sludgexstruder

This is a raw idea I just got. I've been contemplating alternatives to filament. What's happening now 3d printing is not cost effective. A commodity like ABS, which cost's $1/lb, is marked up to $30/lb when extruded into filament. I haven't seen much progress in granule extruders, So here's my solution:

I was walking through my local CircleK today (substitute your local stop-and-rob here) and I noticed the slushy machine was squeaking; "Hmm, bearing must be going bad I suppose." My mind works in mysterious ways .

Anyway, I purpose extruding ABS paste, or ABS blended with acetone, through a contraption kind of like a slushy machine. ABS and acetone wont remain mixed if it sits in a tank, but make an air tight tank with an auger bit that agitates the mixture and in theory, you'll get a uniform distribution.

Then, attach a hose to the bottom of that tank to a tool head, with a solenoid valve to turn the flow on and off, then you could have an extruder that uses raw pellets instead of filament. Obviously there are pressure issues to deal with; You cant use normal air to push the paste out or you'll just get a big mess of hardened ABS in a big expensive tank, but maybe nitrogen or helium? I don't know.

Anyway I thought I would release my sludgexstruder into the wild and let you guys nitpick it apart. Cheers.

It's not a terrible idea. I have some (limited) experience with polymers in solution and can maybe add some information to this.

Firstly, there is a solubility limit for the amount of a given plastic that you can dissolve in solution. Suppose, for instance, that the solubility limit of ABS in acetone is 15% by weight. That means that every bit of plastic you attempt to dissolve above the 15% limit phase separates as a solid precipitant. So you don't get a "paste" as you would expect, but rather a viscous solution of ABS in acetone with some precipitated ABS sitting on the bottom of your tank.

Now, it may be possible to dissolve ABS to the solubility limit and then evaporate out the solvent after deposition. You would need to use a solvent that has a high vapor pressure (so that it evaporates quickly). The vapor pressure of acetone might not be high enough, but something like chloroform/polycarbonate could work. You would then need to rapidly heat the deposited "goo" to remove the solvent before it relaxed too much, leaving solid plastic. Something like a hot air rework gun might work for this.

But in general, I'm afraid that the viscosity of the solutions might be too low for this to work... although maybe something with very long molecular chains like silicone rtv could work.

Edited 1 time(s). Last edit at 08/13/2013 07:48PM by iquizzle.

I'm not sure about chloroform. It's not something ubiquitous like acetone. I like the idea of a hot air rework gun though. I'm sure if you heated it fast enough it shouldn't be a problem. Plus I don't want people going comatose over a bottle opener!

Chloroform is at least non-flammable. Acetone isn't exactly ubiquitous when you have a vapor and potential for a spark. You don't exactly want to constantly breathe either chemical anyway, so regardless this would have to be an enclosed, ventilated system. IMO, in a ventilated system, acetone poses much more of a hazard.

In any case, I'm not advocating that everybody go out and buy chloroform to test this out. I'm not even certain how available it is to people without business addresses. But if you do decide to test this with acetone, just don't blow yourself up!

With a %15 acetone %85 ABS solution, I'm not sure how much of a risk there would be. But consider the alternative. A 230 degree C hot end poses as much, if not more of a potential fire hazard. It's really a pick your poison scenario. Besides, plenty more houses burn down from space heaters than 3d printers.

You missed my original point. You can't have an 85% ABS/15% acetone solution. It doesn't work that way. Once the solvent reaches a saturation value, you get solid/liquid phase separation.. i.e. similar to what happens when you try to add more and more sugar to water. I think the best you can do will be somewhere in the neighborhood of 15% ABS / 85% acetone.