Nut Backoff Question 3

[kat6787]

I'm looking for any information about nut backoff. More specifically, the probability that nut backoff will occur when using 1 nut vs. 2 nuts. Also, I'd like to know if there is any documentation (codes, standards, papers, etc) that would provide some information. And finally, does the material of the bolt have any effect on nut backoff. Any thoughts or comments are much appreciated.

Cheers,
Kat

 

[CoryPad]

What is your definition of nut backoff?

How are the two nuts attached? Stacked upon each other mated to a single screw?

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MikeHalloran]

Codes and standards do not prevent nuts from backing off.

Castellations and cotter pins do.



Mike Halloran
Pembroke Pines, FL, USA

 

[kat6787]

I'm considering nut backoff to be any loosening of either nut that will result in the loss of any structural integrity to the joint. The nuts are mated to a single stud used on a flanged connection. I've found a lot of informaiton about jam nuts, but nothing really concrete enough to use in a formal report. I was hoping there was some documentation that I could reference about this subject.

 

[CoryPad]

I doubt you will find this kind of information in a published format. The fastened joint body of knowledge hasn't been systematically studied and published. The material of the bolt will have an effect due to its elastic modulus - more compliant bolts usually have better resistance to loosening.

The best thing to do is to search journal articles, SAE technical papers, and ASTM STP's.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Screwman]

Sounds like a lawyer looking for supporting documents.....

 

[kat6787]

I resent that comment. I didn't spend 4 years taking upper level calculus and sit thru the EIT exam to be called a lawyer.

Thanks Cory, I found a few papers that were very helpful.

Cheers,
Kat

 

[dimjim]

You might want to search the forum
on "jam nuts". The question sounds
familiar.

 

[MintJulep]

NAVAL SHIPS’ TECHNICAL MANUAL CHAPTER 075 FASTENERS

Discusses them. There is a link to download it somewhere on Eng-Tips.

 

[kenvlach]

Link to NAVAL SHIPS' TECHNICAL MANUALS is below. Selected NSTM chapters are available to the general public.

http://www.fas.org/man/dod-101/sys/ship/nstm/index.html

 

[Screwman]

Sorry Kat,
Every now and then a lawyer comes trolling around looking for help on developing his case and I for one don't like helping them.
Returning to our original program:
If I recall correctly there was a VDI study a few years ago in Germany that dealt with double nutting. I am not sure which university was involved. I am not aware of any code documentation...I don't think that the Bolting Technology Council has looked at this area at all.

 

[tab1999]

It is sometimes useful to switch to LeJune ( excuse my spelling ) bolts for structural members that are subject to dynamic loading or vibration. These work if you have access with an impact gun/wrench.

 

[RARWOOD]

I don't know what your application is, so its hard to reply. The question I would ask, is does bolt back off effect the strength of your joint, or is your concern about the nut working itself off the bolt.

In wood connections the bolt design strength is based on tight or loose nuts. When I am concerned about the nuts working loose or being helped off, I call for the threads to be damage after installation.