How many of you use helical split lock washers in bolted joints? 8

[Tunalover]

Anyone want to weigh in on their pros and cons?


Tunalover

 

[drawoh]

What if the bolt is being used essentially as a pin, such that it can drop to near zero clamping force and still be effective? In that circumstance, the helical split washer would seem to serve at least to some extent to keep the fastener from rattling completely out of the joint.
...

If if dropped to near zero clamping force, why should it not continue dropping?

--
JHG

 

[moltenmetal]

OK, I get that the washer behaves as a flat washer when completely compressed, and that it has a huge spring rate when fully compressed. But it does act at least to some degree as a spring once the joint has loosened a bit, generating at least some useful force to keep the fastener from falling completely out of the joint. A flat washer ceases to be any kind of spring once the bolt head has left contact with the face.

I was commenting to screwman1's post. My point was that not all joints where bolts are used will fail once the joint merely becomes loose. Some joints rely primarily on the presence of the fastener in the assembly rather than needing the fastener to be fully tightened.

Why wouldn't it continue to loosen? It certainly would! The washer in our case merely buys us time to find the loose fastener and re-tighten it rather than finding out what hole it rattled out of to end up in the belly tarp of the truck. Is that a meaningful amount of time? Dunno. That could be tradition rather than fact- but it's pretty strong tradition around here to the point of being not on argument with the folks who install our plants.

 

[drawoh]

moltenmetal,

Bolt Science has a page on Vibration Loosening of Bolts and Threaded Fasteners.

It is widely believed that vibration causes bolt loosening. By far the most frequent cause of loosening is side sliding of the nut or bolt head relative to the joint, resulting in relative motion occurring in the threads. If this does not occur, then the bolts will not loosen, even if the joint is subjected to severe vibration. By a detailed analysis of the joint it is possible to determine the clamp force required to be provided by the bolts to prevent joint slip.

The force required to completely compress a spring washer is way below the tensile strength of your bolt. If the bolt has been loosened from its proper snugged down condition, the helical spring washer will slow the failure, at best.

Incidentally, I used to work with a guy who claimed that you tightened down a screw by carefully watching the helical spring washer. When the washer is compressed flat, the screw is tight. Articles that claim helical spring washers are a cause of failure, never explain the mechanism. Could this be it?

--
JHG

 

[Tunalover]

I've worked on projects where this type of lock washer was prohibited not because they simply don't work, but because they can break, separate from the joint, and cause metal fragments to short out electrical connections. The same argument was made for the Nordlock washer because the wiping action of the teeth against the flat washer might cause metal flaking. I never believed the split-lock washer would ever break but I wasn't in the position to make policy. Regardless, the decision was made not to use them and that was a good decision IMO.




Tunalover

 

[MintJulep]

Despite overwhelming quantifiable evidence, despite sound engineering explanations of their worthlessness....

Many organizations have someone of sufficient influence who remembers seeing a failed joint at just the right moment before the nut fell off and concludes "Look Look! The lock washer prevented this nut from falling off!"

And apparently there is never anyone around at that moment who knows enough to point out:

"But it's a 'lock washer' and obviously it didn't 'lock' this tight"

"What good is this bolt doing now? It's rattling around. It's not holding anything"

 

[moltenmetal]

Oh poor MintJulep- I feel your pain! Sorry for adding to it...but the revolution that would occur if I went into our shop and started dumping all the bins of "lock washers" into the scrap bin is just not worth the effort! LPSs to both you and drawoh for your help in educating me on the topic.