Need help selecting a suitable material.
Need help selecting a suitable material.
(OP)
I have a mechanism in an assembly that is causing a problem and I need some suggestions. The application is on the wet end of a paper making machine. Chemical environment is typically alkaline. We prefer to use 316 SS when we can. 316SS has a tendency to gaul when used for threads. We have successfully used a material combination in the past of a drive nut that is 70/30 copper Nickele alloy and a drive screw that is 17-4 PH ss with a heat treat spec of (900 full hard after machining)thread size is 3/8-16. Recently an assembly was returned because the drive assembly had stripped out. I removed the assembly and had our shop split the assembly with a wire EDM (photo attached). It appears as though the threads on the nut were weakened by corrosion and stripped out.
One though would be to make the nut have the same spec as the screw. I just don't have any experience to tell me if it would be a good idea or not. All input is appricated.
Thank you,
One though would be to make the nut have the same spec as the screw. I just don't have any experience to tell me if it would be a good idea or not. All input is appricated.
Thank you,





RE: Need help selecting a suitable material.
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Need help selecting a suitable material.
Thank you,
RE: Need help selecting a suitable material.
RE: Need help selecting a suitable material.
RE: Need help selecting a suitable material.
Another possibility would be to use the H925 heat treatment. Slightly less strength/hardness, but would probably not suffer SCC since the H900 apparently hasn't.
It's just not a good idea to let 17-4 in the H900 cond. get wet!
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Need help selecting a suitable material.
Use Nitronic 60 or 2205 and a bolt of 17-4 in the H1100 condition.
They will be galvanicly similar, offer good strength, and be available.
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Plymouth Tube
RE: Need help selecting a suitable material.
RE: Need help selecting a suitable material.
In the past your 90/10 was providing some galvanic protection to the 17-4. Without that you might bet enough corrosion to have hydrogen cracking issues in the 17-4.
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Plymouth Tube
RE: Need help selecting a suitable material.
Thanks.
RE: Need help selecting a suitable material.
I have a very reasonable quote for the Nitronic 60 and will probably go that way.
RE: Need help selecting a suitable material.
I think the high pH is what saved the day for the H900 part.
I learned way back ~1960 the US Navy forbade the use of the H900 for aircraft use--a lesson I never forgot.
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Need help selecting a suitable material.
Besides Nitronic 60, both PH13-8Mo or 15-5PH would give strength and corrosion resistance as good or better than 17-4PH without the SCC issues. You might also consider 718 Inconel.
Nitronic 60 is not a heat treatable alloy, so must be worked in its final hardness condition. If your part's threads must be rolled, this may be an issue with Nitronic alloys at high strengths.
Good luck.
Terry