Pressure pot based plastic recycler filament extruder

Haven't built a prototype, but wanted to share an idea.

I use to do a lot of Resin pressure casting. Using an inexpensive Harbor Freight paint pot:



I was looking at a stack of black coca cola 2 liter bottle tops and thinking it would be great if this plastic would not go in the garbage but maybe used to print something. Maybe I could do a grinding to break this plastic down a bit.

Most filament extruders use pellets an auger and a heating element. In injection molding pressure is used to shoot the hot plastic into the mold.

What if we could isolate say a small 1lb capacity container within a 5 gallon pressure pot. Use some refractory if needed to keep the outer chamber from getting to hot or thermally sucking out the heat like a heat sink. We would only be heating 1lb of recycled plastic. We would need a heating pot and thermistors to monitor the temp. Was even thinking of using the melting pots (under $100) used to melt lead for people who cast their own bullets. Just need to figure how to control the temperature, maybe a solid state relay and PWM from an arduino.

We could take the time to melt the plastic slowly and evenly.

We could then attach the paint pot cover, raise the pressure. In silicone or resin casting, we use pressure to eliminate bubbles. And we get more detail in a cast.

Here is the deviation. There could be a heated metal tube with a valve ported out of the pressure pot. Into a 3mm or 1.75mm nozzle.

In jewelery making, we have a wax injector. molten wax gets injected when you place the molds to a pressure valve. press in and the wax flows. release and the valve closes.

We could then use the pressure in the tank to push out the plastic. No motors needed. Just need a way to wire out THERMISTOR, Input power to the heat pot. And maybe a secondary back up thermistor.

This would not be the solution to mass produce filament. But, a quick run of a pound of any recycled plastic could be very useful. What would be extruded would not have any air pockets.

Just theory at the moment but I'd like to hear thoughts.

Alex


Here is a $50-70 Lee Bullet Casting melt pot

You do have a good idea!
If you melt plasic in a pot you dont need to shred the plastic material firs, just put in all bad prints you have.
To get rid of bubbles in the melted plastic you should first lower the pressure, that will also suck out all moist. after that put on pressure to get the plastic thru an extruder.
It would be rather easy to get good control of the two major parameters, temperature and pressure. PID regulators for temperature are rather inexpensive on ebay. Reducing valves are standard on most small compressors. Vacuum pumps I don't know much about, but it will only be used while melting before extruding the plastic. As I see it it is best to have a container that can hold all the material you want to recycle and make one 'big' batch. A couple of kg will not need a big container.
If you try it be sure the container will withstand the pressure at the temperature you will use. A container with plastic at 230 degrees that explodes is very bad.