Break away torque calculation of lock nut against rotating/acceleating bolts? 1

[srimanishreddy]

I have a Scenario where my lock nut is tightend using a prevailing torque of 14 Nm (as mentioned by the manufacturer) on to the rotor placed between bearings (But the tightening direction and the rotor rotating direction is same unfortunately). The lock nut is loosened after particular life cycle of usage as the rotor rotates with a acceleration of 1230 rad/sec and every time it starts, the sudden acceleration loosens the lock nut. Is there a simple approch to calculate a appropriate prevailing torque for this situation, so that the lock nut does not loosen up when the rotor starts accelerating towards it's max RPM of 9400 in 1 second?

 

[3DDave]

It's just the moment of inertia that is resisting the acceleration that provides a torque. That's roughly the mass of the item times the square of the average radius. Multiply that by the angular acceleration to get the torque. If you have a CAD program, model the nut and the software should be able to provide a better estimate of the value.

 

[srimanishreddy]

I have angular acceleration as 1178.09 rad/sec2 and moment of inertia about z axis to be 4.7639498 Kg/mm2. But when, i calculate the torque, the output value was more and not logical.

 

[srimanishreddy]

Please refer to the CAD model below

 

[3DDave]

It's not kg/mm^2, it is kg*mm^2.

Rounding,

(5kg-mm^2)*(1200rad/sec^2) = 6000 kg-mm/sec^2 * mm = 6n-mm. of torque.

Since you did not show your calculation I cannot guess what you meant.

 

[desertfox]

What preload are you putting on the locknut before running the rotor? The prevailing torque is only the torque to overcome the friction in the threads during assembly unless I am mistaken

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