It is no exaggeration to say that without nuts and bolts, the world would fall apart. Bolt connections are everywhere, from the frame of the DIY 3D printer to the lug nuts that hold the car wheels. Although the latter's failure penalty is definitely higher than the former, the self-loosening of nuts and bolts is rarely a good thing. Engineers have come up with dozens of ways to ensure that the world does not fall apart, and some methods are better than others. Let us explore some of these methods to find out which ones are effective and which ones are ineffective. In the process, maybe we will understand how these fascinating fasteners work.

There are many ways to fail a bolt connection, but self-loosening caused by vibration may be the most insidious. Anyone who has ever knocked on a stuck bolt or used an impact wrench to remove a rusty nut knows that vibration can really help. Put the same joint into service and subject it to proper vibration, the connection is likely to loosen on its own and cause the joint to fail.

In the 1960s, German engineer Gerhard Junker studied self-loosening and concluded that lateral vibration was the cause of bolted connection failure. He designed a simple test device that can provide fast lateral vibration and use a load cell to monitor the pretension of the fastener. The pretension as a function of the number of cycles of vibration draws clues to the effectiveness of various locking methods. This test is called the Junkers test, as the standard DIN 65151, it is still the gold standard for testing self-releasing.

There are some fascinating videos showing the actual effect of Junker's test, and some videos are very scary. Usually, we will install a simple spiral spring lock washer on the stud or bolt, tighten the nut, tighten the nut, and then call it a day. It feels like we have made a strong joint. but it is not the truth. In fact, the video below shows that not only does the lock washer hardly increase the safety of the bolt connection, but other commonly used methods (flat washers, nylon insert nuts, and stacking nuts) do not help much.

Obviously, the video above is aimed at marketing the company's fancy wedge lock washers, and it's clear that they work well. But why do they still work when a simple lock washer fails? To answer this question, it is necessary to see what else works, something that has not been tested in the video-a properly installed lock nut.

A lock nut is a low nut, usually half the height of a standard nut, and is installed under a larger nut. After installing the lock nut, tighten it only to about a quarter to half of the full final torque. Next, install the thick nut and tighten it to the final value, while holding the lock nut in place with a wrench. This effectively pulls the bolt up through the lock nut. Then the thread of the bolt contacts the top side of the internal thread of the lock nut, and at the same time contacts the upper side or the pressure side of the top nut. Since the top and bottom nuts provide opposing forces on the bolt, the chance of the nut self-loosing is much less.

A similar mechanism works in wedge lock washers. The two halves of the washer have interlocking wedges whose angle exceeds the pitch of the bolt thread. When the bolt is tightened, the higher pitch of the washer pulls the bolt back up, providing the opposite force to jam the thread and prevent the fastener from loosening.

If we look at all failed locking methods, they all have one thing in common: they all rely on friction. Lock nuts and wedge lock washers provide tension against lateral vibration that causes self-loose, and are therefore more effective.

Of course, there are other ways to lock threaded fasteners. I thought of adhesive thread lockers, and more complex methods such as wired nuts and lug washers, which may be very effective methods. But for low cost and easy installation, it is difficult to beat a simple lock nut to prevent the world from falling apart.

"It is no exaggeration to say that without specific details, the world would fall apart."

Another episode of the soap opera sponsored by Procter & Gamble, "With the Rotation of Nuts".

They obviously have never heard of E7018... and who cares what marketers think?

Giggling…he used the words "marketer" and "thinking" in the same sentence. …… what! ! what! ! what! ! I just did it too! !

How is the "jam nut" different from the double nut they tested? What is the difference between halving the width of the lower nut? Considering that they are greased on the threads, I did not expect the performance of the lock nuts to be any different.

Oh, when I tried to find out what I saw on the "jam-nut" wiki page, it links to: http://www.boltscience.com/pages/twonuts.htm, which contains several from Junker The small nuts above and below the main (large) nut are tested, although the bottom has a "loop" instead of the "time" done in the marketing video (we have never seen the installation method of the double nut).

(I haven't watched the video)

Lock nut: You will not tighten it, but hold it in place when you tighten the "main" nut

Double nut: When you use the upper nut, the lower nut can turn, so both nuts (possibly) are engaged on the lower surface of their threads.

Except for the size of the second nut, I did not see the difference between the lock nut and the double nut shown in the video.

If I understand it well, not enough friction is the cause of the loosening problem. How about pour the abrasive into the thread before the final tightening? Nuts and bolts need to be replaced every time they are unlocked, but at least it is easier and faster to remove them than to remove the rivets.

During installation, you only need to center the nut/bolt boundary and pop out. All problems are solved except for removing it when necessary. :)

Oh, you will hate yourself.

This actually works very well, unless this thing is screwed to F-tight, you can easily get enough torque to release it.

You can even place a solder joint at the connection, and if you need to undo it, just grind it back.

The heat generated by welding will destroy the bolt/nut tempering.

Anything other than the abrasive entering the fastener connection?

Depending on the abrasive, it may crush under pressure/vibration and wear the fastener surface during installation. I suspect that this combination might actually make the fastener loosen faster.

The powder will eventually work like miniature ball bearings between joints.

There are already products made specifically for this purpose. Called thread locker, it is a kind of glue that hardens without air. When you buy a bottle of it, it is always half empty, so the air inside keeps the glue liquid.

I'm pretty sure this is not its cure; it needs metal ions.

PS Or maybe there is some very hard sand between the washer and the nut, the washer and the bolt head?

...Or a drop of ScrewGrab, something you use when you have a bolt or screw with a peeling groove. It appears to be a finely pulverized particle of tungsten carbide in suspension, biting between the tip of the screwdriver and the groove. This is the closest thing to magic in the tube, and it has saved me many times. No contact with the manufacturer, just a fan of the product, I totally recommend it to anyone. I bought a small tube 15 years ago and it may last my life.

Combined with impact driver. There is also the technique of sticking the drive bit to the fastener. One it hardens, take both out and throw away.

After the bolts are loosened, you can use heat to break the adhesive and restore your drive bit

This is a wrong generalization because it tests the situation where two bolted surfaces can slide freely against each other. This is an incorrect design because the bolt itself should not be subjected to lateral loads-it should simply press the two parts together.

In a properly designed bolt joint, the tension on the bolt is sufficient to withstand any force that may cause the two surfaces to slide and the joint to move, so the lateral vibration depicted in the small gif animation does not occur at all. If so, you will fire the engineer who designed the joint or the technician who installed the joint but forgot to tighten the joint properly.

In some structures, this looseness is unavoidable because the material will bend and may be significantly deformed, such as in car brake discs. In these cases, you can drill a hole in the bolt and then thread a wire or pin through it to make sure it will not loosen.

-Spring washers or wave washers are almost always completely useless. When you fully tighten it, the spring will flatten, just like a normal washer. They are intended for use in mechanisms where bolts form hinge pins, so spring washers provide them with some slight tension.

-Washers are usually harmful because you now have two movable friction surfaces instead of one friction surface. If the materials to be connected are too soft to withstand the tension in the bolts, use them, so the washers spread the load over a larger surface area. If the material is not soft, the gasket should not be used.

-When the two pieces to be connected are not thick enough, washers are also used. The material of the bolt is like a tensioned spring. If the spring is too short, it is easy to be over-tightened/over-tightened, or when the clamped material is deformed under pressure, it may lose its tension because it only stretches A few microns, so the washer gives it some extra length and extra travel. If the parts to be connected are not thin, washers should not be used.

I am familiar with aircraft riveting, and the clamping provided by the rivet is an important part. The correct rivet work will not produce any lateral force on the rivet. Similarly, bolts are very strong springs, and tightening them is to treat them as springs. For example, head bolts with excessive torque may exceed their elastic limit. They are no longer springs and must be replaced.

However, I do not follow the part about the gasket; perhaps because the real behavior is not as ideal. Under ideal circumstances, friction does not mention surface area. Friction is simply the normal force multiplied by the coefficient of friction. The friction of the nut and washer is the same as that of a separate nut. The friction between the fastened part and the washer is the same as the friction between the washer and the nut, and the latter is the same as the friction between a separate nut and the part. It does not matter how many washers you stack. What happened to make this not true in the real world?

For friction, there is mechanical friction, that is, uneven surfaces lock each other, and chemical friction or more appropriate adhesion, which is mainly acted on by electrostatic force, and then there is surface deformation related to mechanical friction. When the same force is spread over a larger area, the contact surface of the hills and valleys deforms less, and the friction of the joint becomes smaller, so it is easier to slide.

You can think of it as a plastic sled for children on the snow. If the sled is small, the child sitting on it will cause it to sink into the snow, and it will not slide much, but if the sled is long and wide, it will not damage the surface and will slide easily. Push it, it keeps going, and in the first case, you push it, and once you release it, it stops.

But contrary to intuition, racing cars use fatty tires-because they provide more surface area, because the hot rubber leaning on the road is sticky and provides greater grip, especially when the tires start to skid. The slender wheels have almost no lateral dynamic traction, so those old cigar-shaped race cars with motorcycle wheels are truly deadly traps-they come out with just a little slip.

So the friction in the high school version is not entirely accurate. It works under moderate surface pressure, but when you deal with nuts and bolts that will be tightened near the elastic limit, they will bite into each other and the simple description of friction no longer applies.

I just want to say that if thin tires are made of the same material, they have the same friction as fat tires, but the surface contact area is too small, and the force is more likely to exceed the strength of the tire material and rubber. More square inches of contact means less force on the material per square inch, and hopefully it will not tear. In addition, modern racing cars have high downforce, which greatly increases friction.

The normal force multiplied by the coefficient of friction is why rock climbing shoes work well on small "chicken heads" and flat places. That is, unless the rock is so small that the force will tear the sole material.

Based on your description of bolts and washers, I don't understand why a stack of washers is different from a single washer or a nut with the same surface area as the washer.

"Over-twisted bolts may exceed their elastic limit. They are no longer springs."

This is not entirely accurate. They are still springs, but they will have permanent elongation. Exceeding the elastic limit will cause work hardening, which will change the characteristics of the steel, so you now have a bolt that is different from other bolts, the number of which is unknown, and the head may be warped. Qu gets hot with the weather.

Sometimes the bolts are deliberately over-tensioned, and I forgot the exact reason.

This is why the head bolt should be replaced when you remove the head bolt to work on the head. The torque specifications they gave "stretched" them to the point that they no longer meet the specifications.

They are sometimes over-tightened, because this is the maximum force they can withstand, no matter how much it is, you will only make them longer and narrower ;-)

Putting the fastener into the plastic range mainly changes the unloading length. It does not change the spring stiffness, that is, it does not change the shortening of the fastener when unloading. Confusingly, the tensile test of the material is based on the original length, so when the material begins to yield, the slope of the stress/strain curve begins to flatten. Early in the process and before the fastener significantly shrinks, the release of tension will show a linear relationship between stress and strain, which is parallel to the original elastic curve.

The inherent elasticity of metals is due to the atoms in the crystal changing their distance while maintaining bonds. As long as there are crystals, the metal will be elastic. (Metallic) plastic deformation occurs when atoms in the crystal begin to transfer to neighbors. They are still connected, just connected to a new location.

Especially for head bolts, the torque for mounting bolts is generated.

A tightening method measures the relationship between the rotation and torque of a continuously tightened fastener, and detects the change in rotation/torque as a sign that the fastener has begun to yield, which means that it has been loaded to the maximum load it can handle. This is a valuable method because it does not matter what the friction is and does not leave any unused tension capacity. Since elasticity is a characteristic of bulk materials, the yield strength can be tested by sampling, and the diameter can be controlled, which makes the joint have a very tight and uniformly controlled fastener tension. Generally, these fasteners will have a precise ground diameter where plastic deformation will occur.

In some cases, the installer skips the torque and rotating equipment and generates instructions that guarantee plastic deformation of the fastener. This is a more crude method, but it achieves the same end result, except that it does not minimize necking. The command is to adjust the torque to a moderate value, and then turn a certain number of turns, which will be enough turns to produce a bolt.

As mentioned earlier, this is all good, but every time this method is used, there will be fewer and fewer fasteners. Depending on the sensitivity of the revolution and torque measurement, especially in the torque and revolution methods, this may be a large number; therefore they are not reused.

If the fastener does not apply enough load to force the gasket faces into close contact, gasket stacking may be a problem. If there is a gap, there is a possibility of movement, and the direction of movement will eliminate the preload. The more washers, the larger the gap. A single thick gasket is a better choice.

There has been some significant progress in understanding how friction works. The best theory is that every surface has small protrusions called bumps, which collide with other surfaces. In the past, people thought they were mechanically interlocked, but why are the friction levels different? The current experimental theory is that they are more like tuning forks, flicking each other to make them vibrate. The higher friction is due to uneven joints and causes greater vibration. Friction is the energy lost due to heat when the material suppresses vibration to a stop.

A lower contact area means that those contacting areas have a higher degree of engagement, which makes the friction force only dependent on the appearance of the normal force. For general use, this simplification is correct.

This only works if the surfaces are very close to the point where they can share electrons, and the van der Waals force takes over and the surfaces begin to glue-as can be seen in screwing gauge blocks together and gecko toe hair on walls and windows. At higher levels, wear will occur with material transfer.

Otherwise, this friction theory is very suitable-polishing tends to remove long unevenness, which will require a lot of energy to vibrate, and polished surfaces tend to reduce friction. Harder materials have a harder roughness, so they don't deform too much, don't store much energy, and have lower friction. Rubber stretches and can store a lot of energy-so there is a lot of friction. Graphite layers are weaker between layers and harder inside layers-so there is not much friction. (Did I mention that this is greatly simplified? Just a reminder.)

OK. I thought that when they gave in, they would lose their temper or the modulus of the young man changed or something similar. I have students who often unscrew the heads of 8 types of bolts, which are used to compress chemicals into the disk used in the infrared spectrometer. I must equate it with what happens when you start stripping.

Still can't imagine the stacking problem. The force on all interfaces is the same and equal to the force on a single washer. The force will not be distributed between the washers, otherwise the force on the top washer will be zero and the force on the bottom washer will be the greatest. Testing on a vise with a few hands will show that this is not true.

Each gasket has an uneven surface, which creates a small gap. When you screw the two washers together, they will not fit perfectly, and vibration tends to make them stick and slip.

The reason that the bolt joint must be designed tight enough to hold the parts together by friction is that if the joint is designed to be "loose" so that the parts may slip, the parts will be fretting when they rub against each other under load, and this is very This will quickly cause cracks to form on the surface, even if the bolt is locked in place and cannot move, it will quickly lead to fatigue failure of the joint.

It is possible and sometimes permissible to design a joint that is held together by the shear force of the bolt itself, but it would be foolish to do so under dynamic loads. If you think you may need a lock washer or lock nut to prevent the bolt from loosening, please return to the drawing board and design a better joint.

Use rubber washers under compression to increase friction and allow a small amount of elasticity between the surfaces.

At this point, the bolt is only used to maintain the clamping. If lateral movement is possible, sockets, pins, hollow pins, bonding features, etc. should be used to bear the load.

Advertisements use positive cases to sell products shocked!

Just like those shopping channel gadgets; "Are you tired of knocking over your Cheetos bowls?"

http://cdn.gifbay.com/2012/12/thanks_obama-16196.gif

When fixing the safety ground cable to the amplifier chassis, I always feel a little uneasy. Can you recommend the safest way to install the bolts on a single metal plate that will vibrate without loosening?

For higher output, please consider PEM fasteners. They are crimped on the metal plate in a reliable way, but they do require suitable installation tools, so they are difficult to use at once. I also fix the cables to prevent the load from vibrating so that they can be applied to the connectors.

This is a hobby project, but thanks for your suggestions.

The second nut is tightened on the first one.

I have always wondered why my nylon insert nut is still loose! thanks.

Are they fully engaged with the threads? In the video, I find it suspicious, like the bolt is a bit short, so the nylon insert does not fully grasp the large diameter. They are also considered suitable for only a few bolt cycles, because nylon can deform, so they are not suitable for frequent loosening.

I have been reusing them and it is definitely my fault.

Nylocks are like condoms, you can reuse them, but you really shouldn't.

The authoritative (readable) paper on fasteners is almost Carol Smith’s fourth book, followed by Tune to Win, Drive to Win, and Preparing to Win, appropriately named "Nuts, Bolts, Fasteners and Piping Handbook". It will tell you more about fasteners than you want to know. When you see how things are maintained in the real world, please frighten you.

Carol wanted to name it "Screw to Win", but the publisher refused. If you buy a copy from Carol, it will have a sticker in the correct style, etc., which can be placed on the cover.

For those who don't know Carol, he is an amazing aerospace and automotive engineer who has won victories in all forms of car races. What an amazing guy. Years ago, I was lucky to spend a few hours with him and another Carol (Shelby). Unbelievable time, I will never forget.

"Engineer to Win" is my favorite. It has many chapters on bolting and metallurgy, and overall it is pleasant to read. I am so jealous that you have to hang out with two Carols!

Nord locks are a godsend for things that move due to thermal cycling, namely turbocharger/manifold joints...In addition, a properly designed joint without movement will pass the correct torque and spots Ordinary nut stays firm...I like a nylock or pin nut, as if the fastener is a bit lost, it will rattle/degrade in performance, etc., but will not be completely separated from its installation, so for example, the suspension arm may be It rattles, but does not fall off completely. The mylon part (or pins, etc.) is like a second layer of security. My background is purely automotive, so please forgive me for my ignorance.

For all strong purposes, when it is clamped or bolted together, can all this north lock prevent the nut from vibrating from the bolt, just like fixing the tire nut to the wheel (for simplicity)... .If I am wrong, please correct me (because they demonstrated that you can’t correct me)...but all this is to ensure that the nut does not vibrate. Somewhere in the video, they said...I am confused about this.... "Adhesives are considered'safe', and regardless of repeated testing, there will be significant differences in their performance in maintaining clamping loads... These solutions are largely up to the operator"... How to Lock Tite 、Lock Tight...How do you want to spell it differently from Nord Lock? Frankly speaking, they have different strengths from light to permanent (I had to use a flashlight to heat the bolts, and use a permanent one to break 2 wrenches without it) LT I don’t think the heat problem will affect it, in It is -500 degrees on my engine 300, and I had to screw the torch to a height of more than 1k to loosen it slightly. I think Lss perm will do. However, no one has tested these. LT will be cheaper, you can use it multiple times from a bottle or tube, it is cost effective because it is cheaper to use than Nord Lock, because I bet you can only get a pack of 3-10 about 5-10 dollars ? So you can only use them once? From the appearance of it, they are not hardened, the bottom is squashed, and the top threads look warped or at least flattened. If you are lucky, they may stay at the top 3 times, but I think they can only stay at most 2 times. But they seem to be used all 1 time. So if you have to replace them every time (or worry if you use the second one)... then why use them instead of LT, because you have to reuse it anyway when you remove the bolt/nut. Yes, you can buy them in bulk, but even so, I used 1-3 drops of LT on the bolts on the truck, from the engine to the wheels, and I never need to redo them.

All in all, if LT doesn't move at all, how can it reduce the clam load? The bolt mentioned above does stretch over time. This is physics... Whether you use NL or LT, you can use either method. It doesn't matter, it will stretch for a period of time.... But this has nothing to do with vibration...Vibration and stretching are two different things.

As for "heavily dependent on operators" WTH? Shouldn't you rely on your "operators" or "technicians" because that is their job? (General) So you have to hire an idiot to do your bolt connection, he is not trained to remember to do things like putting LT on bolts. This is why we have technicians to remember and trust them...I believe that the 100KV wires on my head will not fall on me and shock me, because I believe this city will hire people who know what they are doing People don’t at least put LT on the bolt so that it doesn’t fall on my head. What are they talking about, if I’m right, we should now hire untrained people to install things, and don’t know that they install things from a hole in the ground, because these NL things cause and/or people are against them 'S work is so stupid! I really got something out of it.

Psst, this sentence is "for all intents and purposes"

However, yes, their videos have many loopholes and are easy to be censored. Like many things, if they are installed improperly, almost everything will fail, so it depends largely on the skill and care of the people who work.

Yes, I'm sorry... I was so angry... I didn't check or even proofread my posts. Thank you.

At least I am not completely crazy and think like this. I thought I lost it somewhere (mentally), or just lost the meaning of things.

> Then the thread of the bolt touches the top side of the internal thread of the lock nut, and at the same time touches the upper side or the pressure side of the top nut.

This is confusing-is this standard terminology?

The "top" side is the opposite of the "upper" side? !

Or maybe it was a typo, it should be read as "reduction or stress",?

Interesting article, I am often asked to put star-shaped or split washers on things, but because I am an electrician, I will not bother to argue about this issue...

The video is very interesting and also an explanation of the new invention, but in the comparison, they do not include toothed washers, as far as I know, it should work on the same principle.

What about the safety lines used in aviation?

And racing. PS, if you want to buy a second-hand sports car or motorcycle, please look for the small holes drilled in the drain plug of the engine and transmission oil pan and the nearby heat sink or other parts. Racing rules require wires to pass through these holes to prevent the drain plugs from loosening and dumping large amounts of oil onto the track. Therefore, if the product you plan to buy has these small holes, it is likely to have been used at some point.

Now, if it has already participated in the competition, is it a good thing or a bad thing? If the seller doesn’t mention it, then the engine is probably being abused, right? But then again, most racers treat their machines very well.

The article is not ripped from https://engineerdog.com/2015/01/11/10-tricks-engineers-need-to-know-about-fasteners/?wref=tp at all

I am surprised that there are so many comments... and there is no link to NASA's fastener guidelines.

Coil spring washers are clearly stated on page 9. "All in all, this type of lock washer cannot be used for locking." However, the nylon insert nut is good, but it can only retain about 20% of the initial clamping torque, as you can see in the video above. But they can only be used once.

Serrated (tooth) washers are great for locking, but they can damage the surface.

NASA’s guidelines call jams unreliable, which is not surprising, because they are too easy to screw up.

Not mentioned, but it's not cheap either. http://www.smartbolts.com/

This may save tens of thousands of dollars on my site. What was bad was that several bolts broke, and the whole machine started to self-destruct. No, I will not go into details.

Checking the bolts every day for instructions will have to become an SOP. Is there a more obvious version for the tall bolts near the top of the machine?

Many years ago, I saw a product that would cause a broken bolt to "bleed". A small tube was drilled into the bolt, which was filled with red liquid. When the bolt breaks, the dye leaks and is very obvious. The example given is an airplane landing gear, which works very well. I don't know if it goes anywhere (it will be very expensive), and there may be something similar for loosening bolts (the dye flows back along the loosening line).

OK! I will investigate.

Someone mentioned that nuts like this are only suitable for a few inconveniences. I want to build ul-listed assemblies in a field, use these for their lists, and they will become a miracle. If you take it apart, you will use a new gasket. As mentioned earlier, the ridges are flattened, so the characteristics of the washers have changed and they will no longer work in the same way. But for those who are required to follow instructions, inspections, and code, this is not an uncommon problem. Aircraft mechanics spend a lot of time rewiring bolts after major repairs. Mechanics will not reuse the oil in the vehicle they took out of the oil change (unless they hacked it and dumped it on the driveway). Wire nuts are classified as disposable products Pv panel installers use only weebs to bind the panel to the shelf component icbm, not reusable once I eat the pie, I will not reuse it

"Mechanics will not reuse the oil in the vehicle they get from the oil change"

But they did so-they just sent it elsewhere for filtering and cleaning, and then bought it back in buckets.

Someone mentioned that nuts like this are only suitable for a few inconveniences. I want to build ul-listed assemblies in a field, use these for their lists, and they will become a miracle. If you take it apart, you will use a new gasket. As mentioned earlier, the ridges are flattened, so the characteristics of the washers have changed and they will no longer work in the same way. But for those who are required to follow instructions, inspections, and code, this is not an uncommon problem. Aircraft mechanics spend a lot of time rewiring bolts after major repairs. Mechanics will not reuse the oil in the vehicle they took out of the oil change (unless they hacked it and dumped it on the driveway). Wire nuts are classified as disposable products Pv panel installers use only weebs to bind the panel to the shelf component icbm, not reusable once I eat the pie, I will not reuse it

The technique I used once or twice is to make flat washers with coarse sandpaper. Make two and put their rough sides together with a little glue in the middle. Want to know how this will happen in the Junker test.

It would be great if you use appropriate lock nuts, toothed flange nuts, and nuts in combination with toothed/overlapping washers for these tests...:/

Let us not forget the split pin, which has been used by the automotive industry for a long time to lock wheel bearing nuts.

This is interesting when you say that vibration will loosen both and may cause them to fail. My father is looking for U-bolts for his truck. I think I will let him read your article for further reference on how to use bolts effectively.

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