Lock washers don't work?

[bcp]

I was looking for some information on when to use which type of lock washer: split, internal tooth, and external tooth.

I found good material on the toothed ones (use internal with small heads).

On split washers, several comments showed up that they didn't work, such as this:
----------------
From:
http://www.boltscience.com/pages/helicalspringwashers.htm

"Helical spring lock washers have been in use for well over 100 years. They are still used on many applications in the belief that they will will "lock" the nut/bolt to the joint and prevent loosening. The body of evidence, based upon both experience and experimental results, is that they do not prevent loosening and can be shown to actually speed up the rate of loosening in many cases. "

(Interesting videos linked at page)

------------------
More searching found a NASA report:

http://gltrs.grc.nasa.gov/reports/1990/RP-1228.pdf

Recommendations are usually for using lock nuts or bolts of various types, and not lock washers.

I've been using mostly split lock washer on machinery most of my life, and some have loosened. Maybe I'll start using toothed ones more.

What do you think?

Bruce

 

[k0ua]

Well, its like a lot of things I was taught in school that later proved to be false. I have always wondered why sometimes fastners with spring washers came loose anyway, I knew they were not much good, but continued using them because they are cheap and I was always "told" to. I also knew that nylock or the kind of bolt head with the ridges that catch when it is loosened were very good, but rarely use them because of the cost/availability. Oh well live and LEARN! Thanks for the info.:thumbsup:
James K0UA

 

[doall]

I hate nylon nuts. but have always had good luck with split lock washers. If the nut loosens a fraction the edge should come up a touch and bite into the nut on one side and the base material on the other(but I don't believe that either). So for me I guess lock tite is the best option. or crown bolts and cotter pins. I know i will continue to use split lock washers though.

 

[ray66v]

My brother is an engineer at the same NASA facility, so I knew about this when it was researched, decades ago.

I have thrown them away since.

However, like many old traditions, using lock washers, still won't die.

 

[Baby Grand]

Weather or not they will work will depend on a lot of things:

Installation torque.
Coeffient of friction between the threaded parts.
Coeffient of friction between the materials contacting the helical washer.
The hardness of the materials contacting the helical washer.
The pitch of the thread.
The amplitude and frequency of the vibration.
If the bolt loses proload due to reaction loads or thermal loads.
Probably a few I have overlooked.

In the case of space vehicles (what NASA does best) they are a poor choice. In the case of an adjusting bolt on a rear blade, they seem to work fine for me. Pick your poison carefully.

-Jim

 

[Mickey_Fx]

Interesting topic. I see that someone mentioned Loc-Tite. I'm a fan of these types of thread lockers. They do come in various strengths and one should be knowledgeable in which is the correct one for the application.

One area where they are especially good is in applications where rust/corrosion is an issue. Properly applied the thread locker will seal the threaded area between the nut and bolt. Corrosion then can't form so you don't end up fasteners that can't be disassembled.

 

[SPYDERLK]

Split lock washers can be very effective when the split point is designed so that it bites in. I have had just snugly tightened temporary fastenings bite both sides scoring the metal surfaces as the nut is removed. I have seen them bite enuf in a long term joint that the washer is unwound and destroyed during disassembly. A lock washer under both heads is totally effective if they bite. Still, when I service a joint I take them off and replace with high strength flat washers and tighten the joint to the top limit of torque or a little more. The larger flat washer spreads the intense clamp point a little, stabilizing the assembly and reducing the crack potential. A truly stable joint wont loosen.
larry

 

[BHD]

this is my take and understanding on Lock washers,

If one torques the bolt properly and the bolt is properly sized, is the best way to keep the nut on tight,

the reason why a bolt looses it because it moves, to torque a bolt properly, one tightens the bolt to where it has all the stretch removed yet not stretching it to a point of failure,

if it tightened to less than torque specification the bolt will stretch and move thus giving it opportunity to loosen,

about the only location where lock washers are used in abundance is in agriculture,

and I think the reason is that bolts are not torqued the majority of the time, and in many applications in flexing frames and to hold on tillage tools and so on is that there is frame flex, and there is dirt and wear, that keeps one from properly torquing the bolt correctly, and so many bolts in Ag related situations the bolts would not work for the designed purpose if they were torqued to proper specifications,
the lock washers are springs and have edges to bite the face, and the bolt or nut,

and I am under the impression that some lock washers actually hinder the proper torquing of the bolt,

(we have a old fork lift, and we could not keep the bolts on the frame to the axle tight about ever few weeks tighten them up, I finally bought a planetary gear head torque multiplier Torque Multiplier | Torque Wrenches | Northern Tool + Equipment and then used the 3/4 torque wrench to tighten them to estimated requirements, and they have not loosened since),

 

[SPYDERLK]

Interesting topic. I see that someone mentioned Loc-Tite. I'm a fan of these types of thread lockers. They do come in various strengths and one should be knowledgeable in which is the correct one for the application.

One area where they are especially good is in applications where rust/corrosion is an issue. Properly applied the thread locker will seal the threaded area between the nut and bolt. Corrosion then can't form so you don't end up fasteners that can't be disassembled.

Very good points. I use them too. #638 is my favorite for hi strength bolting. Very strong, but loses enuf strength at 200-300F to be readily removed without damage to rubber or other heat susceptible stuff.
larry

 

[brandoro]

I'm a fan of chemical locking as well. Loc-tite 242 is my most used. One advantage I like is that I always have the right size.
I occasionally use Ny-lock nuts as well but don't always have the right size. Generally use those on things I don't expect to need to disassemble.

 

[Renze]

We install critical parts of the wheel loaders at work, such as the fan, driveshaft flanges and the axles, with Nord-lock washers. Thats the best mechanical method, period.
For anything else that will never need loosening again such as head studs, use Loc-Tite.

 

[eepete]

I tend to use the nylon topped nuts a lot. Just buy them in boxes of 100, stainless, nylon top. A little extra money, but no problems. Recently discovered the various strengths of Loc-tite, and have started using it more.

There is one area where the split ring lock washer is used, but it's in electronics. When you have a screw holding a part (transistor, TO-220 or other type package IC) down on a heat sink, you use one. The idea is that as the heat sink expands and contracts, you can keep constant force between the package and the heat sink. Good for two reasons- first off, the heat sink grease can cold flow out a bit. Secondly, the lock washer avoids stressing the package, which can cause micro fractures on the plastic or ceramic that can lead to long term reliability issues. Yeah, I know way out there and non tractor but I still have some number 4 and 6 copper split ring lock-washers that I use for this. In production, I've use steel split ring lock washers too. It also lets you use a cheap style of insulator (a plastic) for the screw that goes through the heat sink. As the plastic does a little cold flowing in the initial year or so, the lock washer picks up the slack. Note the torque levels for this stuff is really low compared to tractor stuff. Also good to do this with nylon nuts, so the bolt and nut will never come loose and the split ring can do it's thing.

Pete

 

[SPYDERLK]

I tend to use the nylon topped nuts a lot. Just buy them in boxes of 100, stainless, nylon top. A little extra money, but no problems. Recently discovered the various strengths of Loc-tite, and have started using it more.

There is one area where the split ring lock washer is used, but it's in electronics. When you have a screw holding a part (transistor, TO-220 or other type package IC) down on a heat sink, you use one. The idea is that as the heat sink expands and contracts, you can keep constant force between the package and the heat sink.
Pete

Bellville washers are well suited for this because their force is symmetrical about the center.
larry

 

[eepete]

Yes, they are good too. There's a whole level of detail here depending on what you are doing, the parts, heat sink thickness, the heat they make, cost concerns, etc. I've had MBA bean counters change out the "good" bevel spring washers for split rings to save a penny. Then they turn around and blow $5 on some fancy back-screened mylar front panel. :confused2:.

I was working on a siren unit for a fire truck this weekend. They took a sheet metal screw and worked it in from the outside of the chassis, through the hole on a TIP36 (i think) transistor heat fin and pulled it to the chassis. So the heatsink/fin on the transistor was also the sheet metal nut . The transistor was at an angle. There was no grease on anything. The manufacturer cost reduced the siren horn more so it is what went bad.

This thread is interesting because it shows how there are general hardware parts, but then in specific areas there are some types of hardware and lock washers that you must use.

Pete

 

[Danno1]

.

And then there is the Spiralok thread form. I think this may have come from NASA too. But it's patented so you can only buy the taps from Spiralok. This = $$$.

Spiralock | Your Threaded Fastening Solution


That Bolt Science site is pretty good too. Found it a few years ago. Did anyone check out the tutorial on bolted joints?

.

 

[paul dyar]

I quit using the split lock washers over 20 years ago. A lot of corporations know they don't work and they continue to use them. Because that is the way they have always done it.
Paul

 

[tulenutn2o]

I was looking for some information on when to use which type of lock washer: split, internal tooth, and external tooth.

I found good material on the toothed ones (use internal with small heads).

On split washers, several comments showed up that they didn't work, such as this:
----------------
From:
Helical Spring Washers

"Helical spring lock washers have been in use for well over 100 years. They are still used on many applications in the belief that they will will "lock" the nut/bolt to the joint and prevent loosening. The body of evidence, based upon both experience and experimental results, is that they do not prevent loosening and can be shown to actually speed up the rate of loosening in many cases. "

(Interesting videos linked at page)

------------------
More searching found a NASA report:

http://gltrs.grc.nasa.gov/reports/1990/RP-1228.pdf

Recommendations are usually for using lock nuts or bolts of various types, and not lock washers.

I've been using mostly split lock washer on machinery most of my life, and some have loosened. Maybe I'll start using toothed ones more.

What do you think?

Bruce

We actually studied this in Computer Aided Design Class. Flat washer or no washer is better than a split "lock" washer. At certain frequencies, they do speed up loosening. Neat stuff.

 

[Reg]

Weather or not they will work will depend on a lot of things:

Installation torque.
Coeffient of friction between the threaded parts.
Coeffient of friction between the materials contacting the helical washer.
The hardness of the materials contacting the helical washer.
The pitch of the thread.
The amplitude and frequency of the vibration.
If the bolt loses proload due to reaction loads or thermal loads.
Probably a few I have overlooked.

In the case of space vehicles (what NASA does best) they are a poor choice. In the case of an adjusting bolt on a rear blade, they seem to work fine for me. Pick your poison carefully.

-Jim

Hmmm, I thought it was mostly about thread deformity, bolt "stretch", thread profile and coeff of friction - all of which get figured into recommended torque values.
I have been under the "impression" for some time that there is little/nothing to be gained beyond proper torque setting - so Yes, if it is going to stay the split washer is redundant and if it isn't torqued right then the washer won't hold it.

Ahh, there might be a "human factor" involved, i.e. folk who think split washers work may bother less with proper torque values.
Same with factory assembly processes (shoddy manufacturing engineering processes) "We have split washers in there, no need to use torque wrenches at that station."

 

[varmint]

Yet another great educational discussion on TBY! I remember that back in the day that my dad was in the aviation business, beginning with piston engines and finishing with a fleet of DC-9s, there were no split lock washers. Inside toothed, more often deformed lock nuts, and when it had to stay tight, plain old SS safety wire. There was lots of safety wire used- I think I still have several spools of it I inherited. But, I don't fly in anything I have worked on, so it doesn't get much use. Sure, they sometimes used Lok tite, but never when it just couldn't fail. Funny, but I miss the sound of radial engines and the smells of engine shops.

 

[Defective]

I miss the sound of radial engines

Nothing in the world better than a pair of R-985s winding up early in the morning...

OK everybody...back to your regularly scheduled discussion...