Design And Simulation Of High Speed Thrust Bearing For Small Size Turbodrill

With the increasing demand for oil and gas resources,downhole drilling needs more miniaturized and efficient high-speed turbodrill.The thrust bearing of turbodrill,as a component bearing the axial load of turbodrill,has always been the weak link in the operation of turbodrill.The performance of thrust bearing is directly related to the overall performance and working life of turbodrill.Based on the basic structure and performance parameters of turbodrill with small size and high speed,by comparing the performance,advantages and disadvantages of rolling bearing and sliding bearing suitable for turbodrill,this paper summarizes the law of design and development of four-fulcrum contact ball bearing and PDC(Synthetic Polycrystalline Diamond)sliding bearing,which provides important reference and guidance for the design and development of thrust bearing under non-oil lubrication,high speed,heavy load and other working conditions.The pitting life calculation model of traditional four-fulcrum contact ball bearing is modified,the life calculation model of abrasive wear is adopted,and the life experiments of four-fulcrum contact ball bearing samples are carried out.According to the experimental data,the wear theoretical life calculation model of four-fulcrum contact ball bearing is modified,and a new abrasive wear life calculation model of four-fulcrum contact ball bearing is obtained.Using three-dimensional finite element software,the three-dimensional models of four-fulcrum contact ball bearing group and PDC sliding bearing group are established,and the downhole working conditions are simulated,and the axial load is applied.It is concluded that the axial load is not the same between the four-fulcrum contact ball bearing group and each row of PDC sliding bearing group.The first to bear the total axial load of the first row of bearings,the load accounted for the highest proportion of the total axial load.The difference between the actual load and the average load within the bearing group,the four fulcrum contact ball bearing group is about 10% to 20% of the total load,and the PDC sliding bearing group is about 5% to 15% of the total load.The bearing capacity of the bearing group is proportional to the series of the bearing group,but the optimization degree of the bearing group decreases with the increase of the number of bearing groups.If the number exceeds a certain number,the optimization effect can be ignored.The optimal series of the four fulcrum contact ball bearing group is 7 rows,and the PDC bearing group is 11 rows.The Palmgren calorific value calculation model is used to calculate the internal calorific value of the four-fulcrum contact ball bearing,and the Harris bearing convective heat transfer model is adopted to calculate the internal convective heat transfer coefficient.The steady-state thermal analysis of the geometric model of four-fulcrum contact ball bearing is carried out,and the change of internal clearance of the bearing is recorded.According to theoretical analysis and numerical simulation,the effect of temperature on clearance is summarized as an empirical formula,which provides some reference and guidance for the design of clearance of four-fulcrum contact ball bearing.The failure form of PDC sliding bearing is analyzed.PDC sliding bearing can be divided into two forms: mechanical wear and thermal failure.usually,the mechanical wear of PDC sliding bearing is not obvious,and the common failure form is thermal failure.therefore,the thermo-mechanical coupling simulation calculation of PDC sliding bearing is carried out by finite element software,taking the PDC composite sheet reaching 800℃(phase transformation of PDC material)as the limit condition,by changing the speed of PDC sliding bearing.The relationship between linear speed and contact pressure of PDC sliding bearing under limit condition is obtained,and the safe working condition of PDC sliding bearing is clarified,which provides reference and basis for the design and production of PDC sliding bearing.