On the Theory of Quasi-Hydrodynamic Lubrication with Dry Powder: Application to Development of High Speed Journal Bearing for Hostile Environment

Heshmat, H. “On the Theory of Quasi-Hydrodynamic Lubrication with Dry Powder:  Application to Development of High Speed Journal Bearing for Hostile Environment,” 20th Leeds-Lyon Symposium on Dissipative Processes in Tribology, Lyon, France, 7-10 September 1993, Dowson et al. (Editors), (1994) Elsevier Science B.V., Tribology Series 27, pp. 45-64.

This paper describes a series of experiments aimed at the demonstration of the basic feasibility of developing a powder-lubricated, quasi-hydrodynamic (PLQH) journal bearing for high-temperature and hostile environments, where the use of liquid lubricants is impractical.  A PLQH bearing has demonstrated operation at speeds to 2 x 106 DN (58,000 rpm), and it may be the only bearing capable of meeting the ever-demanding tribological goals of a solid lubrication scheme for extreme environments.  The work described exceeds the current state of the art (1.5-million DN) in solid-lubricated ceramic rolling element bearing technology, and there is great promise for integrating this technology in outer space systems/mechanisms and in other hostile-environment applications.

 

Experimental evidence shows that powder lubricant films behave much as fluid films do, whereby mechanisms are provided that lift and separate bearing surfaces and cause side leakage.  these mechanisms reduce the friction coefficient and, consequently, the heat generated in the bearings, which drastically reduces wear of the tribomaterials.  Further, bearing side leakage provides a significant mechanism for heat dissipation because it carries away most of the heat generated by shear, reducing the heat to the critical bearing surfaces (see Figure 1).  Experimental parametric studies have delineated the hydrodynamic effects of power lubrication (MoS2) on bearing performance criteria, such as load, temperature, and power loss as a function of speed, including the effect of powder flow rate on bearing performance characteristics.  Comparison with a liquid lubricant provides evidence for the continuum basis for the phenomenological unification of solid particulates and liquid. 

 


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