Hello everyone, I'm currently developing a paste extruder based on the Moineau pump principle. In theory that design should work well as an extruder, as it has completely non-pulsating output and can pump pretty much anything. Running it with a stepper motor should allow controlling the extrusion just like in a hot plastic extrusion head.
Here's what I have so far: Exploded view. From the bottom, there is a conical nozzle, then the pump stator body and on the top, the pump inlet body, with NEMA17 mount and an inlet pipe. The stepper motor drives the pump rotor with a spider coupling, modified into a long shaft from this thing.
I have already printed the pictured parts and after I fix the designs of the motor couplings and get them printed, I'll be running some actual tests.
I'm not sure if PLA printed stator and rotor will seal well enough to reliably pump fluids. Commercial designs seem to use a molded elastomeric stator. Does anyone have experience with these things?
Also, what sort of paste would be a good starting point for trying this out? I'm thinking of paste made from water and wheat flour. That at least seems to be easy to clean up and non-toxic.
I did a test run (extruding into air) with slightly runny wheat dough: [youtu.be]
Now I'm just missing a printer to put this on... I wonder if printers with moving print surfaces are suitable for this sort of printing or should I try to find a Darwin-style design where the print plate only moves in Z? The Unfold ceramic extrusion project page says that the print plate should not move or it might break the object while printing.
Edited 1 time(s). Last edit at 01/06/2012 06:44PM by ttsalo.
I did a test with a Makerbot a while ago and the object did not collapse as I feared (maybe the acceleration features smooth out rapid shakes?) But more tests need to be done to be sure over this issue of moving print beds.
Cool design, but you know by now from my comments on Thingiverse
It probably depends on all of the following: the material, the shape of the object and the acceleration...
I broke my plastic printer (well, the extruder) so I haven't been able to test this, but I made a design where the stator is constructed by placing a cylindrical insert into the pump. This piece can then be separately printed from elastic material or formed by casting in place, using a separate, removable plastic piece to form the stator hollow.
For this purpose, I bought a roll of plastic called TPE (thermoplastic elastomer) from Orbi-Tech. It's quite flexible, hardness Shore A 50 if I had to take a guess (it didn't come with proper specs). It should be possible to print the stator piece from that. That, along with sealing the motor shaft, should allow the extruder to seal properly and maybe even pull a partial vacuum.
I am modelling the cavity of the stator as a 3d part. Next I will make a silicone model out of it. That will become my rubbery stator. I hope this way I get a good sealing for the rotor, as I have not had much luck with my quite viscous paste till now.