Maximum RPM of a Spinning Disc 1

[Mechdesignron]

Hello,

I would like to know how to determine the max RPM of a disc. I would think it would be the centrifugal force against the Yeild Strength. Any help would be appreciated.

Thanks,
Ron

 

[IRstuff]

I would think most systems will go unbalanced way before anything yields, unless there are structual flaws.

TTFN

FAQ731-376

 

[MintJulep]

thread404-167467

 

[Tmoose]

Machinery's handbook has had a section on simplified, conservative flywheel design. It has some basic recommendations based on rim speed. Some Materials (cast iron) don't have a yield strength worth mentioning for tensile loading, of which there is plenty in a spinning disk.

 

[Canadieng]

For an indepth discussion of rotating disc theory a good reference is:

Strength of Materials - Part II - Advanced Theory and Problems - Timoshenko

 

[sreid]

And remember that a flat disk is not the optimum shape for a flywheel relative to bursting.

 

[flash3780]

Go with Tim O'Shenko - or Roarks for that matter. As was mentioned above, a flat disk is not the optimum shape for a spinning round thing.... A turbine disk is.

 

[MikeHalloran]

A flat 1/16" thick polycarbonate disk of ~13" diameter, secured by a small piloted hub and two axial screws, and spun at 3600 rpm or so, despite being balanced, will develop a really interesting taco/flat/taco vibration mode, with extreme deflections in both directions, and make you really glad you used polycarbonate instead of acrylic. It's not the optimal shape.



Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

We've done something similar. 3/8" thick sandwich of 3 disks of BK7, 6" diameter, spinning 6600 rpm. Truly a sight and sound to behold. We had custom, pre-loaded bearings and some sort of dynamic balancer. One day, after about a month of system integration, the bearing started making a buzz-saw kind of sound. We feared for the worst, and always expected the disk to fly apart into a zillion pieces, but no such luck... After about 3 weeks of that, the sound went away, and we never figured out what the deal was with that. It ran fine until our project was terminated 3 yrs later.

It was extremely well balanced; line of sight jitter was less than 100 microradians (rms).

TTFN

FAQ731-376

 

[Canadieng]

Mike:

Similar to a CD at 23,000 rpm, as witnessed by Mythbusters?

http://www.youtube.com/watch?v=F6avp29GqXo

 

[MikeHalloran]

Mine didn't burst, but the deflection was a lot worse.
When the disk flexed away from the motor, it almost folded on a diameter, and the two halves' edges nearly met, just like a taco shell.
When the disk flexed toward the motor, it hit the motor, which probably limited the speed some.



Mike Halloran
Pembroke Pines, FL, USA

 

[Mechdesignron]

Thanks for all the advice, I did order both Roarks and a copy of Strength of Materials - Part II - Advanced Theory and Problems - Timoshenko. Our product is spinning a flat disc, I need to know how fast it can be spun.

Ron