Research On Working Mechanism Of Rock Bit Floating Ring Journal Bearings

How to improve the working performance of rock bit journal bearings (RBJB) and prolong its life span under high working speed is one of the urgent problems faced by oil drilling engineering. This research, based on the investigation of the primary failure form and causes of RBJB, firstly establishes the theoretical basis for prolonging the life span of RBJB. Using rheology, tribology and dynamics as the ground theories and combining theoretical study with experiments, the present research also investigates the working mechanism of floating-ring journal bearings (FRJB). Besides, a Reynolds equation specially for RBJB in grease lubrication is developed on the basis of some hypothesis. This research is the first attempt to apply the lubrication theory for rough surface into the study of RBJB and thereby succeeds in developing a numerical model of roughness surface thermal hydrodynamic analysis (RSTHA) for rock bit floating-ring journal bearings (RBFRJB). At the same time, simulation software for the working mechanism of RBFRJB is developed and the software, together with the numerical model, is validated by experiment. It is hoped that the present research will provide some fresh insights and methods for the research of the working mechanism of high-speed RBJB system, the improvement of the structure of existing RBJB and the further elevation of the comprehensive performance of the rock bit produced by our country. The major fruits of the present research are listed as follows:(1) RBJB failure analysis is carried out, the factors causing it worked out and the theoretical basis for prolonging RBJB life span established.(2) High temperature rheological analysis for rock-bit grease is studied systematically with the aid of experiment. Results indicate that the roller-bit grease is a typical BinHam liquid, and it can work under the condition of high temperature (>100C) and high cut velocity (>500s"').(3) The performance characteristics and design data of FRJB under steady load are looked into theoretically. Results suggest that the ring dimensions are a dominant factor in deciding the final bearing behaviour and the oil film thickness between the ring and the housing is much thinner than that between the journal and the ring.(4) A Reynolds equation specially for RBJB in grease lubrication is developed on the basis of some hypothesis; the lubrication theory for rough surface is applied into the study of RBJB and thereby the numerical model of dynamical load RSTHA for RBFRJB is set up. On the basis of a generalized average flow model Reynolds equation as well as energy equation, the lubrication numerical model of roughness surface floating ring journal bearing under dynamic load is established and the solution discussed.(5) Simulation Software is developed and the simulation analysis of RSTHA for RBFRJB is conducted. The simulation results indicate that the best clearance ratio to the 8 1/2" RBFRJB is from 2.0 to 3.0. When the clearance ratio is smaller than 1, the floating ring runs fast under a light load but runs slowly or even stops running under a great load (>15kN).(6) Experiment on RBFRJB is done and the torsion, temperature and the speed of the floating ring under different bit loads and rotating speed are measured. It is found that the results are basically in accordance with the simulative results.This research, as is expected, provides a new theory and a new method for RBJB study and design. With the results of this research, the RBJB life span can hopefully be lengthened, the drilling cost lowered, and the competitiveness of the roller bit of our country enhanced in the international market. In this sense, the present research is of much value in both theoretical and practical regards.