Pinch-off Sealant

If the copper is pure and clean, no sealant is necessary. Simply use a pair of bolt cutters with half-round anvils instead of sharp edges to pinch the copper tube off; the copper will weld to itself under the pressure, making a permanent bond. I still have a sample of having done this 45 years ago to seal magnetrons, removing the preliminary (and breakable) glass seal.

Indeed. (This is actually a get-out solution for plumbers when caught short of a stop-end on copper plumbing systems. Nasty, maybe, but it works.)

I am currently looking for one of these pinch-off tools to seal copper tube under vacuum for very long time (>10 years). I would prefer a product with parallel jaws instead of scissors configuration. Does anyone would have some informations about where I can find one?

It would be pretty easy to add a half-round tip and a non-rotating base plate with an opposing half-round to an appropriately sized arbor press. The copper is soft, so it does not take huge forces. If it can pinch the copper tube so any remaining web is less than a tenth of the original wall thickness, it should work. as posted by others here, you could flame melt the tip or silver solder to remove any doubt. As I recall, the anvil tips had about a 3/8" diameter on the unit I used, for pinching-off 1/4" copper tubing.

Dkwarner is right, this is standard practice in the vacuum industry. Typically, the assembly would have been heated in vacuum to remove all impurities. When the tube is pinched off it will cold weld the joint & should be vacuum tight.

Thanks to PWSlack and Guest for confirming my comments.

Actually, thinking on it a bit more, I should have said that any sealant would be detrimental if it is placed inside the tube, because it would prevent direct copper-to-copper contact and thus make the cold weld impossible. Most sealing compounds would also outgass, making it take longer to obtain the desired level of vacuum. A correctly made cold weld on clean copper that was previously heated in a vacuum provides a much more permanent seal than any sealing compound or gasket.

Finally, I assume you are softening a glass tube to make it collapse, then melting to allow removal from the vacuum pump without losing the vacuum. Otherwise, you should do the pinch seal before separation from the vacuujm pump.

Dick

When this procedure is done in the refrigeration industry, the cut end is heated with the oxy torch until a fusion weld at the end occurs, alternatively use 115 silver solder. The 115 can be applied to the outside of the pinch also as this makes good any thickness loss and eliminates stress risers to prevent failure under vibration.

Thanks everybody,

Baris

Hi, I would be pleased if you could comment on this idea,

I have a metal hermetic package which consitute crs1010 case and nickel lid which will be sealed to the case to make a vacuum hermetic package in which temperature sensitive device (temp up to 300 will be OK.) I need a method that the package will be soldered or brazed or welded with pinch off tube on the lid or bottom of the case. And then I can connect it with quick connect to the turbo pump.

which type of material I can use for the tube which can be pinched with pinch off tool.

which method that I can use to bond it to the nickel made lid. and package will be hermetic after pinched it. For welding I can use parallel seam selaer. For brazing not yet have a vacuum oven.

Thanks,

Baris

The malleability and ductility of pure annealed copper make it especially appropriate for pinch-off.

If the lid is pure nickel, a nickel tube (properly annealed after welding or brazing to the lid) might work, and reduce possible electrolysis. The end of the pinch-off is extremely thin, so as an earlier post suggested for copper, you could flame heat the thin tip to melt it and really seal it permanently, with very little heat getting into the container itself.

I'm somewhat less confident if the lid is a nickel alloy, but it might still work.

Good luck! Dick