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Plastic recycler

Posted by Lionel 
Plastic recycler
August 16, 2009 05:02AM
Hi all,

I had an idea lately: why not design a recycler? A machine that could be built with a RepRap, and that would be able to recycle plastic bottles or failed and old objects? That would also make people collect plastic object lost in the landscape... to turn them into brand new plastic thread for their reprap!

I am planning to buy a reprap in the next months, so if anyone is interested in this project, I am ready to help!
Re: Plastic recycler
August 17, 2009 02:51AM
This is being worked on. The problem is reliably producing a consistent filament to run through your extruder.

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Re: Plastic recycler
August 17, 2009 04:53AM
Is there a website or a blog or anything where the work is being published? If so, I could have a look and maybe give some ideas?
Re: Plastic recycler
August 17, 2009 03:40PM
Here's a good chunk of info, off of the main RepRap blog.
The idea is to grind up plastic, or simply use granule form which is much more common than filament plastic, and extrude that.

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Re: Plastic recycler
August 18, 2009 01:48PM
After reading some post and wiki about plastic extrusion I wans wandering if any one tried using a old cast iron meat grinder as a base for a plastic recycler ?

I try to get a second one (my wife will never let me modify our meat grinder) and try this to make my own 3mm filaments. I was thinking of preheating the plastic in the grinder and making a 3mm heated nozzle to extrude the filament.
Re: Plastic recycler
August 19, 2009 05:33AM
Please do try that! I'd be interested in your findings. I've been saving all of the rafts of prints. If I can use this plastic again it would increase the efficiency of the process a lot. Also, it would allow me to use more rafts and support structure, since there would no longer be a material waste.

I know that ABS increasingly gets more beige (and brown after that) and changes its material properties when it's hot for a long time. The change of colour is not really there when you use black ABS, of course...


Erik de Bruijn
[Ultimaker.com] - [blog.erikdebruijn.nl]
Re: Plastic recycler
August 19, 2009 06:05AM
... a method for recycling ABS 'without colorchanging' is grinding and solving in Acetone. For 3mm-filament it's not working, but maybe thinner filament can be extruded horizontally on a heated surface (e.g. big rotating cylinder) so it dries with nearly circular shape.

I tried this for my dispenser where i manually drawed some trays, what's working, but waits until i finish all the other tasks.

But you loose some rigidity - AFAIK dried 'ABS-paste' stability is only 70% compared to solid ABS from injection-molding ...

Re: Plastic recycler
August 20, 2009 05:48AM
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.
Re: Plastic recycler
August 20, 2009 08:08AM
The problem might also be solved by tapering the transition zone so it gets slightly bigger towards the hot end. That means a solid plug of plastic would simply release from it and slide forwards. The same principal as the draft angle on a mould.

Re: Plastic recycler
August 20, 2009 02:01PM

The meat grinder notion is an interesting one. The old-style ones were all metal, which would be good for heating. (I'm a bit concerned that once heated, you'd have to always heat it to get the parts moving again, since the re-solidifyed plastic is quite strong.)
I'd try that, but the only metal meat grinder I have is one of the few things I have from my maternal grandmother, so I don't want to hack on it. (And I dare not touch the (mostly plastic) one that fits on my wife's kitchenaid mixer.)
I just got ahold of a paper shredder, and I'm going to see how that does on soda bottles, at least the thin parts of them. (I got the shredder via freecycle, maybe I can get another meat grinder to hack on, if the shredder doesn't pan out.)

-- Larry
Re: Plastic recycler
August 20, 2009 08:07PM
Paul Midgley and Adrian Bowyer posted ideas/mini test on using plastic bottles.



I think Adrian designed his extuder block with a channel to fold the plastic.
Re: Plastic recycler
August 20, 2009 10:28PM
Used an old fashioned meat grinder to reduce HDPE plastic bottles. It wasn't a great success.


Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison
Re: Plastic recycler
August 21, 2009 05:29AM

I agree with you, I don't think it would be a good idea to warm up the grinder (or whatever will be used to cut the plastic) because once cold, the melted plastic that remain on the sharp edges will be a problem. Why not grind it cold? Then we can use a screw to push the residues into the 'oven'?

Too bad for the grinder, maybe it is too flat? I have seen a video, a while ago, of a machine that could put a whole car into pieces. It was basically something like this :
Maybe we can re-use the concept?
Re: Plastic recycler
August 21, 2009 08:25AM
My meat grinder idea is not for grinding bottles it is for extruding the pellets or grinded plastic. The old meet grinder I have don't have sharp edges, it is basically a meat extruder.

For cleaning I was thinking of extruding something to flush the plastic when I am done like water soluble pva then cleaning with water.
Re: Plastic recycler
September 07, 2009 11:28AM
I've been thinking about this, and I'm wondering about using a two-chamber design with negative-pressure extrusion:

Top chamber heats mass of plastic to liquefy it.
Junction between the layers is a tapering-down section of metal tubing that allows plastic to set at 3mm.
Bottom chamber is where the plastic comes out, and is hooked up to an aquarium pump to create a vaccuum which pulls the plastic down from the upper chamber.

You could try this the other way around, with positive pressure in the upper chamber, too.

Advantages: Simplistic Design, Few or no specialised parts needed.
Disadvantages: Mightn't work at all, requires pump, leaves plastic molten perhaps too long.
Re: Plastic recycler
September 23, 2009 10:20AM
This idea is no doubt riddled with expenses and overall problems, but how about super-cooling the plastic with something like liquid nitrogen? The plastic would be so brittle you would literally be able to powderize it.
Re: Plastic recycler
September 23, 2009 04:16PM
I've done quite a bit of work with ABS plastic, and I've got two methods that should work.

While working on friction welding using plastic rod instead of a drill bit, I needed a use for all the bits of plastic that were going to waist. To that end I made an acetone and ABS slurry, which was thick enough to keep its shape but when the acetone evaporated, it would harden. This worked well but as stated above, it lost a lot of its mass and became a hardened sponge like material. Which was fine but didn't provide enough frictional surface area to weld anymore. The plastic bit would just dig through the stuff.

In short, an acetone slurry paste would work well for rafter material, but your going to have to find a better way to condense it.

One way to condense all materials is with an excessive use of force. If you had a hydraulic ram and a metal sleeve with holes in it, you could push it out of these holes with several thousand pounds of force. With enough force, plastic will become molten to get through the holes and thus you get extruded filament.

They use a similar process for making wood pellets. Unfortunately probably not practical for your home user.
Re: Plastic recycler
September 25, 2009 09:18AM
I would think using a wood chipper would be a whole lot easier. It might not make small enough chips, but it should at least cut it up small enough to fit into a meat grinder (if that would work) or something.

Or... you could buy a plastic grinder. They probably cost about the same as a wood chipper, I would think.

Re: Plastic recycler
September 25, 2009 09:38AM
RE: Grinding/shredding PET plastic (like soda bottles)

Several people have suggested trying to recycle PET plastic (used in many containers, such as plastic bottles for soda and water) into filament to feed reprap extruders.

I rinsed out some 2 liter soda bottles, and cut away the tops and bottoms, leaving cylinders of plastic. I slit the cylinders, leaving a flattenable sheets.
These are marginally shred-able with a paper shredder. A single sheet of PET repeatedly stalled a "15 sheet / CD disk" rated shredder, but I backed the pieces out and repeated until I got several of them shredded.

I'm going to try drying them out before attempting melting them. (absorbed moisture apparently degrades/clouds melted PET.) I'll report more after I've tried that.

Larry Pfeffer,

My blog about building repstrap Cerberus:
Re: Plastic recycler
September 28, 2009 02:18AM
I was just thinking about something sort of like they do with roughing endmills.They stagger the cut, so a high spot on one tooth is a low spot on another tooth, making it cut off small chips as you'll see in this picture.

I'm thinking something that spins fast and has 2 or 4 blades with these stagger cuts on them, and of course it needs to be open source and cheap to make.

I don't think everyone needs to have one in their homes. I can imagine people taking their plastic to a local shredder, to have it shredded and extruded into line. Tiny little recycling shops which look like a road side stand, where you can take your plastic garbage and they'll recycle it and give you half of it back (or so) and sell the rest to pay for their labor or whatever. Maybe even have a 3D printer at the road side stand so you could get parts made for free..

I live in Ukraine, and I see people digging through the garbage regularly for useful stuff. If plastic became a useful substance, they'd be scrounging for that too. Not only that, they'd probably also go to the city dump sites and start pulling plastic out of those as well.

We'll also need a high efficiency open source drier as well.

It is extremely important that all processes are efficient energy wise. If you use boat loads of energy on stepper motors, the parts produced will require to much energy to produce, and that'll contribute to global warming.

Plastic sitting in the city dump does not contribute much to global warming. In fact, it helps reduce the amount of oil burned, because more oil is converted into plastic each year, so less of it is available to burn in cars and stuff. Even so, this project will reduce green house gasses, as long as we don't use excessive energy in the 3D printers.

That is why I'm using servo motors. Servo motors can use almost no power at all. My 3D printer will use about 10 watts or so when it is operating.

Energy also costs money. So if these things use to much energy to operate, that'll make it more difficult for the poor as well.


Creating the society of the future
Re: Plastic recycler
October 03, 2009 01:14AM
Here's an idea:

1) Make a mold for a spindle
2) Melt down all plastic available, or break it up into granules
3) procede to make a plastic pressure molder from scratch
5) free ABS spindles!
Re: Plastic recycler
October 15, 2009 02:25AM
This is very nice idea to recycler. Plastic bottles and shopping bags are every where causes bad effect on environment. I am really interested in this project and will wait to listen from you.

Church Supplies
Re: Plastic recycler
October 23, 2009 11:09AM
is any body know more about How plastic & metal is melted by induction heating process ...?
plz send more abt it to naveenbagalkot@gmail.com
Re: Plastic recycler
October 23, 2009 01:30PM
induction cannot heat plastic, it only heats up magnetically responsive materials. That is, materials containing iron, most of the time.
you can have a look here to see how it works:

basically, it is an effect that uses magnetic fields to create electric currents in a material. These currents heat up the material by Joule heating, and eventually melt it if the temperature reaches the liquid point.

Unfortunately it cannot be used directly on plastics, as they are not magnetically active and non-conductive.
Re: Plastic recycler
November 02, 2009 10:35AM
Hi all

Reading these posts .. I'll add my suggestion as how to shred plastic: I'm not the only fossil in here, so .. does anyone remember the old rye-bread cutter for slicing bread? In graphics, there's an eqvivalent tool, larger and with a sharper knife. I think it could do the job in a proper manner.

I cought sight of the RepRap a couple of days ago and has become absorbed in the idea. I've lately made a minimal 3D-modeller ... what exelence in trying to go the whole way! I'm all too weak in electronics though but, I'll hang around and try to learn.

Re: Plastic recycler
December 11, 2009 09:13AM
hi..i have a project which is in line with environmental issues like garbage problem..Im planning to make a device that will turn plastics into bricks(hollow blocks) do u have any idea about this one??please help..asap..


if you could give me a schematic diagram for this would be a big help..tnx!
Re: Plastic recycler
December 14, 2009 07:18AM
I am not a specialist in plasturgy, but I suppose the first thing you need to consider is what sort of plastic you want to use. There are many sorts of plastics and each one has its own set of properties (thermal, mechanical, chemical). The process you will apply on them depends strongly on these properties, so you will probably have to make you mind on the material before considering the process.
I suppose that you are looking for strong material if you want to make bricks. I think polystyrene is a good condidate: it is a very strong plastic and quite resistant to chemicals. I think its melting point is quite high for a plastic, but you may be able to mould it into bricks. Other processes include pressure moulding of solid materials, or using glue to put small pieces together, for instance.
Hope it helps.
Re: Plastic recycler
February 17, 2010 11:20AM
I've been lucky enough to find someone nearby throwing out a large Fellowes 120C-2 shredder.
It apparently ingested one of it's own clearing combs after a toothed cutter came loose, melted the comb from friction, blew two more wheels and finally popped the side of the assembly with enough force to shear a bolt.
After disassembling and cleaning, the 1/4hp motor still works, no gears are stripped and it still turns (albeit with three idle teeth). Some teeth are a bit chipped.

So far I've fed it (carefully!) Chinese takeaway containers, tongue depressors, and a 3L mineral water bottle. Just squeezing the bottle by hand made it flat enough to ingest it right up to the neck where the plastic got too thick.
It might need to "chew" a bit perhaps though (thinking forward-forward-back-forward-forward-back..). Or need something to do some initial chopping.
The bottle did wrap around the mechanism a lot more, so I'll need to fabricate some new clearing combs (thinking nails spaced along a rod) after I decide the best way to repair it. The three damaged teeth are a bother since they're in the middle of the run. The best solution would be to cut them out and slide the rest of the teeth down to fill the gap, but would need careful heating to allow them to shift on their drive shafts.

If it can do that, thinking the plastic confetti into an agitated hopper feeding one of those old aluminium kitchen mincers, heated and fitted with a single-hole nozzle? It'd probably need a sensor to regulate a motor driving the mincer based on hopper capacity and any thinning of the filament.

Here's some pics..

Guts of the shredder
Halfway eaten container
Shredded plastic
Where it finally got stuck

Also I believe one of the later books in the Gingery Machine Shop series describes building a scrap-using injection moulding machine. I'm only on the first book atm though, making the aluminium foundry.

Peter "Sci" Turpin
London, England

Provider of practical solutions.

(Sometimes stellifying Jupiter IS a practical solution)
Re: Plastic recycler
February 17, 2010 01:18PM
Moulding would be good to make finished parts, but may not be suitable for filament making. Even though, this could be a nice technique to make lots of Mendel parts in no time...

About filament making, I have found this quick explanation of principle (sorry, it's in french but it is easy to understand):

Basically, the plastic bits are placed in a heated extruder (the big screw on the left) which melts everything; then it is shaped into a filament by a 'straight head' just before the outlet (I am not sure why this element is here, I suppose it helps controlling the dimension); then there is a vacuum conformator (I suppose this element sets the diameter to a precise value) and a water tank to solidify the filament; then a pinch wheel, which pulls the filament regularly.
This site is hosted by s school of plasturgy, I suppose it is a good start to make our own filament machine.

By the way, it is also possible to find some expired patents on extrusion techniques:
Why reinvent the wheel? Especially when it is for free smiling smiley

Edited 1 time(s). Last edit at 02/17/2010 01:30PM by Lionel.
Re: Plastic recycler
February 17, 2010 06:57PM
I think the straight head is necessary because plastic is basically molecular cloth, and when extruding filament we want most of the molecules to line up along the filament. A fairly long melt zone helps do this, whereas a short melt zone leaves them chaotic which makes controlling the diameter and tensile strength trickier

Wooden Mendel
Teacup Firmware
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