Single Metal Seal Structure Optimization And Thermal Structure Coupling Research

As a rotary dynamic seal applied in down-hole tools, the single metal seal (SEMS2) can adapt to high temperature, high pressure, abrasive and vibration down-hole conditions. The sealing performance of the SEMS2 directly decides the working life of the bearing in down-hole tools, and influences the rate of penetration and the drilling cost. With the development of various drilling technique, oil and gas development towards to the deep sea and the deep strata, a variety of down-hole tools have been applied in harsh down-hole conditions, and then an urgent requirement needs to ensure and improve the working life of the down-hole tool. Therefore, in order to meet the demand, the optimization of structure parameters and the steady-state temperature distribution of the SEMS2 have been studied in this paper. The main researches are as follows:(1) According to the structural characteristics of the SEMS2, main working conditions and the field application of the SEMS2, the main failure reasons and forms of the SEMS2 have been analyzed, and the main criterions of the SEMS2 failure are given.(2) Based on the structural force characteristics of the single metal seal, the mechanical analysis of the singal metal seal in the assembly and compression process has been researched, and obtaining the theoretical relationship about the dynamic seal surface contact stress^ the axial displacement of the assembly and external pressures.(3) Utilizing ANSYS finite element analysis and Matlab numerical theoretical calculation, the assembly process of the single metal seal has been simulated to establish the fitting relationship between the maximum contact stress of the dynamic seal surface and the assembly displacement. The finite element solutions and numerical solutions of the contact stress and the contact length between the rubber O-ring and static ring has been compared to validate that the finite element model of the single metal seal is effective. Under the high, medium and low pressure conditions, the contact pressure distribution of the dynamic seal surface, the rubber O-ring and the rubber surpport ring has been analyzed, and obtaining the sealing performance insufficient of the initial structure of the single metal seal.(4) Throgh analyzing the change of the dynamic seal surface contact stress under the different hardness of the O-rings and the rubber support ring, the different inclined surface angle of the static ring, the different width of the small end of the static ring, the different wedge angle length of the static ring, the different dynamic seal surface width, the different differential pressure and the different initial compression on the dynamic seal surface contact stress, the influence of the sealing performance has been achieved.(5) Combining with the orthogonal method and the F analysis,while six parameters including the film thickness, the leakage, the contact stress, etc have been as evaluation objectives. The seven structural parameters, two material parameters and two working condition parameters which affect the sealing performance of the single metal seal have been significantly and quantitatively assessed to determine structure paremeters and evaluation objectives as optimal parameters and objectives which are the most influential parameters and objectives. The optimal parameters are the dynamic seal surface width L, the width of the small end of the static ring L3, the inclined surface angle of the static ring a and the wedge angle length of the static ring L1. The optimal objectives are the inside contact stress Pnmax, the outer contact stress Pwmax and the minimum contact stress Pmin.(6) Using BP neural network and the fuzzy weighting coefficient method, the mapping function between the four structural parameters and three evaluation objectives has been established and transformed into a single objective optimization function.(7) Through GA genetic algorithm, a mathematical model of the single metal seal optimization has been builded. Combining with the objective optimization function, the certain values of four optimized structural parameters have been confirmed in a certain scope. The leakage of the optimized single metal seal is reduced 7.45%, the minimum film thickness is reduced 3.837%, the inside contact stress of the dynamic seal surface is reduced 22.733%, the outer contact stress and the minimum contact stress of the dynamic seal surface are increased 10.031% and 0.596% respectively. The results show that the performance of the optimized single metal sealing has been obtained great improvement than the performance of the initial structure.(8) By the finite element method, the steady-state temperature distribution of the rotating ring and statics ring of the optimized single metal seal model has been analyzed under down-hole working condition. Meanwhile, it is researched that the temperature distribution and the temperature rise of the rotating ring and statics ring under different speeds, different ambient pressures and different stratum depths. And some improvement advices about sealing structure design, material choosing and surface technology have been proposed. Thoses provides some reference for temperature distribution studies on the single metal seal.