Strength of cast threads

[cjholl0]

Im trying to specify a torque value for a bolt that is screwed into a cast iron box. The recommended torque, using the recommended preload, is pretty straightforward from the Machinery's Handbook. But, this also assumes your using a similiar grade of nut (I think). I'm using a grade 8 bolt so I'm pretty sure the cast iron threads will break first. I don't want to torque the bolt to it's recommended value and then over stress the weaker cast threads. Is there a rule of thumb or equation that addresses this kind of situation?

Thanks

 

[desertfox]

Hi There

Have a look at this site and just put the values of stress for each different material in the equations

http://www.utm.edu/departments/engin/lemaster/Machine Design/Lecture 28.pdf

desertfox

 

[nickelkid]

You will need to know what grade of cast iron you have.

 

[unclesyd]

As a general rule we would use a bolt stress of 15,000-25,000 psi for all bolting when using Cast Iron.

We would try not to use high strength bolting for CI. . The fasteners were mostly ASTM A108 material.

As posted above knowing your material and with judicious application of torque you could use a higher strength fastener.

 

[CoryPad]

Here is the equation for calculating strength of tapped threads:

thread725-35222


Regards,

Cory

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