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Paste Extrusion

a viscous clay slurry. Months later, again as part of the engineering thesis and after the disappointing work on the auger,we picked up again on the Moineau design, which is my favorite. The length and parameters of the rotor changed based on the analysis of an industrial Moineau pump in order to get a better seal. This is crucial because normally the rotor is stainless steel and the stator a very durable rubber and so the two seal very well. This makes that it dispenses low viscosity material like water with the same ease as a thick clay. In a plastic 3d printed version you will never archive this type of sealing but we also don’t need the low viscosity capabilities, you’ll use high viscosity pastes. Making the rotor longer creates more cavities and seals. Various other improvements taken from literature were sketched out to reduce possible pulsation. The same one minute bench top extrusion tests were done with this 2nd update of the Moineau and the results were vastly more consistent versus the auger based design. At this point the Moineau still needs a lot of improvement but that is mostly on the mechanical part of the design, the working principle itself seems capable to offer what we need.


As indicated in the first section of this article, the Stepper Driven Syringe Pump and Direct Air Pressure Extruder both have their merits but don’t have the potential for growing into a multifunctional software driven and volumetric extruder that operates in a similar manner as our filament extruders.

Because of its excellent volumetric continuous mode of operation, the Moineau Progressing Cavity pump principle is by far the best design to focus development on today and a lot of the initial community work is already there to start with. Lets hope you join in!

photo by Unfold

What needs to be improved is the mechanical strength of the coupling between the rotor and stepper. Because the rotor moves in an eccentric manner, there needs to be a flexible coupling shaft and this shaft ploughs through the material in the inlet chamber. This is now a very basic three prong coupling that has the tendency to wobble up and down and frequently breaks because the torque is too high. Also related to the torque, a standard nema 17 coupled directly to the shaft is really on the edge. Sometimes it works sometimes it doesn’t and your stepper will skip a lot. Either a size up stepper like the nema 23 needs to be incorporated or a geared stepper. So basically the whole extruder needs to be hardened for high torque operation, that’s work that still needs to be done. REPRAPMAGAZINE


RepRap Magazine Issue 3  

The third issue of RepRap Magazine. Interview with Nicholas Seward, Paste Extrusion, Hot-Ends, and much more.

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