play dough vacuum seal

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Guglielmo_D
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play dough vacuum seal

Post by Guglielmo_D » Sat Jun 05, 2021 10:45 am

Hi,

I found a large glass bell to use as a chamber for a demonstration fusor. I had issues with the gasket's air-tightness (My gasket comes from a crappy rubber sheet cut by hand).

Can play dough be used as a substitute for the gasket? Has anyone tried making air-tight seals with play dough? Is it suitable for high-vacuum (outgassing, porosity)? Are there any similar alternatives?

I will try placing the bell on the baseplate and surrounding the interface between the two with ample play-dough.

Cheers!

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Jim Kovalchick
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Re: play dough vacuum seal

Post by Jim Kovalchick » Sat Jun 05, 2021 11:35 am

Please follow the forum rules for posting. At a minimum you need to use your real name.

Regarding play doh, mashed potatoes would be cheaper. There are lots of other household semi-solids you could try. What about flex seal? If it works you could make a commercial.

In all seriousness, I am myself willing to try unconventional alternatives to expensive vacuum equipment. If your research says that play doh will work then I suggest you try it and report back.

If your bell jar was indeed made for vacuum and you have a flat base plate then some silicon grease should work. If not then there are other problems.

Guglielmo_D
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Re: play dough vacuum seal

Post by Guglielmo_D » Sat Jun 05, 2021 11:54 am

Thanks, I changed my username.
I will get back if I get it working.

Guglielmo_D
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Re: play dough vacuum seal

Post by Guglielmo_D » Sun Jun 06, 2021 1:37 pm

I tested it today, but could only reah up to 0.2 atm.

In all fairness, I was not starting with a functioning system to begin with. So, I may have other problems (like the pipe fittings) that are contributing. But, I heard hissing noises coming from the doh interface which leads me to believe that it does not work properly. If anyone else tried it, please let me know.

For reference, I am using a glass chamber similar to:
https://www.amazon.com/Whole-Housewares ... 510&sr=8-2
As pneumatic feedthrough, I am using something like this:
https://www.amazon.com/Pieces-Brass-Ref ... 71&sr=8-15

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Jim Kovalchick
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Re: play dough vacuum seal

Post by Jim Kovalchick » Sun Jun 06, 2021 3:09 pm

I would not use that as a vacuum bell jar. It is not designed for vacuum and failure could be catastrophic and dangerous.

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Richard Hull
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Re: play dough vacuum seal

Post by Richard Hull » Sun Jun 06, 2021 4:46 pm

Following on to Jim's comment...That is not a bell jar!! That is a floral or "my Pretty" display for the mantle. It is made of the wrong type of glass. It is far too thin. Beams from a plasma will see its untempered nature collapse, (Implode), throwing shards of glass everywhere. It is dangerous on so many levels.

Scientific bell jars are of Kimax glass at least 1/4" thick and properly tempered. They are tempered to relieve all internal stresses. They will have a 1/2 thick, flat, ground glass base for proper gasketing. They are very expensive when purchased new. Even they are not recommended for plasma work without a proper implosion shield.

Nuff said.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Chuck Sherwood
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Re: play dough vacuum seal

Post by Chuck Sherwood » Sat Jun 12, 2021 1:06 am

Apiezon "Q" is pretty much like playdough and specifically designed for vacuum sealing. I tried using it to seal a bell jar to a metal plate.
It didn't work any better that a home made rubber gasket and was far less consistent.
Unfortunately this bell jar is an odd size (10 3/8 inches) and I have not found a commercial rubber "L" gasket that will fit.

But seriously, there are recipes for making play dough. The primary ingredient is flour. What are the odds it will seal?

One thing I have learned in the vacuum world. You have to be very meticulous. Murphy is lurking around every corner.

chuck

JoeBallantyne
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Re: play dough vacuum seal

Post by JoeBallantyne » Sun Jun 13, 2021 6:01 am

I don't think anyone here has ever even considered using play dough for a vacuum seal.

It is made with water.

Water in a vacuum chamber is the enemy. Bake outs are used to get rid of it (and other things) in very high vacuum systems.

If you already have real vacuum grease, why are you wasting your time making playdough?

Joe.

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Richard Hull
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Re: play dough vacuum seal

Post by Richard Hull » Sun Jun 13, 2021 4:26 pm

Without a proper bell jar containing a large, broad flat base, a proper mating gasket that is very lightly greased with a suitable vacuum grease, a deep vacuum is just not possible.

This assumes that you wish to run numerous vacuum tests where removing and modifying the internals of the system are part and parcel to the entire plan. Typically, this is the very reason for using a bell jar in the first place, be it a small glass bell jar or an industrial, one meter diameter stainless steel bell jar.

Casual work with a bell jar of questionable type, (mason jar, thin floral or display container, etc.), will yield casual, questionable results.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Guglielmo_D
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Joined: Sat Jun 05, 2021 10:34 am
Real name: Guglielmo l

Re: play dough vacuum seal

Post by Guglielmo_D » Tue Jun 15, 2021 7:10 am

update:

I gave up on using play dough, just could not reach low enough pressures after 2 days of testing. Thanks for the heads up on the vacuum-specific product!
I ended up grinding the bell jar with 80 grit sand-paper to create a somewhat flat lip and placed it on an Aluminum plate. Unfortunately, the plate was not very planar since it got slightly deformed during shipping and the seal had to be complemented with ample vacuum grease.
I tested the system (with ample safety measures in place) and achieved low pressures (0.00 atm on my crappy manometer), but not low enough to avoid having a plasma arc rather than a star. Maybe it is the fault of the bell jar, maybe of the high voltage feedthrough which is just a high voltage cable press-fitted through a hole in the Al plate, surrounded by a JB-weld seal (by the way, has anyone ever tried this type of feedthrough?). I agree with Richard, this solution is way too unreliable, and debugging the seals is just a nightmare.

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