Integrated Physical Field Research Of Heavy Hydrostatic Thrust Bearing

The heavy hydrostatic thrust bearing is the key component of the heavy numerical control equipment; the machining quality and the operating efficiency are directly influenced by its performance. The gaps between friction pairs are uneven because of the low machining precision of the large-scale components in domestic. Under working situations of high speed and heavy load, the bearing body and the temperature of the lubricant film rise alonge with the speed of the worktable increasing, that causes the load bearing lubricant film to thin, as a result, the lubrication is failed due to the deformation of the hydrostatic bearing, then, the actual structure of the oil pad is deviated from theoretical designing model, the spindle speed is also limited. Consequently, the studying on the flow field, the pressure field, the temperature field and the deformation field of heavy hydrostatic bearing is the key to solveing all those problems.This thesis based on the summary of studying on the structure optimization, performance calculation, rigidity property, damping property and experimental apparatus of the hydrostatic thrust bearing, takes the hydrostatic thrust bearing with the multi-oil pad circular guideway as the research object, to carry on the theory research to the integrated physical fields of the heavy hydrostatic thrust bearing with variable viscosity, The followings are mainly included:First of all, the thesis based on the lubrication mechanism research of two parallel plates and circular oil pad obtains the simplified model of the hydrostatic thrust bearing, then, the viscosity-temperature equation of the gap film is set up, and the viscosity-temperature curve is fitted by B-Spline curve. Further, the mathematical model of the single oil pad is established, that includs the flow equation, the carrying equation, the oil film rigidity equation, the friction equation, the friction power equation and the temperature rise equation.Secondly, aiming at the actual physical model (set up by data of factory offered), the pressure field, the flow field and the temperature field of heavy hydrostatic bearing based on the FVM(finite volume method) are respectively carried on the analysis of three-dimensional characteristics in constant and variable viscosity condition, then the Influence Law of the viscosity to the hydrostatic thrust bearing is found.Thirdly, the pressure field, the dynamic pressure and the temperature field of lubricant film in different rotating velocity and cavity depth are respectively simulated under considering the variable viscosity condition. Influence laws of rotating velocity and cavity depth to the pressure field, the dynamic pressure and the temperature field of oil film are also found. At the same time, temperature distributions of oil film in different film thickness are simulated, and influence of film thickness on the temperature field also is formulated.Furthermore, the finite element models of rotating worktable and multiple oil pad circular guideway of heavy hydrostatic thrust bearing are established. Numerical simulation results of oil film temperature field are treated as a body load applied to the worktable to calculate thermal deformation. Considering the weight of rotating worktable and load on it, numerical simulation results of lubricant film pressure field are coupled to upper and lower ring surface and base contacting with lubricant film to calculate force deformation. Finally thermal deformation field and force deformation field are superposed to obtain the total deformation of hydrostatic thrust bearing.At last, in order to validate the mathematical model and the numerical simulation results, practical measures of lubricant film pressure and thickness of hydrostatic thrust bearing are performed on the double column vertical lathe—DVT1000×50/150Q-NC in different working conditions. The results demonstrate that the theoretical results of lubricant film pressure are consistent with the measurement results and numerical simulation results. It shows that the results of numerical simulation of hydrostatic thrust bearing pressure field and the established mathematical theory model are creditable; and the upper and lower ring surface deformation of worktable and base contacting with oil film through lubricant film thickness tests is obtained, the shape of lubricant film deformation from inside to outside in radial is a bugle, that accords with deformation field calculated in the finite element method. With the research on integrated physical field of heavy hydrostatic thrust bearing, this thesis reveals the flow law of gap fluid of hydrostatic bearing with multiple oil pad and the failure mechanism of hydrostatic thrust bearing. It provides theoretical basis for design, simulation analysis and performance research of hydrostatic thrust bearing in practical projects.