)度和彈性模量隨厚度增加而先增加再減小。密度越大壓縮率越小,回彈率隨厚度的增加而增加。ePTFE的蠕變松弛率隨材料厚度的增加而增加。 (2)對(duì)不同厚度ePTFE進(jìn)行拉伸蠕變實(shí)驗(yàn),發(fā)現(xiàn)ePTFE的蠕變性能具有厚度的相關(guān)性,選用合適的Kohlrausch-Williams-Watts(KWW)方程解釋了厚度影響蠕變?nèi)崃康臋C(jī)理,并從疊加材料內(nèi)部結(jié)構(gòu)的角度給予了合理解釋。獲得了利用拉伸蠕變實(shí)驗(yàn)評(píng)價(jià)螺栓法蘭墊片連接系統(tǒng)長(zhǎng)期蠕變松弛行為的特征參量△J/J0。 (3)在不同條件下,對(duì)不同厚度ePTFE墊片進(jìn)行氣密性試驗(yàn),探討ePTFE墊片的泄漏規(guī)律,以及密封性能、蠕變、力學(xué)行為、厚度的內(nèi)在關(guān)系。結(jié)果表明：在小密封比壓下,ePTFE墊片的泄漏率隨介質(zhì)壓力增加有較大增加,只適合于介質(zhì)壓力波動(dòng)較小的工況。但在高密封比壓下,ePTFE墊片的泄漏率隨介質(zhì)壓力增加較化不大,適合于介質(zhì)壓力波動(dòng)的工況；ePTEF的主要泄漏方式為界面泄漏,且由于ePTFE的回彈率較小,使得抗蠕變性決定了密封性能的好壞。繼而成功將材料蠕變?cè)囼?yàn)的研究應(yīng)用于評(píng)價(jià)密封材料的性能,可以采用特征松弛時(shí)間τ在一定程度上評(píng)價(jià)密封材料的密封性能。 (4)在考慮ePTFE墊片蠕變的基礎(chǔ)上,利用ANSYS有限元軟件,模擬了安裝ePTFE墊片的螺栓法蘭系統(tǒng)的長(zhǎng)期機(jī)械性能,并和實(shí)驗(yàn)值相互驗(yàn)證,模擬值和實(shí)驗(yàn)值的相對(duì)誤差在10%以內(nèi)。并且通過有限元法模擬,分析了ePTFE墊片厚度、彈性模量對(duì)螺栓法蘭系統(tǒng)中螺栓力的影響。
[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.
【學(xué)位授予單位】：華東理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TB42;TQ317

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