Plastic recycler

The wikipedia article on plastics extrusion is actually very good, by the way. It mentions a few rather frightening issues, such as extrusion barrel pressure exceeding 5000 psi and the extruding scews being as much as 6 inches in diameter. [en.wikipedia.org]

I think you only need those massive pressures to do it quickly for an economically viable process. We only need to do it fast enough to feed our machines, which is very slow. The pressure to extrude 3mm filament very slowly will be far less than that required to extrude 0.3mm filament quickly in the extruder.

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[www.hydraraptor.blogspot.com]

Lionel Wrote:
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> The blog presents quite a good work! the author
> also says that he managed to make a machine work
> the first time (19 dec 2008), but that a problem
> arised when the machine cools down because the
> plastic gets stuck in the machine from the
> previous extrusion.
>
> Well, I think there is a solution for that: in
> industrial processes for filament extrusion, there
> are two pinch wheels that pull the filament out of
> the extruder as it comes out, still hot. These
> wheels are there to control the thickness of the
> filament (by adjusting their speed) and can
> probably remove the melted plastic from the
> extruder when the process is finished. They are
> also cooled down to help solidifying the filament,
> but a cooling system may be harder to built at
> home.


Industrial machines are shut down after LDPE is run through them to purge production materials. It's soft, much easier to remove by pushing out in turn with fresh production material. When its melt temperature is exceeded it's almost as fluid as oil - and as greasy.
The exit die of the extruder is the initial cooling zone, the filament's skin has been cooled below fluid point to set dimension, the cooler bath is to continue solidifying it internally.
The drawing wheels are cooled because they hold the filament for consistent cutting into lengths or granules. With the material cooler and more brittle,it's less likely to jam the equipment.

I see... thanks, Triffid, this makes sense.

I still wonder how the vacuum conformator works. Its role is clearly to set the filament diameter, but I cannot find any information about how this thing can be build. I think this is a very important parameter since the control of the extrusion speed assumes that the filament has a fixed diameter. If the filament is uneven, the extrusion rate will be uneven.

If anyone has an idea...

I don't think it is anywhere near so complicated. Some of these things they talk about, are to align the molecules to give more tensile strength. We don't care about tensile strength, 'cause we are not using this filament for string. Also, we are not making small filaments. It is a quite large filament, so pressure similar to what is in a hot melt glue gun should be plenty.

We'd probably not want to use contact with water to cool the filament, 'cause plastics need to be dry. If they contact water, they'll need to be dried after words.

As for the different types of plastics. They'd need to be sorted before grinding and extrusion. Also, need to check to make sure there's no dangerous gasses produced by each type of plastic, and some plastics need different temperatures, but other than that, we'll just have to try them and see if they work. Some plastics will work better than others for 3D printing.

Tony

naveen Wrote:
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> is any body know more about How plastic & metal is
> melted by induction heating process ...?
> plz send more abt it to naveenbagalkot@gmail.com

Quote
Lionel
induction cannot heat plastic, it only heats up magnetically responsive materials.

I've been trying to do some selftraining courses in electronics recently, and stumpled upon a section about induction, where he claims that capacitance can be used to heat non conductive materials, quite like induction can heat magnetic materials, I've searched the net on how to do this, but all I can find is melting capacitors and burning holes in plastic, not heating in a controlled manner.

I'd love to figure out if capacitative charges could be controlled and used to dry/heat the plastic.

anton Wrote:
> I've been trying to do some selftraining courses
> in electronics recently, and stumpled upon a
> section about induction, where he claims that
> capacitance can be used to heat non conductive
> materials, quite like induction can heat magnetic
> materials, I've searched the net on how to do
> this, but all I can find is melting capacitors and
> burning holes in plastic, not heating in a
> controlled manner.

If there is any relation to an electrostatic motor vs electromagnetic motor, it would seem the voltages needed for a 'capacitance based' heater would be beyond what we would want to use in a small printing device. (E.G, magnetism is simply easier to generatate than electric field, because current is easier to generate than voltage.)

For reference, a large electrostatic motor with sub-watt power requires voltages on the order of 4000+ (nice if you have static electricity supply, not so nice for a conventional power plug.)

About plastic toxicity, thermoplastics are not toxic (as long as they are used well below their ignition temperature, of course, and as long as they are polymerised. Monomers are usually toxic).
What may be toxic are the adjuvent: these are chemical added to the plastic to give it some additional properties. It can be antistatics, fungicides, lubricants, UV protectors, and so on. More documentation about them would be good in order to have a better idea of the risks, but for small amounts a well ventilated room should be enough.

Lionel Wrote:
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> About plastic toxicity, thermoplastics are not
> toxic (as long as they are used well below their
> ignition temperature, of course, and as long as
> they are polymerised. Monomers are usually
> toxic).

Upon heating beyond a certain range, some thermo-plastics will decompose into dangerous chemical, the most common one being chlorine gas, which has a nasty habit of forming hydrochloric acid in your lungs when inhaled. This can happen even below ignition temperatures.

HDPE, PLA, and the other more common RepRap plastics should be fine, though I'd recommend not sticking your head over a combusting sample, just to be safe.

Hi guys!

[objects.reprap.org]
[dev.forums.reprap.org]
[reprap.org]

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

So, does this still have anything to do with the topic "Plastic recycler"?

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* homeprototype free 3d design repository
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So, does this still have anything to do with the topic "Plastic recycler"?

As long as the conversation generally comes up with something productive, it's all good. And I've learned to take contributions to RepRap as they come*. "Argument kills uploads"

More documentation about them would be good in order to have a better idea of the risks, but for small amounts a well ventilated room should be enough.

Yup. I've pasted your conversation snippit up in the wiki. You are welcome to have a go:
[objects.reprap.org]

*Aside from "I want a mendel" in the For Sale forum.

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

MarcusWolschon Wrote:
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> So, does this still have anything to do with the
> topic "Plastic recycler"?


Whether is on topic is always to a certain degree subjective, but since the topic of drying shredded plastitc, is IMO is part of the recycling process, means and dangers related to the heating is on topic.

But that's just my subjective opinion.

Good links Sebastien, thanks! One of the machines (the one with the big screw) is pretty much like I imagined things.
Now, it looks like the problem is the control of the heated zone. If the recycler is to be build from Reprap plastics, it needs to contain the heat in the metal parts very well. I will think about it... it looks like a nice problem for a finite element modeling project

Ok, I have some answers from wikipedia:
[en.wikipedia.org]

The straight head is indeed used for the alinement of the molecules, to make the filament stronger. This may be a parameter of importance for a good extrusion in the reprap: if the wire tends to twist easily, it will be more likely to jam the extruder. However, it does not seem like the straight head is necessary if the filament is created in the direction of the flow. I suppose it needs testing...
Bubbles will probably be a problem: so far, the recyclers produced in the reprap community have only been tested using commercial plastic filament, but I suppose that it will be much more messy using bits and pieces of plastic with lots of air.
The cooling seems to be a critical part too: the plastic is water-cooled, though I suppose the water does not come in contact with the plastic. If the cooling is not done correctly, the filament shrinks and the diameter is no longer controlled. The diameter of the filament has to be accurate for a regular extrusion.
There is also a filter to remove all the dirt. This will probably be very important for recycled plastic since impurities can easily plug the extruder outlet. Maybe we can do without if we wash the plastic correctly before feeding? One more thing to test...
Good news: the additives are not a problem. They are added before the plastic is melted down, so they are temperature-resistant. However, the temperature should not exceed the glass transition temperature too much, I think.

So, to summarise:
- Clean correctly the plastic before recycling, maybe use a filter (like a mesh)
- cool down when the diameter is correctly set
- let the air bubbles go away easily
I have some ideas, I will make some tests soon, hopefully.

The mini filetador PET or mini shredder is able to cut a 2 liter PET bottle in a 50 meters long thread without heat.
You can see in our website how to make this device and how to use the PET thread.
Takashi
www.utsumi.com.br/pet

Takashi Utsumi Wrote:
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> The mini filetador PET or mini shredder is able to cut a 2 liter PET bottle in a 50 meters long thread without heat.
> You can see in our website how to make this device and how to use the PET thread.
> Takashi
> www.utsumi.com.br/pet
From website above:


That's really interesting, and their cutters go down to 1.5mm. Even a 'how to make' page: [www.utsumi.com.br]
Very simple and could be motorised and wrapped on a spool! How well does PET print?

Hi all, brand new user here wondering about all this stuff.. recycling bottles like this seems like an excellent idea... A couple of thoughts (stop me if they've been suggested and/or dismissed already, or are otherwise utterly stupid):

On a smaller scale, how about running a pair of drill bits countering each other? you'd probably have to mount them with the shafts on opposite sides so as to be able to get them close enough while still held-in, but twisting them in towards each other, with the spirals shearing across each other, you could get them in very close, and they should tear things up into relatively small pieces. You could also go from a large pair that can deal with big pieces easily, into a V profiled chute to some smaller bits which could reduce them.

Feed from there into something like the mechanism from a conical burr coffee grinder and you should wind up with quite a fine powder..


On the whole 'spinning sawblades' idea.. I'm thinking that the offset teeth in a sawblade is potential for trouble.. However... how about angle grinder cut-off discs? An array of those things spinning against each other would make a nice mess of stuff.

here is a nice and simple destroyer:

little dangerous without a chute though!

[www.youtube.com]

That looks like the machine the Makerbot group coppied to recycle their ABS posted some where in the forum .. or in the WIKI

The one they show is a much bigger version as it is shown eating shopping trolleys.

[recyclebot.tumblr.com]

They show details of the teeth and the seperator plates in their blog..

[recyclebot.tumblr.com]

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mlagana Wrote:
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> here is a nice and simple destroyer:
>
> little dangerous without a chute though!
>
> [www.youtube.com]
> ded&v=ibEdgQJEdTA


This looks dangerous as hell, definitely needs a chute!

For Plastic Bottles you won't need such a strong mechanism so you could use thinner blades from a laser cutter.


Has anyone worked on a way to directly extrude plastic bottles yet?
I was thinking of 3 big screws with a triangular hole between them in which the bottle is pushed down into a heated pipe.
The screws should compress the bottle so it would build up enough pressure so that we get a filament.

Why not just build an extruder for PET ribbon?



It wouldn't recycle printed parts, but at least you could give yourself a cheap supply of plastic "filament".

I've read that plastic soda bottles need quite high temperatures and pressures to extrude. I have no idea what the properties will be once extruded. Perhaps it won't stick to an earlier layer? I don't know. But I like the idea of finding a use for this ubiquitous source of plastic.
I know that my experiences won't carry over to other designs, but I just ran into a problem with the pressure involved in PLA extrusion with my Techzone extruder. It would certainly need a different design for higher temp/pressure materials.

-Shay

Yes PET is quit viscous, similar to ABS but even more so.
We would need a sharper temperature gradient so it would work. But it is possible - I did some hot-air welding of PET once.

The thing with PET is: It stick only to itself and only if both sides are sufficiently hot, so we would have to print at a certain speed in order for it to work. The advantage is that PET has enough strength to support itself even above the glass transition temperature.

I just thought of something, we can use Takashi Utsumi's bottle cutter to cut strips of plastic and make a special pinch wheel that fold the strip to prevent it to curl on the entrance of the hotend.
I tested the concept by folding a strip of PET from a bottle and feed it manually thought my 3mm hot end. It extrudes, but I have almost no control of the output flow.

On the topic of induction heating...
Any material which is electrically conductive can be inductively heated. Here is why: induction heaters consist of a coil which is subjected to a high frequency AC current. The AC current creates a magnetic field. The magnetic field induces an electric current in the part to be heated (but only if it is electrically conductive). The induced current experiences some electrical resistance. That resistance converts induced electric power to heat.
I believe antistatic plastics contain an additive to make them slightly electrically conductive.
One could also heat the extrusion die inductively, and the hot extrusion die would heat the plastic. A resistive heater wrapped around the extrusion die is simpler and may also be more efficient.
Tyro

We in my company in Brazil just bought a reprap and i just can`t settle down on using virgin plastics. Can i use recycled plastic pallets straight on the reprap or can i use only fillaments? I already have suppliers of recycled PET and biodegradeble vergetable origin plastics in pallets, so it would be much easier to be able to use them. If i had to use only fillaments and i find a way of doing them... do i have to use a material with the same heating temperature and proprieties of the ABS?

Best regards,
Pedro

Hi Pedro,

the normal RepRap can only print with filament - there are some experiments with pellet-extruders, but this is not really usefull yet.

When making own filament, the biggest hurdle to overcome is maintaining a constant diameter of the filament ... here even big companies have problems ..

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Viktor
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Seems like this project is progressing...
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