"Eric R Snow" wrote in message
...
On Tue, 11 Apr 2006 23:24:21 -0500, Joseph Gwinn
wrote:

In article ,
Eric R Snow wrote:

On Tue, 11 Apr 2006 11:21:34 -0700, "Ken Davey"
wrote:


O.K. As long as you don't spin the bearing with the compressed
air. *That* can be disastrous.

How so?

It can spin up to a fast enough RPM so the centrifugal force (I
know -- there really is no such thing) will cause it to fly apart
-- turning it into shrapnel -- and *you* into a target. I don't
know whether there is any size limit for this to happen, but it
has been known to happen and to harm or kill people nearby.

Ahh. I can see a large bearing being driven fast enough to
explode,
especially as bearing races are designed to be reinforced by being
pressed into a recess in a larger housing.

However, One would think that overspeed isn't going to be an issue
with small bearings already specified for 30,000 rpm, unless one's
air supply is something else.


Spinnning a bearing with compressed air is a complete NONO!
Firstly this practice will ruin the bearing - think no lubrication.
Dangerous - as has been mentioned the bearing can explode and sometimes
the
bearing will seize.
As the handiest workholder is a finger a seizure at high speed will
severely
damage said workholder.

Cleaning with air is quite allright - oil the bearing immediately after
such
treatment as moisture will be present in the air and/or will condence
on the
(now) cold bearing.

Regards.
Ken

--
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Years ago I was blowing out some bearings with air. Goofing off, with
the bearing on my finger, I spun one up and listened to the pitch. As
it spun the pitch got higher until I couldn't hear it. Just as it
passed into my ultrasonic range it exploded with a bang.

Ultrasonic! Wow. That implies a ball-passing frequency exceeding
20,000 per second or so. If the ball cage has ten balls in it, the cage
is rotating at 2000 rps, or 120,000 rpm, and the outer race a factor
faster. No wonder it exploded.
MY ultrasonic range. I know my high frequency hearing is damaged. But
it was still really spinning fast.

Do you recall the dimensions of the deceased ball bearing?
The ID was about 5/8 and the OD maybe 1 1/2, 1/34.


The bearing
axis was perpendicular to my body so that the bearing parts were
embedded into the wall and not me. My finger hurt like hell. I think
the bearing must have exploded pretty equally because otherwise that
finger would have probably broken instead.

Yes. Lab ultra-centrifuges are built inside a heavy steel box, to
contain the shards of the rotor, when (not if) it explodes. When this
happens, the centrifuge is totally destroyed.


I don't spin up bearings
any more. Not even a little.

It sounds like there is actually quite a wide safe range here. Just
stay in the sonic range?
No way. A small bearing may take the rpm. But a larger one will
explode much sooner. Just don't spin 'em up.

Joe Gwinn

The other reason not to spin up a bearing with air:
Consider the setting.. You just cleaned out a nice bearing and want to dry
the solvent out. You spin it up with air to MHS speed and suddenly it
starts feeling rough and noisy. You just dislodged a piece of your favorite
hard stuff that went into the bearing race and got mashed at even a nice
"safe" 30,000 RPM. If you are spinning up a bearing dry you are running at
very high speeds with no lubrication and no shields or seals.
Having said that .. they sure make some interesting sounds and go really
fast when you release them on the garage floor Dad was NOT amused LOL
Glenn