How does a spring washer work? 4

[Swedishrigpig]

Is it the tension of the washer that nips the threads that stops the nut from unscrewing itself, or is it the sharp edge of the spring washer that digs into the underside of the nut and base surface that holds it?

Is it then wrong to use a flat washer under the springwasher? It would then stop the sharp edges from digging into the bottom surface, only into the top of the flat washer?

 

[desertfox]

Hi Swedishrigpig

Look at this site this is how tthere supposed to work

http://www.wclco.com/pdf/lockwash/lw05-08.pdf

Then look at this site becuase it is now believed that they don't work

http://www.boltscience.com/pages/vibloose.htm

desertfox

 

[MintJulep]

They don't.

faq404-1257

 

[Swedishrigpig]

Thanks a lot.
I'm gobsmacked!
How come more people are not aware of this?
And the theory of the edges diging into the bearing surface seems to be completey rubbish.

Thats why I like this site, I get real facts rather that listen to Urban Myths.

Anyone familiar with these locking washers:

http://www.nordlock.com/default.asp?url=2.16.37

I know Hydril recommend them on their Sub Sea BOPs, so I assume they have done some research about it. They use Stainless Steel bolts that are exposed to big temperature differences (Blazing sunshine vs 4 degrees Celsius on the sea bed a few hours later)

 

[desertfox]

Hi Swedishrigpig

Yes Nordlock are very good to my knowlegde I have used them for joints on steel rolling plant frames, you must use them in pairs though, there serrated and you place one on the top of the other for them to come undone one washer would have too rise up and climb the over the other.

desertfox

 

[unclesyd]

http://findarticles.com/p/articles/mi_qa5357/is_200507/ai_n21376287/

 

[unclesyd]

My fingers overloaded my brain and created another of the what comes first situation. Now all I can say is that the article speaks for it's self.

 

[Tmoose]

"How come more people are not aware of this?"

If I use a split type lockwasher on my trailer hitch ball, and the ball does not loosen in service, then it MUST have been the lockwasher. Or maybe the rabbit's foot on my keychain. Or, Maybe that I tightened the 1 inch nut to over 250 lb-ft, and it is now exerting over 15,000 lbs over clamp load, so it would take over 3000 lbs of push or pull to make the ball's flange slide on the tongue. That's hard to do with a loaded trailer weight of about 1000 lbs. I'd have to accelerate or brake at over 3 gs.

Look at real high performance bolted joints. Dodge Hemi flywheel to crank, con rod and main bearing bolts. Not a lock washer in sight.

 

[electricpete]

I acknowledge there are certainly references that say helical spring lockwasher is worthless. There are also references that provide a different picture.

http://books.google.com/books?id=gT...be a fairly inefficient way to resist&f=false

A more complete quote from 4th ed of same book: "An introduction to the design and behavior of bolted joints" By John H. Bickford is listed below:

FIGURE 14.20 A helical spring lock washer would appear to be a fairly inefficient way to resist selfloosening;
but recent research—described in the text—shows that this washer twists and rolls when it’s
fully loaded. Since that requires a clamping force that can equal 65% of the proof load of the bolt, this
washer can, indeed, provide significant resistance to self-loosening.

14.6.7.3 Helical Spring Washer
At first glance the helical spring washer shown in Figure 14.20 would appear to be of as little
value as the wave washer; unless the cut ends manage to bite into joint and nut and resist
relative motion the way the toothed washer does. Research at the Lawrence Technological
University in Southfield,Michigan, however, suggests that this device is more effective than it
appears to be [22]. Dr. Clarence Chambers has shown that, while this washer is flattened by
bolt tension equal to only 5% of its proof load, increasing bolt preload to 70% of proof will
cause the trapezoidal cross section of the washer to roll and twist down on the outside
diameter, which also grows. This complex action results in a washer spring rate which can
approach 65% of the spring rate of the fastener. That spring rate will dominate the behavior
of the fastener under load, and will reduce the amount of preload lost under a given applied
load. Retaining preload, of course, is an effective way to resist self-loosening.

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[CoryPad]

The statement of dominating behavior is misleading. Fastener spring rate has some influence on joint behavior, but its effects (when varied from 65 % to 100 %) are small compared to the effects of preload, adhesive bonding, and special fasteners like the Nord-Lock system.

 

[MintJulep]

In the Chambers case the spring washer becomes a springy ply in the joint. I don't understand why he referencs the behavior of the fastener.

Adding a spring as a joint member softens the joint as a whole, and causes the bolt:joint stiffness ratio to increase. Generally a bad thing.