Lock Nut Type

[atlarson]

What are the advantages or disadvantages of a deformed thread locknut as compared to a nylon insert locknut, other than higher service temperature?

Thanks in advance.

 

[CoryPad]

Supposed advantage: higher prevailing off torque after five reuses

Advantage: cost

Disadvantage: high probability to gall/ruin the mating thread

Regards,

Cory

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

 

[IceStationZebra]

---------------------
| Supposed advantage: higher prevailing off torque after five reuses
---------------------
My experience with the deformed nuts has been:
- with the typical cheap deformed nut you are only going to get a single use.
- I have seen some difference between those that are deformed on the "top" or in the "middle" of the flats - but I have always wondered if it was more manufacturer dependent.
- The nyloc nuts will have a more consistent torque vs. clamp load value.
- The center deformed lock nuts are more assembly friendly because it doesn't matter which way the nuts are started onto the fastener.
- I think its easier to find locking flange nuts of the deformed variety.

ISZ

 

[Pressed]

The deformed nuts that I have used the amount that wouldn't assemble was too large, often locking up or snapping under an impact wrench. So that would also indicate torque repeatability trouble.

The amount of re-use would be affected as well, as indicated above.

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[jistre]

All reasons why I like a chemical thread locker if it's compatible with the environment that the nut will be in. From hand-tool removable to blowtorch removable, you should be able to match the aggressiveness of the locker to the strength needed and frequency that you'll open the joint.

 

[reidh]

Just keep in mind that most thread lockers are electric insulators, so they should not be used on fasteners used as an electrical ground.

-Reidh

 

[proinwv2]

I agree with jistre, chemical thread lockers are excellent, when applied to clean threads and better still with the primer.

I have never had good results with plastic inserts.

The most effective methods, are not assembly friendly. These are castle nuts with cotters or lockwiring such as used on aircraft assemblies.



Paul

http://www.ostand.com

 

[unclesyd]

We were very careful with the use of plastic insert lock nuts and had a cut off point of .75". We also stayed away from deformed type lock nuts with safety wired fastener being the norm. We used chemical thread locking products on thousands of small fasteners again with around 1" being the nominal cutoff.
On several very critical applications we replaced a deformed nut with a nut from Superbolt.
We took the added precaution to safety wire the jack screws on these nuts.
We also used the Spiralock thread form on numerous rotating applications.

http://www.superbolt.com/products.html

http://www.spiralock.com/

 

[MikeHalloran]

Liquid thread lockers do not prevent metal to metal contact during makeup, so a proper ground can be established.

Once cured, they exclude water and oxygen, so the ground contact is less likely to degrade with time.



Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

About a year ago We had to deal with 240 deformed thread locknuts. Non-stainless hardware, and Despite using a MIL spec graphite-in-alcohol lube, galling to some degree was common and prevailing torque was all over the map, between modest to nearly the max for the fastener. As the nuts' function was strictly to set a dimension it was OK.
If instead bolt clamping was important we would have had a tussle keeping track of all the prevailing torques at initial installation, and retorque would have been a small nightmare.

The disadvantage of all types of locknuts is they may try to trick me into thinking they (the locknuts) are sufficient, and proper torque is not THE pre-requisite for a successful dynamically loaded structural joint. Some days I doubt or forget that friction from bolt applied clamping is critically important. All I have to do to get back on the right track is look at the pictures of the damaged crankshaft key I took out of our Integra after a few hundred miles of gentle street running. As a secret favor to me and my spare time my wife and daughter had a recommended local mechanic (also a motorcycle "racer") change the timing belt and water pump on my daughter's car. Afterwards It was way down on power, despite him insisting he "re-checked" it 3 times. At that point In tears my daughter told me her car was messed up. On my way in to check the cams' timing (one cam was a tooth off, which also made the cam mounted ditributor out of range on ignition timing) the crank bolt was obviously under-torqued at maybe 20 lb-ft. The crank key's faces already had visible steps pounded an easily detected few thousandths deep. tick, tick, tick, BOOM.


In 86 cases out of 100 a locknut buys a few extra hours of service (which can be quite useful) while the poor bolt dies a painful death acting as a pin, but not having the nut "loosen" in the first place would be way better.

 

[reidh]

Mike,

There is certainly an increased electrical resistance when liquid threadlocker is used, and Loctite can provide data to support this. I agree it would seem that there is still sufficient metal-metal contact for an electrical ground, but there is good reason that military aircraft permit the use of liquid thread locker on fasteners that need to be at the same potential as the mating material.

Reidh

 

[MikeHalloran]

I could swear that Loctite published a tech paper asserting that liquid threadlocker was beneficial in electronics assembly for the reasons I've already stated. It seems to be buried in the Henkel haystack just now... as is any contrary indication.





Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

Within the last 6 months Loctite tech support told me on the phone NOT to use thread locker on our electrical connections.

But, since it is pretty widely published bad form to include anything but the clamped surfaces in the conduction path design, it would seem any impairment in fastener conductivity would properly be invisible. The British Copper Development Association has some guidelines that suggests there is a significant streamline effect in lengthy joints, and that would seem to me to make the clamping fastener even less electrically relevent.

http://www.cda.org.uk/megab2/elecapps/pub22/sec7.htm#7. Jointing of Copper Busbars