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In article , says...
According to Ned Simmons :
In article ,
says...

[ ... ]

What alloy are bearing races made of? What's the tensile strength?

By far the most common material is AISI 52100, UTS is around 300,000
psi. I don't believe that centrifugal force alone is enough to burst the
bearing race. I figure a peripheral speed of around 1700 FPS would be
required to reach 300 ksi stress. That's close to 2x the speed of sound,
almost 20 miles/second, or about 250,000 RPM for a common 6203 (17x40mm)
bearing.

Hmm ... assuming eight balls in the race, that would get you to
33.3 KHz frequency from the balls modulating the airflow.

I have a very hard time accepting that the air at the outlet of a
blowgun supplied with shop air is traveling at close to Mach2.

And the bearing which failed on somebody's finger was 5/8" ID
(15.875mm) -- slightly smaller than the one which you postulated.

Eric said, "The ID was about 5/8 and the OD maybe 1 1/2, 1/34," which is
pretty close to a 6203, and 6203s are common as dirt - much more so than
any radial bearing with an inch dimension bore.

But
we don't know how many balls it had. No doubt, no fewer than 6, which
would get us to 25 KHz. And we don't know exactly when his hearing
dropped out at that time in his life, nor how much more speed the
bearing got in the time since it passed his hearing range.

(Those numbers may be a bit high, depending on how chunky the
bearing is, i.e., how far it deviates from a "thin cylinder.")

I suspect that lubrication failure leading to galling of the balls and
consequently jamming is the big culprit. Perhaps the race expands enough
from the centrifugal force to rattle around and hasten the failure,

That might hasten the failure of the surface of the balls, but
if they *really* failed, all of that energy stored in the spinning outer
race would be transferred to the finger on which the bearing was
mounted, perhaps twisting it off.

Not if the race fractures and the pieces fly off, which is apparently
what happened.

Hmm ... the story did not describe whether the bearing's inner
race remained on his finger -- nor what happened to all of the balls.

but
it seems unlikely to me that it's possible to get the bearing spinning
fast enough for this to be much of a factor. The strain in the
hypothetical 6203 race would be about .15% at 100 KRPM - in other words
the bearing might loosen up a thousandth or two at that speed.

I would expect the outer race to be spinning faster than the
ball cage (think of it as a planetary gear setup with the planet gears
being driven),

That assumes that there's no slip between the inner race, the balls, and
the outer race, which is not the case even at rest. If you hold the
races of an open bearing stationary and push on the ball and cage
assembly it'll slide around easily. That's the reason that a ball
bearing is not happy operating with a load that's very small compared to
its capacity. As the bearing's outer race spins faster the clearance
between the various parts will only increase.

But that last thought does point up something I neglected. The balls are
being thrown against the outer race, so are adding to the force on the
race without adding any strength. If you do the numbers, doubling the
density of the outer race to account for the balls (which I think is
conservative for a couple reasons), you still need to go supersonic,
1300FPS, to burst the race.

Here's another couple possible failure modes related to the retainer.
The retainer, typically mild steel or plastic, distorts or disintegrates
from the centrifugal force and either jams the bearing or frees the
balls to crowd together and the races separate.

so a six-ball race at ultrasonic could indeed have the
outer race spinning fast enough to fail explosively.

I don't buy it, at least not yet. A reference to a common blowgun
producing supersonic flow would be a start.

Huh, look what a google on - supersonic air flow blowgun - turned up...
http://yarchive.net/metal/ball_bearing_spinup.html

Ned Simmons