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Thursday, May 23, 2019

Foil Bearings

Turbomax Air Bearing Animation

Foil Bearings are curious devices. Most bearings that are employed in ordinary devices like cars, appliances and power tools use some combination of oil and rollers to keep things running smoothly. Not so Foil bearings. The rely on nothing but ordinary air. There are some air bearings that require a supply of pressurized air, but they are another animal entirely.

Foil bearings are used in jet engines and possibly in some turbochargers. Why they work is a mystery. The rotating parts of a large jet engine might weigh as much as a ton, yet the few square inches of bearing surface are enough to support them. In the animation above, the foil ring expands as the shaft speed increases, which should indicate that the air pressure has risen above the ambient. How does that happen? Is air somehow attracted to fast moving surfaces, kind of like girls are attracted to guys with fast cars?

WPC Surface Treatment Demo - Air Bearing Effect

Then we have this video about WPC Surface Treatment. They have a metal rod and a bushing that have been subjected to the WPC treatment and while they are not touching air can still not escape through the gap. Very weird. Dan Gelbart got me started on this.

The WPC treatment is somewhat like sandblasting, but the particles are much smaller than sand. Near as I can tell it bashes all the high points down so the surface is much smoother, not that you would be able to tell by touching it. At a submicron level, I imagine the difference is something like this:

Precision ground surface versus standard
On the other hand, a highly polished surface that has been subjected to the WPC treatment is no longer mirror-like. Probably has something to do with the wavelength of light the size of the 'dimples'.

WPC Metal Surface Treatment Demo #2 of 2

1 comment:

Robert the Biker said...

It's due to things like this, that we can have actual scale gas turbines for model aircraft.