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The best way to protect a bolt from loosening?

The best way to protect a bolt from loosening?

(OP)
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

RE: The best way to protect a bolt from loosening?

Have you considered jam nuts or prevailing torque lock nuts in certain locations?
Consider using a combination of locking methods: liquid thread locking, a prevailing torque nut that isn't nylon (i.e. deformed thread), and a split lock washer.

Using finer thread helps as well.

Quote:

Results from testing show that a
fine-pitched locknut endures twice the cycles of vibration than does a corresponding
coarse-pitched locknut, provided all other conditions are the same.
"
-Experiential Analysis of Thread Movement by Auburn U.

There's some interesting information in that paper.

RE: The best way to protect a bolt from loosening?

In my experience, forget the washers.
It sounds a bit like the bolts are undersized and flex too much on impact.
Another solution might be castle nuts with cotter pin.

Cheers,

Benta.

RE: The best way to protect a bolt from loosening?

2
Bolts depend on elastic preload to hold tension. If you are losing tension it's because you are exceeding the preload. No retaining device will work if the preload is being exceeded. It is likely the preload is gone because of plastic deformation of the parts. Either the bolts are stretching or the flanges they are through are getting dented under the nuts/washers.

Check the web site Bolt Science for better information. http://www.boltscience.com/pages/vibloose.htm

Another thing to consider is the use of match-reamed press-fit pins to take the shear load between items so that the movement of parts cannot happen and cannot cause that mode of motion to damage the bolted connection.

RE: The best way to protect a bolt from loosening?

All advice above is worth considering.

Consider bigger bolts, and mechanical anti-rotation devices like french locks or stage 8:

http://stage8.com/

Mike Halloran
Pembroke Pines, FL, USA

RE: The best way to protect a bolt from loosening?

"because it never has to be disassembled"

Just weld the whole thing solid? But off hand, it does sound like bolts are too small.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: The best way to protect a bolt from loosening?

Does the "minor movement of construction elements" cause any problems, like cracking or wear of mating surfaces?

Bolts holding "sheet metal" together don't have much grip length, so even proper preload is not accompanied by much bolt elongation.
If faying surfaces get buffed down a little when things shift, preload is lost, and the party is over. Using substantial thick walled steel spacers with well finished ends would allow using bolts at least 7 diameters long, and help a lot keeping things tight under duress.

RE: The best way to protect a bolt from loosening?

I am guessing that your joint subjects the fasteners to transverse shear loading. This topic has been covered extensively, try these:

SAE 2014-28-0035
SAE 2007-01-1663
SAE 2007-01-0807
SAE 2006-01-988
SAE 2005-01-1320
J Mech Des v127 (2005) 1191-1197

The best way to prevent the loosening is to prevent the shear force overcoming the friction preloading from the screws. You can use shear pins, or larger fasteners, or more fasteners, or higher fastener preloading. Without more details, it is difficult to select the best solution.

RE: The best way to protect a bolt from loosening?

(OP)
Honestly, I haven't expected so much serious answers. Thank you very much everybody for your help. It will take time for me to read those sources, but running quickly through them already gave me good thoughts on this issue. Thank you!

RE: The best way to protect a bolt from loosening?

Have you tried Nordlock washers?

RE: The best way to protect a bolt from loosening?

Hi

Java999 see my post dated the 11.01.2016

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: The best way to protect a bolt from loosening?

(OP)
I have considered Nord Lock, but I didn't use it. It is very expensive, and I need a lot of them, so it would increase the price of the construction noticeably. I will try to find another reasonable solution. Anyhow, thank you for your input

RE: The best way to protect a bolt from loosening?

I think dowel pins in match drilled holes near your bolts would be a simple and cheap solution. The dowel pins take the shear loads and prevent any movement, and the bolts provide the clamping.

RE: The best way to protect a bolt from loosening?

(OP)
Well, this is an interesting idea. Never thought of this, though it is a reasonable suggestion. Thank your for advice!

RE: The best way to protect a bolt from loosening?

I'd want to know lots more details about the bolted components. And the assembly method currently used. Installation torque first of all.

Relying on dowels to resist repetitively varying lateral forces makes me very nervous.
There have been plenty of VW ( four 8 mm dowels) and even Porsche ( eight 8 mm dowels) cranks and flywheels ruined, even in non-abusive passenger car service, when the clamping provided by the "gland nut" was sub-standard after a clutch job.
http://www.aircooledtech.com/8_doweling_crank/4-do...

RE: The best way to protect a bolt from loosening?

Developing a long-term solution requires understanding the magnitude of the loads being resisted.

According to this http://bobhooversblog.blogspot.com/2007/04/4-into-... VW didn't originally use much engagement, but US hot-rodders did, with VW copying the fix.

This (http://www.thesamba.com/vw/forum/viewtopic.php?p=3...) write-up suggests that the dowels have clearance holes in the flywheel, which means they aren't ordinarily carrying shear, so when the nut is loose they just get beaten up as opposed to match-drilled, match reamed, and controlled interference fit.

For reference:

4 cylinders at 3000 RPM is 100 impacts per second; 10,000,000 cycles in 28 hours of operation. Since those dowels aren't press fit in both parts, it is reasonable to see that they are undersized for that sort of duty in the material they are joining.

(3000rev/minute)*(2 strokes/rev)*(1 firing/4 strokes/cylinder) * 4 cylinders * 1 minute/60 seconds = 100 firing/second.

RE: The best way to protect a bolt from loosening?

Hi 3DDave,

I think it is less about the dowel fits, and more about the limitations inherent in a doweled joint when it comes to dealing with alternating loads.

IF the VW or Porsche gland nut is tightened enough, and IF the dowels fit snug in the flywheel ( they are always danged tight in the crank ) and IF mating faces are carefully detailed, the joint does not move and the dowels remain perfect for the life of the vehicle in reasonable street use. However, Any deficiency in the installed clamping preload, or mating surface condition and parts are ruined.
As you said, probably by zillions of loading cycles.

Note your Samba link has a few responses about "match reaming" the flywheel and crank using a fixture.
That was the standard method of adding 4 dowels to a VW crank/flywheel back in the 70s. Reaming the crank dry, and the flywheel lubricated (or maybe vice-versa) was done to make the crank fit very tight, and the flywheel somewhat dis-assemblable.
How accurately do you think VW or Porsche could make a few million crank and flywheel dowel patterns?

VW and Porsche abandoned dowels as a significant flywheel attachment detail in the 60s, as soon as their engines exceeded 70 HP or 4 cylinders.

From the beginning the Porsche 911 used a bolted flange connection.
https://transporterwerks.files.wordpress.com/2011/...

The VW 4 cylinder "Type 4" abandoned the dowels, save for 1 for "clocking" location purposes.
http://www.volksbolts.com/faq/fly1.jpg

Ask any Chevy or Ford or Dodge racer about what they had to do to upgrade their 6 or 8 bolted flywheel attachment from 160 to 800 or more HP, and they may have bought some better (non-fitted!) bolts for $20.

Factory DURAMAX flywheel attachment is with 8 bolts. ~ 400 HP and over 750 lb-ft (average) torque, delivered in Diesel pulses.
http://www.socaldiesel.com/rawimages/StrokerKit.JP...

If you need to transmit 10,000 HP and maybe 6000 lb-ft of torque reliably ( at least for 10 seconds ) then this is a proven attachment method.
https://i.ytimg.com/vi/KPBCCuFLCXk/maxresdefault.j...
Looks like 8 bolts to me.

Similarly, it used to be pretty standard to attach automotive flanged hubs to rear axles with a key and a taper fit, with a nut torqued to 100 lb-ft or more.
Practically everyone migrated to axles with integrally forged flanges, probably due to issues with loosening and even long term axle breakage. Granted, wheel loading is pretty complex and variable, but securing the wheel and brake hard against the flange with a handful of bolts/nuts is generally pretty reliable. All I have to do is keep the bolts are "tight enough.".


RE: The best way to protect a bolt from loosening?

For dowel pins to work they must be interference fit and large enough in diameter to to provide a enough bearing area so that the yield strength of the holes is not exceeded. Just like the bolts, if there is any movement in the joint from the impacts, they will wear loose.

Perhaps simply using twice as many bolts could also work. This would be simpler than match drilling dowel pins.

RE: The best way to protect a bolt from loosening?

Are dowel pins going to cost less than larger bolts and Nordloc washers?

Ted

RE: The best way to protect a bolt from loosening?

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.

RE: The best way to protect a bolt from loosening?

I suspect (as many others have suggested) that the bolted joint in the current design is not strong enough for the loads it is subjected to. When you have applied the thread locking adhesive did you see failure of the adhesive bond or did the joint loosen first?

Have you considered trying to dampen the impact forces rather than deliver them directly to your frame structure. If you can add dampened mounts (or even just springs) to this steel wall if could drastically reduce the magnitude of the impact force by spreading the energy out over time.

Also split lock washers are a pet peeve of mine as they preform worse than a flat washer ... at least until the bolt has already become loose.

I have found the NASA fastener design manual to be a good reference, covering the design considerations for bolted connections at a high level.

RE: The best way to protect a bolt from loosening?

Another choice is to use a Dardelet thread. It is a self locking thread. You still may be exceeding the strength of the fastener and stretching, but it won't come loose.

Bill

RE: The best way to protect a bolt from loosening?

Re threadlock...

It comes in various grades - make sure you're using the correct one.

Also, relies on an 'active surface' for it to work properly. Doesn't work as well on Aluminum or SST because of the inactive surface. There are primers available that may help.

http://www.loctite.com.au/aue/content_data/133403_...

I seem to recall that reference has previously been given to a report (NASA?) that points out the limitations of many retaining methods such as Jam nuts and most variations of locking washers. Additionally some locking methods only ensure the nut doesn't fall off completely - but don't install the preload is maintained.

May have been in this forum: forum725: Welding, Bonding & Fastener engineering
This FAQ also came up when I searched: http://www.eng-tips.com/faqs.cfm?fid=1257

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: The best way to protect a bolt from loosening?

I'm assuming most of the respondents have not worked in a sawmill environment. Fancy fixes to this problem will not be appreciated by the customer the next time the line is revised or requires maintenance.

I'm assuming the log is falling from a trim saw or sorting machine onto a drag chain or rollers. Many manufacturers use a small ramp to let the log roll past the chain a small distance up the ramp then back onto the chain to reduce the impulse. This can reduce the mass of steel and fasteners needed in the area substantially.

Re the locktite or similar, well prepped bolts with the permanent grades won't likely loosen but require use of a torch to heat them for removal. This can be a problem if the line is inside near the headsaw or planers, trying to clean the floor and machines adequately for hot work isn't fun.

Unless there is a good reason not to, welding with good details to prevent cracks from forming is an excellent option.

Increasing fastener size and switching to fine threads is another option but increasing bolt length and double nutting works well too. Also re: welding nuts to bolts, its better to double nut and weld the two nuts to each other than to weld to the bolt. Much easier to service later, a grinder or sawzall can cut the weld and the relatively cheap nuts removed quickly.

RE: The best way to protect a bolt from loosening?

I’ve been there with issues where we just could not get fasteners to stay tight. Honestly, I’d suggest moving away from torque based locking methods and find a mechanical solution (“positive locking”). The match drilled pin or castle nut are example of this. Lockwire is another, it is slightly labor intensive but shouldn’t be very expensive per unit.

We have also used lock plates and tab washers that index to something on the hardware to prevent rotation. Tab washers are bent/deformed around the bolt head/nut after assembly but lock plates usually need to be installed first. Maybe modify the assembly operation and install a lock plate on the bolt side and torque against that, then use a tab washer on the nut to lock it after torqueing. You can also design the hardware itself to lock one end of the fastener by making it captive (have a slot that locks the faces of a hex bolt, etc).

RE: The best way to protect a bolt from loosening?

A method discovered by Rolls-Royce engineers was to use nylocks in reverse, that is with the nylon bit going on first. The nylon is squeezed tighter by the nut following it.

RE: The best way to protect a bolt from loosening?

Reduce impact by putting rubber behind the back-stops (steel wall).

Load bolts in tension, with long shanks to absorb impact over the length.

RE: The best way to protect a bolt from loosening?

Any weldment ,assembly if subjected to repetitive impacts, will loosen in time !
I have to agree with bdeuell. deceleration of the item (log) before impact, IMHO ,will lessen the chances
of failure.

RE: The best way to protect a bolt from loosening?

Ever tried lock bolts? Google Huck Bolts. They are used in the rail industry for putting rails an box cars together, the repetitive hammering over the rail joints messed with bolts. They are used in many other industrial applications, are available in a wide variety of sizes and grades. They have special removal tools that make it easy in the future.

RE: The best way to protect a bolt from loosening?

There have been a couple of responses that are getting more towards a non-brute force method, but what I would suggest is just putting springs under the nuts. The springs will maintain tension on the bolt and hold the thing together when it's repeatedly getting pounded by logs.



You just need to find a fairly heavy spring and don't let them torque them all the way down.

RE: The best way to protect a bolt from loosening?

I would be extremely careful using a helical compression spring as this would work on the same principle as a spring washer and the are well documented for loosening under any vibration.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: The best way to protect a bolt from loosening?

Springs are very effective keeping side rod and foot bolt nuts tight on paving breakers and mine drills.

Ted

RE: The best way to protect a bolt from loosening?

desertfox,

The helical compression spring can have a much lower spring rate than a helical spring-lock washer, which will make it much less sensitive to vibration loosening. Having said that, I always favor preload as the primary method to avoid vibration loosening.

RE: The best way to protect a bolt from loosening?

I would add a second jam nut to Kowalski's design, currently the nut is only torqued against the spring so there's very little preload to keep the nut from loosening. adding a second jam nut and then tightening them against each other would lock the nuts on the end of the bolt. this wouldn't increase the preload in the length of the bold but the intent of the spring in this case is not to add preload but to increase the time over which the impulse force is applied to the frame thereby reducing its magnitude.

I think it is still important to understand why the failure is occurring to ensure the solution is appropriate, i.e. is the joint failing because the bolts are not strong enough for the impulse forces they are subjected to or is it failing because vibrations are working the nut loose.

RE: The best way to protect a bolt from loosening?

This thread is drawing more attention than it truly deserves !
Without a schematic of the production line, it is difficult to visualize how the log strikes the stop plate.
Perhaps it's time to go back to the proverbial drawing board.

What happens to the log after it strikes the plate ?

Where does the log strike the plate ,top, center or bottom ?

More detail is needed !

Would hydraulic damping be of value here ?

RE: The best way to protect a bolt from loosening?

Hi

Unless we know more about the external forces that the joints experience using a spring behind the nut could make matters worse.
The bolt preload is limited by the amount the spring is deflected and its stiffness, so how do you know what preload to apply if the external forces are unknown?
A bigger problem with the spring and nut arrangement in this particular instance is spring ratcheting, this can happen during any impact and the spring as a tendency to rotate, if this occurs the nut could be slowly rotated off the bolt as the spring relaxes it's preload.
The final problem is also one of spring natural frequency because if the logs hit at regular intervals the spring alone could vibrate and again loosen the joint.

Just to give some idea of what might be involved in maintaining bolt preload using a spring I've attached this link to a paper on using beiville springs for the same purpose:-

http://www.sealing.com/fileadmin/docs/Using_Bellvi...

To use a spring behind each bolted fastener seems an expensive and time consuming option if you want to design it correctly and I don't think this application warrants this.





“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: The best way to protect a bolt from loosening?

Drill a hole through the nut and bolt and use a stainless steel tie wire. I've never seen a tie wired nut and bolt come loose.

Bill

RE: The best way to protect a bolt from loosening?

I used to think that lockwire was an absolute protection against fastener loosening.

... until I heard a rumor about a union nut on a high pressure ball valve that was so thin that it could be stretched enough to jump a thread (without rotation and without fracture of the lockwire) when the face seal o-ring failed.

( Those of you who work in hydraulics know that when a face seal o-ring fails, the effective area producing a separating force goes from the area corresponding roughly to the o-ring ID, to the projected area of the entire face, in this case, roughly the area corresponding to the inside diameter of the union nut, effectively roughly doubling the separating force. )

Of course, it was just a rumor, as was the rumor that the design persisted despite several known service failures, because an engineering vice president held a patent on the particular stupid valve design.

... like that ever happens.

Mike Halloran
Pembroke Pines, FL, USA

RE: The best way to protect a bolt from loosening?

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.

RE: The best way to protect a bolt from loosening?

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).

RE: The best way to protect a bolt from loosening?

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.

RE: The best way to protect a bolt from loosening?

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

RE: The best way to protect a bolt from loosening?

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

RE: The best way to protect a bolt from loosening?

+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
www.phoenix-engineer.com

RE: The best way to protect a bolt from loosening?

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 !

RE: The best way to protect a bolt from loosening?

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

Link

RE: The best way to protect a bolt from loosening?

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.

RE: The best way to protect a bolt from loosening?

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

RE: The best way to protect a bolt from loosening?

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.

RE: The best way to protect a bolt from loosening?

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.

RE: The best way to protect a bolt from loosening?

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

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