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Old 07-29-2013, 01:19 PM   #11 (permalink)
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Quote:
Originally Posted by Occasionally6 View Post
It's unlikely to be a problem though.
True, however the rim is moving 225 ft/sec (154 MPH). If it breaks apart, the pieces will make big dents in a concrete block wall. I'd have a scattershield around it, just to be safe.

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Old 07-30-2013, 04:41 AM   #12 (permalink)
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Quote:
Originally Posted by Christ View Post
Jargonjargonjargonjargonanswer.

Good answer. LOL
The two relevant formulas are actually pretty simple, even if that is somewhat hidden by the clumsiness of word processing absent Greek symbols, subscripts and superscripts.

Unfamiliar units might not help either . You will be able to get the same result using the appropriate Imperial units.

Quote:
I'm 'fuging used motor oil with random densities, probably a quart or less will actually fit in the area inside the bowl after I attach the cap to it.

Really, short of someone saying 'yeah, that should work', I was just going to build the whole plan inside a cage, turn it on and walk away for about 3 days, checking on it once in awhile and then ultimately checking it for signs of fatigue, cracking, or an out-of-round condition after running full speed for that period of time.

Seemed like a good enough stress test to me.

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Originally Posted by JRMichler View Post
True, however the rim is moving 225 ft/sec (154 MPH). If it breaks apart, the pieces will make big dents in a concrete block wall. I'd have a scattershield around it, just to be safe.
With the last sentence I was referring to the additional force due to the fluid being centrifuged. If that is just one quart and motor oil it will weigh about 1/75th of the drum rim itself (assuming ~3/4" wall thickness), so not add appreciably to the stress in the drum.

Otherwise, yes, as general advice, it would be wise to be conservative. Perhaps a couple of inches of cloth or wadding backed by 1/4" mild steel plate?

Actually, a bigger risk than the extra mass of the oil is spinning the drum a lot faster than 3450 rpm. The stress is a function of the square of the rim velocity. At 3450 rpm there's a lot of room for error. At 5000 rpm the stress will be (5/3.45)^2 = 2.1 times greater. I consider that's still OK but wouldn't want to go too much higher.

Spinning it twice as fast (as 3450 rpm) will result in a stress 4 times greater and closer to the failure stress: 136 MPa vs 170 MPa. Checking the motor speed is what it is supposed to be might be sensible.

To put it into perspective, a car flywheel will spin at similar speeds, be of similar size and made of the same material, although of different configuration.

Last edited by Occasionally6; 07-31-2013 at 03:05 AM..
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Old 08-01-2013, 10:14 PM   #13 (permalink)
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Yes, I actually changed the design to something more... proven.

A torque converter. It's already the proper shape, no modification [other than cutting and gutting] needed, I can bolt it directly to the existing flexplate, which bolts directly to the end of a crankshaft, which I can have a machinist center drill, cut a keyway, and re-balance for me, enabling me to sit the whole assembly on the motor head like a hat of sorts, and we all already know that torque converters on average can spin 7k+ RPM FULL of fluid and counter-rotating forces inside them without blowing apart at modest power levels attached to automobiles, so I'm thinking it should be fine [i.e. less potentially catastrophic] spinning at 5k RPM generating ~5,000g with about a quart of oil in it. [probably less in practice]

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