Meso Scale Air Journal Bearings

Meso scale air journal bearings are widely use in miniaturized rotary systems such as hard disk drives, laser scanners, micro motors, miniature precision machines, dentist drills, meso scale gas turbines, etc. In these systems the bearings are self-acting and thus no auxiliaries are needed. The generation of hydrodynamic pressure is taking place through the relative motion between journal and bearing.

An increase in demand of lighter, compact, and eco-friendly miniaturized rotary system urges more research on meso scale air journal bearings. Geometrical features of these bearings lie between macro scale and micro scale bearings, and particularly suitable in miniaturized systems due to their distinct advantages over the rolling element or oil-lubricated bearings.

The main advantages of meso scale journal bearings are that the lubricant (air) is freely available, environmentally friendly, poses no leakage issue, and thus offers maintenance-free operation. Additionally, it is simple in design, can operate at higher speed with lesser heat generation, low noise, and minimal energy loss.

The low viscosity of air generates weak hydrodynamic pressure in the bearing which affects its load carrying capacity. Although upon increasing speed the load capacity of the bearing can be increased, shear loss and instability issues dominate. Furthermore, instability of the bearing affects frictional properties which significantly degrade the system performance. It is also noted that the appearance of friction and wear under frequent start-stop operation causes lower start-up rotational torque and smaller effective output which ultimately reduces the life of the bearing. These tribological issues limit the applications of meso scale air journal bearing and its further advancement.

Figure 2. (a)Plane air journal bearing; (b) textured air journal bearing [3].

Surface texture has potential to address these issues of meso scale air journal bearings [1-2]. Textured surface profile design helps to improve the tribological characteristics and increases the life span of the surfaces in relative motion. Numerical modelling tools are used to determine the optimum position, orientation shape and depth of the dimples maximizing the load carrying capacity of the fluid film under the operating conditions of the application [3-6].

Recent advancement of meso/micro machining technology (e.g. laser surface texturing) enabled to produce accurate surface textures which, with the right knowledge, can improve the performance of this kind of journal bearings while prolonging their lifespan.

Nilesh D. Hingawe; Skylab P. Bhore

Rotor Dynamics and Vibration Diagnostics Lab

Department of Mechanical Engineering

Motilal Nehru National Institute of Technology Allahabad

References:

1. Bhore, S. P. and Darpe, A. K. 2014. Rotordynamics of micro and mesoscopic turbomachinery – a review. Journal of Vibration Engineering & Technologies 2(1):1–9.
2. Kim, D. and Bryant, M. D. 2004. Hydrodynamic performance of meso scale gas journal bearings. ASME International Mechanical Engineering Congress and Exposition 47136:1089–1098.
3. Hingawe N. D. and Bhore S. P., (2020) Tribological performance of a surface textured meso scale air bearing, Industrial Lubrication and Tribology. 72 (5), 599-609
4. Hingawe N. D. and Bhore S. P. (2021), “Design and optimization of texture geometrical parameters for meso scale air bearing”, Surface Topography: Metrology and Properties. https://doi.org/10.1088/2051-672X/ac0f35
5. Hingawe N. D. and Bhore S. P. (2021), “Improving tribological performance of meso scale air journal bearing using surface texturing: an approach of green tribology”, Green Tribology: Emerging Technologies and Applications. CRC Press (Taylor & Francis Group)
6. Hingawe N. D. and Bhore S. P. (2019), “Effect of partial texture on the hydrodynamic performance of meso scale gas bearings for meso scale turbo-machines”, Proceedings of the ASME 2019 Gas Turbine India, ASME GT-INDIA2019, IIT Madras, India, 5-6 December 2019