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Why PTFE lined throat instead of metal throat?

Posted by Veesta 
Why PTFE lined throat instead of metal throat?
August 07, 2016 10:06AM
Hi there,

Yup, dumb question but i'm interested.

My PTFE throat just arrived and i have two metal throats in the box.

What is the benefit for using PTFE instead of metal?

Also, which end is the nozzle? The open PTFE end or the closed metal end?

I'd guess the open PTFE end should be facing the nozzle?

My extruder is the MK8 thingy, which currently has a metal throat from E3D V6 with a heatbreak.

Edited 1 time(s). Last edit at 08/07/2016 10:06AM by Veesta.
Re: Why PTFE lined throat instead of metal throat?
August 07, 2016 11:06AM
Ptfe is super slippery and some what insulates the filament so that it doesn't soften and clog the throat.it can also withstand up to 450 degrees ferinheit.before degrading and out gassing.
Re: Why PTFE lined throat instead of metal throat?
August 07, 2016 11:26AM
About 230°C, that is good to know. smiling smiley

So, PTFE prevents this form happening? And even if it does, it might still push through?

I have some problems printing. A large surface infills nicely, but small details like screw holes and thin walls might stop extruding -> it will grind into the filament.
And once i pull the filament out, the tip looks like that. The tip is melted and thicker.

(On successful prints, tip looks different)
I have played with the temperatures, but it seems like the temperature good for small details is not good for large surfaces. (And vice versa)

I hope this will solve that problem then. smiling smiley

Edited 1 time(s). Last edit at 08/07/2016 11:27AM by Veesta.
Re: Why PTFE lined throat instead of metal throat?
August 07, 2016 02:18PM
It should help a lot, even though ptfe expands a lot, roughly 1 eighth on an inch for every 100degrees ferinheit per foot, it has almost no friction. That's why is was used in cook ware for so long and is still used for high quality linear slides. It is also really soft and will deform to mechanical defects easily . So if the movement is tight just work it for a while and it will be supper smooth. So even if the filament swells in the throat from heat and back pressure it shouldn't stick and still move into the nozzle.

Edited 1 time(s). Last edit at 08/07/2016 02:20PM by lockezio.
Re: Why PTFE lined throat instead of metal throat?
August 09, 2016 12:59PM
Aww, shit...

These PTFE lined tubes are fragile! angry smiley
Broke the throat when tightening it.

-> to eBays! again... This time maybe few more tubes?
Re: Why PTFE lined throat instead of metal throat?
October 18, 2017 06:50PM
The PTFE lining will melt at 280 C. The problems this will cause are plenty and hard to find. As I found out on my TEVO Little Monster when I got a filament jam that took a month to recover from. Basically, I had a jam and in the process of clearing it up did a lot of cold pulls and did clear out the nozzle and heat-break What I did not know was that the original controller (MKS-SBASE) temperature channels were failing and the temperature it was reading was 25 to 40 C below actual temp. I also assumed that since it was advertised as capable of extruding to 300 C, it was an all metal hot end.

In the process of trying to get it working I set a temperature of 260 C (actual was probably 285 to 305 C), which melted the PTFE and got it into the nozzle. From what I could tell it coated the walls with thin wisps of teflon that kept peeling off and blocking the nozzle at random times. Could not get the printer working for a month because it kept getting blocked and other parts of the TEVO were failing because of the frequent filament blocks. I was only able to extrude ABS at 265 C or higher (probably because it was softening the PTFE). It was impossible to clear it out with cold pulls because the PTFE let the plastic plug slide past it.

I only cleared it out by heating the nozzle with a hot air blower and using a 1.95 mm bit by hand to pull all the plastic out, then soaking the bit in MEK to dissolve all the remaining plastic and using the drill bit to pass along the walls to make sure all of it is out. When I found some white wisps of plastic in the MEK I realized what happened must have happened. Since then the printer works and extrudes without a problem.

I have since switched to an all metal heat-break to avoid this issue if the controller or the thermistor fail and cause a temp hike.
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