Study On Strength And Stiffness Of Welded Metal Bellows For Mechanical Seals

Welded metal bellows mechanical seal is an important way of end face seal.Due to its unique structure and properties of constituent materials,it is often used in some high temperature and high pressure units in the petrochemical field,such as diesel hydrogenation unit,continuous reforming unit,wax oil hydrogenation unit,fuel oil hydrofining unit,coal tar hydrogenation unit,etc.In these situations,the strength and rigidity of welded metal bellows are required to be very high.At present,in the strength analysis of welded metal bellows,most of the research is limited to reducing the local material yield caused by stress concentration,and there is less research on solving the instability limit pressure of welded metal bellows as a whole;in the stiffness analysis of welded metal bellows,most of them are analyzed only from theory or simulation,and lack of comprehensive theoretical,simulation and experimental stiffness research.In view of the above problems,the paper takes 60 single and double welded metal bellows provided by the project party as the research object,analyzes the instability design limit pressure from the aspects of theory and simulation,and analyzes the axial stiffness and bending stiffness from the aspects of theory,simulation and test.(1)Solid Works is used to establish the three-dimensional model of single and double welded metal bellows.The stress of bellows wave plate is analyzed by using thin shell theory.The deformation of welded metal bellows wave plate under axial force is solved.It is pointed out that the axial displacement of inner and outer welding mushroom can be regarded as rigid translation,and the deflection angle with wave plate is 0.(2)This paper analyzes the strength of welded metal bellows,and points out that the key point in the strength analysis is the instability failure analysis.Using EJMA theoretical formula,the instability design limit pressure of 60 single layer welded metal bellows is 1.199 MPa,and the instability design limit pressure of 60 double layer welded metal bellows is 2.398 MPa.The finite element models of 60 single and double welded metal bellows are established in workbench to simulate the actual working conditions.Based on the buckling analysis module,the buckling design limit pressure of 60 single welded metal bellows is 1.588 By comparing the theoretical calculation results with the simulation results,it is pointed out that the theoretical calculation errors of 60 single and double welded metal bellows are24.5% and 17.6% respectively;by using the control variable method,the influence of different compression,speed and temperature on the instability design limit pressure is analyzed through simulation,It is found that the compression amount and rotating speed have little influence on the instability design limit pressure of welded metal bellows,but the temperature has great influence,and the instability design limit pressure decreases with the increase of temperature.(3)Based on the research of domestic and foreign scholars on the theoretical axial stiffness,this paper points out that there is no pure theoretical formula for the axial stiffness of S-type welded metal bellows,and adopts the engineering empirical formula to calculate the theoretical axial stiffness of 60 single and double welded metal bellows,which are 49.9 N/mm and 99.8 N/mm respectively.According to the definition of stiffness,the simulation axial stiffness of 60 single and double welded metal bellows is 41.33 N/mm and 84.00 N/mm;the axial stiffness of 60 single and double welded metal bellows is 41.00 N/mm and 85.22 N/mm by test method.The theoretical,simulation and experimental data are compared and analyzed,and it is found that the error of the engineering empirical formula is larger than that of the simulation calculation,and the engineering empirical formula is modified according to the test results;the control variable method is used to analyze the influence of different wave number,wave distance and thickness on the axial stiffness of 60 single and double layer welded metal bellows,and it is found that the welding metal bellows has a large error The axial stiffness of the tube decreases with the increase of wave number and wave distance,and increases with the increase of thickness.(4)The definition of bending stiffness of welded metal bellows is described.Based on the research of scholars at home and abroad in solving the bending stiffness,the approximate solution of bending stiffness is obtained by equivalent bending moment to axial force.The theoretical bending stiffness of 60 single and double welded metal bellows is 23698 N.mm/rad and 49257.2 N.mm/rad respectively N.Through ANSYS Workbench static analysis module,the bending moment bending angle data of 60 single and double welded metal bellows are obtained,and the simulation bending stiffness of 60 single and double welded metal bellows is 27987.3 N.mm/rad,52387.5 N.mm/rad;the bending stiffness of 60 single and double welded metal bellows is 28162.0 N.mm/rad,52820.1 N.mm/rad measured by test method.The results show that the error of theoretical calculation formula is larger than that of simulation calculation,and the theoretical calculation formula is modified according to the test results.The control variable method is used to analyze the influence of different wave number,wave distance and thickness on the bending stiffness of 60 single and double-layer welded metal bellows The bending stiffness of bellows decreases with the increase of wave number and wave distance,and increases with the increase of thickness.