Open Source Waste Plastic Granulator

[MOST]

In order to accelerate deployment of distributed recycling by providing low-cost feed stocks of granulated post-consumer waste plastic, this study analyzes an open source waste plastic granulator system. It is designed, built and tested for its ability to convert post-consumer waste, 3-D printed products and waste into polymer feedstock for recyclebots of fused particle/granule printers. The technical specifications of the device are quantified in terms of power consumption (380 to 404W for PET and PLA, respectively) and particle size distribution. The open source device can be fabricated for less than USD$2000 in materials. The experimentally-measured power use is only a minor contribution to the overall embodied energy of distributed recycling of waste plastic. The resultant plastic particle size distributions were found to be appropriate for use in both recyclebots and direct material extrusion 3-D printers. Simple retrofits are shown to reduce sound levels during operation by 4dB-5dB for the vacuum. These results indicate that the open source waste plastic granulator is an appropriate technology for community, library, makespace, fab lab or small business-based distributed recycling.



For further information on the project, visit here:
https://www.preprints.org/manuscript/201909.0003/v1

Download the paper here:
https://www.mdpi.com/2227-7080/7/4/74

[DIYer]

Thanks MOST! We've added your Plastic Granulator to our 3D Printing category,
as well as to your builder page: MOST's Homemade Tools. Your receipt:

Plastic Granulator by MOST

tags: 3D printing, recycling

[Frank S]

what type and size of cutter knives are on the shafts.
I have been thinking about building one using the coarsest tooth pattern 7 1/4" carbide saw blades I can find spacing them just far enough to allow for the matting teeth to pass beside them

[MOST]

1/2" 3" × 3" Angle Iron 8" Length Bed Blade Mount 10.56 1 10.56
3/4" × 2-1/2" Flat Stock 12" Length Flyknife Arms 10.43 1 10.43

See complete BOM in paper https://www.mdpi.com/2227-7080/7/4/74/htm

[Frank S]

After reading your extensive collaborative study I see a couple of areas where discrepancies in the design may exist.
first off the feed area appears form the cad drawing pictures to be the cylinder in which the guillotine blade system is contained appears to be dis-portioned relative to the screen area additionally in the picture the design appears to only show the cylinder as being a half circle This would appear to reduce the efficiency of the machine while allowing cut materials to be thrust back out of the feed chamber.
It would seem to me at least that the containing cylinder encompassing the shaft and rotating blades should have at a minimum of 270° to 330° of the circumference contained. while the screen area would be better having at least 180° of perforations.
Since all granulation of this design occurs due to centrifugal movement of the cut materials being sheared by the perforations in the screen I would surmise the material the screen is made of should be hardened.
These are just a couple of observations which are only one man's outside opinion unless I were to construct the exact design incorporating both yours and my ideas I would not have sufeincent data to confirm or deny my observations.

[MOST]

Hi Frank - Thanks for the detailed comments. This is a very interesting reply. This was a project done over many years with multiple students participating so it was evolutionary - but the current design is shown right with the cut pipe. Based on what we have run through the granulator, the plastic sometimes shoots all the way back up the PVC pipe and that you are right and having a more complete pipe could provide us with better results and would simplify the manufacturing process. If we kept the pipe together and only cut out a small section for material to feed into the granulation screen, it could improve the accessibility of making the granulator as well since heat treatment of the pipe would no longer be needed. I'm not sure how we would handle the granulation screen given that our current design is using a 3D-printed screen in poly carbonate. Looking at the paper, I don't think we talked much about the 3D printed granulation screen in enough detail -- so the comment saying "cut materials being sheared by the perforations in the screen I would surmise the material the screen is made of should be hardened" is incorrect, but that may be where we are losing some of our efficiency as well. Most of the cutting occurs at the fixed blade location and not at the granulation screen.

Overall, I want to thank you again as I think the comments could be used to improve the design and possibly improve the machine's capabilities.

[Frank S]

OK I see where you are depending on the mass of cut material to be carried around in the cavities between the rotating knives then being re cut as the centrifugal motion and slight vacuum created by the rotating knives continue to recut the shredded material until it becomes small enough to pass through the screen.
All the more reason why I would think increasing the degree of wrap of the pipe encompasses the spinning knives while making a screen which would share in the shearing of materials could improve on the output. Elongating the holes in the screen may or may not be well served.
I have a few hundred lbs of drink bottles that I need to granulate so maybe one day I will test my theory. Possibly by making a 3 rotor design using counter rotating carbide tipped saw blades for the initial shredding and the rotating knives passing by a fixed knife and screen for the granulation process