Crazy granule extruder idea

Hi, I'm Stephan from Switzerland.

I haven't really been involved in RepRap until now, but I just had an idea I wanted to share and ask for your opinions.

This is for extruding polymer granules.

Feed the granule in a single line through a flexible tube (inner diameter = granule size). Then, use a peristaltic pump [en.wikipedia.org] to transport the granule inside the tube. The tube leads to the heating nozzle.

I have no idea whether enough force can be applied to overcome friction. What do you think?

Btw: the forum software sucks. How do you format links? Or are there mailing lists?

Cheers,
Stephan

Edited 1 time(s). Last edit at 05/18/2008 06:33PM by Stephan Walter.

I'm afraid that the pump roller would just roll over the granules in the tube, and not be able to push them along. In addition, one of the advantages of a granule extruder ought to be, I think, to allow for recycled plastic to be used, which means it needs to be able to handle granules of varying coarseness. How would this system deal with that?

I was just thinking about how one could recycle plastic parts into granule form. I think that if you wrap an electric heater around a kitchen meat grinder you could use it to produce uniform granules, much like the extruders used to make pasta shapes.

i dont get it.
why all the fus with building it from crash when you can extrac most of the components out of a old printer.
and or a scanner. scanner for the Z axes
grind the abs plastic to powder en use a laser which are cheap these days of you cant replicate the laser diode but in powder form and a laser print head would be faster and have a awsome resolution.
you could even use the scanner eye as calibrating tool too ot make auto corrections.
then you could actualy build a reprap base from the powder it self.
plus you dont lose any plastic.
the powder not used can be reused again.
less feder fus.
the print head could easely replaced with a other tool.
just my meaning...

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why all the fus with building it from crash when you can extrac most of the components out of a old printer

I don't have any old printers here. I spent a little time searching for some, to no avail. Not everyone has access to such things.

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grind the abs plastic to powder

This is slightly more tricky than it sounds. Freezing the plastic and blending it might work, but producing actual fine powder isn't trivial. Using lumpy plastic shrapnel isn't going to do wonders for your build quality.

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a laser print head would be faster and have a awsome resolution

Possibly. Your resolution is limited by how fine your powder is, and how accurate your positioning system is. Making highly precise positioning systems is also not a trivial task.

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you could even use the scanner eye as calibrating tool too ot make auto corrections.

Well, yes. Yes you could. However, this sort of image processing is also quite tricky, and yet another discipline someone has to master. You can't just handwave these sorts of very complex technical issues away.

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plus you dont lose any plastic.

You wouldn't be able to do sparse infilling on enclosed objects... you'd need to leave holes for the powder to be able to escape from the insides. A minor point, but one worth remembering.

I don't have any old printers here. I spent a little time searching for some, to no avail. Not everyone has access to such things.
i cant imagine this my self.
but okay you have a strong point there.

on the other hand with this kinda printing i am thinking of some kinda water proof build area and as you print.
it slowly adds water in it so you could build higher or even faster as the plastic becomes back to solid state.
it could then also make support rods for complex designs.
just keep the water level under the printing level.
the water pressure would cool down the platis and support beter.
just a tought.
greetz

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as you print.it slowly adds water in

Powder and water? I don't see this working at all. You'd have to add it in very carefully so as not to disturb the powder, to start with. Also, with any sufficiently fine powder you may find that you get capillary action effects which make the water soak the whole build area, making it impossible get 'just below the build layer'. Not to mention the extra thermal conductivity of a cold, soggy layer underneath that will make it that much harder to heat up the layer above and get it to adhere nicely to the layer below.

Ru Wrote:
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> as you print.it slowly adds water in
>
> Powder and water? I don't see this working at all.
> You'd have to add it in very carefully so as not
> to disturb the powder, to start with. Also, with
> any sufficiently fine powder you may find that you
> get capillary action effects which make the water
> soak the whole build area, making it impossible
> get 'just below the build layer'. Not to mention
> the extra thermal conductivity of a cold, soggy
> layer underneath that will make it that much
> harder to heat up the layer above and get it to
> adhere nicely to the layer below.

no no not with powder but with a extruder build.
like the guys here from reprap are doing.
if the platic that you uses floats it will have the tendency to pull up the structer you are printing plus the side wards pressure would keep it beter in place plus the cooling. for more complex structers you could add some software that auto calculates were to build support rods ( small ones ) wich you could easyly cut away.

I don't think that you want extruded plastic to cool too fast, or you'll get lousy inter-layer adhesion and the final part will be crap. I also don't think that any of the reprap materials will be buoyant enough to use in this way.

I'd worry about one design at a time, if I were you

Now if we were to extrude a wall around our part as we build it (using the current edarwin extruder etc) and fill the area inside the wall with HOT waterfrom a pipe in the z platform - the built layers would be kept warm to reduce warping.

This is like keeping the whole machine in a hot air oven but better. (or wetter). Keeping the water level below the top may be tricky - wasnt someone workig on a 'altimeter' ?

The water level would need to be high enough to prevent warping, but low enough no to contaminate the fresh layer's bonding surface.

Sorry to be off topic again. No granules here.

Keeping the waterlevel shouldn't be very tricky.

Water keeps the level itself, all you need is calibrate the waterlevel let's say in a big bottle (big diameter) just a milimeter below the buildingplattform.

If the plattform get one step down the water will "rise" (in fact it doesn't move at all)


I know, water will reduce it's level somewhat because of the space it's given within the printed outlines, that's what the big diameter bottle (or use the sink) is for

'sid

[EDIT]
And now back to the granules

Please don't get me wrong..
making a granule extruder is a superp idea, but isn't it much easier to
just make our own filament by melting it and let it flow through a matching hole by gravity ?
I'm not sure if that will work or only be a big mess afterwards..

Edited 2 time(s). Last edit at 07/15/2008 10:42AM by sid.

sid Wrote:
-------------------------------------------------------

> Please don't get me wrong..
> making a granule extruder is a superp idea, but
> isn't it much easier to
> just make our own filament by ,elting it and let
> it flow through a matching hole by gravity ?
> I'm not sure if that will work or only be a big
> mess afterwards..

In another thread nophead (I think) said that the draw-by-gravity approach may be impractical because of the melted plastic's viscosity. It sounds like some active extrusion system may be necessary - but that doesn't mean it needs to be as complicated as an auger. What about a heated, pressurized chamber with a small hole in it that plastic is forced out of? Dangerous for sure, but if you shield it right you should be able to mitigate that risk.

Kyle Corbitt Wrote:
-------------------------------------------------------
>
> What about a heated,
> pressurized chamber with a small hole in it that
> plastic is forced out of? Dangerous for sure, but
> if you shield it right you should be able to
> mitigate that risk.
>
Well, you can certainly do that and the pressures aren't terrible, about 15 bar, but the question is how do you feed new polymer into that rig to make the extrusion continuous?

Forrest Higgs Wrote:
-------------------------------------------------------
> Kyle Corbitt Wrote:
> --------------------------------------------------
> -----
> >
> > What about a heated,
> > pressurized chamber with a small hole in it
> that
> > plastic is forced out of? Dangerous for sure,
> but
> > if you shield it right you should be able to
> > mitigate that risk.
> >
> Well, you can certainly do that and the pressures
> aren't terrible, about 15 bar, but the question is
> how do you feed new polymer into that rig to make
> the extrusion continuous?


There's no simple way to do this while the chamber is still under pressure/heat. I was envisioning a largish hopper - let's arbitrarily say a 20cm diameter cone - that is filled with a significant quantity of plastic junk, left to heat for an hour or so, then you plug the steam hole at the top, unplug the extrusion hole at the bottom, hook up a bike pump and pressure it up. You get a filament out that's a few (dozen?) meters in length, and feed that to your actual powderizing (use a router bit/rasp) or granulizing (chop it up into very short segments) or refilamenting (remelt it to a consistent size) recycler bot. That goes into either your powder- or granule- or filament-based extruder. This may not be the best way to make powder or filament - I'm not sure. But it sounds easier to me than most of the alternatives I've heard kicked around for making consistently sized granules.

I think that you will find that ordinary home air compressors are quite cost-effective for this sort of thing. From a practical standpoint (I've done such melts and observed what happens when you melt plastic scrap), I think that you will find that when your melt starts, pressurized or not, your big problem is going to be getting trapped bubbles that formed from air between chunks of scrap out of the melt. Really big ones tend to pop. It's the little ones that are upwards of a cm in diameter that get trapped towards the bottom of the melt that are the real problem. Those will, if you give the melt days of heating will eventually migrate to the top and pop. The viscosity makes that a real problem, though, and the smaller the bubble the slower it migrates upwards.

This all argues for the scrap being ground very fine indeed.

What happens if you ignore the bubbles? You get a segmented extrusion stream, but depending on the application that may or may not matter.

I can also think of a couple of complex geometries for the pressure chamber that may mitigate the risk of bubbles, but it's better to keep things simple if possible.

Ok, so first part of the cycle, you connect your compressor as a vac pump. THis expands all the bubbles and makes them rise & burst out.

I still think it needs some simple version of existing plastic extrusion technology - lets not re-invent the wheel here. (ok, im the clever one - I know exactly how it should be ..... paint it blue)

Uh yes bubbles....
"what's that bubbles??? I'm the f** prince of darkness and you come up with bubbles???" (end of quote)

What was I supposed to say? Oh yes.

I forgot those tiny little chimps that may ruin the melt.
Okay, as far as I know, "they" cope with bubbles by compressing the molten plastic with counterrotating wormgears.
And if we do already have to add a wormgear (if the vacuum wont do) then we can even go and put it in the extruder itself

So nevermind, keep going with the extruder

'sid