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.
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Lockwashers - To Use or Not to Use 9
- Thread starter kthree
- Start date
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
Regards
Dave
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4
- #3
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.
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.
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1
- #5
btrueblood
Mechanical
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?
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?
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.
Or the US Navy.
Or the British Ministry of Defense.
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.
GregLocock
Automotive
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.
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.
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"
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"
- Thread starter
- #10
Twoballcane
Mechanical
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."
Tobalcane
"If you avoid failure, you also avoid success."
btrueblood
Mechanical
Mint,
Your answer was the most complete synopsis I've seen, I'm gonna paste it in whole as a FAQ suggestion.
Your answer was the most complete synopsis I've seen, I'm gonna paste it in whole as a FAQ suggestion.
btrueblood
Mechanical
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.
automatic2
Industrial
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.
In production environments we have often found that a hardened flat washer with a locking compound to be most effective.
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:
Chris
This is what I would call a lockwasher:
Chris
btrueblood
Mechanical
"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.
LOL - why not? Then have your anonymous internet source sue your real self for plagiarism.
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.
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.
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