Bursting speed of a flywheel 1

[Spinninghead]

Hi.In a previous thread(404-167467) the bursting speed for a spinning steel disc was quoted(rule of thumb)as v=sqrt(10*s) where v= velocity in f/s
And s=tensile strength.in psi.
I applied this to a 14 inch concrete cutting disk (6000 psi tensile strength) and obtained a figure of 4435 rpm.As the working speed of said disk (cutting concrete)
Is rated at 5400 rpm, could someone tell me if the differing figures is my calculations(I usually work in SI) ,the formula,or a huge safety factor" built in"
The weight is 1.8 kg. T.I.A.

 

[hydtools]

6000 psi sounds too low for steel. Especially steel used in cutting wheels.

Ted

 

[racookpe1978]

A concrete cutting disk could be fibre-based, if it is a resin-impregnated grit with a consumable disc. Metal cut-off wheels are consumeable - they are intended to wear down as they are used.

A diamond-faced concrete saws might certainly be "steel", but then you need to know the alloy AND the factor of safety in the manufacturer's calculation.

Depends too on RPM: The smaller disc's (as on my 4 inch and 4-1/2 grinders) must be rated to 13,000 rpm, but larger 7-1/2 inch and 14 inch concrete saws are slower. Air driven tooling is usually much faster than electrical-driven.

Yours is apparently 5400 rpm, much faster than my 14 inch chop saw.

 

[3DDave]

Check

http://www.eng-tips.com/viewthread.cfm?qid=264452

Also, keep in mind that tools are subject to shock, dents, and binding so that the defects can lower the effective strength of the materials involved due to stress concentrations as well as power concentration - that is, taking the energy of the rotating disk and concentrating it where it binds or jams. This can yield enormous amount of power in a small volume, which is how cutting tools work.

 

[Spinninghead]

Thanks! Traps for beginners, I took the manufacturers rating as for the disk. Turned out it was for the teeth. Googling the correct psi. Gives me 14700rpm, so I won't worry as much when I'm next cutting concrete. Thanks again

 

[hydtools]

The steel is most likely AISI4140.

Ted

 

[dvd]

It is probably worth the effort to conduct a more thorough analysis of grinding wheel failure modes.

 

[Spinninghead]

Bloody hell! He wouldn't even have noticed if it was steel,he'd be looking for the other third of his head though.

 

[racookpe1978]

That's one for our next safety briefing.

 

[berkshire]

Anecdotal story related to this,
Back in the late 1950s The company I was apprenticed with bought a bad batch of the depressed center wheels. We had one or two come apart in the shop without hurting anything or anybody, the boss told us to "use them up" after people complained. The very next day I had one come apart, one half went across the shop floor the other half hit me in the gut and folded a metal buckle on my belt in half. After I got up off the floor, and realizing that I only had a bruise there the size of an ostrich egg, I went over to the shop foreman, and punched him in the nose. I got suspended for a week , and the company quietly got rid of the remaining batch of discs.
B.E.

You are judged not by what you know, but by what you can do.