Very High Vacuum 2

[123Dog]

Chamber approx 400mm square, 316 SS, Wall thickness Approx 30mm
I need a very high 10 to the minus 9 torr vacuum
Somebody has said they can cast it with zero, porosity!!!!!
Is that possible without casting it in a vacuum ?
You have to avoid welds with a vacuum this high too
What would be your recomendation from a job of this type

Thank you

 

[EdStainless]

All high vac equipment that I have ever seen was welded construction from rolled plate. No castings of any kind.
Multipass welds with good inspection is capable of this service.
Will this system ever be opened to air? I am thinking that if it is you may want to consider electropolishing the entire inside surface in order to reduce contamination.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[arunmrao]

Please get more process details of zero porosity from the foundry? Unbelievable for vacuum applications.

 

[JTreglio]

I've never worked with a cast chamber, and I've been working with high vacuums for over thirty years. The welds are not a problem if you weld on the inside. Definitely do not weld on both sides. You definitely should electropolish the interior. Make sure the chamber is made with all metal seals, then bake it out under vacuum for 24 hours at 400 C. If you can't use all metal seals, make sure all of the "o" rings are Viton, and bake at 250 C. The baking drives all of the junk out of the surface, so for the most part it need only be done once. How do you intend to pull down the vacuum? For the kind of pressure you want, I would suggest you use a cryopump. Rough it down with an oil-free mechanical pump.

Jim Treglio
Molecular Metallurgy, Inc.

 

[GRoberts]

The thing that comes to mind when you mention "Zero porosity" and casting, is getting the casting HIPped (hot isostatic pressed). Do you know if that is part of the casting plan?

 

[arunmrao]

GRoberts,
I was thinking of a post casting treatment like Hipping. But I was wondering the kind of equipment needed for a 30mm wall thick plate and the effectiveness for a hollow casting.

Also I was thinking about the difficulty in decoring the casting if it were completely enclosed.

 

[123Dog]

Thanks
Its a curly one
I will try and find more about the casting
process, and get back

 

[123Dog]

Would it be OK to get a test piece of this cast Matl say 150mm dia and test it vacuum wise, to 10 to the minus 9
Would this accurately represent a 400mm square chamber ?????????
Thanks