We have started work on a pellet extruder for our printers, with the end goal being able to print from trash plastic. We will be periodically updating this thread and would love to answer any questions you have about this project.
This is the current cad model. For size reference the motor on top is a nema 23
we have been hard at work on the pellet extruder. over the past week we have been doing testing on our current in house pellet extruders to test torque and help us pick the proper motor for the job.
You may have seen the short video on the re:3d tech youtube channel of our recyclebot
https://www.youtube.com/watch?v=Qz5vgjowTco
this is one of the two machines we have been using to get data on torque required to turn the screw for extrusion.
The other is a 20 single screw extruder from Robotdigg, this unit is using the same screw we have so far planned on using in our final unit.
Recyclebot
Robotdigg extruder
The current screw is about 20mm in diameter
our machine shop is also hard at work making parts for the machine
An issue we ran across that we are currently working through is the constant feed of pellets without jams. The pellets have a tendency to get caught between the screw and the wall of the barrel when being fed in this forces the screw to have to shear through the pellets to continue turning. To counter this we have tried redesign the hopper to help the feed. These are the revisions we have gone through so far. They have not been fully successful so there will be more revisions to come.
We have had our nose to the grindstone for the past few week testing and getting new designs ready. There has been a major shift to a new screw. we have gone with a smaller diameter screw, that has a lower compression ratio and fewer flights. What this theoretically will allow us to do is use a smaller motor as well as be able to push out more filament.
Using the screw we have already made a ton of filament
which has been a huge step in the right direction, with the old screw we had issues getting even 100 mm of filament consistently.
So we got to work on the computer and we now have a first revision design in place. We are going to mount it to one of our in house test platforms.
This will be a number of first for us. If it works it will be our first successful pellet extrusion. secondly we are going to be using two linear rails on the carriage for weight purposes. Having two rails may not sound like much but this will allow us to adapt larger and heavier extruder assemblies to our bot, something that my come in handy down the road.
Lastly we have been hard at work on some better documentation for the public. We have started using GitHub as a storage area for this project housing every revision of this cad we have up until this point. If you want any of this please check it out here and give us your thoughts.
Thanks and happy printing everyone!
Over the past few weeks we have made huge leaps and bounds. We have gotten a rough first revision done of an actual extruder on the bot and have gotten it printing. to do this we had to create a whole new revision that looks quite different from anything else we have done thus far.
We made a quick cad of the entire assembly. Drawings were made and we manufactured and built the whole thing in a week.
the cad about 75% complete
start of the assembly
we had to have a bot to mount this to. The platform that was easiest to modify was our gb4 prototype. We added a new bridge rail with two linear rails for support. the wiring was also changed by adding a relay to control the heater as well as a larger speed control to provide more current to the motor.
gb4 before the mods
the new bridge rail
the modified wiring in the electrical box
the new relay controller (wiring diagram on the github). Controls the 110v heater cartridge.
the new motor control (wiring diagram on github)
extruder minus the heater band on the bot.
Once the install was done we were able to start testing. There were some minor issues with heat creep and some pla parts hitting glass transition, those were replaced with polycarb pieces and the issues seems to be resolved. We got the machine running once we tuned in our profile for simplify printing began.
our first print not much to look at but a good start
this was our first large print. It took three hours to complete. Using master batch pellets we were able to change the color throughout the print.
some of our test with abs, we are still getting some retraction issues but we are working on figuring those out
an early calibration piece using pla. there is some heat issues with this part but again a problem we can start to address now that we have a working unit to tinker and tune.
There are still a couple of issues we need to address some of which have been stated above. The major one we need to work on is the feed, currently our hopper is too small which mean we need to babysit the machine. we are looking at ways to increase the capacity and make the machine more self reliant. The other issue is the deterioration of the hopper. the pellets are shearing against the side wall and removing plastic creating a channel impeding flow of the pellets and and possibly contaminating the plastic (no evidence just a possibility that needs to be avoided at all cost)
it is difficult to see but behind the hole the plastic is starting to ware. This was only after one run.
So we have definitely made a huge leap, and are way closer to our goal of printing with trash. we will be further refining this design and will be updating as we go on the github so look for that!
Thanks and Happy printing!