Energy dissipation of steel washers

[Evan.99]

Is there an optimum number of washers to be used on a threaded bolt in respect to dissipation of energy towards the nut? And how would one calculate the dissipation rate of each washer?

 

[Jon B]

Is there an optimum number of washers to be used on a threaded bolt in respect to dissipation of energy towards the nut? And how would one calculate the dissipation rate of each washer?

Standard washers have two main purposes: To distribute the pressure of the nut evenly over the surface, so that the surface isn't damaged, and To ensure that the nut is pressed against a smooth surface, reducing the chance that it'll gradually loosen because it's in contact with an uneven surface. Another use for a washer is to reduce the friction when tightening and loosening. You can reach a greater tension on the bolt with a washer and when removing a bolt less torque is needed to break the bolt free from it tightened position. The so-called dissipation has to do with torque. The Washer should have a hardness that complies with the pressure expected based on the torque specification of the bolt.

 

[Evan.99]

Thanks. But does that mean that a single washer should always be enough or is there an advantage to having two or more (besides in cases where extra washers are used to distribute the load)?

 

[Jon B]

Depending on the application you may need a washer at the bolt head and one at the nut for the stated reasons.

 

[Evan.99]

Ok, cheers. So just to clarify, adding more washers between the nut and the surface gives no advantage in terms of allowable tension applied to the nut or ease of releasing the nut again?

 

[Jon B]

Ok, cheers. So just to clarify, adding more washers between the nut and the surface gives no advantage in terms of allowable tension applied to the nut or ease of releasing the nut again?

If the hole is considerably larger than the shank people use multiple washers of different sizes to compensate instead of using a larger diameter bolt, washer and nut. Washers are used to spread the load of a bolt or screw over a larger area or to help prevent loosening under vibration.