Shakeable vacuum chamber

[meekg]

I'm trying to put together a vacuum chamber that is both rigid enough and light enough to be placed of a shake table.

The operating pressure is 10-7 torr.
Shake load peaks at 20g between 20hz and 60hz

The actual experiment is relatively light, but we're trying to fit the chamber and accessories at under 30kg.

The basic configuration I have in mind is a 12" belljar, with a turbopump either bellowed in (so it is not shaken) or a detachable pump with a gate valve (max experiment time is 20 minutes or so)

There are several questions I'm asking really:
1: is there anyone reading this that did something similar?
2: bellowed vs. detachable turbopump
3: stainless vs. aluminum - minimal wall thickness, how much can I save, aluminum alloy and surface treatment choices
4: any experience with gate valves under vibrations?

Thanks,
Ben.

 

[hacksaw]

Depending on how much outgassing your are dealing with ,you can pump the system down seal it and disconnect from the vac. system.

forget about using a conventional bell jar, you need to design a custom enclosure that can be properly attached to the table.

 

[meekg]

I figured as much.
Leak rates for gate valves are acceptable, but the valve may not stay sealed under the vibe conditions.
I'm thinking the slide-type gate valves may be more resilient then the butterfly ones.
Manually operated, probably.

I'm looking in particular on information regarding the aluminum - best type of alloy, and surface treatments.

Heard some conflicting information on anodizing.

 

[hacksaw]

10-7 torr is not particularly high vacuum at room temperature. a lot of materials can be used.

anodized aluminum tends to be pourous. you'd be better off without it.

 

[vacuumsage]

T6061 is a commonly used aluminium alloy for vacuum chambers and tooling, it has good machineability and weldability, so it is quite easy to work with.

I have never done anything like this, but I have had chambers shipped across the country (USA) on trucks under vacuum, with gate valves on, and they haven't leaked. This won't be as rigorous a test as you are going to do, but it's the only vibration experience I have. These gate valves were the slide type, which have an over center type mechanism to lock the valve shut. It might be worth making sure you get one that can be oriented with the O ring seal such that the vacuum helps to keep it closed.

As for the bellows vs disconnected turbo, I should think either will work. Be careful in your choice of bellows, some of them are still quite rigid and will transfer the vibration.

I think hacksaw is right about building a custom chamber and the anodising.

Good luck!