Study Of Surface Texture On Lubrication And Antifriction Mechanism Of The Rock Bit Journal Bearing

How to further improve the working performance of rock bit journal bearings(RBJB)and prolong its life span under complicated working conditions of low speed,heavy load,high temperature and high pressure is one of the urgent problems faced by oil drilling engineering.Based on the adhesive wear failure of RBJB,This research,through lubricating and antifriction analysis of bionic texture,creatively puts forward to introduce the surface texture into RBJB to prolong the service life.Non-Newtonian lubrication hydrodynamic theory model of textured rock bit journal bearings(TRBJB)was established.The simulation analysis for the effect of texture parameters and layout area on the carrying capacity of RBJB is completed.At the same time,the mathematical model and simulation results are validated by the unit experiment of TRBJB.Unit experiments of TRBJB are carried out under sealing leakage harsh conditions.The experimental research on the influence of texture parameters on tribological perfonnance of RBJB is done by the experimental bench of RBJB.The main research results are as follows:(1)On the basis of domestic and foreign study and our laboratory team,this reaearch creatively brings forward a new method that surface texture were introduced into the friction pairs of RBJB,which provides a new idea for prolonging the service life and improving the lubrication performance of RBJB under severe and complicated working conditions.(2)On the basis of some hypothesis,the equivalent viscosity power law model and Reynolds equation of non-newtonian medium lubrication,combined with built mathematical equations of ellipsoid,cylindrical,oval and triangular textures,the hydrodynamic lubrication theoretical model of TRBJB with smooth and rough surface is established.This theoretical model provides a theoretical basis for simulation analysis of the tribological performance of TRBJB.(3)The relationship between the geometric sizes,area ratio,distribution region of elliptical,ellipsoidal and triangular textures and Maximum dimensionless oil film pressure of under steady load is systematically analyzed under steady load.The theoretical analysis shows that there are optimal texture geometric size,area ratio and distribution region,which can effectively improve the carrying capacity of RBJB,when the texture depth is fixed.It provides theoretical basis for the texture parametric design and the development of experimental scheme during unit experiments of TRBJB.(4)Based on Hertz contact and fluid lubrication theory,pin-disk unit experiment scheme is established to approximately simulate the working condition of RBJB.The designed surface textures are placed in the surface of the unit disk sample of the sleeve,respectively using precision mechanical engraving,nanosecond lasers and femtosecond laser processing technique.Unit experiments obtain the influence rule of texture shape,geometric size,arrangement,grease rheology and Stribeck parameters on the tribological properties of RBJB,and verify the feasibility of improving the lubrication and antifriction of RBJB by surface texture.(5)Under the harsh condition of sealing leakage,rheological tests of RBJB grease mixed drilling fluid with different volume ratio and the experimental study of tribological properties of RBJB unit pairs with preferred texture parameters are carried out.Experimental results show that optimized texture parameters can make the friction coefficient of matching pairs decreases more than 12%and wear mass loss more than 25%.It provides effective means to improve the lubrication and antifriction performance of RBJB under sealing leakage harsh conditions.(6)Based on the geometric similarity and Sommerfeld similarity,bench tests of triboligical performance of TRBJB are developed.Laser processing technology and measurement evaluation method of journal surface with surface texture are formed.Bench tests obtain the change rules of the friction coefficient and wear mass losss of TRBJB along with texture types,area ratio and angle.It provides experimental basis for design and optimization of TRBJB under the given working conditions.In conclusion,this study provides technical support for using surface texture technology to enhance RBJB service life,which will further enhance the performance of RBJB and prolong the service life of RBJB.Finally,it will increase the comprehensive performance of RBJB and competitiveness in the international market.Therefore this paper has important significance and academic value for the design of TRBJB and the improvement of drilling efficiency,and it has a broad application prospect.