What is the quality of 304 stainless steel that makes it so preferable to fusioneer?

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Jack Puntawong
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What is the quality of 304 stainless steel that makes it so preferable to fusioneer?

Post by Jack Puntawong » Fri Sep 14, 2012 3:12 pm

Hi,

I have seen that many of the folks here uses either a spherical or cylindral 304 stainless steel fusion chamber. Is there a reason why you cant use standard steel or other stainless steel?. I know one reason that it blocks weak x-ray. Could I use a standard steel 8" tube as my alternative if I couldn't find the 304 stainless steel?

Thanks

Jack Puntawong

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Doug Coulter
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Re: What is the quality of 304 stainless steel that makes it so preferable to fusioneer?

Post by Doug Coulter » Fri Sep 14, 2012 4:13 pm

Regular steel always has a tiny (or more) layer of rust which acts like a slow leak - rust actually decomposes in vacuum, slowly. It's not that you can't use it, but most all the standard fittings are SS anyway, and it's easier to mate like to like (think melt points for welding, and tempco thereafter). The reason to use 304(L) rather than something else stainless is price and ease of machining, as well as it being one of the less magnetic stainless alloys.

It's one of those things - you pay a little more upfront for a lot less trouble down the road. I don't bother with the fancy SS/silver plated 12 point bolts myself - I just use steel for those and degauss once.
Why guess when you can know? Measure!

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Re: What is the quality of 304 stainless steel that makes it so preferable to fusioneer?

Post by Dan Tibbets » Sat Sep 15, 2012 6:06 pm

For what it is worth, I have seen that stainless steel is best for deep vacuums, followed by aluminum, then iron (due to rust?).

The best flavor of stainless steel is those low in zinc, which apparently has a low enough vapor pressure that it starts evaporating at deep vacuums. I'm uncertain if this is significant at fusor pressures of ~ 10 Microns.

Dan Tibbets

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Re: What is the quality of 304 stainless steel that makes it so preferable to fusioneer?

Post by Jack Puntawong » Sat Sep 15, 2012 10:18 pm

Thanks you Doug and Dan,

I think I might have to go with the stainless steel because I live in Thailand, near the tropics and equator. I don't want to have trouble with rust down the road.

Forgive me for asking question unrelated to this thread. But, what material should I use for my view port. I was thinking of using thick acrylics but I'm not sure if it would withstand the temperature. Another material I was thinking is glass, but I'm not sure which type is best that could withstand the temperature within the fusor.

Jack Puntawong

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Re: What is the quality of 304 stainless steel that makes it so preferable to fusioneer?

Post by David D Speck MD » Sat Sep 15, 2012 10:31 pm

Jack,

Standard factory made Conflat vacuum viewports use borosilicate (e. g. Pyrex) glass. Quartz is even better if you happen onto an inexpensive piece, but it is usually pretty expensive. Acrylic or any plastic material will outgas far too much, and is unacceptable.

Your window materials have to be able to withstand a lot of heating, because when you get jets or beams from your center electrode, the windows will get very hot. Acrylic will not stand up to that sort of abuse.

It is a good idea to place a sacrificial piece of clean plate glass inside of your viewport, but not touching it. Metal will sputter off your central electrode and plate onto the window, eventually mirror coating it. It's a lot easier to drop your piece of sacrificial glass into an acid bath to remove the plated metal than it is to clean an expensive viewport.

Dave

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Re: What is the quality of 304 stainless steel that makes it so preferable to fusioneer?

Post by Brian_Gage » Sat Sep 15, 2012 11:38 pm

Hi Dave,
Was delighted to read your post on fusor.net. Didn't know you were both GCE and interested in fusors. 'duh!' Should have guessed...
Envisioning a view-port, it should be fairly simple to add in a glass window before the more expensive Pyrex port window to protect it from sputter.
Hey, this from a blind guy who hasn't even got a plasma chamber and vacuum system working yet!
Geo at GCE has my money for 2 scint probes, so I'm still in the RAD groove.
Regards, Brian

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Re: What is the quality of 304 stainless steel that makes it so preferable to fusioneer?

Post by David Geer » Sun Sep 16, 2012 4:40 am

Also, you can look into lead glass instead of standard plate glass to reduce x-ray emissions from the viewport. That's just my 2 cents but everything the others have mentioned are all very good and valid items for you to take into consideration.
- David Geer

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Re: What is the quality of 304 stainless steel that makes it so preferable to fusioneer?

Post by Jack Puntawong » Sun Sep 16, 2012 9:15 am

Thanks Dave,

I will think I might have to order the view port from Wiederslab. Better be safe than sorry.

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