Rotational Application - Bolting 1

[daparojo]

I have an application that has 12 bolt in a rotational flange that has speeds up to 3000 rpm.
As the nuts are external, and have a relative weight to them, I have calculated the total bending stress in one bolt as around 500 N/mm2 - this is subject to a centrifugal force if the nuts move due to centrifugal forces parallel to the face.

As the bolts are stretched via torque, the combined stress in bending and tensile is approx. 725 N/mm2.

This the maximum condition @ 3000 rpm.

The material of the bolt is 750 N/mm2 Yield and the UTS is 840 N/mm2.


Would this be acceptable in your opinion?


The torque in the flange is driven by the shear area of the bolt.

 

[desertfox]

Hi daparojo

Can you post your calculations and a sketch of the joint please I'm not understanding how the bolts in bending.
I can see the bolts being subjected to shear during rotation but not bending.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[drawoh]

daparojo,

Your bolts cannot bend to the side unless the centrifugal force exceeds the friction force due to clamping. You need them tightened down hard.

--
JHG

 

[zcp]

How do you load bolts in bending in a rotational flange? If the joint is loaded in bending, the top / bottom bolts will have a tension in them. Make sure your preload is higher than this to keep the joint from separating. Preload the bolt to the point where it will not fail during initial torqueing and is ok in fatigue.

You need to determine the alternating and mean stresses in tension and shear and use some form of fatigue / failure analysis (such as modified Goodman) for the multi directional stresses.

There is some good stuff on Wikipedia and boltscience if you do not have a mechanical design textbook or machinery handbook handy.

ZCP

http://www.phoenix-engineer.com

 

[daparojo]

I will submit a sketch and calcs later. Thanks.

I calculated that the centrifugal force could be greater that the frictional force on the nut face, hence the slight possibilty of bending.

 

[SwinnyGG]

Unless your flange is really really big, I'd guess you have a calculation error somewhere. Drawdoh is correct in that in order for the bolt to experience bending load, the radial force on the nut due to motion must exceed bolt tension.

I just did a sample calculation really quickly- for a 1/2 bolt rotating on a 12 inch radius at 3000 rpm, the radial force on the nut was about 115 lbs, compared to a bolt tension at proof load of approximately 6,000 lbs. Not even close.