Sealed smoothing station - Success! (Page 1 of 3)

Sealing is a bad idea.  If you create a zone of cold air at the top by running chilled water through a copper coil, the acetone will condense before it can get out.  When I did this, I could put my nose right at the top of the pot and not smell anything.

Here's another idea. 

Instead of a expanding container (which nobody seemed to understand) why just use a mason jar (which is rated for full vacuum) and a hand held vacuum pump to shift the acetone boiling point? 

Since the boiling point of acetone is so low to begin with, it should boil into vapor at room temperature by putting it under a slight vacuum (229mmHg ~ 5psi?).  Then you get vapor in a safe enclosed container with no heat source.

Yes.  My original thought was to use a cap with an air escape hose and put something like a balloon over it to capture and measure the gas volume.  Of course a regular balloon would probably be eaten up fairly quickly by the acetone, but a zip loc bag (polyethelyne) should not.  It's been a long time since chemistry class for me too, but I think it should be in the range of 1-2 liters of gas generated per cc of acetone.

As I recall, in any enclosed space,  at any given temperature, a liquid will want to evaporate until it either runs out of liquid or builds up enough pressure to reach its equilibrium vapor pressure.  At 56.5 degrees C, acetone has a vapor pressure of 760mmHg (1 atmosphere) , which is why an open container of it starts to boil at that temperature.    At room temperature, however, acetone only has a vapor pressure of about 0.3 atmospheres (a partial vacuum).  Thus, if you put acetone in an enclosed jar and try to pull a vacuum, the acetone will start to boil off when the pressure tries to drop below 0.3 atm.  The more you try to drop the pressure, the more acetone will boil off to keep the pressure at exactly 0.3 (until you run out of liquid).  If you then instead try to increase the pressure back to 1 atm, any acetone gas that had boiled off will immediately condense back into a liquid, again "trying" to keep the pressure at 0.3 atm, until all the acetone gas has condensed back into liquid.  The setup should be perfectly safe because the acetone can never generate net positive (> 1atm) pressure at room temperature; it really "wants" to be at its equilibrium vapor press of 0.3 atm.

The only reason I would go this route over the presto is if you want to smooth a larger object like something that was multiple prints and put together.

I want to find something in the 5gallon range with an open top that wont be eaten by the acetone.  I wish glass carboys for homebrewing had the same open bucket design as the plastic primary fermenters.

My current thought is to find a metal or plastic 5gallon bucket made out of the correct material. Which leads to the next question.  What plastic number should we look for on the bottom of our buckets. I believe Class 2 is HDPE and is acetone safe.

I have a 23qt pressure canner that I picked up cheap. (at a yard sale) that I am going to try.

the only problem is you have to go by time as you can not see the part.

here is the link
http://www.walmart.com/ip/Presto-23-Qt- … er/2625289

OK, so after some quick reduced pressure testing with a glass jar, a metal lid, and a cheap Mityvac hand pump I was able to just pull 10 inmg from the jar and at room temperature got nothing, apart from a hand that now aches
Now it could be that the acetone was a bit to cold or I couldn't hold the vacuum (I had way to many leaks, it was a very quick test) but I would guess to make it work well you would need a proper vacuum pump which would make the whole idea rather expensive.

I also noticed a probable flaw in the idea which would stop you from even trying. When pull out the air there is still some acetone vapor in the jar and that gets pulled through the pump so the internals aren't going to last long, making it even more expensive.

So a good idea if you have some pressure vessel and a stainless pump with special seals, but I think for the rest of us it isn't economically viable when Ian has already found a cheap and easy solution.

However, I still want to play with the idea of the sealed vessel, mainly so I can use it inside without having to worry about it exploding or gassing myself.

Hmmm, going to try again once I have glued up some parts to make the vacuum better.

So some further success on pulling a vacuum. After the glue had set holding the pipe in the can lid and I had cleaned the jar seal I was able to pull 20 inHg fairly quickly by hand.
At that point I did notice a single stream of bubbles in the jar, but it was small and it is fairly cold this morning in here. So I counted that as a success.

It got interesting when I then released the pressure, as the acetone vapor instantly condensed on to the walls of the jar. Which proved that acetone rich vapor was present.

OK, so now for the bad news, clearly my thoughts on getting acetone through the pump were correct as I then tried it a couple of more times to confirm and started to get acetone dripping out of the pump and now it make some very odd squeaky sounds that it has never done before. The seals are still good but I do wonder for how long that would be if I kept going.
I might just give it one more go to get a decent video of the whole thing but after that it is a dead end.

So next step finding a usable diaphragm to put on the jar.

I also need to find something similar to the Presto cooker in the UK. Currently a rice cooker is looking good for the job, cheaper but smaller and less control of temperature.

I've been using a rice cooker recently, and I'm happy with the results, except for when I open the lid, the rush of fumes is very nasty.

This vacuum system seems to have several advantages:

• No electricity required

• Acetone not heated

• Instant condensing of vapor when vacuum is released or lid opened which is super safe

Potentially all you need is a large acetone proof clear container with something attached to it to draw a vacuum. Watch the vapor do its thing and then release it for instant opening without fumes.

Can anyone say whether a vacuum pump like this would be suitable? I'd build a winder to do it by hand:

http://www.ebay.com.au/itm/Mercedes-Ben … 500wt_1203

You would definitely need an electric pump to pull the vacuum as I have only been using a 3 inch diameter jar with a 2 inch throat, so you could only do small parts, and it takes a bit of effort to pull the vacuum to 20 inHg.

Hmmm, spending money get this sorted seems a bit excessive, I am way to tight for all that
I must have something kicking about that can do the trick. When it stops snowing I'll head back out to the garage and see what I can find.

I had thought of some secondary chamber that you could use with a diaphragm so you could separate the acetone fumes from the pump but your idea of adding the acetone in after the vacuum is simply genius.

You would only need to have to tee in to the vacuum pipe with a small reservoir attached containing the acetone and a simple clip to hold back the pressure (no fancy valve that would probably fail). The pipe I currently use is silicone model fuel pipe as it is resistant to most things. Then once you have the item in and the vacuum pulled you would just need to open the clip and the acetone would be drawn in and vapourise instantly. I will need extend the vacumm pipe to the bottom of the contain so the item doesn't get sprayed with acetone, but that is an easy fix.

In the mean time I have gone and bought a rice cooker (the shop owed me some money so it actually cost -£6 ) which looks like it will do the job just fine following Ians idea, you just can't get things like that presto cooker over here. Only problem so far is the tray inside it is plastic, so I'll have to find something to hold the models whilst their "cooking".

Hehehe, I went searching on ebay for vacuum pumps, and ended up finding lots of penis enlargement pumps Not sure if they would work.......Hmmm, maybe I should get one, just for investigation purposes of course

Well I found an old tire inflater that I took off of one of those jump start packs some years back, I need to add a fitting to enable the input side to be connected to anything as currently it is just a hole in the housing, but it is too cold for me in the garage so it can wait for a slightly better day. I also need to find/make some fittings to connect all of this together. Should make a fine vacuum pump, but I have no idea how much it will pull.

How about flipping the whole setup upside down. Then you would fit the container over the model instead of putting the model in the container. That way the original lid becomes the base and any holes that are added are now in the bottom, and the lid acts to make a nice drip tray. It will need some careful fitting of the pipe to make sure the acetone can drip back but it should just want to fall back in to the reservoir. Very similar to a bell jar setup basically.

To remove the air from the acetone reservoir it would probably be easiest just have to make sure the reservoir was completely full. Which wold be easy as is is now underneath with a simple pipe coming out the top.

I feel the need for some drawings now as this is now sounding quite viable again.

Zarni, you might also appreciate this budget solution, reversing the seal on a manual bike pump (saving your hands from using the mityvacXZ):

http://www.instructables.com/id/make-a- … y-convert/

or this homemake pvc solution (maybe not the best material for this application, though):

http://sci-toys.com/scitoys/scitoys/aer … index.html

The first link also references an instructable for what you are doing with an inflator pump:

I'm not sure which one I'll do yet.

http://www.instructables.com/id/E791HNXF23Z39P6/