Thermal Oil Carryover Analysis And Dynamic Performance Study Of Large-scale Hydrostatic Bearings

Hydrostatic bearing is a kind of externally-pressurized sliding bearing,which uses fluid static pressure to support itself.The bearing whose cutting diameter that beyond 5 meters is generally called large-scale hydrostatic bearing in project.Large-scale hydrostatic bearing is the key component part in high-duty numerical control equipment,which has some problems as below when running:Stress,heat and running time easily cause the oil film to become thin,which directly affects the manufacturing accuracy and operational reliability of the whole machine.The large constructional dimension of the hydrostatic bearing that this thesis involves leads to uneven heat,besides the linear velocity is high when it is running,which causes the temperature of oil film to increases quickly.So the problem of hot oil carrying easily happens.The dynamic performance of hydrostatic bearing is changing as the oil film thickness changes after it runs for a certain time from initial state.It is hard to forecast its dynamic performance by conventional theoretical calculation formula because the error is large comparing with engineering practice.For that reason,after comprehensively investigating and surveying the research results of hydrostatic bearing,this thesis takes the large-scale circular hydrostatic bearing with multiple oil pads that Qiqihar Heavy CNC Equipment Co.,Ltd uses as a research object.This thesis does the transient study and experimental analysis about its bearing capacity,lubrication and calorification,elaborates its mechanism of calorification and discusses how to confirm its oil film local zero flow state parameters,all of which are to get greater rotational velocity and running accuracy and to improve its operating reliability.Aim at the existing problems when the hydrostatic bearing is dynamically running;the thesis establishes the transient mathematical model considering multiple factors about the oil film of large-scale constant current hydrostatic bearing.First it establishes the transient oil film thickness equations of lubricating oil,and on this basis,establishes the transient mathematical model of load-carrying performance,lubricating performance,heat evolution about large-scale hydrostatic bearing.This part elaborates its mechanism of calorification,raises the concept of hot oil carrying divisor,and finally derives temperature rise governing equation that considers the effort of hot oil carrying.This thesis adopts finite volume method to make numerical computation on oil film temperature field of hydrostatic bearing with multiple oil pads,and reveals the influencing rule of loading,rotational velocity on temperature distribution and temperature rise.From the angle of interstitial oil film flow principle,the thesis concretely derives the theoretical expression between revolution speed and load bearing in oil film local zero flow condition.Meanwhile,through numerical simulation methods,it monitors the flow amount of sectional plane in fluid region that need to study primarily by changing revolution speed,load and so on,obtains the relation curve between flow value and revolution speed and load,and then verifies verify the correctness of theoretical expression.This paper puts forward a new method to analyze the dynamic performance,which uses multilayer dynamic mesh technology and multiple physical fields coupling to solve it.This method obtains the lubrication performance of oil film at different revolution speeds and load bearing and obtains the transient data of load-carrying performance by exploring the change of lubrication parameters when the oil film thickness is changing,and realizes to effectively forecast the dynamic performance of large-scale hydrostatic bearing.This stage experiments with different working conditions of large-scale hydrostatic bearing to provide corresponding boundary conditions for the numerical simulation and verify the validity of the theoretical research.Through the systematic research on the analysis of hot oil carrying and dynamic performance about large-scale hydrostatic bearing,this thesis has consummated and supplemented computational method and design theory of large-scale hydrostatic bearing,which will have significant scientific value to design and application of hydrostatic bearing.The textual theories and methods can be extended to research a series of large-scale circular hydrostatic bearings with multiple oil pads,which will have practical effects on prevent the hydrostatic bearing from lubricating failure and on improve its operating efficiency.And this research will also provide theoretical basis for designing large-scale hydrostatic bearing or structure of similar products,and provide prediction data for reliable operation of the large-scale hydrostatic bearing system.