| Hydrostatic spindles with high accuracy,loading capacity and stability are often used as important components of high-speed precision machine tools,and the theory of hydrostatic bearings is the basis for designing and interpreting their technical performance indexes.Although the existing bearing theory based on the Newtonian shear model of the liquid film is more mature and a large number of scholars have used the theory for design,the group found in the long-term research spindle and follow its practical application,the existing theoretical calculation results and experimental results there are significant differences,the higher the speed,the greater the difference.This contradictory phenomenon indicates that the shear action and surface characteristics of the spindle lead to profound changes in the flow characteristics of the bearing film,and the existing theory is difficult to meet the needs of accurate quantitative design of the spindle.and it is necessary to re-examine the key scientific issues of the bearing theory for the actual working conditions.The main studies in this paper are as follows:(1)A new liquid-film shear model at the liquid-solid interface was reconstructed,and the bearing characteristics were derived based on this model,laying the model foundation for further development of a new theory that can accurately carry out bearing design.Considering the effects of shear action of the main shaft and surface characteristics on the liquid film shear characteristics,the liquid film shear model was reconstructed by adding the characteristic parameters reflecting surface slip and modified flow velocity in the pressure flow velocity distribution model,and adding the characteristic parameters reflecting the effects of shear velocity in the shear flow velocity distribution model,and the flow,pressure,load carrying capacity and stiffness characteristics of the bearing were derived based on this model.(2)A hydrostatic spindle test rig was developed,the experimental study and the solution of the new liquid film shear model corresponding to different surface characteristics were carried out,and the relative errors between the theoretical and measured values of the bearing flow were analyzed.The bearing flow rate and other parameters were tested under different clearance,surface roughness,speed and oil supply pressure,etc.The flow rate characteristics and test data were fitted to solve the new liquid film shear model under different surface characteristics,and the error between theoretical and measured values of bearing flow rate was analyzed and found that: The flow values calculated based on the existing liquid film shear model were significantly different from the measured values,up to 40% to 100%,and also validated the accuracy and reliability of the reconstructed new liquid film shear model.(3)According to the error analysis between the theoretical calculated and actual tested values of bearing flow rate under different surface characteristics,the influence law of surface characteristics on the liquid film shear characteristics is revealed: the liquid film shear characteristics are mainly affected by the oil film gap,and the relationship with the surface roughness of the journal is very small.(4)The inverse of the new liquid film shear model was completed based on the relationship between the model characteristic parameters and the gap,and a new model of the pressure flow rate of the liquid hydrostatic bearing,which is more consistent with the experimental measurement results,was obtained to improve the accuracy of the theoretical design,and the shear flow model of the liquid hydrostatic bearing was derived based on the new model.The research work in this paper provided some theoretical guidance for the reconstruction of the shear model of the liquid-solid interface,the analysis of the bearing characteristics and the experimental testing of the liquid film shear characteristics,and also provided a reference for the research on the speed limit of high-speed precision spindle. |
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