In article ,
Ned Simmons wrote:
In article ,
says...
In article ,
Ned Simmons wrote:
I have no interest in exploding a bearing g. I just wanted to get it
spinning fast enough to run the tests described.
How fast did you get it to go?
About 6500 RPM. I didn't have the needle valve opened all the way, but I
don't think it would have gone much faster with the small tube.
Sounds about right. And needle valves can slow things down too.
I bet your Son can test your hearing limit.
He tests many limits.
Heh...
I agree that higher speeds than 20 KRPM should be attainable, but the
deterioration will limit the speed, and that may be why he couldn't go
faster. As the bearing gets beat up it'll take more power to keep it
spinning at a given rate.
Will deterioration really be that much of a limit on an unloaded
bearing, especially if it isn't in contact with the inner race all that
much? And, the airjet has plenty of power.
There's lots of power in the compressed air - transferring it to the
bearing is another matter. Even air motors are notoriously inefficient.
Even if it's inefficient, it may be sufficient. How much power does it
really take to spin that little steel ring?
Based on the numbers, and 25 years of machine design experience, I'm
very confident that the bearings did not explode from centrifugal force
alone. The reports of the noise going ultrasonic do give me pause, but
not enough to make me believe that the bearings were spinning at 1300
FPM. I guess someone needs to volunteer to explode a few properly
instrumented bearings. Not me, I'm off to Boston for college visits with
the boy tomorrow.
OK.
One quick test would be a cheap electret microphone near the bearing,
the whole affair being down under a pile of sandbags for safety, to
convert the siren tone into an electrical signal one can display on an
oscilloscope and measure the frequency. Knowing that the siren tone is
ultrasonic would very much constrain the problem.
Joe Gwinn