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Posted by Joseph Gwinn on April 12, 2006, 12:24 am
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> On Tue, 11 Apr 2006 11:21:34 -0700, "Ken Davey"
>
> >>
> >>>>>>> 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
> >
> > --
> >Volunteer your idle computer time for cancer research
> >http//www.grid.org/download/gold/download.htm
> >Return address courtesy of Spammotel http://www.spammotel.com/
> >
> 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.
Do you recall the dimensions of the deceased ball bearing?
> 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?
Joe Gwinn
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