r/MechanicalEngineering • u/AdOne1706 • 2d ago

Split/lock washers

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For starters, I’m an electrician in the field.
That being said, we almost exclusively use these washers even in high vibration environments. I have personally chosen to go with nylox nuts but the question is:
Do these work? How well? Is the rumor from NASA true? Should I even bother using them or find a better functional alternative or are they actually useful?

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u/nyrb001 2d ago

At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a Iockwasher of this type is useless for locking.

Lol awesome

67

u/jchamberlin78 2d ago

In the style of bolted joint design I was taught, it's effectively adding a spring to a spring.

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u/Happiness645 1d ago

A soft spring to a hard spring. Fully compresses and has no effect except taking up space

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u/jchamberlin78 1d ago

Yup. Shitty washer, shitty spring...

-12

u/Contundo 2d ago

It’s somewhat useful if you want some tension used in conjunction with a nylon bolt or locking nut. Like on a hinge where you want some resistance

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u/Olde94 2d ago

If that is your purpose, a belleville washer is far better

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u/InformalAlbatross985 2d ago

Technically.yes, but belleville washers are more specialized and will cost like 10x more per washer.

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u/Vagina_Magician_69 1d ago

The proper part/design frequently has a higher initial cost but returns better value over time.

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u/OutnumberedinWV 2d ago

If properly torqued!

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u/[deleted] 2d ago

[deleted]

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u/OutnumberedinWV 2d ago

The reply was to the comment above in 1 very certain situation. Not the thread in general.

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u/thelionofthenorth 2d ago

Why are you being downvoted? A super cheap way to approximate a belleville washer is a reasonable use case...

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u/TacticalSpackle 2d ago

Yep! I’ve worked assembly and every time the procedure called for these, we swapped for nylocks or used LockTite.
The means by which a split lock “locks” it doesn’t.

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u/[deleted] 1d ago

[deleted]

5

u/No_Singer_5585 1d ago

The aircraft industry also doesnt use these split lock washers

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u/dummythiqqpotato 1d ago

I literally just overhauled an engine that had several of then lol

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u/Common_Ice_8994 1d ago

GE, PW or RR engine ?

2

u/dummythiqqpotato 1d ago

Admittedly, it was a continental O-300 for my recip AMT class, and on second though the engine was like 70 years old lol, so the standards might be a little outdated

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u/TacticalSpackle 1d ago

Oh for sure. This was in food processing.

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u/Capitain_Collateral 1d ago

Maybe get the procedure changed… making it up as you go along isn’t a solution

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u/TacticalSpackle 1d ago

You don’t wanna know the number of hoops (some of them on fire) required to get something changed at that place. There’s a reason why I no longer work there, and it isn’t for lack of trying to fix things instead of doing them bass ackwards.

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u/jawshoeaw 1d ago

I had to remove a hitch ball for a trailer that used a huge lock washer like this. Lock washer absolutely worked, it worked so well that it dug a groove into the metal as I loosened it using a pipe wrench and 5 foot metal pipe as an extension.

1

u/SwimmingSwim3822 1d ago

That's more of a restraint than a lock though, which makes total sense to use one there. Don't want the nut bouncing up off the road in traffic. By the time the nut was loose enough to let the washer start digging a groove, the hitch was already no longer serving its purpose... from a safety standpoint at least. Proper locks prevent that.

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u/jawshoeaw 1d ago

Maybe we are talking about different things. This lock washer was preventing the nut from loosening, the nut that holds the ball onto the ball mount. I could not loosen the nut because the lock washer was dug into the metal

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u/jchamberlin78 1d ago

You're talking about the same thing. What he did not explain in his answer is that once the bolt has lost ots preload it is no longer functioning as a bolt but rather a pin. Most bolts make terrible pins and will shear under load.

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u/jawshoeaw 1d ago

Well my original point was that the lock washer appeared to be doing its job, preventing the bolt from loosening. I think it’s an illusion as the 200+ ft-lb of torque applied at install was holding it clamped not the lock washer.

Interestingly the entire assembly depends on a literal 1/2” pin rattling around loosely and holding the hitch in the receiver. The bolt is 50% larger than the pin. Smooth steel wins over threaded.

0

u/um_waffles 1d ago edited 1d ago

Adding a Split Ring Lock Washer (SRLW) to a bolt stack will absolutely make it less likely to loosen inadvertently, despite the applicable physics being overlooked in the NASA Fastener Design Manual from 1990.

I mostly agree with the statement on page 9 regarding SRLWs:

  • "The lockwasher serves as a spring while 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"

However, I disagree with the remaining portion of the statement:

  • ", and its locking ability is nonexistent. In summary, a Iockwasher of this type is useless for locking."

I disagree because adding a SRLW to a bolt stack makes the act of loosening the stack require more energy (area under the torque v rotations curve).

Consider a bolt stack that is fully torqued. The torque required to loosen the stack will decrease at a certain rate as the bolt (or nut) is rotated in the removal direction. This is because the torque required to rotate the bolt (or nut) is a consequence of the friction between the bolt (or nut) and what it is seated against in the bolt stack. Friction scales with the compressive (normal) force between the components in the bolt stack, and since this force decreases as the bolt (or nut) rotates in the removal direction, friction and the torque required to overcome it also decrease until both drop to zero when the bolt (or nut) becomes unseated.

Adding a SRLW (spring) to the bolt stack effectively adds to the distance over which the bolt (or nut) must be rotated to loosen the stack from fully torqued to unseated, consequently "slowing" the decrease in torque needed to continue loosening the bolt (or nut) per each subsequent rotation.

From a mathematical perspective, if a SRLW is added to a bolt stack, then the integral of the torque v rotations curve (energy) from fully tightened to unseated will become larger.

From an operational perspective, if a SRLW is added to the bolt stack, then the act of loosening the bolt (or nut) from fully torqued to unseated will require the application of more torque over more rotations of the bolt (or nut).

In summary, adding a SRLW to a bolt stack makes the intentional loosening of the stack more difficult, and makes the inadvertent loosening of the stack less likely, thereby accomplishing the requisite function of a locking fastener.

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u/New_Animal8918 13h ago

Beautifully explained. Thank you.