| In industrial production,the gate valve is one of the most commonly used valves.There is an extremely close relationship between the strength of the middle flange of the gate valve and the flange leakage,which plays a vital role in the sa fe operation of the valve.The middle flange in gate valve belongs to non-standard flange.The lack of reliable design method often leads to unreasonable product structure design,which will bring serious potential safety hazards.At the same time,if the structural strength is over-considered,it will cause the middle flange to be too bulky in structure and increase the production and manufacturing costs.Therefore,it is of great significance for the design,manufacture and safe use of gate valves to esta blish a reliable method for strength analysis and structural optimization of middle flanges of gate valves.Taking the middle flange structure of gate valve under high temperature and high pressure as the research object,the main work is as follows:Firstly,based on the steady-state temperature field and thermal-structural coupling,the stress-strain distribution of middle flange under pre-tightening and operating conditions was studied.The results showed that the stress and strain distributions of the whole middle flange and its parts tended to be the same under the two working conditions,and the maximum stress and strain occurred at the large end of the cone neck of the lower flange.The stress distribution on gasket sealing surface was basically the same,showing "external tightening and internal loosening".Under operating condition,due to the influence of internal pressure and temperature load,the stress of the whole flange and its components increased,while the compressive stress of the gasket decreased.It can be seen that temperature and internal pressure had a great influence on the gasket sealing.Secondly,according to the stress classification design,the strength of the weak part of the middle flange was checked,and the sealing performance of gasket was checked according to EN13445 seal judgment basis.The results showed that the flange of the gate valve met the requirements of strength and tightness under two working conditions.,and the structure size had a larger safety margin,which can be further optimized for the middle flange structure of gate valve.Thirdly,through the finite element analysis of the influence of the structure size of middle flange on the strength of gate valve,it was concluded that the thickness of large end of cone neck,the thickness of flange ring and the height of cone neck can be used as factors to optimize the middle flange of gate valve.Using Workbench collaborative optimization analysis platform,three structural parameters of flange ring thickness,taper neck thickness and taper neck height were set as design variables,the strength of middle flange of gate valve was constrained,and the mass and maximum equivalent stress were objective functions.Structural optimization of middle flange of gate valve was carried out from the point of view of safety and economy.On the premise of satisfying strength and sealing,the optimum structural size of middle flange of gate valve was obtained,and its weight was reduced by 9.6% compared with that before optimization.Finally,the strength and sealing property of middle flange of gate valve before and after optimization were compared.The results showed that the stress intensity of flange after optimization was higher than that before optimization,closer to the strength limit value,and the mechanical properties of material were fully utilized.The pressure stress on gasket sealing surface decreased,but it met the sealing requirements.Therefore,after optimization,the middle flange structure of gate valve was more compact,the force was more uniform,and the production cost was lower,which met the requirements of enterprise economy.The engineering design method for optimization of middle flange structure of gate valve is established for enterprises. |
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