Study On Lubrication Model And Performance Regulation Of Tilt Pad Dynamic Static Bearing

The accuracy,performance,life and reliability of machine tool are greatly influenced by the performance of bearings because bearings are indispensable components of spindle system.The hybrid bearing with tilting-pad is proposed to apply in the spindle system of precision milling machine based on the application background of high-end CNC machine tools in this paper.The static and dynamic performance and regulation law of the tilting-pad hybrid bearing are studied according to the temperature rise and stiffness of the bearing.The purpose of this paper is to break the blockade of the key technology of the precision machine tool spindle system abroad,which is of great significance to realize the localization of high-end CNC milling machines.The main research work of this paper are as follows:(1)The new scheme of tilting pad hybrid bearing is proposed by decoupling the hydrodynamic and hydrostatic performance.The hydrodynamic and hydrostatic performance of bearing can be individually control by bearing decoupling.The lubrication model of the bearing is established according to the decoupling characteristics of the bearing structure.The calculation method of the bearing performance is proposed based on the synthesis of the equilibrium property.The ratio of pad wrap angle of tilting pad hybrid bearing is optimized.The comprehensive performance of bearing is the best when the ratio of static oil pad wrap angle to tilting pad wrap angle is 1:1.The loading performance at low speed and the dynamic characteristics at high speed are compared and analyzed for hydrostatic bearing,hydrodynamic bearing and tilting pad hybrid bearing.The comprehensive performance of tilting pad hybrid bearing is the best considering the temperature rise and stiffness.(2)The performance of tilting pad hybrid bearing under different pad numbers and loading directions is analyzed based on the orifice throttling.The optimal pad number and reasonable loading direction are determined.The static and dynamic characteristics of tilting pad hybrid bearing with the capillary throttling and orifice throttling under different working conditions are analyzed by taking the bearing structure of four tilting pads with four oil pads as an example.The throttling parameters of the capillary throttling and orifice throttling are optimized.The structure scheme of performance control for the static pressure part is provided.(3)The circumferential position and radial position of pivot can be characterized by the pivot coefficient and preload coefficient of bearing.The influence of pivot position on the static and dynamic characteristics of 3 watts with 3-pad and 4 watts with 4-pad hybrid bearings under different working conditions is compared and analyzed.The bearing stiffness increases first and then decreases with the increase of the pivot coefficient.The minimum film thickness decreases monotonically.The bearing stiffness increases monotonically and the minimum film thickness decreases monotonically with the increase of preload coefficient.Overall,the influence of preload coefficient is more significant.The influence law is almost the superposition of the influence law of single parameter when the pivot coefficient and preload coefficient change at the same time.The adjustable range of the pivot position of the tilting pad hybrid bearing under different working conditions can be obtained considering the stiffness requirements and temperature rise constraints.The control structure scheme of the tilting pad hybrid bearing is preliminarily provided.