【作者】 王捷；

【导师】 马咏梅； 王泽平；

【作者基本信息】 四川大学 ， 机械工程（专业学位）， 2022， 硕士

【摘要】 焊接金属波纹管是机械密封中的一种弹性补偿元件,在石油化工行业中充当着机械密封的重要一环,其性能直接关系着整个机械密封装置的运行。为了满足各种工况下对机械密封技术的要求,对焊接金属波纹管的材料性能、结构参数、加工方式等方面的优化方案进行探究是十分有必要的。当前,国内外文献中针对焊接金属波纹管的波宽、波厚、波形等结构参数对性能的影响的探索研究较多,而针对波片层数对性能的影响的研究较少。本文针对某企业生产的同系列单层和双层S型焊接金属波纹管产品为对象,基于实际工况,分别对两种产品的刚度、振动特性、疲劳寿命、热稳定性进行了对比分析。为此类焊接金属波纹管的结构优化、性能预测等方面提供了科学的依据。基于薄壳理论,分析焊接金属波纹管的受力情况,并根据美国EJMA标准,对S型焊接金属波纹管的刚度采用工程近似法进行理论计算。然后分别介绍了振动特性、疲劳寿命、热力学的相关理论。运用三维建模软件Solid Works,对单层和双层S型焊接金属波纹管进行了三维建模,并将几何模型导入ANSYS Workbench中建立了有限元模型,并对模型进行材料设置和网格划分等前处理工作。分别对单层和双层S型焊接金属波纹管进行轴向刚度、扭转刚度、弯曲刚度的仿真计算,并设计轴向刚度实验。将刚度的理论值、仿真值、实验值进行对比,以验证建模的准确性。对EJMA标准中的U型波纹管的工程近似公式进行修正,得出S型波纹管的工程近似公式。分别对单层和双层S型焊接金属波纹管进行模态分析,提取前6阶固有频率及模态振型。对焊接金属波纹管的密封环端面施加一个扭转激振力来模拟转动过程中的摩擦力矩,并对其进行谐响应分析,查看其响应区间和应力幅值。分别对单层和双层S型焊接金属波纹管在介质压力和不断启停的实际工况下进行疲劳强度分析,对其寿命进行预测,找到寿命最短的部位。在轴向压力一定且温度逐渐升高的情况下,分析单层和双层S型焊接金属波纹管的应力及应变的变化趋势。结果表明,S型焊接金属波纹管轴向刚度的仿真值与实验值的误差小于5%,验证了建模的准确性。双层S型焊接金属波纹管的轴向刚度、扭转刚度、弯曲刚度分别为单层S型焊接金属波纹管的1.39倍、1.7倍、1.51倍,因此双层焊接金属波纹管预防失弹的效果更好,且能够承受更大的启动扭矩,单层S型焊接金属波纹管的径向柔性更好,能更好地适用于需要角位移和横向位移补偿的场景中。在振动稳定性方面,单层S型焊接金属波纹管的前6阶固有频率以及谐响应的应力幅值均高于双层S型焊接金属波纹管,在极限工况时,双层S型焊接金属波纹管更容易发生共振,因此单层S型焊接金属波纹管在极限工况下运转时的振动稳定性更佳,产生的噪音更小。在疲劳寿命方面,双层S型焊接金属波纹管的启停次数远大于单层S型焊接金属波纹管的启停次数,因此双层S型焊接金属波纹管的疲劳寿命更长。在热稳定性方面,双层S型焊接金属波纹管的热应力与热应变均远小于单层S型焊接金属波纹管,因此双层S型焊接金属波纹管的热稳定性更佳。更多还原

【Abstract】 Welded metal bellows(WMB)is an elastic compensation element in mechanical seals,it is an important component of mechanical seals in petrochemical industry,and its performance is directly related to the overall mechanical sealing device operation.To meet the requirements of mechanical sealing technology under varing working conditions,it is critical to explore the optimization scheme of material properties,structural parameters and processing methods of WMB.There are many studies on the influence of structural parameters such as wave width,wave thickness and waveform on the performance of WMB at home and abroad,but few studies on the influence of the number of layers on the performance of WMB.In this paper,the stiffness,vibration characteristics,fatigue life,and thermal stability of a series of single-layer and double-layer S-shaped WMB produced by an enterprise are analyzed based on actual working conditions.It provides a scientific foundation for WMB structure optimization and performance prediction.The stress of WMB is analyzed using thin shell theory,and the stiffness of Sshaped WMB is calculated using the engineering approximation method according to the EJMA standard.The related theories of vibration characteristics,fatigue life,and thermodynamics are then introduced.Solid Works creates geometry models of single-layer and double-layer S-shaped WMB,which are then imported into ANSYS Workbench to create finite element models.The axial,torsional,and bending stiffness of single-layer and double-layer S-shaped WMBs are simulated,and axial stiffness experiments are designed.To validate the accuracy of the finite element models,the theoretical,simulation,and experimental values of stiffness are compared.In the EJMA standard,the engineering approximate formula of U-shaped WMB is modified to obtain the engineering approximate formula of S-shaped WMB.In the EJMA standard,the engineering approximate formula of U-shaped WMB is modified to obtain the engineering approximate formula of S-shaped WMB.The modal analysis of singlelayer and double-layer S-shaped WMB is performed to determine their six natural frequencies and modal shapes.To simulate the friction torque in the rotation process,a torsional exciting force is applied to the end face of the WMB’s sealing ring,and a harmonic response analysis is performed to obtain its response interval and stress amplitude.Under the actual working conditions of medium pressure and continuous start and stop,the fatigue strength of single-layer and double-layer S-shaped WMB is analyzed,their life is predicted,and the position with the shortest life is found.The changing trend of stress and strain of single-layer and double-layer S-shaped WMB is investigated under constant axial pressure and gradual temperature increase.The results show that the error between the simulation and the experimental values of the axial stiffness of S-shaped WMB is less than 5%,which verifies the accuracy of the finite element models.Double-layer S-shaped WMB has 1.39 times the axial stiffness of single-layer S-shaped WMB.Double-layer S-shaped WMB has1.7 times the torsional stiffness of single-layer S-shaped WMB.Double-layer Sshaped WMB has a bending stiffness that is 1.51 times that of single-layer S-shaped WMB.As a result,the double-layer WMB prevents elastic loss better and can withstand higher starting torque.Single-layer S-shaped WMB has greater radial flexibility and is better suited for conditions requiring angular displacement and lateral displacement compensation.In terms of vibration stability,the six natural frequencies and stress amplitude of harmonic response of single-layer S-type WMB are greater than those of double-layer S-type WMB,and resonance of double-layer S-type WMB is more likely to occur under limited working conditions.As a result,the vibration stability of single-layer S-type WMB is improved,and noise is reduced in limited working conditions.In terms of fatigue life,the start and stop times of double-layer S-type WMB are much longer than those of single-layer S-type WMB,resulting in a longer fatigue life.In terms of thermal stability,the thermal stress and strain of double-layer S-shaped WMB are much lower than those of single-layer Sshaped WMB,implying that double-layer S-shaped WMB has better thermal stability.更多还原