Ideas for High Temperature Extruder (printing Polycarbonate)
Posted by RP Iron Man
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Ideas for High Temperature Extruder (printing Polycarbonate) April 27, 2013 07:56PM |
Hey guys,
I have been brainstorming ideas for a high temperature extruder that would be capable of printing higher temperature thermoplastics (especially Polycarbonate). Since Polycarbonate can be extruded from 280C - 320C, I was going to design the hot end to be able to handle up to 350C/400C.
From my experience and based on what I have read on the forums, hot end designs that use PTFE or PEEK as thermal insulators cannot withstand the temperatures required for PC. (The melting points of both PTFE and PEEK are under 350C, and PTFE starts to deteriorate at temps above 260C.) The alternative to the PTFE/PEEK thermal barrier is the all-metal extruder design. While this eliminates the danger of melted PTFE insulators, it creates a bunch of other issues (heat creep, added fans, increased number of CNC machined parts), so ultimately, it is not the ideal solution. What we really need is a rigid thermal insulating material that can withstand temps of 350C for long periods of time. Why not MDF?
I am not sure if anyone has tested this before, but it seems like the best solution to this problem. The thermal conductivity of MDF is 0.05W/mk, compared to 0.25W/mk for PTFE/PEEK! Additionally, MDF shows very little deformation at high temperatures, and since it is made of wood fibres, it will not melt
At 1/5 the thermal conductivity of PTFE and with it's consistent rigidity, MDF seems like it would be the perfect candidate for a thermal barrier in a high temperature extruder. I have not tested this yet, but I was wondering if anyone else had. Is there some unappealing property of MDF that I am overlooking? This could also cut down on the number of necessary CNC machined parts and junctions where the parts meet by replacing the conventional PTFE tube and brass barrel combo with a single MDF part. I was thinking that you could have the drive gear push the filament directly into the MDF insulator, which could have an M6 external thread on the bottom end with the brass nozzle/ heater block attached to it. Since the filament would feed directly from the "MDF barrel/insulator" into the brass nozzle, the melt zone could be reduced to about 4 to 10mm (depending on the nozzle design). This would really reduce the chances of the hot end clogging (right?). Sorry, I am explaining a lot of things in words...I wish I had of drawing of this -__-
While there do seem like a lot of advantages to using MDF as an insulator/barrel, I can imagine that there are also many drawbacks. For one, MDF is not very durable so it may wear away quickly with the filament constantly passing though it. Also, the external threading may not work out as the brass nozzle threads may cut right through the MDF threads. I was also thinking that MDF is not nearly as smooth as PTFE, so the added friction may significantly impede the movement of filament through the "barrel". Additionally, MDF quickly absorbs moisture from the air, which may block the passage of filament through the insulator (though I think the high temps of the hot end would eliminate this problem). Lastly, there could be a problem of hot plastic sticking to the inside of the MDF barrel and jamming the hot end (though I am not sure of how well different thermoplastics would stick to MDF...). Anyway, that is all I could come up with in terms of using MDF as a thermal insulator. What do you guys think??? I am not too sure about anything that I just mentioned, its all very theoretical, so let me know if I am completely wrong Are there any other thermal insulators that would be better suited for the higher temps required for PC? I am trying to avoid the all-metal hot end at all costs. It seems like waaayyyyyy to much trouble than it's worth.
Ok, so other than the thermal insulation issue, there is the problem of heating the nozzle to 320+C. Would I be able to achieve this with 2 standard 6.8OHM heat resistors (Nophead?). I haven't tried this because I don't have a spare hot end and don't want to melt my PTFE insulator
Also, a more significant problem would be the thermistor. The standard Honeywell NTC thermistor is only rated up to 300C, so going up to 320C or 350C may be risky (can someone verify this?). Most of the thermistors that are commonly used are rated at 300C. Does anyone know of a cheap thermistor that can handle up to 350C or 400C?
That's all I could come up with for now. I was thinking that the RepRap community really needs a stable high temp hot end design, so we can start experimenting with higher temperature thermoplastics. I was focused on Polycarbonate because it seems like the next step above ABS. Its has an extremely high impact strength, it is resistant to bending and it is very clear. It is also used as "bullet-proof glass"!
Also, initially I was looking at the possibility of extruding PTFE, but I discovered that it undergoes pyrolysis at above 260C... It may end up forming a charred mess/carcinogens before it reaches its melting point (anyone tested this?). It would be really cool if we could use this extruder to reprap PTFE thermal barriers for other printers!
Are there any other thermoplastics besides PC that could be extruded with higher temp capabilities? How about Nylon?
Jeez, looks like I wrote an essay! I'll stop now before the mods ban me for spamming the forums Let me know what you guys think!
--
Eric
I have been brainstorming ideas for a high temperature extruder that would be capable of printing higher temperature thermoplastics (especially Polycarbonate). Since Polycarbonate can be extruded from 280C - 320C, I was going to design the hot end to be able to handle up to 350C/400C.
From my experience and based on what I have read on the forums, hot end designs that use PTFE or PEEK as thermal insulators cannot withstand the temperatures required for PC. (The melting points of both PTFE and PEEK are under 350C, and PTFE starts to deteriorate at temps above 260C.) The alternative to the PTFE/PEEK thermal barrier is the all-metal extruder design. While this eliminates the danger of melted PTFE insulators, it creates a bunch of other issues (heat creep, added fans, increased number of CNC machined parts), so ultimately, it is not the ideal solution. What we really need is a rigid thermal insulating material that can withstand temps of 350C for long periods of time. Why not MDF?
I am not sure if anyone has tested this before, but it seems like the best solution to this problem. The thermal conductivity of MDF is 0.05W/mk, compared to 0.25W/mk for PTFE/PEEK! Additionally, MDF shows very little deformation at high temperatures, and since it is made of wood fibres, it will not melt
At 1/5 the thermal conductivity of PTFE and with it's consistent rigidity, MDF seems like it would be the perfect candidate for a thermal barrier in a high temperature extruder. I have not tested this yet, but I was wondering if anyone else had. Is there some unappealing property of MDF that I am overlooking? This could also cut down on the number of necessary CNC machined parts and junctions where the parts meet by replacing the conventional PTFE tube and brass barrel combo with a single MDF part. I was thinking that you could have the drive gear push the filament directly into the MDF insulator, which could have an M6 external thread on the bottom end with the brass nozzle/ heater block attached to it. Since the filament would feed directly from the "MDF barrel/insulator" into the brass nozzle, the melt zone could be reduced to about 4 to 10mm (depending on the nozzle design). This would really reduce the chances of the hot end clogging (right?). Sorry, I am explaining a lot of things in words...I wish I had of drawing of this -__-While there do seem like a lot of advantages to using MDF as an insulator/barrel, I can imagine that there are also many drawbacks. For one, MDF is not very durable so it may wear away quickly with the filament constantly passing though it. Also, the external threading may not work out as the brass nozzle threads may cut right through the MDF threads. I was also thinking that MDF is not nearly as smooth as PTFE, so the added friction may significantly impede the movement of filament through the "barrel". Additionally, MDF quickly absorbs moisture from the air, which may block the passage of filament through the insulator (though I think the high temps of the hot end would eliminate this problem). Lastly, there could be a problem of hot plastic sticking to the inside of the MDF barrel and jamming the hot end (though I am not sure of how well different thermoplastics would stick to MDF...). Anyway, that is all I could come up with in terms of using MDF as a thermal insulator. What do you guys think??? I am not too sure about anything that I just mentioned, its all very theoretical, so let me know if I am completely wrong
Are there any other thermal insulators that would be better suited for the higher temps required for PC? I am trying to avoid the all-metal hot end at all costs. It seems like waaayyyyyy to much trouble than it's worth.Ok, so other than the thermal insulation issue, there is the problem of heating the nozzle to 320+C. Would I be able to achieve this with 2 standard 6.8OHM heat resistors (Nophead?). I haven't tried this because I don't have a spare hot end and don't want to melt my PTFE insulator
Also, a more significant problem would be the thermistor. The standard Honeywell NTC thermistor is only rated up to 300C, so going up to 320C or 350C may be risky (can someone verify this?). Most of the thermistors that are commonly used are rated at 300C. Does anyone know of a cheap thermistor that can handle up to 350C or 400C?
That's all I could come up with for now. I was thinking that the RepRap community really needs a stable high temp hot end design, so we can start experimenting with higher temperature thermoplastics. I was focused on Polycarbonate because it seems like the next step above ABS. Its has an extremely high impact strength, it is resistant to bending and it is very clear. It is also used as "bullet-proof glass"!
Also, initially I was looking at the possibility of extruding PTFE, but I discovered that it undergoes pyrolysis at above 260C... It may end up forming a charred mess/carcinogens before it reaches its melting point (anyone tested this?). It would be really cool if we could use this extruder to reprap PTFE thermal barriers for other printers!
Are there any other thermoplastics besides PC that could be extruded with higher temp capabilities? How about Nylon?
Jeez, looks like I wrote an essay! I'll stop now before the mods ban me for spamming the forums
Let me know what you guys think!--
Eric
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Re: Ideas for High Temperature Extruder (printing Polycarbonate) April 28, 2013 12:15AM |
Ok, so I managed to find a spare heat block and did some tests and it doesn't look like MDF will cut it as a thermal insulator 
While it performs well around heat bed temps, it starts smoking at 200C and by 350C it is billowing toxic smoke. Conclusion: MDF is not safe at high temps. Its a pity, MDF is a great insulator (even at 350C, I could touch the small MDF piece without burning myself). It could probably be used in the same way that PTFE/PEEK are used in conventional hot ends. I guess the all-metal/fan cooled design is the only way to go
Also, in case anyone was curious, Using two 6.8ohm resistors at 12V, the temperature of the brass block reached 350C in under 2 minutes easy, so there is definitely no problem with using the standard wire-wound resistors as the heating element for Polycarbonate extrusion. However, I am still not sure about the Honeywell thermistor. While it survived at 350C I'm not sure how it would perform when operating at that temperature for long periods of time. It would probably be better to use a thermistor that is rated for the higher temperatures.
Does anyone know of an alternative thermistor that can handle up to 400C?
While it performs well around heat bed temps, it starts smoking at 200C and by 350C it is billowing toxic smoke. Conclusion: MDF is not safe at high temps. Its a pity, MDF is a great insulator (even at 350C, I could touch the small MDF piece without burning myself). It could probably be used in the same way that PTFE/PEEK are used in conventional hot ends. I guess the all-metal/fan cooled design is the only way to go Also, in case anyone was curious, Using two 6.8ohm resistors at 12V, the temperature of the brass block reached 350C in under 2 minutes easy, so there is definitely no problem with using the standard wire-wound resistors as the heating element for Polycarbonate extrusion. However, I am still not sure about the Honeywell thermistor. While it survived at 350C I'm not sure how it would perform when operating at that temperature for long periods of time. It would probably be better to use a thermistor that is rated for the higher temperatures.
Does anyone know of an alternative thermistor that can handle up to 400C?
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Re: Ideas for High Temperature Extruder (printing Polycarbonate) August 06, 2013 08:21AM |
stainless steel or better titanium alloy work great as heat barrier as long as you keep the walls thin. or make bigger heat sink - but energy goes into space
[3fx.eu]
[3fx.eu]
[3fx.eu]
and works fine: [www.youtube.com]
it's pretty straight forward but i will post some better documentation along with other golemD files.
soon a polish forum friend should make some test on a ABS carriage printer with aluminum plate as interface.
[3fx.eu]
[3fx.eu]
[3fx.eu]
and works fine: [www.youtube.com]
it's pretty straight forward but i will post some better documentation along with other golemD files.
soon a polish forum friend should make some test on a ABS carriage printer with aluminum plate as interface.
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