Is there any alternative to Teflon?

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leadinglights

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thejollygrimreaper
why exactly the push to get away from ptfe?, aside from the temperature limit,what is wrong with having more than one hotend?

we don't have 1 screw driver for 101 different types of screws do we?

Because something else may be better. We don't know until we try.

Mike

agreed... to a point . i look at the situation with hotends currently and by comparison to hotends on other printers eg up! and from my own prototyping efforts, in the end it comes down to what the desired end result is, while it's possible to build a all metal hotend for example that will extrude every material desired it's not always ideal in terms of control over the plastic coming out the end and the end resulting print quality

what we do not have is a widely understood measure of what a "good quality print" actually is?, there is no real reference point( as is evident by some of the parts sold on ebay)

what exactly qualifies as a "reliable" hotend or extruder ? by some of the bench marks set by some of the closed source desktop printers we are well and truely exceeding that

maybe we should define and quantify what we have before we look at what is potentially better,

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@thejollygrimreaper
This launches many questions, some perhaps more suitable to other threads. Trying to address what we can one at a time, and stressing that this is purely my opinion.
Earlier you said

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......, aside from the temperature limit,what is wrong with having more than one hotend?

There is presently no design of hotend that can be interchanged simply and without any adjustment. It would be best to get to the best possible compromise and that means lots of real world trying - and not a little theory.
As far as quality, I think that I have to wimp out and say "I know it when I see it". Many of my best efforts are, in my opinion at least, as good as anything I have seen; but for every one that gets my chest swelling with pride and immodesty, there will be several in the junk pile.
That brings us to reliability: Why does one print work well and another have issues? The most common problem seems to be in the hotend, specifically the pressure required to get the filament moving. After eliminating as many variables as possible, it seems that the "thermal break" area, and what happens there, is the most profitable area to explore.
This in the end, is what I am trying to do. Not break away from PTFE, but not be wedded to it. Perhaps a softish graphite such as used on motor brushes may work, or maybe there is some way of achieving a PTFE non stick coating by electroplating.

Mike

Ok, this has been in halt for a while but finally I have my proof of concept assembled, noy I need to figure out a good way to put the thermistor here, generate the table for that thermistor, recompile marlyn and give it a go, just at a side not mounted on the printer yet, just feeding filament by hand. wish me luck! ;P keep you posted.

@dagusi

I like your prototype

Heater vs. Mass:
The picture makes the aluminum block look large.
The aluminum mass might be too big if the heater is small or located too far from the nozzle with a larger mass.
Coat the heater with thermal compound to help conduct the heat.
I would be inclined to use a cartridge heater for this application, and locate it as close as you can to the nozzle.

Idea/hack:
Since this a bench test, and a hack I'll make the following off the wall suggestion.
For an accurate reading of the nozzle temperature, tie the thermistor to the brass nozzle with graphite tow, or fiberglass rope.
Use a Dremel to create a pocket to nest the thermistor in so it's less likely to move, and apply some thermal compound to help transfer the heat to the thermistor.
Then use some high temp automotive silicone as an insulator, and to hold it in place.

I make my own thermal couples, and found it best to locate it as close as physically possible to what it is that you want to monitor/control.

Glass:
What is the I.D. of the glass, it looks large?
If it's too big the molten plastic could push up the tube.

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@dagusi

I like your prototype

Heater vs. Mass:
The picture makes the aluminum block look large.
The aluminum mass might be too big if the heater is small or located too far from the nozzle with a larger mass.
Coat the heater with thermal compound to help conduct the heat.
I would be inclined to use a cartridge heater for this application, and locate it as close as you can to the nozzle.

Idea/hack:
Since this a bench test, and a hack I'll make the following off the wall suggestion.
For an accurate reading of the nozzle temperature, tie the thermistor to the brass nozzle with graphite tow, or fiberglass rope.
Use a Dremel to create a pocket to nest the thermistor in so it's less likely to move, and apply some thermal compound to help transfer the heat to the thermistor.
Then use some high temp automotive silicone as an insulator, and to hold it in place.

I make my own thermal couples, and found it best to locate it as close as physically possible to what it is that you want to monitor/control.

Glass:
What is the I.D. of the glass, it looks large?
If it's too big the molten plastic could push up the tube.

first of all, yes it's really really big but, as an alpha I prefer everything to be large than small, then I can take away a lot of material, and I have an idea for use only 2 screws.
I have a cartridge of 40W to heat the aluminum.
the thermistor I have it's kind of big, it was the only left made of glass, my idea it's to reach high temperatures, someday, so I need it, but I'm not happy with it, it's only of 2k so it's not precise at all.
And, lastly, my idea it's to be able to change nozzles, so I will put the sensor on the aluminum as close as I can, the other idea is to use a copper washer next to the nozzle, maybe later if all this works.

The glass it's from laboratory equipment, the I.D. it's 3,2 mm, I hope it's ok but I have to try, anyway, if not, I will make my tubes, if this works it's a lot easier. 30cm of usable tube cost 1,5 Us dollars, so, really cheap!!!!! if it works I will post a lot more pictures.

@dagusi

Check out this Zirconia extruder, this is the ultimate
[forums.reprap.org]

All glass one piece nozzle and guide tube:
An idea I got from seeing the glass tubes here.
I recall melting small lab ware glass tubes with a low temperature hand held bottle gas torch.
I would heat the end up and stretch it.
It formed a perfect nozzle shape.
It broke easily but it was also quick and fun to remelt and make another one.

ok, after first test I can say:

PLA doesn't stick to he glass, it's like PTFE so that's GOOD!!!!!!!!!
sadly, it does leak in the gap between the glass and the nozzle (as expected) but I don't know how to sole it yet
Screws transfer a lot of heat, I need to do something there, really really a lot of heat
IF we can isolate the top aluminum part, from heat, we could have a hot end without a fan
last, my new thermistor is PTC, does anyone know a soft that makes tables for it (to use in marlin) all the script I found kind of have problems with that.

I think this is a cool alternative, and cheaper, to all metal hotends, there is anyone interested in continue with this? I AM!

@dagusi

I've designed heat platens for plastic hot plate fusion welding. I had to design tooling to address
the same problem that you are facing, a few ideas for you to consider to reduce the heat transfer from the bolt.

Your goal is to get air to circulate around the bolt,
and to reduce the amount of surface area of the bolt coming in contact with the upper platen (aluminum block).

Techniques to reduce the heat transfer from the bolt into the upper platen:
1. Change the material of the upper platen to one that does not
conduct heat very well, and can withstand the temperature of the hot bolt.

2. Incorporate an insulative coupler between a stud and bolt.

3. High temperature automotive silicone can be applied to all the mating surfaces as a barrier to help reduce heat transfer,
The silicone can be used as an inulative coating inside the bored hole, between the washers, etc be creative.

4. Create a large air gap around the bolt passing through the platen by machining an over sized hole.
Support the bolt with a coil spring.
Use a coil spring with ground ends, and which is significantly over rated (i.e. uncompressible).
The spring OD should be large enough that its ID is located well outside of the large diameter through hole.
Insulate the bolt from the spring with a sandwich of two metal washers and an insulative washer.

The spring should be placed on top of a metal washer, and the metal washer is placed on top of an insulative washer.
Coat the bolt threads passing through the platen with high temperature automotive silicone to help reduce radiant heat,
and/or place an insulative sleeve around the shaft of the bolt.

I tried 3 feeders to the one heater block but the forces in the system are not friendly to the glass tubes(3.5 OD 2.5mm ID) - will Zirconia be any better?
I am going ahead with stainless tubes(2 mm ID) in the place of the glass but will try again with the glass tube inside a stainless tube in the heater block and at the top
with a break in the stainless somewhere in the middle.

What do you mean by the forces are not friendly to the glass tubes?

Zirconia is the ultimate material for this application.

Porcelain would be an excellent replacement for expensive zirconia.

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A2
What do you mean by the forces are not friendly to the glass tubes?

Zirconia is the ultimate material for this application.

Porcelain would be an excellent replacement for expensive zirconia.

No matter how hard I try - there's always one of them breaking apart in the heater block. I do not know what kind of glass it is. Got it from a scrap advertising board's fluorescent tubing.
An option may be to taper the holes in heater blok and fill the sides with silicone. That should shorten the meltzone as well. (thinking aloud here)

Will porcelain be a better choice than glass ?

Material properties of porcelain is all around superior to glass.

In this example the fracture toughness of porcelain is 2X that of soda lime glass.

PORCELAIN
Fracture Toughness K(I c) MPam1/2 NOTCHED BEAM 2.0
[www.coorstek.com]

Glass soda lime
Fracture Toughness K(I c) MPam1/2 NOTCHED BEAM 0.7-0.8
[www.sv.vt.edu]
[www.tech.plym.ac.uk]

I think fluorescent tubing is made of soda lime glass:
[www.econindustries.com]