Preferred method for preventing bolt loosening 1

[jk2017]

Been doing some research on bolt loosening for a job I'm on and while it seems like there are tons of options, I'm curious to know what your preferred method is. Doing some searching in this forum has yielded varying opinions, with some of the most popular including defacing the threads above the top nut, loctite (blue and red), jamb nuts, and tack welding the nut down. I've also seen plenty of suggestions to use spring washers, nyloc nuts, and products like Nordlock. These all seems to have their pluses and minuses. For me, while tack welding seems popular, I'd be pretty worried about cracking, and I've seen varying opinions on spring washers. Seems to me that jamb nuts are a strong option.

 

[drawoh]

dik,

Are Belleville washers really any better than other spring washers? Belleville washers are somewhat better at spreading the bolt/nut load across the clamped part, especially if you stack more than one of them. Also, they don't gouge holes in stuff.

Many years ago, I worked with a guy who insisted that you tighten a screw down until you have just compressed the helical spring lock washer. I have no idea where he got this stupid idea from, but it may explain some joint failures.

--
JHG

 

[dik]

I think Belleville washers are better and have never had any issues with them. I've only used them on electrical stuff where 60 cycle hum and thermal cycling tends to loosen things. I've never had a problem with them in that type of application. Usually sparkies insist on them.

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

-Dik

 

[bootlegend]

I am interested in the Nord-lock washers. I design structures supporting rock crushers and screening equipment.

I have used Hytorc reaction washers in a couple instances where the nylon lock nuts loosened. So far they have performed very well, but the installation process is more difficult than what the Nord-lock washers appear to be.

 

[ATSE]

Good discussion.
Point of clarification.
1. A cut ("split" or "helical") washer is not considered compressible material. The referenced steelwise quote is silly. Compressible material generally refers to gaskets and non-metallic filler in the grip.
2. A cut washer is the least effective method for reducing nut backoff. However, to say it should not be used, or that it is totally useless, is incorrect.
Many thousands of radio and telecom towers have cut washer + pretensioned at the bolted connections. While these are low vibration demand installations for sure, the lock washer adds pennies to the bolted connection cost. Tiny benefit yes, but very cheap insurance when coupled with pretension.

 

[dik]

The actual washer is compressible (not in the sense the material itself is compressible).


due to the uncertainty... I would suggest that it should not be used. I haven't used them for a long time (possibly several decades), once I found out that they were not reliable. I generally rely on 'snug tight' or 'slip critical', and that's what the towers could be relying on. Belt and suspenders, but the suspenders aren't being used.

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

-Dik

 

[dauwerda]

ATSE, take a look at this link that was posted by dik, above.

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

If they are also pre-tensioned it seems pretty silly to me to include a helical washer.
I know that the TIA-222 requires "nut-locking devices" for bolts used to connect load-carrying members. However, when it does require a full pre-tensioned bolt (slip-critical or connections subject to tension where externally applied loads result in prying) it specifically states that nut-locking devices are not required for pre-tensioned bolts.

 

[BridgeSmith]

If the bolt projection isn't an issue, IMHO adding a jam nut (or standard nut used as a jam nut) with red loctite/threadlocker would seem to be an effective and cost-effective approach.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Geoff13]

Ran into this article only a couple of months ago. Very interesting conclusions on jam nuts (thin nut installed first!).

[URL unfurl="true"]https://www.boltscience.com/pages/twonuts.htm[/url]

 

[BAretired]

The video of Geoff13 is interesting, but installing a jam nut seems like a hit and miss proposition. Using a load cell to find the optimum tightening of each nut may be achievable in the lab, but repeating it on site would be more difficult and likely would not be done properly in many cases.

BA