New Extruder Barell Material Idea: Glass

I think that GLASS (borosilicat, quartz or even just the normal one) might be a very interesting material for building the liquifier section of the extruder. Some random thoughts about it:

• NON STICKYNESS (could someone with a running setup conform this?) I think that apolar materials with high moleculare weight shouln't stick to SiO2 because it the Van-der-Waals force is not strong enough and other type of bindings will fail. In HDPE,LDPE,PP is (de-facto) no dipolmoment (as far as I am aware), so it should work best. PLA, ABS and shouldn't stick much neighter. So the extruder force should much lower than using stainless steel.
• CHEAP MATERIAL (compared to PTFE, PEEK etc)
• EASY TO WORK WITH if you have the skills and a rather powerfull burner..
• NO SEALING PROBLEM some extruders suffer from a sealing problem (i think even nophead had some issues). Glass would enable a monolithic design. Entry section, Gradient zone, Hot section, Nozzle - no problem.
• TAPERING is easy possible (even with a monolithic design!). Nophead showed, that tappering can reduce the friction significantly
• ELECTRICAL NON-CONDUCTER: So winding some NiCr-Wire directly on the glass should be possible

Did someone try it? I'm glad to here your comments on that. I will try it, but it will take some time...

babu

Sounds like a good idea to me; the only issue might be preventing cracking and chipping from the constant temperature changes.

How did you envision coupling it to the heater device, and/or to the extruder feed? Did you envision creating the .5mm hole directly from glass tubing, or to attach something else to provide the .5mm hole?

When do you think you might be able to try it out? If it works, this seems very exciting..

mateo24 made one, pics here http://www.23hq.com/mateo24/photo/5169238?usertag=tarpipe. My fear would be that if the heat crashed into a blob of plastic it could snap the glass.

---

[www.hydraraptor.blogspot.com]

@BeagleFury
Thermal stress is a non-issue for borosilikat glass (or quartz). Even active cooling the inlet section with water is no problem. Of course the glass must be then be carefully "blown" but in every day use in a laboratory glass must withstand worse conditions (chemistry essentially IS cooling and heating).

I think that the whole liquifier should be mono-block. The 0.25 to 0.5 mm hole is no problem (think of pipettes). Of course it is not drilled, so you simply can't tell the diameter before measuring but glass is as cheap, that I think one will just have a "selection"

@nophead
thanks alot for the link. I was completly unaware of the "glastruder". Although mateo24 was/is using glass, it seems that the strategy is different: his functional parts (nozzle, cooled inlet) are made of metal.

Concerning the headcrashes: Glass is a much stronger than most people expect. Perhaps predetermined breaking points on the printhead mountings would be a good idea anyway.

Have you (or anyone out there) any data about how much extruded plastics sticks to glass? Or what would be interesting to to ANODIZED Al or Ti (because there are a few layers of Al2O3 on that). Or have you any data what influence the "slippery" property of the thermal barrier has on the needed extruder force (ie comparing PEEK to PTFE to stainless steel barrel)?

Thank you both for your quick responses
babu

i found something:

[dev.forums.reprap.org]

according to this, abs doesn't stick to abs at all (was tried as base material).

Yes but whether it is hot or cold makes a big difference to whether it sticks or not.

The problem I see making it all out of glass is that you need the heater section and nozzle to be good conductors and the insulator to be a good insulator. I see glass is a much better insulator than stainless steel, so not not a bad choice for the insulator but aluminium is 250 times more conductive.

---

[www.hydraraptor.blogspot.com]

>> (think of pipettes)

Is there a technique to reducing the overall length of the .5mm hole at the tip? One advantage I think that drilling would have is that the actual length of the fine bore is very small (In some cases, even thinner than the bore itself.) It requires a lot more work to force the material through a long thin tube than a tiny shallow puncture.

Also, for heating, I could imaging getting good thermal contact by simply melting coils of nichrome right into the glass.. or, perhaps even better, if you can get segments of the nichrome into the interior of the heating chamber for direct contact with the plastic.. might be very tricky work though. That should solve the problem nophead points out on heat conduction near the tip. On the other hand, you'd probably also want the thermistor inside too

I'm not sure how much could be mastered using laboratory glass work skills, but I'm sure a master glass artist would laugh at how trivial it appeared.

You want to avoid hot spots because these will cause your plastic to burn or force you to work at a lower temperature for the cold spots. Having a brass barrel with the wire outside works very good at distributing the heat so the whole thing is close to the same temperature.

---

---

Darwin clone, Gen 2 electronics, Arduino Duemilanove w/ AtMega328, 5D Firmware, Pinchwheel extruder
[www.codeerrors.com]

The glasstruder in the earlier photo is something I made to be able to see how ABS and PLA melt...you can see more photos of it here.

That design with the three screws and wires was one of those things done out of curiosity but completely unnecessary (and the wires quickly snapped from the pressure!!) You can see a more conventional design here.

The boro tube (McMaster 8729K96) with a 3mm wall is really tough. A short piece is not going to easily snap. I'd like to do one where one end is pulled into a nozzle but that is a project for another day. As you can see in the latter photo there was a seal problem between the nozzle and tube but the real value of the assembly was the visualization of the melting process...couple a glasstruder with Chris's rheology piece and you can quickly understand what is happening in the barrel...

Rick

@rick
thank you very much for providing those informations! i will try to form a nozzle, but it will take some time