Double Nut ( Jam nut) Bolting and thermal expansion 2

[Abhijeet242]

In case of Stud, when it is jammed with the help of two nuts i.e. 2nd nut on the top of one nut, is it possible that the Thermal expansion effect will be cancelled. Is it the reason why, normally equipments like Pumps are bolted to Baseframe with the help of Double nut? I think this restricts the degrees of freedom for the stud to expand due to temperature and hence due to equal and opposite forces, it avoids additional preload or loss of preload from stud. Attached please find the picture.

 

[desertfox]

Hi Abhijeet242

The two nut locking mechanism is to prevent the lower nut loosening over time from possible vibration of the machinery it is clamping down, there are much better ways to lock threads from self loosening for example:- Norlock washers, Nyloc nuts, wire locking etc.
Thermal expansion of a bolted joint is slightly different in that depending how the joint is heated then the bolt shank may get stretched as the clamped parts expand in addition to its expansion due to heat, now if the bolt shank is stressed beyond its elastic limit the joint is effectively loosened by the bolt suffering permanent deformation.
If you have a specific problem share the details and we might be able to help you further.
The short answer to your question is no locking two nuts together will not cancel out thermal expansion.


I guess you have seen this link because the illustration you posted I think is from this web page.

https://www.boltscience.com/pages/twonuts.htm

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

 

[drawoh]

Abhijeet242,

If you don't clamp your bottom nut to your baseframe, and you do clamp your two nuts together, your system will be free to expand and contract with temperature, the nuts will not come off, and your system will not tip over. It will not be clamped. Does industry do it this way? I don't know. There generally is a good reason for doing stuff the way they do it.

Have you worked out thermal expansion? Maybe you don't have a problem.

The Jam Nut

--
JHG

 

[dvd]

Using Belleville SpringsTo Maintain Bolt Preload

 

[HTURKAK]

I fully agree with Mr. desertfox (Mechanical) and a pink star to him for this excellent explanation...

I would like to add, if the studs are anchor rods for equipment foundation, the use of double nut will not keep the applied preload on the bolt. It has no effect.
The loss of preloading due to creep and shrinkage of grout and concrete footing.

 

[desertfox]

HTURKAK

Thank you for your kind words


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

 

[Abhijeet242]

desertfox (Mechanical),drawoh (Mechanical),HTURKAK (Structural) and all, Thank you for the answers. As you have correctly pointed out
desertfox (Mechanical), the explanation belongs to the same link you posted. After going through the comments, I have realised that the Stud clamped with Bolts is going to stretch anyway due to thermal expansion as the expansion will not be restricted, in cases what i mentioned-Pump. The clamped part will expand and it will inturn stretch the bolt. Loss of preload can occur in such case. Perhaps the better choice would be to work out the expected Thermal expansion and torque the bolt accordingly so that the required amount of tension will be maintained during the operating condition.

 

[desertfox]

Hi Abhijeet242

You can certainly do some hand calculations that will get you an approximation of the bolt stress during operation in order to do this though you need to know the stiffness of the baseplate being clamped and the stiffness of the bolt. Generally but not always the stiffness of the clamped components is much greater than that of the bolt and if that’s the case most of the additional load during expansion of the joint is taken by the clamped parts provided that the stress in the bolt is still below the yield stress and the initial bolt preload was sufficient at the installation.
Here is a link that might help

https://roymech.org/Useful_Tables/Screws/Joint_Stiffness.html

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

 

[dik]

I use Loctite red works all the time... if double nut, the nuts have to have different depths and fastener is still not secure... From my notes:

-INSTALLATION OF ‘JAM’ NUTS:
THE OUTER JAM NUT SHALL HAVE A THICKNESS OF NOT MORE THAN 75% OF THE INNER NUT.
THE INNER NUT SHALL BE INSTALLED FIRST AND SNUGGED TIGHT.
THE OUTER JAM NUT SHOULD BE INSTALLED SNUG TO THE INNER JAM NUT.
THE INNER NUT SHOULD THEN BE SNUGGED TIGHTLY TO THE OUTER JAM NUT WITH THE OUTER JAM NUT RESTRAINED FROM ROTATING.
WRECK THE THREADS BELOW THE NUT.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Tmoose]

This is how the US Navy felt jam nuts should be assembled back in 1997.

 

[kingnero]

That's how I have seen it done before (I agree there are better alternatives!)
Basically this setup means that the main tensile bolt force gets transferred to the thicker, outer nut.

@ dik, WRECK THE THREADS BELOW THE NUT. => this means "wreck the protruding threads", correct?

 

[dauwerda]

Reading dik's notes, I don't think they are made to accomplish the same thing that this thread is speaking to. The OP is trying to maintain a clamping force on the elements being joined. dik's notes would produce a loose connection where the two nuts are tightened against each other to preclude them unthreading, but they are not clamping the parts being joined (at least that's how it reads to me).

 

[mfgenggear]

keep it simple, single nut with built in lock or locktite.

 

[dik]

yup...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

concur... then double nuts are not the way to go... installation method is correct.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik