rustyhooks
Mechanical
- Mar 27, 2007
- 8
I am connecting two halves of a valve together. I have a 7/16-14 Grade 5 steel screw that is inserted into a clearance hole in a cast iron flange and then threaded into the gray cast iron flange on the other valve half. There are 8 of these in the bolt circle. The maximum load on each fastener when pressurized is 290 lbf. I know how to calculate the torque spec when the male thread and female thread are of equal strength (same material). However, I am not sure how to calculate the proper torque required when the female thread (cast iron) is weaker than the screw (steel). I would think the female thread would fail before the male thread in this case. Also, what is (if any) the difference between thread shear stress area and tensile stress area of a thread?