vibration proof fasteners 3

[wobbles]

I work in a foundry and there is a lot of vibration occuring all the time. We are currently using Grade 5 bolts and in the process of changing to A325. I am looking for a solution to stop fasteners from vibrating loose. I need some help to find a good method to use whether using an threadlocker, split washers, safety wire, or anything else that may be out there to use. Im in the process of getting info about spiralock and nord lock fastners feel free to leave some input about these types of fastners

 

[CoryPad]

The simplest way to prevent vibration loosening is to have sufficient preload to resist applied forces. If "fastener magic" must be used, then consider adhesives, Nordlock, and spiralok in that order. Split washers and safety wire do not prevent loosening.

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

 

[boo1]

The testing i have seen indicates Loctite (or equal) threadlocker adhesives work the best at resisting vibration.

 

[evelrod]

I am with 'boo1' on this. I use a variety of "LockTite" products in race and aviation engines and seldom have a problem. CoryPad is correct in that properly torqued fasteners are less prone to failure from vibration and given that 'extra' little chemical help---should do the job! Oh yeah, last I looked A-325 bolts are grade 5. Perhaps you should go to properly torqued A-490 if you are breaking bolts?

Rod

 

[hydrodude]

I did a lot of safety wiring in the navy as an aircraft eng mech and if a series of bolts can be wired so as one would loosen it will pull the next one tight it will work. For single bolts we used a nut with a plastic insert built into the nut.

 

[ww2]

For all I know there are only two securers against nut loosening:
-Nordlock for high temperature
-Locktite for low temperature
Raymond

 

[diamondjim]

You might want to consider using very heavy
washers as well to lengthen the ratio of
clamped length. Going to a higher strength
bolt should help as you mentioned. I agree
with CoryPad in that you may have to use
greater torque value maybe even into the plastic
range. Have you ever broken any bolts?

 

[Metalman01]

You might try spring washers. These are typically used in vibration applications to prevent loosening. Whether they will work depends on the magnitude of the vibration. Otherwise you will have to try loctite.

 

[nhyankee2]

Tack weld them. then a touch with a grinder (like the one you all use to grind the sprew and flash off) will allow the fastner to be loosened...

 

[BATman2]

Wobble,

I'm with CoryPad. Preload is the key, plus Loctite as a pre-caution. Remeber that the Loctite acts a lub. when wet so adjust your torques accordingly. On the other hand, you may want to consider uping your torques a little, instead of the standard 75% of proof strength, to gain more preload.

Spring washers of any type completely useless. Likewish jam nuts are rarely installed properly, so I wouldn't go there either.

Boozer

 

[cim94sm3]

Be careful with Loctite! It may act as a lubricant but also as what it actually is, an adhesive. Depending what Kind of Loctite (red, green, blue) and how much you put on the threads it will cause a great deviation in preload for a predefined torque.

Most locking systems based on increased friction are risky to use, since you may not achieve the desired preload.

I think the Nord-Lock washer is a better solution, since it is a mechanical locking system based on geometry instead of friction.

 

[diamondjim]

You might want to consider using the
turn of the nut method if the torque
coefficient is in question. It probably
will give you more consistant results.

 

[Binary]

CoryPad - Why do you say that lockwire doesn't prevent loosening? We used to make gear to go on helicopters and MIL-SPECs required everything to be lockwired. Like "hydrodude" said, we did it in a fashion where it was impossible to loosen one without tightening another.

The big issue with lockwire is the hassle of putting it on.

 

[Tunalover]

wobbles-
Talk to any fastener vendor and he can provide you with bolts and screws that have nylon patches pre-installed. These are exceptional at preventing loosening and are good for, say, five remove/install cycles. In situations where you can't get these in a timely manner, you can apply ND INDUSTRIES's Vibra-Tite to make your own locking patch. It takes 24hrs to cure but it's certainly better than the Loctite series of locking compounds. It also doesn't care what size fastener you're using (as does Loctite).

For both of the above solutions, I don't know at what temperature they start to break down. The NORDLOC system of lock washers are good for high temperatures. Don't waste money on helical-split or toothed lock washers. Not only do these fail to prevent loosening, they may actually contribute to joint failure by making the joints too soft.

Tunalover

 

[CoryPad]

Binary,

I say that lockwire doesn't prevent loosening because it doesn't. Its purpose it to prevent complete loss of the fasteners in the event that they loosen. The loose joint should be noticeable, and actions can be taken to prevent catastrophic loss. For example, loose (but not missing) fasteners on helicopter parts would result in diminshed pilot control, in which case the pilot would land immediately to avoid death to crew and passengers.

If my opinion and experience are insufficient evidence, here is a quote from An Introduction to the Design and Behavior of Bolted Joints by J. H. Bickford:

"Lock wires, keyes, and cotter pins are often used. These can effectively prevent total loss of the nut - which may be extremely important - but they are not very effective in preventing substantial loss of preload within the fastener."





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

 

[evelrod]

CoryPad---Easy boy! Most of us that actually do a lot of safety wire work already know it's limitations (and it's 'puncturing' propensity LOL)!

Rod

 

[wobbles]

evelrod--i haven't used safety wire that much before. what are some of the limitations of safety wire.
wobbles

 

[Binary]

CoryPad,

you seem a bit peeved by my question to you. Sorry to have offended you.

In my fairly limited experience with lockwire, it did serve to prevent loosening. Specifically, we were putting fasteners into blind holes on various pieces of electronic equipment on helicopters and submarines.

We installed the lockwire at 9:00 on one screw, wrapped it clockwise over the top and then off tangent at about 1:30 and onto the adjacent fastener tangent at 6:00 and then wrapped it CCW up to about 2:00.

We used a device to twist the wire tight and it formed a pretty stiff connection. The only way for either fastener to loosen was to tighten the other one or to stretch the lockwire. Sufficient torque prevented the former. The latter never seemed to be a problem.

I'm not trying to say that you're wrong, I was just trying to learn more about your experience and understand the applications and why they didn't work when our application did work.

Regarding the quote from Mr. Bickford's book, I notice that he's talking about "nutted" connections. Perhaps that's the difference from our application. It does occur to me that in a "nutted" case that you probably have to lockwire both sides, nut and screw.

 

[CoryPad]

Binary,

Contrary to your last post and evelrod's post, I was not peeved. Anonymous Internet sources are not necessarily sufficient evidence. However, when you come to Eng-Tips, that is what you get. Since that didn't seem good enough for you, I thought I would provide a literature reference for you.

Regarding your applications, are you sure the lockwire prevented loosening? Did the fasteners have any preload? Would that preload have been sufficient by itself to prevent loosening?

Wobbles asked about the problems with lockwire, so here are a few:

low torque resistance
huge operator sensitivity (is the wire tight, etc.)
reduced fastener integrity (holes! in fasteners)
slow installation time
high cost






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

 

[funnelguy]

Wobbles, could you give a more complete description of some of the connections that are failing? Are the bolts being used as tension devices? Does the bolt's purpose prevent using sufficient preload?

OBTW, I have used safety wire to retain blind bolts on race engine sump pans and valve covers. Works like a charm. No worrying about hot, oily bolts screwing up the Loctite. Certainly the joint is not properly designed. Maybe this is where safety wire and castellated nuts and such come in handy?