The best way to protect a bolt from loosening? 15

[EighthBen]

Hello,

our company is manufacturing machines for wood industry. In certain devices we have a wood log rolling down and hitting the steel wall. At the moment of impact there is a huge amount of energy absorbed. This causes minor movement of the construction elements, and sometimes we get loosened bolts in that part of machinery or nearby.

Therefore now I must research the ways of locking the bolt.
We tried: din 985 nuts, din 127 washers, and Locktite glue. Nothing helps, it keeps loosening. After that we started welding the nuts to the bolts, because it never has to be disassembled, so it is not a problem.

So now I want to familiarize myself deeper with the ways of locking the bolts. I've tried to find the textbook or any other kind of source of information about the usage and differences (in effectiveness of prevailing loosening) of these methods:
din 985 - nut with nylon
din 6923 - nut with expanded bottom and with teeth
din 127 - washer with cut
din 6798 - washer with many cuts
nord lock - from wurth - looks serious, though pretty expensive, haven't tried it yet.

If anybody could advice me where could I find more information on comparison of these locking variants, I would be so grateful. We have other machines with smaller impacts where could avoid welding, but I want to get some theory and lab experiment result before going to "try and hope" routine.

Thank you for your advice

 

[RafaelCosta]

I certainly agree with Sawbux and alloyboy.

In my opinion, the concern here is the impact dynamics. There is no assembly which can sustain great impact energy. EighthBen, you should consider increase your damping devices in a dynamic system before blaming the assembly.

Hope that helps.

 

[burningDiesel]

Cheapest solution (similar to your welding solution):
Take a hammer & pin punch and hit (in between) the threads of the bolt & nut after tightening (i.e. a DIY deformed thread lock nut).

 

[Injuhneer]

If spring tension is the goal then simplify; what about using belleville washers? Maybe a version with a splined or grooved face?

You'd get spring tension, load distribution, locking, and anti-rotation in one device.

 

[Tmoose]

OP EighthBen last dropped by about a month ago. I'm guessing he may not be getting notified when new posts arrive.

 

[Jughandle]

Anyone mention the olde school solutions: Lock wire nuts (used for aircraft vibration), or castle nuts & cotter pins?

 

[KENAT]

Yes, they were mentioned & I believe it was pointed out they don't stop the bolt/nut from loosening per se, just from completely falling off.

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[zcp]

+1 for absorb the impact elsewhere
jamnut or castle nut with cotter / wire should then keep it on
why is it bolted if it never needs to be disassembled?

ZCP

http://www.phoenix-engineer.com

 

[alloyboy]

Eigthben has ignored a request to show the actual production line or a drawing of the troubled area !
Fair enough ! It is very difficult to troubleshoot a problem when more information is needed !

In an impact area, bolts will have a tendency to loosen through bolt stretch , wear between the faces of the
bolted assy., etc.

A solution to the problem may be had by spring loading the nut to apply more tension as the wear occurs or the bolt
stretches.

Eventually, there is going to be a failure. Impact damping would benefit your problem immensely !

 

[LCform]

you can check this thread, I think it's an interesting one

Link

 

[SwinnyGG]

The Junkers machine that NordLock and others rely on for proof is interesting.
As best I can tell it enforces some amount of sliding between the components clamped by the fastener.
I can not imagine that components that repeatedly slide don't eventually wear themselves and the fastener faces down, decreasing preload.
As material is lostEven A fastener that does not "loosen" (unwind) will clamp less and less effectively, and someday will be likely even loosen.

My preferred strategy to achieve reliability would always be to keep the components from sliding in the first place.
As others have said, a quantity of sufficiently long well-tightened fasteners is often a pretty economical, easy-to-field assemble method to accomplish that.

ANY fastener application should always be designed such that components do not move relative to each other. In the world that I work in, and I would venture to guess 99.99999% of other fastener applications, if there is relative movement between parts the joint has already failed, regardless of whether or not parts are actually broken.

However, as we all know, there is no such thing as an infinitely stiff component of any type. Even the largest, most robust parts, if mated together by bolts with sufficient preload to prevent movement between mated surfaces, will still impart extremely minuscule displacements between the opposite ends of a tensioned faster as the parts are loaded. The equations tell us so- even if those displacements are too small to practically measure, or difficult to conceptualize, they are there. These displacements drive the mechanics of fasteners self-loosening, which is relatively well understood.

The Junker test, by using bearings between mating surfaces, simulates this behavior, and also magnifies it to a level where testing preload degradation becomes possible within a practical amount of time.

You could collect the exact same data using a machine without bearings, where a bolt clamped two surfaces together- the problem would be that with sufficient preload, you would need to gather data for days/months/years to develop a useful model, instead of seconds.

 

[dicer]

Loctite it or if it doesn't need to come out ever, then weld it.

 

[Pitso175]

Wire locking has been sufficient in the aviation industry.

 

[KENAT]

As discussed ad nauseum Pitso, wire locking stops the fasteners from falling out. I does not maintain pre-load.

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(probably not aimed specifically at you)
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[Tmoose]

From the description in the OP I believe these are bolts with nuts. Also the assembly is "forever."
If so, I'm thinking both nuts and bolt heads would have to be safety wired, and vulnerable safety wire is going to be on the abused side.

 

[dicer]

Also a piece of steel with the correct hex and either bolt it on over the bolt, or tack weld it, to remove just cut the welds off to remove the lock plate.

 

[TugboatEng]

Making the bolt longer works very well. I put a spacer under the head of problem bolts.