Re: 15GP22 Rebuild Attempt in France - Soon!

[eberts]

Originally Posted by ohohyodafarted

jeyurkon:
it is possible that if the getter flashes are very large, we may be able to counteract the infiltration of any small amounts of gas that might get entraped in the ultor ring after it has been sealed.

Bob

Nope, the getter only works on a singular molecular level on the surface it is deposited on. Surface area of getter flash is more important than amount of material in getter. You need a good hard vacuum for the tube to work.
Maybe you could rebuild a tube connected to a molecular ion pump continously, then you won't have to worry about a slow leaker.

[jeyurkon]

Originally Posted by eberts

Nope, the getter only works on a singular molecular level on the surface it is deposited on. Surface area of getter flash is more important than amount of material in getter. You need a good hard vacuum for the tube to work.
Maybe you could rebuild a tube connected to a molecular ion pump continously, then you won't have to worry about a slow leaker.

I think Bob did mean "large" in terms of area and not thickness. I believe the getter flash does do better than a single mono-layer, but its pumping speed decreases.

John

[Eric H]

So the problem seems to be sealing the thin metal ring to the thick metal parts.

It has a nice V shaped crevasse that something could be flowed into, seems like Vacuseal should work on something like that unless it can't survive the baking process.
Perhaps if it was a slow enough leak it could be applied after evacuation and cooling were done?

Whatever is used it has to be impenetrable, flexible to some degree, capable of withstanding heat & so on.

I don't imagine there's any way to weld the thin metal to the thick metal without cracking the glass or destroying the seal there.

I knew a guy who could weld aluminum cans together using a Plasma Welder, there's still a lot of heat involved though.

[ohohyodafarted]

You're right Eric,

the problem is between the thick metal ring and the thin metal ring which are fused together in some sort of fusion welding process.

Yes, we have taken advantage of the fact that you can "flow" a sealant into the area where the thick and thin metal meet. Vac seal is not the material of choice. Too thin to fill the voids between the metal layers. It does however seem to endure the heat of the evacuation oven very well. In our first trial, we used vacseal. When we took the crt out of the oven the Vacseal had left a very nice glassy coating on the surfaces that we applied it to. That tube was however not a leaker.

I also used Vacseal to seal some vacuum pumping lines that I was experimenting with and it did not seal the leaks.

Also, I spoke to a fellow in the business of working on UHV eqipment. He rapairs and services HE leak detectors. He had nothing good to say about Vacseal. He did however say that the material we are now using was very much favored by him for sealing leaks.

Oh yes, I almost forgot, one of the reasons that Vacseal is not the first choice, is that it is a solvent base material and it's curing hinges on the depletion of the solvent. This is a very big problem for sealing a CRT. The issue is that as we pull a vacuum on the crt, the Vacseal will have a tendency to outgas it's solvent into the crt. That could potentially contaminate the crt after pumpdown. The sealant we use is not solvent based.

[jeyurkon]

Originally Posted by ohohyodafarted

You're right Eric,

the problem is between the thick metal ring and the thin metal ring which are fused together in some sort of fusion welding process.

Yes, we have taken advantage of the fact that you can "flow" a sealant into the area where the thick and thin metal meet. Vac seal is not the material of choice. Too thin to fill the voids between the metal layers. It does however seem to endure the heat of the evacuation oven very well. In our first trial, we used vacseal. When we took the crt out of the oven the Vacseal had left a very nice glassy coating on the surfaces that we applied it to. That tube was however not a leaker.

I also used Vacseal to seal some vacuum pumping lines that I was experimenting with and it did not seal the leaks.

Also, I spoke to a fellow in the business of working on UHV eqipment. He rapairs and services HE leak detectors. He had nothing good to say about Vacseal. He did however say that the material we are now using was very much favored by him for sealing leaks.

Oh yes, I almost forgot, one of the reasons that Vacseal is not the first choice, is that it is a solvent base material and it's curing hinges on the depletion of the solvent. This is a very big problem for sealing a CRT. The issue is that as we pull a vacuum on the crt, the Vacseal will have a tendency to outgas it's solvent into the crt. That could potentially contaminate the crt after pumpdown. The sealant we use is not solvent based.

I've only been able to use Vacseal on very small leaks. Even conformal coating works better. There are epoxies that use a reactive dilulent, but they're still not as good as the one that you plan to use. They are water thin though which might be an advantage.

John

[jeyurkon]

Originally Posted by Eric H

So the problem seems to be sealing the thin metal ring to the thick metal parts.

...

I don't imagine there's any way to weld the thin metal to the thick metal without cracking the glass or destroying the seal there.

I knew a guy who could weld aluminum cans together using a Plasma Welder, there's still a lot of heat involved though.

One of our welders has TIG welded Coke cans too. It helps to have that level of skill, but it doesn't mean you can reduce the heat in other situations. Where you have to weld is too close to the glass and the rapid heating would be catastrophic.

I thought about suggesting brazing using preforms in a programmable vacuum furnace, but I don't know if the phosphors would survive. I've done similar brazing in a hydrogen atmosphere, but it might react with the phosphor. I don't know enough chemistry...

John

[Eric H]

JB Weld! heh, heh.

Or 3M Weatherstripping glue, that stuff is the most evil crap ever invented, it never comes off!