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Lock washers what's the point?

  1. Nov 7, 2007 #1
    In a properly torqued bolt the tension in the bolt is much greater than that of the lock washer. It doesn't prevent rotation of the joint and doesn't spread out the force like a flat washer. So I ask, what's the point of a lock washer?
     
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  3. Nov 7, 2007 #2

    mgb_phys

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    Either to provide a minimum level of force for delicate assemblies where you can't torque the bolt or to provide some shakeproofness (is that a word?).
     
  4. Nov 7, 2007 #3

    jim mcnamara

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    I asked this same q once - got this answer:
    Lock washers are meant for applications where the components of the joint or the threads may permanently deform enough to reduce bolt tension. Properly applied lock washers are not "mashed flat" they are left with some spring in them.

    There are applications, ex some automobile starter motor mounts, that stipulate the use of lock washers.

    And your observations are correct - for example a lock washer is a poor choice for an application where joint rotation is possible and not desirable.
     
  5. Nov 7, 2007 #4

    mgb_phys

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    Where parts can shrink or vibrate a lot, I would use a stack of Belleville washers.
    The small searated lock washers I would use as anti-shake on small parts.

    Shakeproof nuts are a better solution but cost more.
     
    Last edited: Nov 7, 2007
  6. Nov 7, 2007 #5

    FredGarvin

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    I agree that lock washers are a taboo. There's no real reason to use them. Like has already been mentioned, they are flattened by the time you reach full torque, so they are really only acting as a flat washer. If proper joint analysis is done, there should be no need to use them. Belleville washers have their place and are a good choice for keeping a constant preload on a fastener.
     
  7. Nov 7, 2007 #6

    jim mcnamara

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    Pete -
    I'm just citing what some manuals I read have to say. The OP is right: lock washers can cause problems. But. Any fastener used the wrong way will cause problems.

    Also, I take serrated washers and nylon inserts in nuts to be a 'lock washer' kind of application, even if they aren't a metal donut with a slice in it. Beveled washers, I dunno.
    They are not meant for what you cited. My beveled washers are like these:

    http://www.portlandbolt.com/products/washers/malleable_beveled_washer.html
     
  8. Nov 7, 2007 #7

    mgb_phys

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    I meant Belleville washers as Gavin said, can't type straight today.
    They are curved washers that you can either stack opposing each other for more extention or with each other for more spring force.
    http://en.wikipedia.org/wiki/Belleville_washer
     
  9. Nov 7, 2007 #8
    I never thought of a lock washer working by maintaining tension on the bolt.
    I always thought they worked by preventing rotation, the sharp corners bite into the nut or bolt and the material they are installed in when it tries to turn. Anti rotation device not a preload devise. Just my thoughts.
     
  10. Nov 7, 2007 #9

    stewartcs

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    What type of lock washer?

    Split lock washers, once torqued, will flatten out and act like a normal flat washer and distribute the force evenly.

    Until they are flattened out, they provide a spring force on the bolt (while tightening).
     
  11. Nov 7, 2007 #10

    turbo

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    Split lock washers should probably not be used in any critical application, or applications involving hardened nuts, but they can be pretty darned handy in preventing softer low-grade nuts from backing off during vibration/shaking.
     
  12. Nov 12, 2007 #11
    I've seen certain instances where lock washers can actually bite into the metal of the bolt, and the material being held down where the washer splits apart. Do you think this may be part of the locking the name refers to?
     
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