Assembly Torque of Cylindrical Housings 1

[SwaggingIt]

I'm working on what torque value to call out on our prints but these are not bolts/screws, but thin-walled cylindrical housings. Therefore, I'm not sure the same clamping torque calculation applies. For example, one housing is 15-5PH stainless at 3.875" diameter and the bolt clamping formula says I'd be at over 50,000 in-lb at about 80% Sy of the 15-5PH (Sy = 145 ksi). That cant be applicable to my situation with thin-walled housings being fastened together. So my question is: what, if any, reference is available as guidelines for assembly torque for custom housings/fasteners like I'm working with?

Thanks in advance!

 

[SwaggingIt]

I just read another post which highlighted an important design criteria. I should be torqueing to a preload based on my expected operational load through the housing, not based on 80% of Sy. This makes a lot more sense to me. That said, the load going through the housing is pretty low, so my question still stands: are there any formulas that exist for establishing assembly torque for threaded cylinders instead of bolts?

 

[Stress_Eng]

When it comes to threaded cylinder joints, a number of analysis aspects need to be considered. They mainly consist of thread shear, thread bending, thread jumping and thread undercut analysis, consisting of kt factored bending with axial loading at the run-outs (kowalski’s method). When it comes to preloading, you need to first understand all the applied external loads going through the joint. You want sufficient preload to stop gapping of the joint, under axial and possibly bending loads.

 

[SwaggingIt]

Thanks for that feedback. I figured a lot more goes into it than I initially expected. That said, my updated approach is to establish min assembly torque limit from operating torque load through the housing plus 25% for preload sensitivity due to thread inconsistencies. Then for my max limit, I'm looking at galling threshold psi since its stainless on stainless. Then subtract 25% from that galling preload (derived preload with thread shear area from ASME B1.1 formulas). Now I have my rough boundaries. I'm fortunate to have test samples arriving this week so I'll be able to incrementally increase torque and maybe find a sweet spot somewhere within my limits. I think this would suffice for now until I have time to create a calculator that addresses all the factors you mentioned.

 

[mfgenggear]

What size threads, 1/4, 1/2, or 10 mm, or?
Complicated, what is the pressure involved.