vibration proof fasteners
vibration proof fasteners
(OP)
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





RE: vibration proof fasteners
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: vibration proof fasteners
RE: vibration proof fasteners
Rod
RE: vibration proof fasteners
RE: vibration proof fasteners
-Nordlock for high temperature
-Locktite for low temperature
Raymond
RE: vibration proof fasteners
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?
RE: vibration proof fasteners
RE: vibration proof fasteners
RE: vibration proof fasteners
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
RE: vibration proof fasteners
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.
RE: vibration proof fasteners
turn of the nut method if the torque
coefficient is in question. It probably
will give you more consistant results.
RE: vibration proof fasteners
The big issue with lockwire is the hassle of putting it on.
RE: vibration proof fasteners
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
RE: vibration proof fasteners
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.
RE: vibration proof fasteners
Rod
RE: vibration proof fasteners
wobbles
RE: vibration proof fasteners
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.
RE: vibration proof fasteners
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.
RE: vibration proof fasteners
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?
RE: vibration proof fasteners
I appreciate you providing the reference. I guess I communicated to you that your opinion wasn't good enough when I what I was looking for were the reasons behind the opinion like, "I say it...because studies have shown that the stiffness of the lockwire is typically less than the torque cross radius blah, blah, blah." I was wondering about what led to your opinion rather than just the opinion itself (which you made very clear). Anyway, I'm pleased that I didn't inadvertently offend you.
In my application, I cannot say for certain that the lockwire prevented the loosening only because we always did it. However, I must presume - given the cost and hassle of using it - that it was implemented in response to a specific problem and that it rectified that problem otherwise why would my predecessors have adopted it in the first place?
Also, in thinking about the physics of the situation I do not see how it's physically possible for them not to prevent loosening.
The fastners certainly had some preload because they were tightened down but I don't recall that we always used torque values on everything (we did some, though).
In my judgement, there are suitable applications for lockwire, funnelguy's being an excellent example (acknowledging the drawbacks that you cited).
RE: vibration proof fasteners
Go to Chapter 7, Section 7, Safetying
http://av-info.faa.gov/dst/43-13/
Flores
RE: vibration proof fasteners
It clearly shows what I so ineptly tried to describe.
RE: vibration proof fasteners
Binary, I understand what you are trying to say but I am sorry that it just won't wash. I have been doing safety wire on race cars and aircraft since 1958 and have seen various failures due to incorrect installation, that is true. I have also had correctly wired units fail due to other reasons not the least of which was failure due to loss of tension. The link supplied by Flores is a perfect place to go. The very first paragraph on safety wire should answer your questions and solve your doubts as to the abilities of safety wire to prevent loss of torque.
7-122. GENERAL "...These practices are not a means of obtaining or maintaining torque, rather a safety device to prevent the disengagement of screws, nuts, bolts, snap rings, oil caps, drain cocks, valves and, parts."
CoryPad, I was just a teasin' y'all a bit. I agree with you 100%
Rod
RE: vibration proof fasteners
Again, I'm not arguing the conclusion, I'm just trying to understand it from more than simply an empirical viewpoint. I like to understand the "why's" behind the "what's".
RE: vibration proof fasteners
You are correct regarding stiffness and yielding. The stiffness problem is twofold - material stiffness (elastic modulus) and structure stiffness (wire diameter, path to next part).
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: vibration proof fasteners
Here is another solution, its called stage-eight locking devices. It has a positive locking system that should resist all vibration.
http://www.stage8.com/Groovelok.htm
Naturally, any bolted joint can lose some preload from thermal cycling, vibration, gasket/joint relaxation. To prevent these factors from affecting the fastener pre-load, do the following:
- Make the length of the bolt between the nut and bolthead, which is actually under tension, as long as possible. This increases the elasticity of the bolted joint, which makes the fastener act like a very stiff rubber band which can resist vibration and thermal loosening (you mentioned that these are in a foundry).
- Load all fasteners to 75% of their proof load.
- Minimize the number of surfaces in a joint. For example, if your bolt rests on a washer, and on the other side of the flange, the nut is also resting on a washer, then you have a total of five surfaces sandwiched in your joint; the bolt head to washer-> the washer to flange-> the flange to flange-> the flange to washer-> and the washer to nut surface. Solution: Purchase what are called flanged bolts, and flanged nuts(these are standard fasteners). These have a built-in washer integral with the bolthead and nut. Result: Only three surfaces remain, which increases joint integrity, since there are less surfaces to slip/imbed.
- Increase fastener diameter to the maximum possible, as this allows a greater preload.
- Eliminate all non-metallic gaskets in the joint(if any), and if necessary, apply O-rings or soft metal gaskets instead. This allows a metal to metal joint, which greatly resists loosening as compared to a gasketed joint with pliable gaskets.
- If separate washers must be used, these should be of hardened steel, and have a minimum thickness of 3/16 inch, for fasteners below 1.0 inch diameter. For fasteners of greater size than this, the minimum washer thickness should be 5/16 inch.The washer diameter should be at least 2x fastener diameter.
- The fastener outer diameter,should, as much as possible, be fitted snugly into the joint hole, if the main problem is vibration.
-Increase the thread engagement, by using nuts with a height at least equal to 1.5 x fastener OD. The increased threads spread out the preload more evenly, which reduces the internal thread deflection, thus maintaing more thread surface area under load. The same applies for blind threaded holes.
- Confirm the flatness of all joint surfaces to be joined. Nonflat surfaces introduce bending loads in the fasteners, and reduce the actual forces holding the joint together. Same thing goes for the surface quality of the joint surfaces; rough surfaces allow embedment, which produces a loss of preload. Misaligned flanges are another bad actor application.
- When torquing, apply antiseize under the surface of the nut or bolt head , including the threads. This increases the amount of bolt torque which actually ends up as pre-load; otherwise much of the torque will be lost in friction. If there is a vibration problem ==> do not torque with anti-seize or oils, only use locktite style adhesives, as these will act as a thread lubricant, and give chemical bond locking afterwards.
Abdul
RE: vibration proof fasteners
RE: vibration proof fasteners
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: vibration proof fasteners
http://www.rotabolt.co.uk/
Of course as already expressed by the engineers above, it is important that you use a bolt/screw that is man enough for the task in hand, so look at optimum bolt size, length, minimum nuber of joint faces (components) and especially bolt grade 10.9 or 12.9 are ideally what you require for heavy fixing. A correctly specified joint and installed fastener will not come loose.
evmundo2003
RE: vibration proof fasteners
RE: vibration proof fasteners
http://www.apmhexseal.com/selfseal/catalog_pdfs/apm_sf-200.pdf
RE: vibration proof fasteners