PS ..... no I mean the plastic

What is PS plastic and can it be used in the reprap system too?
I got several old scanners, gutted them for the glass, stepper motors, and MXL timing belt. I thought I might be able to recycle the several pounds of plastic I have left over.

Dylan

ok, I just did some searching on wikipedia (yay) and found some info.
[en.wikipedia.org]
PS is polystyrene and is used in machine cases, packing foam, disposable cups, plates, cutlery and CD cases.
Glass temp at 95

I don't think PS would make a good target for RepRap for a number of reasons.

First off it is not safe-Some further research got me here:
[www.wind-lock.com]
Where we learn that PS has a flash ignition temp of 310C which is a little too close to 240C for my tastes. Flash ignition means the material catches fire by itself in air. Sparks or open flame can ignite PS at any temp, but the hotter the material is the more likely combustion is to start. PS is regarded as highly flammable and produces an array of toxic products when it burns.

Secondly PS, while plentiful, is normally found in a foamed state, thus a lot of it needs to be processed to create a useful amount of filament. We extrude by weight, not volume.

Third, PS is very rigid and hard in its natural state, and therefor would probably have problems with the current extruder design.

While it would be nice if RepRap could allow people to become their own recycling centers, I think HDPE is a better candidate for that, even with its warpage problems.

That sounds like what I feared. I guess I just needed confirmation.

What about PETE? It's fairly abundant too.

The kind of plastic you use isn't going to be nearly the issue that getting it in filament will be, aside from questions of flammability and the like.

The guys I buy from have...

(CA) Cellulose Acetate
(CA Cellulose Acetate Butyrate
(PVC) Polyvinyl Chloride
(HDPE) High Density Polyethylene
(HMW) High Molecular Weight Polyethylene
(UHMW) Ultra High Molecular Weight Polyethylene
(LDPE) Low Density Polyethylene
(LLDPE) Linear Low Density Polyethylene
(ULLDPE) Ultra low Density Polyethylene
(MDPE) Medium Density Polyethylene
(HPP) Hompolypropylene
(CPP) Copolypropylene
(TPU) Thermoplastic Urethane
(PETG) Polyethtlene Terephthalate-Glycol Modified
(ABS) Acrylonitrile Butadiene Styrene
(HIPS) High Impact Polystyrene
(FPVC) Flexible PVC

[www.plasticweldingrod.com]

[www.newimageplastic.com]

I did a lot of work with HDPE quite some time ago with the idea that eventually somebody would put together the shredder and filament extruder that would be needed to recycle plastics. So far, however, nobody has had the time what with all the work needed to get an inexpensive 3D printer like Darwin going.

I expect in the next couple of years, however, that somebody will tackle the job. After all, a small-scale commercial filament will cost you only about $75,000, iirc.

[www.waynemachine.com]

Just the extruder you can get for about $20-25,000. Mind, I'm quoting good equipment that will last, not junk that will wear out in a few years. Some of the equipment that is on the market is just downright dangerous. The big design problem is taking up the back pressure extruder through the auger back into the gearbox for the extruder. Not all designs do a good job of that.

Then there are the godets, the annealing ovens and the winder.

Don't let that put you off, though. After all, when we started work on Darwin the cost of a entry level 3D printer was $30,000+

The only way we are going to be able to do any of the recycling we talk about on this site is to have our own filament maker. It also won't be feasable to take all our plastic to someone else to turn it to filament (unless it's a local reprapper).
I've already started work on my filament maker. I do see some of the problems, but so far have a 2 part design in mind that seams feasable. The hard part is probably getting the plastic into the small pieces to go through the machine. I'll have to put some more work into that section.

I'm really not putting too much effort into that yet as I want to complete my cartesian system first.

If you can make a workable filament production system you are going to be one popular dude!

Yo Dylan,

I agree with Forrest, a granule extruder will make us like gods.. or at least we'll be able to turn garbage into shoes. Please go for it!

In case you haven't seen any of these pages yet, the granule extruder prototype is described at:
[reprap.org]

and the experiment on casting an auger is described at:
the [forums.reprap.org]

and a thread which includes some info on a granule extruder is at:
[forums.reprap.org]

Also it's useful, but not necessary to make 3 mm filament. Something that can directly take the place of the current extruder would be great also.

Cheers,
Enrique

I don't think a granule extruder would work too well. If there isn't enough in there to cause the right amount of pressure, you woudn't get enough out the nozzle (opposite if there is too much). This is why I am trying for the filament maker.
The actual extruder for the filament shouldn't be too hard, but getting the plastic (except for the capa granules) to the right size is the problem. The $350 blender at willitblend.com looks great for this, but too much money. I'm probably looking toward a dual shaft system with teeth rotating in opposite directions. I'll have to look around for a cheap way to make the gears and teeth though.

I'll post some sketches of my ideas for the filament part of it and see if anyone can make it in the right material.

Enrique Wrote:
-------------------------------------------------------

> Also it's useful, but not necessary to make 3 mm
> filament. Something that can directly take the
> place of the current extruder would be great
> also.


trust me. it's necessary. an extruder that can eat granules is going to be too heavy for a 3D printer.

Forrest Higgs Wrote:
-------------------------------------------------------
> Enrique Wrote:
> --------------------------------------------------
> -----
>
> > Also it's useful, but not necessary to make 3
> mm
> > filament. Something that can directly take the
> > place of the current extruder would be great
> > also.
>
>
> trust me. it's necessary. an extruder that can
> eat granules is going to be too heavy for a 3D
> printer.


I don't know... those Fab@Home folks made a fairly reliable granule extruder down in Australia, I think it was. Of course, they used hot glue, but isn't it just a matter of scaling the temparature/robustness up from there to get to a really useful thermoplastic?

I'm not saying that it will be easy, I'm just saying that it is definitely too early to write it off as impossible!

Here's the problem. If you use an auger to push the plastic bits down into a melt zone under pressure the amount of force that is going to try to push that auger out of the extruder is proportional to the cross sectional area of the auger or the square of it's diameter.

Think about that 3 mm filament, then think about that 12.5 mm auger (1/2" which is about the minimum size that you can run pelletised resin (the most usual form of raw plastic) through. The auger is going to be trying to come out of that 1/2" extruder barrel with 17 times the force that your 3 mm filament is going to try to be coming back out of your Mk II extruder. That says that you are going to have to make special arrangements to counter that thrust in a way that doesn't create a lot of friction or you are going to see the power requirement for your extruder go through the ceiling. Suppose you are running 200 psi in your extruder barrel. That's not an unusual pressure to encounter. You're going to be resisting 40 lbs thrust with your granule extruder. With your Mk II you are going to be resisting a shade over 2 lbs thrust. That's why you can force a piece of filament through a heated Mk II extruder barrel literally by hand. You won't be able to do that with your granule extruder, at least for very long. Indeed, I wouldn't want to be on the back side of your granule extruder if your thrust bearing fails. You'd be skewered.

Edited 1 time(s). Last edit at 05/26/2008 12:46AM by Forrest Higgs.

I'm not questioning your numbers, but out of curiosity, how did you determine 200PSI? That is a useful number to have when trying to solve a variety of engineering problems surrounding the current extruder.

Kyle Corbitt Wrote:
-------------------------------------------------------
> I'm not questioning your numbers, but out of
> curiosity, how did you determine 200PSI? That is
> a useful number to have when trying to solve a
> variety of engineering problems surrounding the
> current extruder.

Operating pressure is a bit of a thumb suck which depends on the rate of flow you are looking for. For big commercial machines you can be looking at as much as 20,000 psi. We're nowhere near that. If you think about it you'll know that given enough time your plastic will flow as soon as you get it past the glass transition temperature. It flows really, really slow though. I use the ASTM D3835 test that they use to get the Melt Index for plastic. That machine is simply a little heated cylinder and piston that's loaded with a weight at the top and an extruder die (orifice) at the bottom.

[photos1.blogger.com]

The cylinder is 3/8 inch in diameter and the orifice is 0.0825 inches in diameter with an L/D ratio of 5, typically.

[composite.about.com]

With a 2.16 kg weight you get about 43 psi in a static (, iirc. That's running plastic through a 2 mm orifice. I figured 200 psi because we look at pushing plastic at those sorts of temperatures (~190C) through a much smaller orifice (0.5 mm).

That's another very good very good reason to have it as a separate machine. I'm sure everyone knows that they don't want a car tire to be overinflated and blow up in their face, and the maximum safe rating on most of those is in the 40-50psi (which is less than the explosion rating, but you get my point). Imagine a novice engineer (most of us probably fall into that category) trying to make and use a machine reliably and safely with pressures 4 times that while keeping a good quality output and of construction that isn't rated for that pressure. Using a filament maker first means that you are using a hole 6 times bigger than the 0.5mm to push the plastic through. Admittedly, an extruder head won't explode, but it would take a lot of work to make sure it didn't fall apart or burn out the motor, etc etc.

This topic if fast off course, but hey, that's how conversations change from one thing to another seamlessly.

That's why I stay with filament, preferably made by somebody else. If we start having extruders coming apart and hurting people we're going to be unpopular in one big hurry.

Force on it's own isn't particularly dangerous. A good example of this is ice, which can generate very high levels of force breaking glass bottles but I've never heard of ice exploding even when breaking a bottle the glass doesn't fly off it cracks and then falls off. The ice and the bottle have very little potential energy, it can only produce that force over a small distance when the glass breaks setting the ice 'free' the ice rushes forwards a tiny amount but then runs out of energy.

When steam boiler are being tested they are filled with water not stream. If the boiler fails the water is forced out until the potential energy from the stretching of the boiler has dissipated normally resulting in something like a pressure washer for a second. If the boiler were full of steam at that pressure it would cause a large explosion.

In both the above examples the stored energy is very low, even though the force is very high. So long as the plastic and extruder aren't storing significant amounts of energy the danger is quite low.

Given the low flow rate of the plastic when it is being deliberately forced out the extruder I see two possible scenarios: If a hole smaller than the extruder's were made it would have an even lower flow rate than the extruder. If a larger hole were formed then it would have a higher flow rate but behave like the ice, running out of energy rapidly after the initial surge.

I'm not advocating ignoring the possibility of failure under pressure, but I feel it can be easily accommodated in the design. I think it was Forrest Higgs's site where I saw the suggestion on making the motor hold down the weak point in the extruder feeder to avoid costly damage elsewhere. Something like that, with a cut off if this is to be used 'unguarded', would be all it should need.

Also of cause knowing the pressures is essential to avoiding the failures in the first place.

Well if we lean more towards a "melting pot" rather than a auger I think we can cut down on a fare amount of issue we have with torque on jbweld cast auger and getting the granules the same size. Of course these would mean a having a small pool of molten plastic which can be dangerous.

So I think the idea would be to have a heated melting pot with a heated tube attached to a slightly heated piston that when moving down would only forced down by weights and then would "reset" and be pulled up with a motor. I know not exactly energy efficient because everything would need to be heated so that the plastic would not clot in the tube or the piston. The piston would have to be something along the lines similar to a bicycle pump, were the flow is only in one direction. It would mean the filament might have breaks in it, but depending on the piston size and high from the floor you could easily make 3 meter lengths at least. The biggest draw back is that this method would be slow and take fair amount of heating. The good news is the actual design is a little more flexible in how it is made and what materials it can be made from. The melting pot it self could easily be made from high temp ceramics poured into a reprap made mold.

Of course until someone has the time this will just remain a nice idea.