Differences Between Run on Torque and Breakaway Torque

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Differences Between Run on Torque and Breakaway Torque  


Breakaway torque is defined as the torque required to start a part’s rotation from a stationary position. It is usually a higher value compared to the maximum tightening torque value as per specification . This is because this torque is required to not only overcome the inertia of the part but also the static friction due to the adjoining components.

There are two common situations. One is the torque required to get a mechanism to rotate, such as a crankshaft of a car engine. The other is checking the torque of tightened attachment hardware by applying enough torque to get slight additional tightening. (this confirms proper torque) A torque wrench with a dial or digital display can be used for either situation.
If talking about using a torque wrench the context drop in tightening fastener bolts, some bolts needs to be torqued out very accurately like motor cap fastener bolts, torque wrenchs have some spring loaded handle that can either be adjusted to break/bend when limit is reach or just bend proportionally to torque and operator need to stop when needle reachs right reference. The right value should be taken from maintenance manual for the motor.

On the other hand motors do have their own breakaway torque for crankshaft, some trucks have a controll that opens all valves during the starting operation, then when shaft runs fast enough the valves are allowed to close and allows compression to start the engine.

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.

So Finally,

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?




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