Performance Of Split Mechanical Seal Based On Multi-field Coupling Effects

Split mechanical seal(abbreviated as SMS) has become a hot topic in the field of fluid equipment for its convenient assembly and disassembly, in such a world as mechanical seals being indispensable, resources being depleting and environmental requirements being increasing.At present, researches of SMS at home and abroad are largely confined to structural study while less emphasis was put on theoretical study, which only solved the problem of the design feasibility. Therefore, theoretical research on performance of split mechanical seal considering thermal-force-fluid-solid multi-field coupling effects is theoretically and practically significant.In this thesis, theoretical derivation, numerical calculation and experiments were combined to develop the SMS performance research based on multi-field coupling effects, to explore deformation law, temperature distribution and sealing performance of split seal rings under the thermal-force-flow-solid multi-field coupling effects. The contents and conclusions are as follows:Based on shoulder-shoulder contact theory of asperities and PC average Reynolds equation,a theoretical model of frictional heat under mixed lubrication was established and calculated by MATLAB. The influences of operating parameters and surface topography parameters on frictional heat were analyzed. The results show: frictional heat from asperity contact takes more proportion of total frictional heat when rotation speed ω is less than or equal to 2800r/min, but the viscous part gradually rises as the rotational speed increases and eventually equals to the total;with the increased friction gap, the asperity and viscous frictional heat both decrease, the former decreases to zero when friction gap d is larger than or equal to 2.8σ(σ refers to the comprehensive standard deviation of roughness respectively on stationary and rotating seal end faces) while the latter changes little; As the roughness of seal end faces increases, the total frictional heat dramatically falls at first and then tends to invariable, which indicates it is profitable to reduce mixed frictional heat to properly increase the roughness on seal end faces.When considering lubrication, lubricant with high viscosity and slight variation with temperature should be chosen.With the finite element method, thermal-force-flow-solid coupling deformation of split seal rings was calculated and approximate characterization parameters of the deformation were determined. Significance analysis of the influence of operating parameters on deformation was conducted by orthogonal experiment method and functional relationship between the dominant factors and deformation of seal end face and parting surface of each seal ring was established.Influences of friction material as well as single factor of operating parameters on deformation were studied. The results show: under the coupling action of multi-field, split seal end faces forms into a radially convergent taper with two cycles of waves in the circumferential direction where wave crest is generally formed in the region of parting surface location; parting surface forms into a wedge which converges radially from outside diameter to inner diameter and axially from the seal end face to the opposite end face; deformation of hard split rotating ring is very small and parting surface deformation can be ignored while deformation of soft stationary ring is large; the deformation of seal end faces and parting surfaces is increased with rising medium pressure, the pretightening force of parting surfaces should be designed to zero, the deformation of parting surface can be reduced by increasing spring pressure in limited range, the deformation of parting surface reduces when rotation speed rises in low speed range while then is not obvious when the speed continues to increase, however, the deformation of both seal end faces and parting surfaces is almost unaffected by the medium temperature; friction material has a significant impact on the circumferential waviness of seal end faces and parting surface deformation, especially on radial the taper of seal end faces.A three-dimensional steady-state heat transfer model of split seal rings was derived with separation of variables. Maple language was used to programme so as to calculate and analyze the influences of rotation speed, medium temperature, flare angle of parting surface and taper of seal end face on the temperature distribution seal end face. The results indicate: circumferential temperature gradient increases with rising speed; the effect of medium temperature on the temperature gradient is very small; when the flare angle of parting surface or taper of seal end face is increased, the seal end face temperature will be decreased while circumferential temperature gradient will be increased.Taking roughness into consideration, geometric equations of fluid film within the sealing gap when operating in steady state were established. Three dimensional model of fluid film was solved by the finite volume method for hydrodynamic analysis. A comparative analysis of the sealing performance of SMS and IMS was carried out. The effects of rotation speed, medium pressure, spring pressure, flare angle of parting surface, taper of seal end face and the relative position of wave crest on seal end face and parting surface on leakage of SMS were studied. The results show: the bearing capacity and the ratio of fluid film open force between seal end faces to leakage of SMS are larger than IMS; the leakage is reduced when the speed increases in low speed range, linearly increased with increasing medium pressure and increased with the increase of the spring pressure; when increasing flare angle of parting surface with keeping the seal end face deformation constant, the total leakage is increased, fluid film open force between seal end faces is reduced and when the flare angle tanγs is less than 3.3×10-5, the leakage from the seal end face is decreased with increasing flare angle and almost free from the impact when tanγs becomes larger; keeping the flare angle of parting surface constant, when the taper of seal end faces is small, increasing the taper can significantly reduce the leakage of both seal end face andparting surface.Experiments were conducted for verifying the theoretical results. The temperature and deformation of seal end face of split stationary seal ring operating in steady state as well as the total leakage of SMS were measured. A confocal laser microscope, OLYMPUS 3D, was used to measure the three dimensional profiles of split stationary seal end face after wear to verify the theoretical results of seal end face deformation. The measured results show that the experimental results basically coincide with the theoretical ones, which confirmed the rationality and correctness of the research methods in this thesis.The results of this thesis have a guiding role for SMS design, provides foundations and references for further study on the performance of SMS and gives a necessary theoretical basis for the application and promotion of SMS technology.