On Tuesday, December 6, 2016 at 8:07:33 AM UTC-5, Christopher Tidy wrote:
Hi folks,

I need an example for an article. Can anyone think of a modern product which uses plain bearings in a demanding application? I'm not talking about the extremes (like dental drills and steam turbines), but more common applications such as supporting lathe spindles and engine crankshafts. It used to be common to have plain bearings in these machines, and some were incredibly durable, but I haven't seen any in a new product for a long time. Are there any examples, or have they been entirely displaced by standardised ball and roller bearings?

Thanks!

Chris

The large majority of IC engines use plain bearings, and always have. Honda's experience with motorcycle engines in the '60s is instructive. They used roller crankshaft bearings until their development work actually showed less friction was developed with the latest plain bearings and lubricants. IIRC, the first engine for which they switched to plain bearings was the 4-cylinder 750, in the late '60s.

Be careful with a couple of points about plain bearings. "Hydrodynamic" bearings are those in which the rotating shaft drags lubricant around with it to maintain a film. The pressure of the oil supply in this case, as in automobile engines, has nothing to do with the film. It's just a supply for the oil to get *into* the bearings.

"Hydrostatic" bearings are those in which oil is supplied at much higher pressure and the film is maintained by that external pressure, even if the shaft is not rotating at the time. Thus the "static" part.

High-speed milling and grinding spindles in some of the more exotic machine tools look like plain bearings, but the film in their case is air -- pneumostatic. There also were pneumodynamic bearings used in toolpost grinders before 1925 or so. They ran hardened-and-polished steel spindles, running in hardened-and-polished steel bushings, at up to 10,000 - 12,000 rpm. There was no external air supply. They just dragged air around dynamically, like a car engine does with oil, and the air created a lubricating film when the spindle got up to speed.

You're dealing with a potentially complex subject. Good luck!

--
Ed Huntress