by Bender24601, published
I have got the OK to upload the drawings and other files needed to make this Extruder to the Universities' website. Not sure if in future I may upload the files to Thingiverse, but for now you can see most of the files here:
The list of files there isn't yet complete but I am working towards that. If I find time I may add a BOM and instructions as well, but for now I am very busy writing my thesis.
Newest tests are very promising in regards to consistent Diameter. Currently its 2.9mm so the Die diameter may be increased a tiny bit. Very little diameter variations can be measured at the moment. Any current variations are due to manipulation of the not yet solid filament.
Biggest drawback at the moment is the extrusion speed, which is still rather slow, but could easily be increased with a bigger motor. At the moment the motor spins at 35RPM and is extruding ABOUT 4cm per minute.
Feel free to ask questions in the comment section, if I have time I will try to answer these as soon as possible.
Update: Added a BOM in the downloads
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p.s. I added a picture of the auger and the nozzle so you can see how far up the plastic is melted. I produces very good results with this setup
ill answer your questions one at a time:
1. Yes, the space is filled with molten plastic
2. The auger tip will always be submerged in molten plastic, no matter how big the space between the tip of the auger to the nozzle is. This does indeed MIX the plastic, which is something that is desired to avoid bubbles in the extruded material.
3. This will always be the case.
4. It is desireble for the plastic to melt quite a bit before being extruded. This allows more mixing of the plastic, resulting in fewer lumps and air bubbles.
5. After shutting down the extruder the plastic will indeed solidify and stick to the auger. When restarting the extruder you have to make sure to give it enough time to heat up and melt all the plastic still in the barrel. This may take a little time, but would not be different if the tip of the extruder was not in the molten plastic since you should not turn the auger on untill all of the plastic is melted again.
So to answer your question: I do not believe thatit would be better to pull the auger tip outside the molten zone. This is because it is beneficial to mix and knead the molten plastic before it reaches the nozzle. I also do not think that there would be enough pressure to extrude the plastic if the auger is not conveying molten plastic but rather the solid pellets. The pressure just before the nozzle should be as high as possible to ensure a consistent and high quality filament.
I was under the impression that it should be close as well and I simply wanted verification. My thinking is this and maybe Bender can verify your points are true and some actual help the thorough mixing of the molten material.
The primary reason I see to have it close is so that the auger itself will push the molten material directly into the recessed opening made for the nozzle instead of simply increasing pressure in all directions inside the open area.
Another aspect, a large plug un melted plastic will exist and may not heat evenly enough to melt smoothly or completely enough when extruding operations begin and could end up pushing the solid material into the nozzle. The auger moved all the way down will prevent the possibility of this floating solid piece of material from ever existing by its simple existence in the empty area. This would seem to be beneficial to the entire process.
Although the auger would allow transfer of heat away from the nozzle and into the the area where the pellets are added I found when I did some extreme testing the temp of the auger was greatly reduced by its passing the through the heat blocking plastic pieces and that it never got anywhere near hot enough to start melting pellets prematurely.
The last area I think it helps is when you want to change filament colors or types have a large empty area that is free flowing there is no process in place to move new material in and out of that chamber and the time required to get 100% purity of the new material is greatly lengthened as the material can mix freely. It will take a long time for all of the old material to be removed and replaced by the material. imaging going from black to white how long with an large open area would you end up getting grayish material. The auger would expedite this.
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