Study On Thermol-fluid-solid Coupling And Multi-objective Optimization Design Of Single Metal Seal For Cone Bit

Cone bit is the main rock-breaking tool in petroleum development and mining engineering,accounting for about 70%of the total oil field bit.The single metal seal is an important part of the cone bit system,and its performance directly affects the efficiency and cost of drilling.However,with the diversification of the bottom layer and the increase of the drilling depth,the drill bit sealing system often works under severe conditions such as high temperature,high pressure and abrasive particles,which make its sealing stability face a huge test.In particular,under the action of complex thermal and mechanical load,the single metal seal is prone to irregular deformation,which leads to the increase of seal leakage and wear,and then causes seal failure.Therefore,developing research on thermo-fluid-solid coupling of single metal seals is of great significance for predicting and improving the performance of single metal seals,as well as improving the efficiency and reliability of downhole drilling.In this study,the single-metal seal for cone bit was taken as the research object,and a thermal-fluid-solid coupled mathematical model was established for single metal seal.In this model,the asperity contact,thermal-mechanical deformations and viscosity-temperature characteristic of sealing face were considered comprehensively.Furthermore,the deformation of single metal seal face and the evolution of seal performance under multiple parameters were studied.By using BP neural network and NSGA-II genetic algorithm,the optimization model of single metal seal,and multi-objective optimization solution were completed,which provided theoretical basis for the construction of metal seal design system of cone bit.The main research contents and conclusions are as follows:1.According to characteristics of the cone bit operation and sealing system structure,the steady-state mechanical analysis model of the single metal seal was established,and the finite element analysis of the single metal seal structure field and the structural-thermal coupling field was conducted.The effects of environmental pressure,assembly displacement,and material thermal conductivity on the stress field and temperature field of a single metal seal were studied.The results show that when the ambient pressure increased from 3 MPa to 30 MPa,both the maximum contact pressure and the highest temperature rise of the sealing end face migrated from the outer diameter side to the inner diameter side.Additionally,increasing the assembly displacement can effectively increase the sealing force,while increasing the thermal conductivity of the material can strengthen the heat dissipation ability of the seal ring,which can effectively control the temperature rise and deformation of the end face.2.A thermal-fluid-solid coupled mathematical model has been developed for single metal seal in cone bit.The interrelated system of sealing ring,lubricant film and sealing medium was constructed through comprehensively considering the asperity contact,thermal-mechanical deformations and viscosity-temperature characteristic of seal face.Furthermore,the influences of key parameters including environmental pressure,contact width and O-ring hardness on the film thickness distribution,temperature rise and sealing performance of single metal seal were further studied,and the lubrication mechanism of the single metal seal system for cone bit was revealed.According to the results,it can be concluded that when the ambient pressure was lower than the critical pressure p_crit,the sealing face formed a convergent gap,otherwise the sealing face formed a divergent gap.Moreover,with increasing the contact width of the sealing face,the film thickness was more uniformly distributed,which caused the leakage rate to drop by 47.1%.However,when the hardness of the O-ring increaseed from 70 HA to 90 HA,the friction force of the single metal seal increaseed by approximately 12%.3.According to the influence degree of each factor on the sealing performance of single metal,the design variables of the sealing performance optimization of single metal were selected.Based on the thermal-fluid-solid coupling model of single metal sealing,the data sample were collected.Then,the single metal sealing optimization model was constructed by BP neural network.Finally,the multi-objective optimization solution of single metal sealing was completed by NSGA-II genetic algorithm.Based on the analysis results,the final scheme was determined,as follows:rotational speed n=100 r/min,roughness?=0.07?m,contact width L=2.5 mm.After optimization,the leakage rate was reduced by 51.6%,and the friction force was reduced by 11%.The research results in this article provide the theoretical basis and technical support for the design of high-life and high-reliability drill bit seals,which indicate the remarkable academic value and engineering significance.