Thermal Characteristics Analysis Of High-Speed Motorized Spindle With Water-Lubricated Spiral-Grooved Hydrodynamic Bearings

Motorized spindle with water-lubricated bearings has technology advantages of high rotation accuracy,long serving life,low heat generation,and low temperature rise.However,an expensive high-pressure water supply system is essential for water-lubricated hydrostatic bearings;as a consequence,the high cost seriously restricts the engineering application of motorized spindle with hydrostatic bearings in machine tool industry.To overcome this obstacle,a novel motorized spindle supported by water-lubricated hydrodynamic spiral-grooved bearings has been proposed.Nevertheless,this new kind of motorized spindle contains multiple heat sources and the process of heat generation,heat transfer,and heat dissipation is complicated;furthermore,the effects of pressure flow and shear flow on heat generation of water-lubricated hydrodynamic journal and thrust bearings are significant which cannot be ignored.Therefore,it is of great importance to investigate this new motorized spindle under high rotation speed.The main concepts are as follows:Firstly,thermal model of the proposed motorized spindle has been developed.The structural features of the motorized spindle system has been analyzed;based on heat transfer theory,the process of heat generation,heat transfer,and heat dissipation has been studied and the power flow model has been established;3D geometry model of the proposed motorized spindle has been established using Solidworks;thermal model of the motorized spindle has been developed by the aid of finite element method.Secondly,internal heat generation and boundary condition have been studied.Based on fluid lubrication theory,formulas that describe heat generation of water-lubricated hydrodynamic journal bearings and thrust bearing have been established and then solved using finite difference method to obtain heat generation,leakage flow rate,and temperature rise.Then,based on heat transfer theory,thermal boundary condition has been studied.Thirdly,thermal characteristics analysis has been performed.Steady-state temperature distribution and deformation distribution have been obtained using FEA software(ANSYS Workbench18.1).Effects of heat sources on thermal characteristics have been studied.Based on the results,the main conclusions can be drawn:(1)Temperature rises of hydrodynamic journal bearings and thrust bearing are in a low level;the proposed motorized spindle with hydrodynamic bearings has advantages of simple structure and good thermal performance,and is supposed to be applied in high-precision machine tool industry.(2)The established thermal model for the motorized spindle is feasible and convenient to obtain temperature distribution and deformation distribution,which provides an effective method for thermal characteristics analysis of such kind of motorized spindle.(3)For the proposed spindle,the temperature rises of hydrodynamic journal and thrust bearings are obviously lower than temperature rise of motor rotor;as a consequence,motor plays an importance role in thermal expansion of the proposed motorized spindle;several measures for improve the thermal behavior of the proposed spindle are proposed.