The Re-Extruder project is intended to be a companion piece to the RepRap, a machine that can take scrap plastic and re-extrude it into feed filaments. Like the RepRap, it should be as simple as possible so it can be built at home from inexpensive and commonly available materials. Unfortunately, it's unlikely that RepRap'd plastic parts will make up any substantial portion, 'cause they'd all melt.
I have identified 5 essential components:
1. Power supply
2. Melting pot or crucible
3. Extrusion orifice
4. Plunger or piston to force melted plastic out
5. Microcontroller and programming
I have about 40 transformers with 120V/240V split primary and 23VAC 8-10A secondary, or about 180-240 VA. My initial power supply designs will be built around these transformers, 'cause I got 'em. They will produce about 32VDC, rectified and filtered. Buck-mode switching converters can produce +5V and +12V to power the microcontroller and ram motor. One large P-channel FET will switch the crucible heater power.
My idea is to use a piece of galvanized steel water pipe as the melt chamber. A short piece of pipe threaded on both ends, commonly called a "nipple", can be found at most any home improvement or hardware store for a few dollars. I think a 2" diameter X 4" long piece would do - that's 50 mm X 100 mm for those of you still in the Old Country. The local Home Depot sells them for $4.17. A small cylinder hone, as used for rebuilding lawnmower engines, can be used to smooth out the inside. Half of a matching pipe coupler - a short fitting with internal threads in both ends - can be used as a mounting collar on the upper end. The bottom would be a pipe cap, with a hole drilled and tapped to hold the extruder nozzle. The crucible upper support could be a piece of ceramic tile with a hole bored in the center. The mounting collar rests on it. One or more strands of Nichrome wire would serve as a heater. I was thinking of using a high-temperature epoxy for electrical insulation and to bond the heater and a thermistor to the pipe. Surround the crucible with a box structure on legs, and pack fiberglass insulation around it. Only the extrusion nozzle needs to be exposed.
Should be fairly simple to build. Some sort of quick-change mechanism would probably be a good idea.
Possibly a short piece of slightly smaller pipe, or it might have to be machined. The ceramic tile hole cut from the upper crucible support could make a good piston cap. Plumbing supply stores sell a kind of Teflon "rope" as replacement valve packing, which could be used to make a piston seal. To push the piston, how about an 8 mm threaded rod, and an 8 mm hex nut embedded into a toothed pulley, driven by a stepper motor and belt.
It would probably be best to go with the same one used in the RepRaps. Programming to communicate with a Linux host, set and maintain temperature, and push the piston.
- The Recycler project takes another approach to recycling -- mechanically shred scrap plastic into small pieces, then use a GranuleExtruder rather than a filament extruder.
- "One of the great unsolved problems for Reprap has been that of either figuring out how to make plastic filament locally from scrap or how to design an extruder that can digest scrap." -- "Stovetop recycling of HDPE swarf"
- Recyclebot at Appropedia
- Open source controller for polymer extruder
- Waste Reclamation System from PSU
- Printing with Wood has some tips on mixing wood fibers into the plastic before extruding.