摘要
双自转研磨盘球体研磨机是用于批量加工高精度球的重要装备。双转子转盘的轴承作为旋转支承件,对球体研磨机的加工精度具有重要影响。现有的双自转研磨盘球体研磨机都采用滚动轴承,具有摩擦磨损大、精度寿命有限、寿命分布离散、减振性差等固有缺点。液体静压轴承由于具有精度高、寿命长、减振性好等优异性能,是替代滚动轴承的理想方案,但应用于双自转球体研磨机还存在整体结构布局困难、双层供油难以实现、立式结构油液密封困难、双油膜轴承流场性能和承载特性优化困难等技术难题,迫切须要进行针对性的系统深入地研究。
本文根据球体研磨机双自转研磨盘独特结构,开发了双油膜静压转子系统。该系统为外主轴采用空心结构,内主轴位于外主轴内;外轴承紧固于壳体内,内轴承嵌于外主轴内壁。针对内轴承随外主轴同步旋转,供油难以形成的难题,提出了在外主轴外表面开设环形油槽以实现内轴承四个油腔同时供油的新方法。针对球磨机采用双转子立式结构,提出利用高压气流的屏障作用有效克服回油槽的油向下渗漏的气密封方式,弥补了传统机械密封方式难以实现有效密封的弱点。
建立了利用CFD方法的小孔节流无周向回油槽静压径向轴承计算模型和小孔节流环形油腔静压止推轴承油膜流场数值计算模型;探讨了符合无周向回油槽静压径向轴承和环形腔静压止推轴承油膜几何尺度特征的离散网格划分与边界条件及计算参数选择的方法,采用非结构网格与分块划法及网格尺寸函数确保了径向轴承和止推轴承三维油膜网格的协调性,以实现计算效率与计算精度的综合最优。利用所建立的模型和CFD计算方法系统研究了径向轴承供油压力、偏心率和进油孔径对流场分布的影响规律;研究了轴承间隙、节流孔径和供油压力对轴承承载能力、刚度和流量的影响规律;揭示了供油压力和节流孔径等对低速重载环形腔静压止推轴承油膜流场形态与静态特性的影响规律。
对现有文献工程计算方法和本课题提出的双油膜静压转子动态特性数值研究方法进行了比较研究。研究表明,根据本课题数值模拟方法计算的结果能够反映双油膜静压转子的工程特征,可以作为双油膜静压转子系统动态性能分析和优化的基本方法。
本文提出的研究方法和研究的相关结果为球体研磨机双油膜静压转子系统设计和动态性能分析提供了重要参考。
The dual-plate lapping machine is the important equipment for mass producing of high precision balls. The bearing of dual rotors plate act as whirling support member, which has important influence on the machining precision of the dual-plate lapping machine. The existing dual-plate lapping machine uses rolling bearing, so it has following inherent shortcomings, the big friction and wear, the limited precision life, discrete life distribution, and poor vibration damping. The hydrostatic bearing has the high precision, long life, excellent performance and good vibration damping, so it is the ideal program for replacing rolling bearings. But the overall structure and layout of the dual-plate lapping machine is very difficult, the double oil supply is difficult to achieve, the oil seal is difficult, and the optimization of the double film performance and load characteristics of the flow field’s bearing are difficult and existing other technical problems, so it is urgent to further study.
According to the unique structure of double rotation grinding plate in the ball grinding machine, developed a double oil film external static pressure bearing rotor system. Which the outer spindle is a hollow structure, and the inner spindle is located in the outer spindle; the outer bearing is located in the box, and the inner bearing is located in the outer spindle. Because of the problem of oil supply within the spindle bearing in synchronization, the new method is applied which opening oil groove in outer spindle face for the inner bearing. According to the ball grinding machine with double rotor vertical structure, the high pressure gas is used for sealing oil leakage, which making up for the traditional mechanical seal to realize the effective way of seal weakness.
The hydrodynamic lubrication model of hydrostatic bearings based on finite volume method and computational fluid dynamics is established. And the discrete method, discrete scheme, and solution of algebraic equations of basic equations in fluid dynamics are discussed, aiming at the classical hydrodynamic lubrication problems, the comparative study on the three-dimensional numerical simulation based on CFD and one-dimensional and two-dimensional theoretical calculation based on Reynolds assumptions is carried out. In order to ensure the bearing performance meet the design requirements, the performance of dual-oil-film bearings is analyzed. The radial bearing system model and the thrust bearing system model are built. The built models are used to study the flow field distribution and the static characteristics of bearings.
Comparing the existing literature of engineering calculation method and the dynamic characteristics numerical research of a Dual-Oil-Film static pressure Rotor that were proposed by this topic. Research shows that, according to the result of numerical simulation method of this topic ,it can reflect the engineering features of Dual-Oil-Film static pressure Rotor, also can be used as a basic method of dynamic characteristics analysis and optimizationa of Dual-Oil-Film static pressure Rotor system。
The work offers important reference and effective approaches for the structure design and dynamic performance of hydrostatic spindle for the rotated dual-plates lapping machine.
引文
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