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
Regards
Dave
RE: Lockwashers - To Use or Not to Use
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
RE: Lockwashers - To Use or Not to Use
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
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.
Or the US Navy.
Or the British Ministry of Defense.
RE: Lockwashers - To Use or Not to Use
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
RE: Lockwashers - To Use or Not to Use
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
RE: Lockwashers - To Use or Not to Use
Tobalcane
"If you avoid failure, you also avoid success."
RE: Lockwashers - To Use or Not to Use
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
RE: Lockwashers - To Use or Not to Use
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
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
RE: Lockwashers - To Use or Not to Use
LOL - why not? Then have your anonymous internet source sue your real self for plagiarism.
RE: Lockwashers - To Use or Not to Use
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.
RE: Lockwashers - To Use or Not to Use
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
{always thought that was because the EE's didn't know better
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
RE: Lockwashers - To Use or Not to Use
RE: Lockwashers - To Use or Not to Use
RE: Lockwashers - To Use or Not to Use
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
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
RE: Lockwashers - To Use or Not to Use
RE: Lockwashers - To Use or Not to Use
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
http://www.nord-lock.com/video/nl_uk.wmv
RE: Lockwashers - To Use or Not to Use