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Posted by pyotr filipivich on April 13, 2006, 10:28 am
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wrote on Wed, 12 Apr 2006 15:18:35 GMT in rec.crafts.metalworking :
>wrote:
>
>>On Tue, 11 Apr 2006 23:24:21 -0500, Joseph Gwinn
>>
>>>
>>>> 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.
>>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
>
>
>Im going to have to try that one of these days.
>
>Safely of course.
After watching the video of the guy spinning up CDs on his Dremel, and
having a few explode on the wheel ... bearings seem to be a logical next
step. Should be simple to whomp up a bearing holder so that you can do
this with your hands in your pockets.
--
pyotr filipivich.
as an explaination for the decline in the US's tech edge, James
Niccol wrote "It used to be that the USA was pretty good at
producing stuff teenaged boys could lose a finger or two playing with."
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