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Thermal fit of SS316 parts

Thermal fit of SS316 parts

Thermal fit of SS316 parts

What would be the best method of thermal fitting SS316 parts onto one another? I have a long shaft and a machined bush which is to be fitted on the shaft. What I have come up with is to have a small machining cut on the shaft of about 0.3mm on the diameter so create a "step" where the bush gets a mechanical stop along the shaft length. Then the bush I.D will be 0.005mm more than the shaft diameter. Then soak the bush at 80C for 1 hour + cold soak the shaft at -30C for 1 hour and then insert the bush using a holding tool within 20 seconds of removing both parts from the chambers. Then as a secondary mechanical locking, can do laser welding on both sides of the bush with same filler material. I think this should be reliable enough. What say you, pro engineers?

RE: Thermal fit of SS316 parts

Good so far, but a few things have escaped consideration. If you were doing this once, ever, then I'd say just go get it done. But you mention reliability. As if you might do this more than once. How many times? 10 times? A thousand? That question alone changes the equation.
Tolerances of each component will have a big effect. There are interference fit ranges better suited to freeze plugs than other kinds of fit, so you'd better make sure you're using them. I can't keep those details in my head, so just go to Machinery's Handbook like everyone else.

The step is a great idea, but may not work every time, yet. Does the bushing have a chamfer on its ID? If so, will it positively come to rest on the step in the chamfer? If that's true, then I suspect that the tolerance on the chamfer, and the point radius on the tip of the tool that made the step on the shaft, will rule the position of the bushing. I hope you recognize that this sounds silly, and now see that the proper location feature for a bushing is a shoulder that the end face of the bushing comes to rest against directly.


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