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Glass nozzle

Posted by cozmicray 
Glass nozzle
August 07, 2013 03:13PM
What happened to glass extruder nozzle development?
Are there glass nozzles to be purchased out there?
Re: Glass nozzle
August 07, 2013 05:01PM
I've seen the article on the reprap website, but nothing else. I think it might be fragile and prone to cracking due to a thermal shock.
Re: Glass nozzle
August 11, 2013 03:16PM
Woodencase is right. Thermal shock is a huge issue with glass. However, I think it would be really cool to have a transparent hot end as it would enable us to actually visualize the transition from solid to molten plastic.

The closest thing to a glass hot end is a Zirconia ceramic hot end. Zirconia is extremely strong, and has very low thermal conductivity so it is an ideal insulator. Unfortunately, the manufacturing processes used to machine Zirconia parts are very limited due to the fact that the ceramic is brittle. The traditional grinding process applies a lot of force to the work so thin walled parts are not possible. On the other hand, there is also the high-end laser sintering process (SLS 3d printing!) but that is EXTREMELY expensive. A while ago I came up with a 1 piece zirconia hot end design and contacted some Chinese manufacturers for quotes, and the unit price was about $550 eye popping smiley So I dropped the idea right there. Alternatively you can design the hot end to be manufactured using the grinding process like This one but then you just end up with a modified J head...

Re: Glass nozzle
August 11, 2013 06:55PM
Eric, thank you for this useful information. I wondered how they made their ceramic hot end! I personally own one, 1.75mm version, and it is a great design, but I haven't gotten good results with it. The heat just kept rising through the hot end and even with a fan, I wasn't able to cool it enough. I've asked some support and they've shown me another user who had to use two fans with a complex setting to get it work.
Re: Glass nozzle
August 11, 2013 08:46PM
That's the problem. Their hot end was manufactured with the grinding process so they were doubtlessly limited in their design. Notice how their "chess piece" design has very thick walls. I presume that this is because they needed the part to be strong enough to withstand the force/vibrations involved in grinding the internal 6mm thread. The probelm is that these thick walls render the low thermal conductivity of Zirconia useless. You would get much better results with a thinner walled Stainless Steel insulator. While Zirconia has the perfect properties for thermal insulation (extremely strong, temp. resistant, and low thermal conductivity) at the end of the day every design has to be manufactured and the processes used to manufacture parts from engineering ceramics like Zirconia are very constrained.

Re: Glass nozzle
August 12, 2013 08:00AM
We'll have to wait for a ceramic powder die then winking smiley

I'm using a personal prototype, all metal hot end, right now and performances are a lot better. The cold side doesn't heat over 40°C at 300°C on the hot side, I was very impressed.
Re: Glass nozzle
December 12, 2013 02:07PM
I know this isn't the most recent of posts, but I was surprised not to find very much on this topic aside from what's here: [reprap.org] I would think the thermal shock wouldn't be as much of an issue with borosilicate.

McMaster has several options with 3mm ID here: [www.mcmaster.com] I have a few pieces on order and am planning to do some testing with it.

I'm planning to heat and pull the tube to a point, sort of like this, just a little larger scale: [www.youtube.com]

I'm not sure how consistent a nozzle diameter I'll be able to get and keeping it centered might be tricky, but I think those are details that could be worked out. Anyways that's the plan, maybe it'll be a flop, but either way I'd be happy to share what I find.
Re: Glass nozzle
December 12, 2013 06:55PM
With glass being such a good insulator -- hard to get into a melt zone
Inductive heater inside glass sounded really good but no one developing it.
Perhaps glass above metal melt zone
maybe glass nozzle below melt zone

there is ceramic hot end --- ceramic insulating above hot zone


Its all keeping PLA/ABS HOT and flowing
insulating the HOT from the holder

confused smiley
Re: Glass nozzle
December 23, 2013 03:50AM
Hi Cozmicray,

A glass nozzle would work for sure, i'd love to try it out smiling smiley

but for now we have made an all 100% ceramic hotend using zirconia, see here a youtube clip where we are printing polycarbonate.

Polycarbonate printing at temperatures > 300C

as you can see only using an fan from the side of the printer.

Re: Glass nozzle
December 24, 2013 06:33PM
hp_ Who are WE?

got a URL to your site for ceramic hotend

Is it 100% ?
ceramic body, ceramic heater, ceramic nozzle, ceramic thermistor?

confused smiley
Re: Glass nozzle
February 28, 2014 04:59PM
Most of the work was done years back, when there wasn't a reliable hot end design. Most people had to make their hot ends by hand, usually with limited tools, and so drilling the orifice became a particular challenge. the impetus to work with glass was that it's relatively easy to draw a glass tube into a pipet with a fine orifice. It also doesn't conduct heat well, so would be a good insulator.

of course, once there were reliable designs to buy, there was less reason to develope the design.

I worked with it so here are some of the problems i encountered:
- Drawing the glass, while somewhat easy, was hard to do with any precision by hand. you could not get a reliable orifice size. an option was to pull the glass to a fine point and then grind back the glass to get to the orifice size you wanted, but now it's not easy and you have to deal with glass dust.
- it's hard to get the heat through the glass and into the filament. you end up needing a big heatblock, which increases the melt zone, which contributes to oozing.
-with a drawn nozzle, it's really hard to get the heat at the orifice, where it's needed most.
-you need a ptfe liner for PLA so that it still slides when the plastic swells.
- it was hard to fix the hot end to the cold end without a flange, and it was hard to fix the heatblock to the glass. clamping induces stresses that can cause breakage when heated (which can be ok as long as the glass is thick enough, but then your problem with getting the heat into the filament is more pronounced)

I was working on a design that used a metal nozzle clamped onto the end of a non-drawn tube. it worked, but my design (it used layers of 2mm flat alumnium bar stock) leaked all over the place.) I needed gaskets that could stand the high temps. plus if i didn't clamp the block onto the glass tight enough, it slipped off when the metal expanded, and if too tight, it broke the glass.

when J-head came out, i snapped one up and haven't had an issue since.
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