Vacuum Chamber Window

[RickWood]

Sorry for the "noob-ness" of my first post. Hopefully I've put it in the right forum.

I am trying to design a vacuum chamber window with a working range as low as 10^-7 Torr. The size and form of the window are dictated by the existing chamber and the blank aluminum panel that the window will replace. The window is for normal observation and doesn't require specific optical properties other than visible light transmission.

Originally I wanted to use a cast acrylic but I'm concerned with outgassing. The advantage of acrylic is the ability to make it 477x777mm at a relatively low cost.

Fused-Silica Quartz seems better suited for VH/UHV but is seems much more expensive per unit of viewing area.

The task will get axed if it is prohibitively expensive or minimally functional. Is there an option that I have overlooked?

Thanks,
Rick

 

[CorBlimeyLimey]

To minimise the outgassing, could you bond a sheet of suitable glass to the vacuum side of a cast acrylic block?

 

[CoryPad]

There are several visibly transparent polymers (acrylics, polycarbonates, polyesters, vinyls) as well as ceramics (soda-lime glass, borosilicate glass, quartz).

How are you sealing the window to the chamber?

Have you investigated the wide variety of current commercial solutions?

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[RickWood]

CorBlimeyLimey: Finding suitable glass in that size would render the acrylic useless.

CoryPad: The current blank panel uses a standard Parker face o-ring seal with a dovetail groove. The panel is secured with M10 SHCS around the perimeter.

I have looked at M.D.C., Huntington and Abbess Instruments webpages. There isn't a problem finding materials that can handle that range of vacuum. Rather, I need a material that is inexpensive at such large sizes AND capable of handling that level of vac.

You mentioned Acrylic and Quartz... they both have problems that are mentioned in my first post. I guess I will look into the others you mentioned in the meantime.

 

[Artisi]

What ever you decide to use - remember that a vacuum vessel is classed as a pressure vessel (at least here in Australia)and must meet the appropriate pressure code including any opening / inspection cover.

 

[bnrg]

I have successfully used acrylic for applications in this pressure range. A big issue is the pumping capacity that you have available. I have used an acrylic window roughly on the order of 11 square feet using 2 4500 l/sec (on N2) pumps and would get down into the '6' range very quickly. The system had much other plastic, blind tapped holes and other bad vacuum practice things, but it ran ok. If you are going to bake, the acrylic is pretty much useless over 120 F. Ultem is likely a better choice in that case.

 

[RickWood]

bnrg: The window would be just over 3 sq. ft. in exposed area. There are several pumps in the system; a roughing pump, a cryo pump (2200 liters of air/s) and 3 turbo pumps (2200 liters of H2/s each). There won't be any other features on the panel inboard of the o-ring groove.

I will look into the ultem but I'm holding out hope that the acrylic will work out.

Thanks for all the replies. Keep 'em coming.