How to expand a metal seat ring (SS316) with a teflon insert to fit in a bore that is too big?
How to expand a metal seat ring (SS316) with a teflon insert to fit in a bore that is too big?
(OP)
The OD of the metal seat ring is about 75 mm (3") and about 25 mm thick. It is suppose to be fit into a bore with ID of approximately 75.5 mm (standard carbon steel). So obviously this is not a correct size as the bore needs to be smaller than the OD of the metal seat by about .30 mm. So the OD of this seat needs to 'expand' at least .80 mm or to 75.80 mm or the bore needs to be 'shrunk' by 0.80 mm or to 74.70 mm.
Welding or other type of thermal spraying the seat is out of the question as it may damage/distort the seat and or teflon insert. Rewelding/remachining the bore is also not considered due to time and work involved. I have two ideas here but would appreciate it if someone has some input to share...
1) Machine a new sleeve with ID of 74.90 mm (to shrink fit the seat into it). This new sleeve would have an wall thickness of 3 mm or OD of 80.90 mm. Once I use liquid nitrogen to fit the seat into the sleeve, I re-machine the sleeve to the exact size I need or 75.8 mm. The question is, would there be any problem when re-machining the new insert to about 0.8 mm thickness, would it crack being so thinned after being shrink-fitted? If it all works out, I would shrink fit this again into the bore.
2) Machine the bore bigger so you can insert a metal sleeve about .10 mm bigger than the bore and shrink fit it inside the bore. The new 'bore' would have a new ID approximately 74.70 mm. But how 'thick' of a metal sleeve can be machined effectively without it being distorted?
Welding or other type of thermal spraying the seat is out of the question as it may damage/distort the seat and or teflon insert. Rewelding/remachining the bore is also not considered due to time and work involved. I have two ideas here but would appreciate it if someone has some input to share...
1) Machine a new sleeve with ID of 74.90 mm (to shrink fit the seat into it). This new sleeve would have an wall thickness of 3 mm or OD of 80.90 mm. Once I use liquid nitrogen to fit the seat into the sleeve, I re-machine the sleeve to the exact size I need or 75.8 mm. The question is, would there be any problem when re-machining the new insert to about 0.8 mm thickness, would it crack being so thinned after being shrink-fitted? If it all works out, I would shrink fit this again into the bore.
2) Machine the bore bigger so you can insert a metal sleeve about .10 mm bigger than the bore and shrink fit it inside the bore. The new 'bore' would have a new ID approximately 74.70 mm. But how 'thick' of a metal sleeve can be machined effectively without it being distorted?





RE: How to expand a metal seat ring (SS316) with a teflon insert to fit in a bore that is too big?
Usually, an interference fit is no more than 0.006 - 0.010 inch.
RE: How to expand a metal seat ring (SS316) with a teflon insert to fit in a bore that is too big?
http://www.sealanddesign.com/category/Retaining/20...
Regards,
Mike
RE: How to expand a metal seat ring (SS316) with a teflon insert to fit in a bore that is too big?
As for loctite, its out of question, maybe if we were talking about .05 mm gap. Even then, if the bore is bigger, the seat may pop out under 5000 psi pressure which can lead to various disaster....
RE: How to expand a metal seat ring (SS316) with a teflon insert to fit in a bore that is too big?
The repair sleeve is thin and has minimal radial stiffness compared to the thick section seat and housing.
RE: How to expand a metal seat ring (SS316) with a teflon insert to fit in a bore that is too big?
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: How to expand a metal seat ring (SS316) with a teflon insert to fit in a bore that is too big?
RE: How to expand a metal seat ring (SS316) with a teflon insert to fit in a bore that is too big?
You did not mention what the repair sleeve material was, but I can't see there being a fracture issue with any metal I can think of when machining the repair sleeve to a .8mm thickness.
As for leakage past the OD of the repair sleeve when exposed to 5000 psi(d?) fluid pressures, that is not an easy question to answer without having more specific details about the installation. If the 76mm dia x.80mm wide end face of the repair sleeve were exposed to a 5000psi pressure, that would produce an axial force of over 1460lbs on the sleeve. If there is nothing other than friction preventing the repair sleeve from moving axially (like a shoulder on the housing) then it's likely the sleeve will be displaced.
It is also difficult to obtain a leak-free high pressure seal with just an interference fit between two large diameter metal components.
RE: How to expand a metal seat ring (SS316) with a teflon insert to fit in a bore that is too big?
This is actually for open/close ball valve for hydrogen service. When closing, the ball valve would stop the seat from moving anywhere even if the sleeve 'wants' to wonder.
What we have done before (safer) was to re-bore the bore 2-3 mm larger and shrink a 2-3 mm sleeve inside the bore first. The bore has about 25 mm height so does the seat (thickness).
From our experience, seat/bore interference this tight always result in zero leakage at high pressure it is designed for. We tested it countless times and always get zero leakage.
Anyways, thanks for the info about the .8 mm sleeve, we will test that next time to see how it works ;).