metal to metal sealing
metal to metal sealing
(OP)
A project I am working on:
A polished piece of metal is to be pressed against another piece of polished metal. The second piece (the seat) is actually a cylinder, and fluid passes through the cylinder. Fluid pressure, if too high, lifts the first piece off the seat and fluid exits through the center of the seat. When pressure drops, a spring exerts pressure on the first piece, pressing it against the the seat and sealing the system.
The question I have is: what surface finish would be required to acheive a metal to metal seal like this? Pressures and hence seat pressures are low (10-20 psi fluid pressure, seating area of approximately .020 in^2 results in a rough est of 500 psi seat pressure). 4130 steel.
Thanks
A polished piece of metal is to be pressed against another piece of polished metal. The second piece (the seat) is actually a cylinder, and fluid passes through the cylinder. Fluid pressure, if too high, lifts the first piece off the seat and fluid exits through the center of the seat. When pressure drops, a spring exerts pressure on the first piece, pressing it against the the seat and sealing the system.
The question I have is: what surface finish would be required to acheive a metal to metal seal like this? Pressures and hence seat pressures are low (10-20 psi fluid pressure, seating area of approximately .020 in^2 results in a rough est of 500 psi seat pressure). 4130 steel.
Thanks





RE: metal to metal sealing
VAT Swizerland and Swagelok America produce vacuum valves with considerable leak tightness. In general they have do not polished their sealing surfaces. Surface roughness is low at about 1 micrometer(10^-6m) to 3*10^-6 m. And flat of course.
The valve block is generally stainless steel and the valve seat can be different materials but copper is a good option.
The balance of forces you show in your calculation I think is not right. 20 psi (1.3bar) is fluid pressure. The seat has an area of 0.02 in^2 so a FORCE is excerted on the seat of 20*0.02 psi*in^2. The PRESSURE on the seat is the same as the fluid pressure 20 psi.
RE: metal to metal sealing
RE: metal to metal sealing
Also, when specifying your surface finish, you must look at the lay of the machining marks to be sure they correspond with your intentions. If you are polishing the plates with abrasive slurries, the lay wont be a factor when you hit "mirror" type finishes.
Now, also, the rheology of the fluid might be a factor, it probably won't; but, I don't know what you are using. Very flat polished plates, when wet, will have a fairly strong bond. This may affect your "opening" performance.
RE: metal to metal sealing