Article on Paste Extrusion in RepRap Magazine

Hi all,

I've written an article for the new RepRap Magazine that gives an elaborate overview of paste extruders and concepts, summarizing much of the experiments me and others have done over the years. Hope you enjoy reading it.
If you don't want to read all those pages, so far there are 3 principles that are useful (ore hopeful) to use for paste extrusion. Direct Air Pressure & Stepper Driven Syringe Pump extruders are fairly established and most used but have their serious drawbacks both in operation and in mechanical construction. The most promising candidate to solve those issues (and I've done a fair amount of testing on that) is the Moineau Pump. What's needed now are some great minds and hands to improve those extruders based on that principle
I will write a follow up post on unfoldfab.blogspot.com soon detailing more of our tests with a modified Moineau extruder based on Tomi Salo's design and what needs to be improved in order to get it working.

Edited 1 time(s). Last edit at 03/24/2014 01:16AM by unfold.

Reading your article now! Interesting read. Thanks for writing this.

Excellent article, just what I was looking for!

I had thought this was a fairly "solved problem" and was considering slapping a syring-based extruder on a printer whose plastic extruder had failed, but apparently it's not quite that simple

You mention that commercial Moineau pumps use a stainless rotor and rubber stator to maintain a better seal than is possible with a printed unit, however could you use a flexible filament (Ninjaflex, etc.) to print the stator part in order to approach these sealing capabilities?

Hi Unfold,

I have recently gotten the idea to 3D-print in clay and spent a fun afternoon of internet-research which amongst other material turned up your recent article in the Magazine and other places where you talk about your experience with extruding the stuff.

One problem with the more simple of these extruders seems to be controlling the flow rate as various parameters of the material or even just the amount left in the reservoir change.

Could that maybe be solved by doing a closed-loop and measuring the current rate? Possibly by putting scales under the build-platform?

I have once watched a 3D-printer at work. That is the complete extent of my experience with the things, so please disregard me if the question is just daft.

Ciao, MM

Indeed Marian, a closed loop system would solve a lot of issues in the air pressure based extrusion systems. I though of some ways to measure the flow rate but could't come up with something that would work. You weighing idea is pretty interesting although I would have no idea if that is feasible. The already printed clay looses weight when drying as water evaporates. Maybe you're up for the challenge

Thought of reusing the optical flow sensor of a mouse, if the paste is grained enough, it might be able to measure a paste flow rate.

We've talked about tis before but none tried so far. I believe one could add some colored specs to clay that burn away when fired.
Would be cool if you wanted to try using this sensor.

I just read your article in RepRap Magazine. Thanks, it was very interesting.

I knew nothing about Moineau pumps before. It seems to me that the rotor looks very much like a rope thread, described in ISO 10208, which is used in the Rock Drilling industry. Maybe it would be possible to use something like a part of an Atlas Copco MAI SDA R32L as the rotor. It would have to be cut to a suitable length of cause but it is made in large quantities of abrasive resistant steel.

If the geometry of the rope thread seems work I would propose to print a floating stator from iglide tribo-filament.This would make it easy to print new ones when they are worn out and also ensure low friction. When the rotor eventually becomes worn it is possible to print a tighter stator.