×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Lockwashers - To Use or Not to Use
9

Lockwashers - To Use or Not to Use

Lockwashers - To Use or Not to Use

(OP)
About the same time Ed introduced us to the Beetles I was working as assembly labor in a shop whose propriatary line was mfgd mostly from cast iron and structural steel. At that time it was explained to me that lockwasers were used under a (NC) nut or a screw head when they pulled up against steel but a lockwasher wasn't necessary when the mating surface was cast iron. And it seemed they had many years of success in this procedure to support their claim. Now my circle has brought me back to a very similar cast iron and steel situation. Now that I am more aware of time involvement in the production process, I am amazed at the substantial amount of time our assemblers spend fumbling with the thousands of lockwashers we go through every month. Captive lockwashers and serrated flanges have been looked at so far. Neither has offered a set of pros and cons we are anxious to accept. Any ideas, comments, or suggestions anyone would wish to share in this matter would be greatly appreciated. Thanks, K.

RE: Lockwashers - To Use or Not to Use

KTHREE:  I have mixed emotions about lockwashers.  They work, but I think one has to consider the application and operating environment.  I would suggest looking at thread locking compunds.  If it absolutly, positively, must stay together then consider mechanical locks such as cotter pins and locking tabs.  Regardless of the locking method, I would also suggest multiple passes in assembly so the tension in the bolts are near each other.

Regards
Dave

RE: Lockwashers - To Use or Not to Use

4
Lock washers have been discussed on these forua many times.  The consensus is that they do NOT work.

Locking tabs prevent gross rotation, but can introduce a large mount of embedment and relaxation into the joint, potentially resulting is a total loss of preload.

Cotter pins prevent gross rotation, but can allow sufficient rotation to loose preload.

Adhesive locking compounds are great.  If you can trust your workforce to use them correctly - clean the parts, prime if needed, apply correct amount...

Prevailing torque fasteners are the way to go.

RE: Lockwashers - To Use or Not to Use

Quote:

Lock washers have been discussed on these forua many times.  The consensus is that they do NOT work.
Lock washers can be as good and efficient as anything else when used in the proper places. They certainly don't belong everywhere. Saying they don't work is disingenuous.

 

RE: Lockwashers - To Use or Not to Use

Fabrico,

The consensus Mint spoke of is that a lockwasher will not prevent loosening and loss of preload on a typical joint in a typical application (i.e. placement between a steel nut and a steel frame member, and subjected to vibration).  The problem is that the washer is compressed flat in use, and the single tang no longer bites into the nut; significant rotation can occur before the washer will stop reverse rotation.  I've worked for a couple of aerospace companies that showed us young punks test data where a lockwasher was shown to be no better a torque-retention device than a properly torqued joint with a flat washer.  This conclusion is backed up by NASA RP-1228, Fastener Design Manual, R. T. Barret, 1990, among others.  Can you quote a source stating they do work in the subject scenario?

RE: Lockwashers - To Use or Not to Use

When a lock washer is fully compressed, as it is in a joint that is holding its design preload, the lock washer behaves exactly like a flat washer with a crack in it.  Or, if you prefer, a spring that has gone solid.  It no longer acts like a spring in further compression and its stiffness, as it relates to the joint performance is determined by the modulus of elasticity of the material.

If the joint loosens sufficiently so that the lock washer acts like a spring again then the joint has lost its design preload and the only tension left in the bolt is whatever small amount that is provided by the lock washer.  It doesn't matter.  The joint has already failed.  The lock washer may postpone the inevitable departure of the nut from the end of the bolt.

But if you don't want to believe me, perhaps you would believe NASA.

Quote:

NASA Fastener Design Manual RP-1228:

The lockwasher serves as a spring whilel the bolt is being tightened.  However, the washer is normally flat by the time the bolt is fully torqued.  At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent.  In summary, a lockwasher of this type is usless for locking.

Or the US Navy.

Quote:


Naval Ships' Technical Manual, Chapter 75:

Although lockwashers may be encountered, using the flat washers with selflocking nuts, self-locking fasteners, self-locking inserts, or thread sealants such as MIL-S-22473 anaerobic compounds is preferable.

If loosening has been a problem, however, replace the lockwashers with self-locking fasteners.

The helical spring lockwasher (Figure 075-5-11) is flattened when the bolt is torqued down. Once compressed, it acts as a flat washer, contributing normal friction between the nut or bolt and the bearing surface during tightening.

Or the British Ministry of Defense.

Quote:


Vibration Loosening of Threaded Fasteners (Light):

If the plain fastener is taken as the datum any washer reduces locking effectiveness

RE: Lockwashers - To Use or Not to Use

Agree with the "no" vote, except in the horrible case of electrical terminations, where the washer is no longer the softest spring in the system.

But then, that is not a bolted joint, that is an electrical termination!

Cheers

Greg Locock

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

RE: Lockwashers - To Use or Not to Use

They work fine on wood.

RE: Lockwashers - To Use or Not to Use

I have covered the question many times as well. Heres the best case I have found aganist helical lock washers. Reference:
Fastener Design Manual - NASA Reference Publication 1228, Richard T. Barrett, Lewis Research Center Cleveland, OH

Quoting from page 9 "in summary a lock washer of this type is useless for locking"

RE: Lockwashers - To Use or Not to Use

(OP)
Thank You everyone for taking the time to consider and respond to our question. You have provided a great deal of information that is going to be used to reconsider our design. We greatly appreciate your help. K.

RE: Lockwashers - To Use or Not to Use

I don’t know if it was motioned, but another alternative may be to use locking helicoils.  At the last three or four threads are angled slightly to lock the screw.

Tobalcane
"If you avoid failure, you also avoid success."

RE: Lockwashers - To Use or Not to Use

Mint,

Your answer was the most complete synopsis I've seen, I'm gonna paste it in whole as a FAQ suggestion.

RE: Lockwashers - To Use or Not to Use

Urg.  Sorry Mint, I should've suggested that you post it as a FAQ - I didn't know about the FAQ rating system until I'd posted it and read the little follow-up blurb.  I did attribute the whole thing to you in the text...sigh.

RE: Lockwashers - To Use or Not to Use

btrue,

No worries.

I would have stated "preload retention" rather than "torque retention" however.

Now that I'm immortalized in a FAQ, I wonder if my real-world self can cite my anonymous internet forum self as an information source?

RE: Lockwashers - To Use or Not to Use

much consideration needs to be placed on the seating area of the fastener. Lock washers typically replicate the fasteners head, and offers little improvement over not using one. A hardened flat washer has a larger seating area against the retained component. Although elongation of a retainer reduces applied tensions, disruption of the seat has a similar effect.

In production environments we have often found that a hardened flat washer with a locking compound to be most effective.

RE: Lockwashers - To Use or Not to Use


This thread seems to concentrate on what I would refer to as a springwasher, whereas the subject says lockwasher.

This is what I would call a lockwasher:

http://www.nord-lock.com/

Chris

RE: Lockwashers - To Use or Not to Use

Wouldn't that effectively be just a thick flat washer?

RE: Lockwashers - To Use or Not to Use

"Now that I'm immortalized in a FAQ, I wonder if my real-world self can cite my anonymous internet forum self as an information source?"

LOL - why not?  Then have your anonymous internet source sue your real self for plagiarism.

RE: Lockwashers - To Use or Not to Use

Bumax,

Spring washer, helical spring washer, helical split washer- this thread concentrates on them because the original poster dates his experience and products to a time circa 1960, which precedes the Nord-Lock washer by 20 years.
 

Regards,

Cory

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

RE: Lockwashers - To Use or Not to Use


They must number in billions by now and they're still going strong. You can quote and vote till the cows come home, they can't all be wrong. smile

RE: Lockwashers - To Use or Not to Use

Why not?  Millions of people have less than $10,000 of retirement savings, and they ARE all wrong.

TTFN



RE: Lockwashers - To Use or Not to Use


The US government, US military, and US Navy all have specifications for split lock washers. Does anyone really think NASA is void of lock washers on every piece of ground equipment, test equipment, and all their structures?

How or why this led from cast iron and structural steel, as the O/P mentioned, straight into aerospace and retirement savings, is entirely up to persons here other than myself.

What's at issue here is not application, popularity, or personal preference, but the making of completely false and misleading statements. Doing so helps no one, especially ENG-TIPS FORUMS.



RE: Lockwashers - To Use or Not to Use

The only place lockwashers are regularly seen is in Electrical Connections as GregLocock sez.

  {always thought that was because the EE's didn't know better winky smile - makes 'em feel like they're doing something.}

 Loctite would tend to insulate the joint & there's not much room for a torque wrench in an electric box anyhow.  They'd probably strip/stretch a lot of threads if they went tight enough - you'd have to use strain-hardened stainless or silicon-bronze bolts to get a high enough preload to hold tight - plus the terminals are often soft metal.

RE: Lockwashers - To Use or Not to Use

The ASME also has a standard for lock washers.  In that standard it states:

Quote (ASME B18.21.1):

The word lock appearing in the names of products in this standard is a generic term historically assoicated with their identification and is not intended to imply an indefinite permanency of fixity in attachments where the fastners are used.

RE: Lockwashers - To Use or Not to Use

For what it is worth, I have a friend who is a Caterpillar mechanic and he says Cat uses very few lock washers. Instead they use a hardened flat washer and stress the proper torque/fastener stretch. This holds true for cast iron, steel and aluminum parts.

RE: Lockwashers - To Use or Not to Use

Yup.  I've never seen a lockwasher on a track bolt.  Nor on cylinder heads.

RE: Lockwashers - To Use or Not to Use

Fastener manufacturers can, and do, supply fasteners with the adhesive locking compound "pre-applied."  These parts are processed to include a dry band of adhesive on them (Dri-Loc, Scotchgrip, etc.).  This eliminates the need for installers to apply a liquid adhesive, it's already done.

There are a number of other "locking elements" available that can be pre-applied, including a nylon patch which can be applied with 180^ or 360^ coverage.

RE: Lockwashers - To Use or Not to Use

Agreed on the uselessness of lock washers compared to proper joint design and tightening strategy.

Notice that NO automotive companies have specs for lock washers active for new design.  
The heavy truck industry doesn't either.  
Nor do the diesel engine companies.

The only place that I still see some lock washer use is on farm equipment...primarily in those places where there is likely going to be field adjustment.  In those cases I have been told that they are used because the end user farmers often don't retighten the fasteners up to their full target preload.  The lock washers tend to hold things together somewhat under the low load conditions.  I was also told that the farmers complained when the washers were taken off, even though testing showed that they provided no benefit, so they were put back on some pieces of equipment.

If you are concerned about viration loosening and have a joint design that doesn't allow propoer clamping, then you should look into some type of a prevailing torque thread design on the fastener or nut or the use of a preapplied thread locking adhesive.  Both of those work well and are the most commmon solution used by industry today.

RE: Lockwashers - To Use or Not to Use

HD flat washers along with 'nylok' style nuts anyone?

RE: Lockwashers - To Use or Not to Use

Not bad Maur; but I would just use a Nylock flange nut and eliminate the separate flat washer.  One less item to make sure is properly assembled.  Flange nuts will give adequate bearing surface for all but the highest clamp loads or softest materials.  Nylock nuts are good on prevailing torque and they tend to have less friction variation than deflected metal locknuts.

RE: Lockwashers - To Use or Not to Use

If you want lock washers that do work try Schnorr Washers - these do the business & are fitted to tiens that are critical - such as parts in printing machines & aerospace where detachment of even the screw or nut into the mechanism is not an option.
Search the webfor a local supplier

Bruce L Farrar.
Works Engineering Manager
Marshalls Mono PLC.Brookfoot Works.
Halifax W.Yorks UK

RE: Lockwashers - To Use or Not to Use

2
Even though this is coming from Nord-Lock's website, I found their video to be pretty informative - it shows bolt tension drop off with vibrated joints.  They test their system against spring washer, nyloc, deformed thread, and even double nut.  All of which lost tension with vibration.  I guess Nord's theory is that an initial rise in bolt tension is needed in the loosening direction in order to prevent loosening.  The drawback with their system is that the cam surface between the two washers has to be the lowest friction surface.
http://www.nord-lock.com/video/nl_uk.wmv

RE: Lockwashers - To Use or Not to Use

Star to spectreeng for the video.  Now I may be able to convince co-workers that spring washers are the work of the devil!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources