Torque in bolts

[simthehunter]

Hi,

I would like to know what torque apply to bolts in general. Machinery handbook suggest 75-90 % of yield strength, but what is the best 75 ? 80 ? 90 ? Is it too dangerous to use 90% of yield ?

thx
Simon P.

 

[desertfox]

Hi simthehunter

It really depends on your application.
Have a look at this site:-

http://www.roymech.co.uk/Useful_Tables/Screws/Preloading.html

desertfox

 

[CoryPad]

The best is dependent on the application. If you have precise control of the applied torque and the friction variation of the parts, then 90 % is not dangerous.

 

[simthehunter]

I have an other question in the same subject...

Nut factors have an important influence in the relation Torque/preload but it is really hard to have a good precision on this factor because it depends on coeficients of friction between threads and between surfaces.

Does someone know a good reference for this factor ?

THX

 

[Bribyk]

Try searching this forum, this topic comes up regularly and is usually hotly debated.

 

[MintJulep]

There are no good references for k factor. Only books that list factors that were determined by tests of components that you aren't using under conditions that aren't likely to be similar to yours.

If you're lucky, the book may identify the components and test method used. That's really not much help though, as it doesn't tell you anything about your application.

If you need to be certain of your preload, and you are using torque control, then you should test your components in your application and derive a k factor for your joint.

If you need to be certain of your preload, you shouldn't be using torque control.