Backing stud exposed to high-vibration loading - gr12.9 & lock method?
Backing stud exposed to high-vibration loading - gr12.9 & lock method?
(OP)
Hi All,
I'm a mechanical engineer working at a hydropower plant. The turbine guide bearing takes quite a beating, and they've asked me to look into a larger diameter stud and/or different material.
The current arrangement is a threaded insert welded in place in a thick walled tub/cylinder that the stud screws through. The stud pushes directly onto the back of the guide bearing. Outside the "tub" are a lock nut, and a jam nut behind that.
The current sizing is M30, with what looks to be a 1mm pitch (very very fine).
My first thought is to upgrade to an M33 made from 12.9 with rolled threads. I'm hearing alot of negative things about 12.9 and I was wondering if you would recommend it in an application like this that sees a lot of hammering on the stud (as opposed to the normal application where it is called on to clamp a joint).
With a hard bolting material, would you expect the lock and jam nut to sufficiently hold it. Getting the lock nut and jam nut to "bite" in to the stud may not be easy, or last.
Any bolt materials ideal in this situation?
I'm a mechanical engineer working at a hydropower plant. The turbine guide bearing takes quite a beating, and they've asked me to look into a larger diameter stud and/or different material.
The current arrangement is a threaded insert welded in place in a thick walled tub/cylinder that the stud screws through. The stud pushes directly onto the back of the guide bearing. Outside the "tub" are a lock nut, and a jam nut behind that.
The current sizing is M30, with what looks to be a 1mm pitch (very very fine).
My first thought is to upgrade to an M33 made from 12.9 with rolled threads. I'm hearing alot of negative things about 12.9 and I was wondering if you would recommend it in an application like this that sees a lot of hammering on the stud (as opposed to the normal application where it is called on to clamp a joint).
With a hard bolting material, would you expect the lock and jam nut to sufficiently hold it. Getting the lock nut and jam nut to "bite" in to the stud may not be easy, or last.
Any bolt materials ideal in this situation?





RE: Backing stud exposed to high-vibration loading - gr12.9 & lock method?
You shouldn't start working on the solution before you understand the problem.
RE: Backing stud exposed to high-vibration loading - gr12.9 & lock method?
The high vibration from the shaft through to the bearings is causing the studs to back out and the clearances to open up on the guide bearings. The plant believes it has to do with poor threadform and materials used (Chinese turbine)
RE: Backing stud exposed to high-vibration loading - gr12.9 & lock method?
"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: Backing stud exposed to high-vibration loading - gr12.9 & lock method?
RE: Backing stud exposed to high-vibration loading - gr12.9 & lock method?
RE: Backing stud exposed to high-vibration loading - gr12.9 & lock method?
Your variables are fastener diameter, fastener material strength, and pretension level and method (hydraulic tensioners, torque, etc.). Property class 12.9 provides very high strength, but is susceptible to environment assisted cracking. What is the environment? Temperatures, fluids, other? Property class 12.9 fasteners usually have limited applications due to this issue.
What is the current material strength? What is the current preload level?
RE: Backing stud exposed to high-vibration loading - gr12.9 & lock method?
And you confirmed my suspicions about 12.9. I'll have to look into that further.
Anyone have recommendations on bolting materials?
RE: Backing stud exposed to high-vibration loading - gr12.9 & lock method?
You're dealing with pretty low temperatures, so the sky's the limit when it comes to locking features. Loctite would even work fine.
As far as the material goes, I've always been under the impression that 12.9 was a good material. Perhaps you could investigate why people have a negative impression of it.
RE: Backing stud exposed to high-vibration loading - gr12.9 & lock method?
Just noticed the post about 12.9. I'd wager that stress-corrosion cracking wouldn't be an issue when you're bathed in oil.
If you really want to put it to bed, you could always use Inconel 718 fasteners; they don't corrode, but they get pricey fast.
RE: Backing stud exposed to high-vibration loading - gr12.9 & lock method?