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Extruding in a liquid

Posted by ErikDeBruijn 
Extruding in a liquid
April 11, 2008 01:43PM

When I thought of water soluble support structures (great concept), something made a click.

I had the (crazy?) idea of extruding in a liquid (e.g. water, oil). It may sound crazy, but bear with me... I want to try it, but I'm still waiting on parts to start building the RepRap sad smiley

Extruding in a fluid has two main implications:
1. Flotation support: If the level of the fluid is controlled, this has the potential to make newly extruded thermoplast float. This would replace the need for a solid support structure. We could dissolve salt in the water to make the water 'heavyer' since some thermoplasts may be slightly heavier than pure water (while many plastics are lighter than 1kg/dm^3).

2. Controlled cooling: The fluid will have better heat conduction than air. This means that if you carefully choose the temperature of the liquid, you will cool it more quickly and only to a desired temperature. This may reduce or eliminate warping. From what I read, it seems that the cooling causes shrinkage. If a layer is kept hot enough the object cooling could be postponed until it's finalized. Then, it can cool as a whole. If we need high temperatures we could use a liquid (oil) with a higher boiling point. We'd have to figure out if the liquid interacts with the plastics (in a good or bad way).

Since I cannot try it, anyone, please give it a try! It might be as simple as using a small plastic container and adding x deciliters of water every layer. Eventually it may be hard to perfect this technique, but if it has the potential to improve the product, it is worth giving it a proper try.

Please also let me know what you guys think of the idea, and what remarks or alternatives you have!

The good thing is: water, oils and salt are universally available.

Erik de Bruijn
Re: Extruding in a liquid
April 12, 2008 12:36AM
It could work, just the logistics required to keep the piece from floating away might cause a couple of headaches.

Re: Extruding in a liquid
April 12, 2008 03:36PM
would the plastic glue together properly in liquid? i am rather pessimistic about that. molten plastic doesnt get stuck on wet plastic i think. would work if something like quicksilver were to be used coz then the plastic wouldnt get wet but beside the poisonous fumes quicksilver is also really heavy and hard to get in larger quantities. frankly you coulndt get a pool of it to print in, your printer would collapse
Re: Extruding in a liquid
April 12, 2008 04:36PM
By the time you bought enough mercury to run your printer you could have bought a Stratasys. As well, the EPA would be beating on your door because you'd have more than enough mercury to eradicate a few endangered species if it got loose into the environment.
Re: Extruding in a liquid
April 12, 2008 04:48PM
well basically you need some liquid that doesnt wet the plastic and apart from mercury im out of ideas water and especially oil wont work imho. plastic just wont bond together. feel free to try it out i could always be wrong but imho the idea has little future
Re: Extruding in a liquid
April 12, 2008 05:19PM
Hi r2kordmaa,

... i wouldn't recommend to use fluid metals as support, but you can try with galinstan from [www.geratherm.de] (wikipedia: [en.wikipedia.org] )

I have a small probe, it looks and behaves like mercury, but isnt't toxic and is a bit adhesive to some plastics (PET) ...

Re: Extruding in a liquid
April 12, 2008 05:30PM
hmmzzz... half as dense as mercury its still really heavy to have a pool of it. it might even rip the detail off the bottom and it might end up floating in it. also i think it might be quite expensive stuff. but yeah you can probably print plastic in it better than water/oil anyway
Re: Extruding in a liquid
April 13, 2008 12:42AM
Well what if for you don't submerge the last layer in water/or what ever fluid is in question but the second layer down. So that layer that you are printing on is "dry" but with the average layer size at .5mm the heat will easily through the layer and cool the current printed/printing layer. While but the bigger consern is how do you get the liquid layer to move to the level you want, easily, and can be eventual made from the reprap. In order to get it to kind of work you would have to invert the entire z axis and try and get so you could some how submerge the Darwin into a bucket of liquid... all of this is do able just not practical for our purposes. Much like the idea of enclosing the Darwin in an oven/heat box.
Re: Extruding in a liquid
April 13, 2008 06:37AM
well although i think its not mechanically too hard a task i remain skeptical about the usefulness of it. i think a support material will do much better job than liquid.
Re: Extruding in a liquid
April 13, 2008 06:58AM
Well, if an exclusive and/or expensive material is really needed, it is really not that useful for RepRap. I'm still hesitant to dismiss the use of simply water or oil. I have not yet played with the materials enough to know why it wouldn't work. Many thermoplasts are used to contain fluids such as water (PP perhaps the most), as far as I know many of them do not really interact with them much. IIRC, PLC/PCA can contain some more water (read about water vapour problems) but this water interactions happen AFTER the material is extruded. If the plastic is connected to other plastic and fuses, there would not necessarily be much drifting or floating-out-of-place of these sections. Especially if it cools down faster to a temperature that doesn't have as much shrinkage but does make it pretty much solid.

I'll just give it a go myself when I've built the RepRap. I'll add it to the list of experiments that I intend to do. [offtopic] I'm also going to order Lens alloy or fields metal to try to extrude that. I've got injection needles of which the plastic parts can handle 90'C water at least and the melting point of these metals is below that. The needles are stainless steel so I think they won't dissolve in the alloy.[/offtopic]
Re: Extruding in a liquid
April 14, 2008 01:41PM
How about some sort of wax (paraffin, bees wax)? There might be something close to the right density that's also liquid at a reasonable temperature. Not sure how it'd affect adhesion. Probably depends on the type of wax. It'd be nice if plain old candle wax turned out to work.
Re: Extruding in a liquid
April 16, 2008 01:11AM
candle wax is lighter than water so the question remains: will your plastic sink or swim. also wax wets most materials very well so the question is: will plastic bond together in a wet environment. try it out and tell us
Re: Extruding in a liquid
April 16, 2008 02:49PM
I went to matweb [www.matweb.com] and looked for materials with a melting point below 60C and a density around 1.3 g/cc. Two materials caught my eye:

Sodium acetate trihydride (aka "hot ice"): melting point 58C, density 1.45 g/cc.

Glycerin (aka glycerol): melting point 18C, density 1.26 g/cc.

Both of these are fairly cheap. Glycerin's probably the easiest to handle. Not sure how either of these would affect adhesion.
Re: Extruding in a liquid
April 16, 2008 05:21PM
Glycerol is also the byproduct of making bio-diesel. There are now kits
available for make your own fuel, and in the UK you are allowed to brew up to
2,500l per year without tax. The raw material is cooking oil, either fresh
or used. So we can even be green while reprap-ing!

Re: Extruding in a liquid
May 06, 2008 03:41AM
hi eric,

noted your water idea above.

i was thinking of the possibilities of printing upside down.

wasps make very light, strong nests from paper this way.

just a thought.

liked the water idea though.

i wonder if it is possible to print ice. at a low temp, a spray of liquid water should freeze instantly through evaporative cooling.

Re: Extruding in a liquid
May 06, 2008 04:59PM
printing in some fields metal wouldnt be such a bad idea, because of you need to keep the liquid hot anyway end result will be warm printing environment resulting in less warping(in theory). the printing ice idea doesnt look too promising tho, you would need to go cyrogenic for instant freeze resulting in uber difficult design. would be interesting tho to print in liquid nitrogen for example with water. you would have to keet the extruder head above 0 degrees somehow without boiling away the nitrogen(good luck with that) but i guess you could get uberinteresting results.

and even when your design fails you can have fun with liquid nitrogen grinning smiley
Re: Extruding in a liquid
May 12, 2008 01:50PM
Actually, I was playing with some of that "Multi Purpose Modelling Plastic" yesterday, the kind that melts around 60 deg C. It sticks to itself just great in a pot of almost boiling water, stuck to the pot, even stuck to the spoon I was using to collect it with. Once it cooled a bit I could get it off the metal parts, but it stuck just fine to itself.

Since the density of plastic is so close to water, you really could get away without much support on overhangs. And with a little immersion heater you could control the temperature very accurately. Might make a big difference in warping. You could have a toilet bowl style float valve that kept the water level just below the print head as the Z axis drops. And it would be very easy to keep the working piece at a temperature near it's melting point, without melting the Darwin.
Re: Extruding in a liquid
May 13, 2008 02:07AM
Actually printing ice isn't too complicated. You certainly don't need cryogenic temperatures, just temperatures below 0 degrees C.

As for printing in liquids, The plastic will only float on the surface if the amount of liquid displaced weighs more than the force applied by the plastic stream from the extruder.
Re: Extruding in a liquid
May 13, 2008 02:15AM
... printing coloured water with an ink-jet on a surface cooled down until -10
Re: Extruding in a liquid
May 13, 2008 09:28PM
Inkjet printing in the cold. I will add that to my January to do list. Sounds potentially more useful than blowing bubbles.

(Frozen soap bubble drifting by)

Small quantities of water freeze quickly when it is cold. I think it was between -5 and -10 deg F when I took this picture.

Re: Extruding in a liquid
May 13, 2008 10:05PM
Now that is truly weird. Frozen nanometer(>100) thin films drifting through the air.
Re: Extruding in a liquid
May 14, 2008 03:58AM
Hi Scorch,

... you need a special setup, where the ink and printer-guts are above 15
Re: Extruding in a liquid
May 14, 2008 10:21PM
My vague plan was to print on a pre-frozen plate of steel. I would bring the printer into the cold environment only when I want to try printing. The printer and water temperature would slowly decrease in the cold environment. If printing continued for a long time a small heating element (or heated isolated bag) might be needed to keep the water at temp.

My guess is that -10
Re: Extruding in a liquid
May 15, 2008 03:35AM
Hi Scorch,

... as the printed slices acts as thermic isolators, you have to cool the ambient down, so the topmost surface of your printed object is in the right temp-range.

When you print small droplets of water, they cool down very fast and because of the doubled shock when firing out of the nozzle and impacting at the surface i think they didn't stay in the 'supercooled fluid'-phase, so it should be enough when you have something below -6
Re: Extruding in a liquid
May 15, 2008 05:45AM
If you print at -18C, or somewhere in that region, you could probably use a water/alcohol solution as support material. It would freeze while printing and once done you could raise the temperature to just below 0C causing the supports to simply melt away leaving the finished object. On that note, I wonder if it would be possible to print with molten wax in a freezing environment using water as support? That could possibly result in usefull objects for investment casting and such.
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