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Machine Tools
Published in David A. Stephenson, John S. Agapiou, Metal Cutting Theory and Practice, 2018
David A. Stephenson, John S. Agapiou
Hydrostatic and aerostatic bearings are used for guideways in precision machines such as grinding and hard turning machines. These bearings have no mechanical contact between elements; the load is supported by a thin film of high-pressure oil or air that flows continuously out of the bearings. Static friction is eliminated and dynamic friction is insignificant at most speeds. Hydrostatic bearings are used at moderate speeds where high load capacity and stiffness are required, while aerostatic bearings provide moderate load capacity and stiffness and are preferable at higher speeds. Hydrostatic bearings provide better vibration and shock resistance with superior damping characteristics. The dynamic stiffness is very high due to squeeze film damping. The damping is very good normal to the bearing surface but low along the direction of motion. A great deal of research and development work on analysis and development of hydrostatic and aerostatic bearings has been carried out [1,6,141–149]. Self-compensating or gap-compensating bearings, which can be used with water as a bearing fluid, have recently been developed [6]. Using water rather than oil as the sliding medium results in more stable temperatures, higher permissible speeds, and fewer fluid contamination problems. High-performance hydrostatic slides have been made entirely from alumina ceramics. The Hydroguide and HydroRail are designs using a profile similar to linear rolling element bearings (Figure 3.45) and have been used in grinding and hard turning lathes [150].
Polygonal Scanners: Components, Performance, and Design
Published in Gerald F. Marshall, Glenn E. Stutz, Handbook of Optical and Laser Scanning, 2018
Aerostatic air bearings provide the ultimate in performance at a high cost. An aerostatic bearing uses pressurized air and closely spaced axial and radial bearing surfaces to float the rotor. When pressurized, the bearing has no contacting parts, resulting in extremely long life. These bearings are very stiff and have wobble errors less than 1 arc s. They are capable of supporting heavy loads and do not suffer from wear at startup and shutdown. They do require external components to supply the pressure to the bearing. This increases system complexity as well as cost.
Performance comparison between aerostatic bearings with orifice and porous restrictors based on parameter optimization
Published in Australian Journal of Mechanical Engineering, 2021
Ruzhong Yan, Liaoyuan Wang, Shengze Wang
The aerostatic bearing with its characteristics of cleanness, low friction and low heat has become an important part of most ultra-precision machinery (An 2010; Long and Bao 2010; Nishio, Somaya, and Yoshimoto 2011). The performance of the aerostatic bearing mainly depends on the structure parameters of its restrictor. Orifice and porous restrictors are the two most common types of throttling for aerostatic bearings, which have been a hot topic for scholars. Now, orifice, gas chamber, gas film for the orifice restrictor (Chen, Chiu, and Cheng 2010c; Gao, Cheng, and Chen et al. 2015; Ma, Cui, and Liu et al. 2016) and the permeability, the gas supply area of the porous restrictor (Rao, Rani, Nagarajan et al. 2013; Szwarcman and Gorez 1978; Yu, Li, and Zhao et al. 2015) have been proved to be the key parameters affecting the performance of aerostatic bearings.
Running Performance of a Squeeze Film Air Bearing with Flexure Pivot Tilting Pad
Published in Tribology Transactions, 2020
Minghui Shi, Xuejiang Liu, Kai Feng, Kai Zhang, Ming Huang
Recent trends in manufacturing fields are creating increasing demand for high-speed, high-precision, and intelligent machine tools to ensure the machining quality of workpieces (1–3). Bearings are an important component of machine tools. Stiffness and rotational accuracy directly affect the performance of the machining process. Many types of bearings have been used in rotor–bearing systems, such as magnetic, rolling, aerostatic/aerodynamic, and hydrostatic/hydrodynamic bearings (4–6). However, these bearings all have limitations. Magnetic bearings must work under strong magnetic flux, which may interfere with electrical equipment. Rolling bearings are a kind of standardized bearing that provide high stiffness and large load-carrying capacity (LCC) (7). However, rolling bearings produce large vibration and noise. Moreover, high contact stress is a serious threat to the oil film (8–10). Aerostatic and hydrostatic bearings require a clean lubricant supply system, and their design is relatively complex, thereby considerably increasing their cost of use (11–14). Aerodynamic and hydrodynamic bearings have a high wear rate during start-up and shutdown, respectively, which seriously affects their life. Therefore, finding a new method for realizing noncontact rotor–bearing systems is essential to overcome some limitations of traditional bearings.