Permanent Nuts and Bolts

Depends on what your definition of normal vibration is, but check out Disc-Lock. I've never had any problems with their products.

Have you looked at Nylocs?

Star, spring and Schnoor washers, Loctite and welding are also worth considering.

What do you call "normal vibration"? It's a long time since my wheel-nuts fell off.

It depends upon what you consider 'normal' Mr Goldabum. Is their any scope for putting a cotter pin through it ( ie one that locks across the threaded shaft ) ? Or if 2 locking nuts are used and sufficient torque applied,can an external hex-profile shaft prevent rotation and thus loosening. Can you specify the application and potential loads etc ? Also , does the assembly ever need to be undone again ( In most applications I'd have thought this useful).

Sure, aircraft-style safety wire or mechanical keepers are common, but a pain in the a$$.

Your question is too vague!!

I would suggest welding them in place!!!

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Go through the learning curve, survive the ups and downs of communicating in a blog!

Depending on what time we answer can defiinetley affect the answer!! After work with a drink or 2. During work while looking out for the boss!!

I've used something called 'aero nuts' in the past, but I can't seem to find them anymore. They where V expensive!

Here you go!

AEROTIGHT NUT A torque prevailing nut of all metal construction. The nut is slotted in two places which, after the nut has been tapped, are bent slightly inwards and downwards. When the nut is screwed onto the bolt thread the two slotted parts are forced back to their original position. Their stiffness causes the nut threads to bind onto the bolt threads and thus provides a prevailing torque.

Depending on the size you need:

http://www.longlok.com/index.htm

http://www.boellhoff.de/web/germany/en/web.nsf/HTML/index_en.html

http://www.matsumoto-screw.com/english/index-e.htm

http://www.nittoseiko.co.jp/e/index.html

Loctite them

Loctite is what we use. there are different strengths. should do the trick.

In German we call it "SPERRKANTSCHEIBE", you can google it. Here it`s obligatory in railway applications where strong vibrations are the common environmental stress.
Regards Uwe

The rail industry, particularly in continental Europe, is moving over to the 'Nord-lock' fastener.

http://www.nord-lock.com/

(usual disclaimer)

http://www.securityfasteners.net/ might also be worth a look?

Another possibility is to replace the nut and bolt with a rivet. Expanding rivets have their uses, as do hot-rolled ones.

There's also a stretch-compression rivet used in the rail industry. It is installed with a pneumatic machine at room temperature. The pin part of the rivet has grooves around its circumference. It is stretched, and then a collar is squeezed onto the rivet as part of the operation. The stretch is then increased so that the unused part of the rivet is snapped off. Installation time for a 25mm Ø rivet is typically 40sec per rivet and the system produces a uniform, predictable, preload. Typical uses are to attach the W-irons to the solebar of a freight vehicle.

You just described the Huck Bolt. An excellent fastener if you don't plan to remove it.

Honda, Yamaha, Kawasaki and Suzuki motorcycles have all answered this succinctly and cheaply - use a lock washer. If they're torqued correctly they _never_ come undone.

You can get some aircraft grade nuts and bolts, more commonly referred to as interference fit. They fit tight and don't come loose. When I was in the service and working on gas turbines, they use these type. Can never recall any of them coming loose. They're not cheap!

As several people have indicated, there are different levels of vibration. If it is severe and constant, the wire or pinned method works best for me. However, if this is not an option or the vibration is not too great, nuts with nylon inserts (some times call Nyloc nuts) work well. However, if elevated temperature or solvents are present, this might be a problem. Sometimes a simple double nut will work with or without a lock washer. The point is to either keep constant load on the nut via a lock waher or similar arrangement or devise some means of preventing the reversing actions such as welding, pinning, Loctite, nylon insert, etc.

When I designed railroad components, we used to put them on a shaker table and vibrate the crap out of them for a couple of days. My experience is that properly designed and installed locking fasteners don't come loose unless they were inferior manufacture to start with. But, we looked at these questions:

Are the fasteners used only once?

Is the fastener rated for the temperatures seen?

Is the preload properly done and allowed for?

Were the fasteners improperly lubricated?

Is the fastener rated (and tested) for the application?

What is the criticality of the fastener?

Has the assembler been properly trained?

Did purchasing really find a cheaper vendor in Faroffstan?

Go see www.phil-lok.com for an applicable locking fastener.

It depends somewhat on the application. Nuts should supply enough tension to stretch the bolt elastically beyond the maximum stress it will see in use (including thermal stresses). If this is done, the nut won't loosen. If the bolt or stud is too short to provide constant tensile stress, the nut may loosen and auxilliary fasteners or means must be provided. The front axle of an auto is a good example.

Prevailing torque and deformed thread fasteners. There is a more recent type that I don't recall the manufacture. They put a third angle on the thread face, sort of like a three angle cut on an engine valve. The peak formed by the third angle "bites" into the mating thread and as I understand, less so than deformed threads, so as to damage the interfacing surfaces less. Any of these used on aircraft must not be reused but in more common use should probably be changed after a couple of cycles depending on safety criteria. I haven't used those Nord-Lock washers. The concept seems solid and should allow for some elongation due to extreme thermal expansion, although for long fasteners, more than a few inches, I'd go with a clinching or interference style.

See post 31 for "three angle thread" info.

I have to agree with the individuals who responded with "Locktite". Its cheap, easy to get and very strong but not so strong you couldn't undo the nut if you had to (granted you'll probably need an impact gun and/or torch to heat it up). Welding the nut in place means you've effectively gone against what nuts and bolts were designed to do: go together and come apart.

You might, depending on the grade of fastener, also be able to peen the end of the bolt. If he length is such that it extends just past the end of the nut, peening it will prevent the nut from coming off. Of course, you'll need a grinder to get it off.

We use Locktite daily & are never disappointed. welding the nut in place can be dangerous because you change the Rockwell hardness and the nut or bolt can become to brittle & snap off!

Many year ago I raced motocross and has lots of problems like this. I found (at that time) that the green Loctite (sort of clear) used sparingly would allow me to keep my spokes from loosening, but if I needed to re-adjust them it would break loose. However, liberal use would require heating (a Presto-Lite acetylene torch) to break them loose.

Better products are available today, as well as self locking nuts.

If money isn't a problem there are many good solutions.

One thing, use a finer thread bolt/nut combo, they are less likely to loosen than coarser threads.

If removal isn't necessary a punch to damage the nut/bolt interface can be used at several points around the bolt.

An extra nut to jam the assembly also works.

Good luck,

Bill H.

The required heating to loosen the nut would not be enough to change the Rockwell. But your right there or more options these days, but everyone has loctite in their tool box. and a quick snap with a 18'' wrench normally does the trick.

You say permanent nuts and bolts. I would say if you want to permanently fasten something use rivets. If you have to weld use silver solder. You will find yourself undoing your permanent bolts some time in the future. Then you would have to drill out the rivets or heat up the silver solder. If a nut is torqued correctly with the lock nut that bites into the metal it will not come loose. You will struggle to loosen it actually.

If you decide to use loctite be sure it is compatible to the surfaces.

I experienced a case where the employer switched types of fasteners and kept using the same loctite. The loctite didn't cure and nuts were falling off.

Most Loctite grades require a ferric ion and the absence of oxygen to initialize crystallization

Loctite see above.

Weekend reply : I think all nuts are permanent.

there was a product called Anco Locking nuts we used to secure pipe hanger materials that were permanent.

Hi Kris,

See if you know this (before you read the solution).

Reputable representatives of the fastener industry, please correct me if I am wrong.

As I understand it, the purpose of the bottom nut is to pre-load (read stretch) the bolt to a percentage of its yield in order that the fastener maintain its "clamping" strength through-out a wide range of conditions, temperature, vibration, etc. It's purpose is not to deform the threads on the bolt, otherwise both nut and bolt would be one time use items due to the galling encountered during disassembly. If the jam nut (thinner) were to be used to provide the pre-load, I would think that because of the fewer threads, hence higher load per thread surface area, there would be a greater possibility of shearing the threads (stripping) of the jam nut.

When installed with the wider nut on bottom, proper pre-load can be provided. When the jam nut is then tightened against the bottom nut with reasonable, not excessive torque, the increased pressure of the threads of both nuts against the threads of the bolt as well as the friction between the mating faces of the nuts is what "locks" the nuts in place with no deformation of the threads of either bolt or nuts.

Older alloy to cast iron (cyl hd to block) used bolts that could be reused- later designs use TTY(torque to yield) bolts that can only be used once- I prefer the earlier!. As to vibration, I remember a motorcycle from my youth(Triumph T110) that you could not keep nuts from loosening!. After every ride, you retightened, & r/p what was missing!.(before Loctite). And you needed a rebore & new pistons & rings every 3,000 miles or so(not to mention burnt valves!).

Dear Guest, Try NAS 21042-xx nuts. xx is for the diameter you want. -3 fitting a 10-32 screw. Sizes up to 1/2 inch at least are available. The nut is self locking,(slightly deformed) and pre lubed additional lubrication such as cetyal alcohol prevents galling and eases installation. It will not affect the self-locking feature. If pretty or conductivity is an issue use NAS 21043-xx it is silver plated instead of moly-coated. This is a very common aerospace fastener and pretty cheap.Try this link Aviall. Check NAS standards for the proper nomenclature for dash numbers. After 20 years in aviation I have never seen one of these come loose unless it was modified before use.(A tap run through it!)

shart

A lot of good answers, however, there is one important point missing; the "Class of Thread"

There are generally three classes.

1. Class 1 is a loose fit.
2. 90 % of bolts are class 2 (medium fit).
3. A class 3 nut and bolt will have a tight fit (nut will not spin on freely on the bolt).

It is very difficult to get a good lock on a class 1 Bolt

It is very easy to permanently lock a class 3 Bolt

If it is important to get a permanent lock, Start with a class 3 nut and bolt.

You have answered already to your question. If the lock not subjected to above or exceeded its normal vibration beyond its spceified strength to resist the vibaration then it reaches its breaking-point, eventually it has to giveup its hold and become loose.

Just a nearly off-topic note:

I'm just back from a 700 mile round trip (fortunately taking in another job en route) to Sellafield to fix a problem with the "control system" on a sample changer. 13 hours on the road. The place I was working involved stripping to underpants & changing into their shirt, trousers, overalls, socks, boots, hardhat & safety glasses, then getting through 2 pass + PIN number controlled security turnstiles. Reverse procedure on the way out (after 3 stages of monitoring for contamination).

The fault? Excessive backlash in a toothed belt drive linear actuator - due to a loose M2.5 grubscrew.

That's one expensive 2.5 grub!

Hope you put some Loctite on that sucker!

Done & dusted!