I have some aluminum clamps we use on our terp trap that are needing to be re-torqued after filling with nitrogen and cooling down. The problem I am having is the vacuum grease is cracking when extra torque is applied.
I assume it is simply the aluminum contracting more than the steel bolt that holds them together. My question is, besides shaving off a 1/16 of an inch off the aluminum, what other method have you guys used? I have more clamps, but this is my second set of three. They aren’t super expensive, but I am always looking for cheaper methods to do the same job.
Picture will be added from my phone for reference.
The coefficient for aluminum is 2.4 , twice that of iron or steel. This means that an equal temperature change will produce twice as much change in the length of a bar of aluminum as for a bar of iron.
not sure I understand
are you using a gasket? not going to find elastomers that work at LiqN2 temps, but PTFE might offer some advantage.
having somebody (say @Soxhlet) remake the Alu blocks out of SS might solve the shrinking problem, but retorquing after chill down is not unreasonable or unexpected.
The best way I can explain it is, that the aluminum is just becoming smaller and not making contact with the top plate. I can visually see the gap after it gets cold. Yes sir, we do have a gasket. I’ll post up a pic in a second.
I think better clamps are the ticket, but am hoping to cheap this part together before digging in to my new clamp pile.
That looks like an ISO LF clamp (next size larger vacuum fitting from KF). Also, only the o ring needs to seal. The aluminum does not need to touch the flanges, that’s just a centering ring.
Agreed. That particular ring stretched at the spring from someone prying it up while it was too cold and the o-ring was worn out/flat in that particular example.
Learning lessons daily and not repeating the mistakes is preached around here. Just like bitching is ok once, then its “provide a solution.”
And thanks for that link. Those are cheaper by far than where I sourced them local. I love buying local, but am not a fan of being raped locally.
These look like clamps for an iso flange, they can shrink when cooled. We could make you some ss ones, although they would probably shrink as well to a degree. @lowbudgetjunk have you torqued them at temp? Do you disassemble the trap between uses?
We make cold traps without the iso flange at the top, too many connections and your asking for a leak.
It gets disassembled and cleaned after each day of running. The shaved down aluminum is allowing the flange to be properly torqued now instead of the torque being applied just to the aluminum. I was hoping it would be simple.
I also agree with the flange begging for a place to leak. We welded out the in feed tube on the roller column, the old #1 leaking spot. The cold trap column needs some attention, but I am just gonna cheap out for now, as long as I can pull good vacuum. We are picking up and in need of a couple more employees…let me know when laborers can be had that will actually work.
You must be hiring our culls or we are hiring yours. The sad part is, money isn’t the cure all it used to be. They expect 20+ an hour to just be there, with zero knowledge. Then it takes about 2 hours to decide to keep or chunk the sob’s.
Agreed 100%. Work to your potential and the money will sort itself out. My nieces and nephews aren’t perfect, but they hold down 40hour a week jobs and are purchasing their own houses @19 $ 21. (Youngest nephew is 16, but no house, but working towards 40 hours) If we could afford one or both, they’d be hired and problems solved. The flaw is, they know what they are worth and they are happy where they work.
& problem solved. I can get cheap clamps now, but shaving a 1/16 means the torque is applied on the cold trap cover instead of clamp to clamp. No retightening needed.
