Scan DeCamillo, manager of research and development at Kingsbury Inc., is responsible for design, analysis and development of fluid film bearings for industrial and military applications. DeCamillo received his B.S. in mechanical engineering from Drexel University in 1975. He may be reached at firstname.lastname@example.org. For more information, visit www.kingsbury.com
The key considerations in the design and operation of hydrodynamic bearings are film thickness and bearing temperature. The film thickness in industrial hydrodynamic bearing applications is on the order of a thousandth of an inch and governs the manufacturing requirements of the shaft, collar and bearing surfaces. A high degree of precision is required of the components to ensure successful operation and life.
The criteria for load capacity in low speed applications is the minimum oil film thickness, which decreases with increasing load. In practice, load capacity is set to achieve an operating film thickness that is larger than the filter size so that the small particles that pass through the filter do not score and damage the bearing surface.
Hydrodynamic films become thicker at higher surface speeds, which would allow higher loads, but friction also increases and temperature becomes the limiting factor. The mechanical and thermal integrity of the bearing materials and the thermal limitations of the lubricant determine the load capacity in high speed applications.
In critical applications, the bearings are instrumented with temperature detectors to monitor the health and integrity of the bearing.
Vibration characteristics are another key consideration in design and application of the journal bearings.
The stiffness and damping properties of the journal bearings influence the critical speeds and vibration levels of the rotor.
The journal bearing type, geometry, clearances and additional factors are design parameters evaluated to ensure that the dynamic response of the rotor satisfies appropriate specifications.