| Welded metal bellows mechanical seal was a kind of equipment which a bellows was used to replace the springs and auxiliary seals in the typical seal.Axial displacement of the moving ring occurred with the rotation of the equipment.However,the displacement could be compensated and buffered based on the characteristics of the bellows.The performance and service life of the mechanical equipment were closely related to the failure of the mechanical seal.In normal conditions,the fatigue failure was the main cause of the failure of the welded metal bellows in mechanical seal.Therefore,it was of great significance to study the fatigue life of welded metal bellows.Centrifugal force was ignored during the analysis of the stress of the bellows because of the well-neutral installation of S-type welded metal bellows in mechanical seal.The bellows was modeled,meshed and analyzed by the common commercial software such as Solid Works and ANSYS Workbench.The contours of deformation and stress distribution were obtained and the fatigue life was calculated.Because of the high temperature condition,it was necessary to explore the effect of temperature on fatigue life with thermo-structural coupling analysis.On the basis of the former research,the transient dynamic stress analysis of S-type welded metal bellows was analyzed.The maximum stress was obtained and compared with the result estimated by the formula.Finally,U-shaped metal bellows was designed according to the geometry of S-type bellows.Finite element analysis of U-shaped bellows fatigue life was worked out with the same conditions of the S-type,and compared with the S-type.557312 nodes and 87000 units were generated in S-type welded metal bellows meshing model.As for static analysis,the maximum deformation located in the free end of the bellows was 3.0586 mm and less than the minimum allowable working displacement of 7.96 mm.The maximum stress was 117.58 MPa,located in the bellows diaphragm in the welding,and less than the allowable stress of the material(206.7MPa).The minimum fatigue life was 3.49 years which meet the requirements of the factory overhaul.Maximum deformation of 2.6728 mm located in the free end of the bellows was given by the thermo-structural coupling analysis,which was smaller than the minimum allowable working displacement.Due to the fixed load,the maximum stress at the fixed end of the bellows was 200.2MPa,which less than the allowable stress of the material.The stress in the bellows diaphragm film welding which was the most vulnerable part was 121.11 MPa.The minimum fatigue life was 2.35 years and the fatigue life is smaller than the result of static analysis,which also satisfied the requirement of factory overhaul.Under normal operating conditions,the transient maximum deformation value and the maximum stress value were obtained while the maximum transient stress of axial vibration was 0.5764 N.The peak of the maximum deformation value and the maximum stress value occurred at 0.021875 s.In addition,the maximum deformation was 2.6881 mm in the free end of the bellows and the maximum stress value was 103.45 MPa in the welding of the diaphragm,which were all in the allowable range.The maximum stress value combined with the stress of thermal-structural coupling at the same position,and the average stress was obtained.2.59-year service life of the bellows was worked out with the formula,which was close to the value of the finite element analysis.278063 nodes and 39432 units were generated in U-type welded metal bellows meshing model.As for static analysis,the maximum deformation located in the free end of the bellows was 0.17926 mm and less than minimum allowable working displacement.The maximum stress was 198.47 MPa,located in the bellows diaphragm in the welding,and less than the allowable stress of the material.The minimum fatigue life was 2.29 years which met the requirements of the factory overhaul.Maximum deformation of 0.16222 mm located in the free end of the bellows was given by the thermo-structural coupling analysis,which was smaller than minimum allowable working displacement.Because of the fixed load,the maximum stress at the fixed end of the bellows was 567.76 MPa,which was three times less than the allowable stress of the material.The stress in the bellows diaphragm film welding which was the most vulnerable part was 166.08 MPa.The minimum fatigue life was 0.16 years which couldn't meet the requirement of factory overhaul.The transient dynamic analysis of U-type and S-type welding metal bellows were presented in the same conditions.The transient maximum deformation and the maximum stress were obtained.The peak of the maximum deformation and the maximum stress occurred at 0.021875 s.In addition,the maximum deformation was 0.14934 mm in the free end of the bellows and the maximum stress value was 110.32 MPa in the welding of the diaphragm,which were all in the allowable range.The maximum stress value combined with the stress of thermal-structural coupling at the same position,and the average stress was obtained.The 0.17-year service life of the bellows was worked out with the formula,which was close to the value of the finite element analysis.Without considering the influences of temperature,the operation needs were met in the two kinds of bellows from the aspect of fatigue life.However,the welded metal bellows was not only a connecting element,but also a part that could buffer and compensate for the axial displacement of the dynamic ring in the mechanical seal.The characteristics wouldn't be effective if the U-shaped bellows elasticity was small.In addition,the fatigue life of U-type welding metal bellows was inferior to the S-type in high temperature conditions.There were still some limitations for U-type welding metal bellows used on the rotating equipment.Based on the above research,some references and guides were provided in the design of mechanical seal practical welding metal bellows.Meanwhile,a new method was provided for the optimization of S-type bellows waveform. |
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