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What are the differences between Run- on torque / Breakaway torque / ?

  1. May 27, 2012 #1
    I've got questions about torque.
    First, what are the differences between Run- on torque / Breakaway torque/prevailing torque?
    Refer to the Boeing SOPM 20-50-01
    Run- on torque – 1. Drive torque. 2. Self-locking torque.

    Drive (or driving) torque – The torque necessary to keep the fastener in motion as it is turned but
    before it comes against the mating surface. When overhaul instructions tell you to tighten to a
    numerical value ‘‘above drive torque’’, add the drive torque value to the specified numerical value to
    get the value to be read from the torque wrench as the fastener is tightened.

    Self-locking torque – The torque necessary to turn a fastener with a self-locking feature on its mating
    threaded part when 100 percent of the locking feature is engaged, and the fastener is not down
    against the mating surface.

    Breakaway torque – The torque necessary to start to turn the fastener from a stopped position during
    a removal cycle with no load on the base of the fastener.
    Some says that Run- on torque and Breakaway torque is the same and we easily find Breakaway torque value with the table.
    If there is run-on torque table, would you send it to me please.

    Second, what's the purpose of Run- on torque / Breakaway torque?

    I think that both torque values helps us determine that self locking nut is serviceable
    2 inches self locking nut's mini/maximum breakaway values too vary 300-1700 in.lbs
    How can I understand those ranges?
  2. jcsd
  3. May 27, 2012 #2
    More than a hundred views so far and no answers? Strange.

    Run on and break away torque are exactly the same thing except for one important difference. Run on is representative of the dynamic friction, and break away of static friction.

    The break away represents that torque available as a self locking feature that prevents the screw from vibrating out once tightened. But as you are turning the fastener to tighten it, some of the torque measured by the torque wrench is wasted in run on torque. So if you measure the run on torque at 20 in-lbs and want to torque the screw to 100 in-lbs, you must set the torque wrench at 120 in-lbs.
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