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Stroke 03-17-2008 09:36 AM

Oil and Bearings a.k.a. Hydrodynamic Bearings - FWIW
A good read for anybody interested...


Hydrodynamic Bearings

Journal bearing design is complex. It involves optimizing clearances, bearing length, minimum film lubricant, viscosity, flow rate, and inlet slots. Design equations are available, but their solution is time consuming unless done on a computer. Fortunately, these equations have been reduced to chart form, and a wide variety of design problems can be solved with various charts in the literature.

For more info see this link 03-25-2008 08:55 AM

Good link. Yes hydrodynamic bearings are quite complex. Big section of Shigley's Machine Design text devoted to it. Guaranteed question on the final of any ME machine design course.

The principle of this bearing was developed on early railroad truck axles (a whole bunch of mechanical engineering technology came from railroads). Designers were using wooden bearings on the truck axles, lubed with animal fat. The lube was filled from the top but kept leaking out the hole on top of the bearing. They tried all kinds of plugs for that hole but the plugs quickly blew out, even threaded ones. Finally did the math and determined that viscous lubricants 'wedged' themselves into the space between the axle and bearing and pressured up to whatever pressure it took to support the two parts on a couple molecules of lube. The hydrodynamic effect actually 'pumps' the lube to very high pressures and prevents metal to metal contact. Lube viscosity vs. temperature, lube temperature tolerance, bearing material pressure and temperature tolerance, surface finish, width and diameter of bearing (needs to be wide and long enough to carry the load, not so wide that friction heat destroys metals and lube), assembly methods, etc. all have to be considered for a successful design.

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