Melting PEEK?

[jesse]

There was some brown goo on my hot end beneath the PEEK.

It smelled sort of like burnt root beer but with plastic. It didn't smell like normal ABS.

Is this a sign of melting PEEK? I had the temperature up to 260 C for a short while to try to clear out a jam.

[img]http://i.imgur.com/KEiB19G.jpg[/img]

[Flateric]

Do not go to 260 you will melt the peek. Trust me on this one, that is well into the melt peek zone!

[cambo3d]

Do not go to 260 you will melt the peek. Trust me on this one, that is well into the melt peek zone!

that's interesting because I thought peek melt temperature was higher http://en.wikipedia.org/wiki/PEEK. there's is a glass transistion temperature also maybe this is the temperature where it starts to get soft?

Looking at the wiki page for j heads, it says peek starts melting at 248 degrees celcius. http://www.reprap.org/wiki/Materials

according to this I probably woudn't go above 240 or maybe even 230 degrees to give you room for error.

[Eaglezsoar]

Do not go to 260 you will melt the peek. Trust me on this one, that is well into the melt peek zone!

that's interesting because I thought peek melt temperature was higher http://en.wikipedia.org/wiki/PEEK. there's is a glass transistion temperature also maybe this is the temperature where it starts to get soft?

Looking at the wiki page for j heads, it says peek starts melting at 248 degrees celcius. http://www.reprap.org/wiki/Materials

according to this I probably woudn't go above 240 or maybe even 230 degrees to give you room for error.

Cambo3d and Flateric are both correct. The numbers Cambo3d gave are right on. There are users on this forum who state that they run at 260 and I guarantee they don't run for long at that temperature. I think
one of the future designs we will see a lot will be to replace the Peek with stainless. I'm surprised that more vendors haven't done this. Perhaps the cost factor? The other problem is the PTFE tubing inside the Hotend,
McMaster Carr indicates that the tubing they sell has a max temperature of 500F, again 260C. So the Hotends of the future needs to also replace the PTFE with a more durable material probably stainless or other metal
tubes.

[Polygonhell]

I agree with the above you don't have to be much above 250 to damage the Hotend.

A word of warning on temperatures posted by people, you should always assume they are approximate, they are almost always what the thermistor is reporting and that is heavily dependent on it's exact mounting and because of the low thermal mass of the Al how they cool their hot ends.
The only accurate way to measure temperature is to put a thermocouple in the nozzle, almost no one does this when they calibrate, so almost no one knows how accurate the thermistor is or isn't.

As a case in point I wrapped the heater block of my Hotend in silicon tape, to prevent the rather large cooling fan I was using from cooling it excessively, anecdotally I'd say my Hotend is now 10 degrees hotter for the same thermistor reading (based in plastic extrusion temperatures) most likely because the outside of the Al block where the thermistor is located now cools slower.

[mhackney]

That's a great point and good tip Polygonhell. I use a little thermal paste (Omegatherm 201) on my thermistor, wrap the hotend in Kapton tape to insulate it, and calibrate with a thermocouple down the barrel of the hotend and in contact with the nozzle. I think that is about as good as you can do!

cheers,
Michael

[cambo3d]

The only accurate way to measure temperature is to put a thermocouple in the nozzle, almost no one does this when they calibrate, so almost no one knows how accurate the thermistor is or isn't.

I planned to do this in order to see what temperature difference there was and adjust firmware/software as needed. use of the second hole in the hotend for a thermocouple could come in handy.

I bought this one from amazon http://www.amprobe.com/amprobe/usen/HVA ... ?PID=73400 it has two thermocouple inputs. maybe use one for heatbed and one for the hotend, maybe permanently mount the thermocouple, if you wanted to.

[Polygonhell]

The only accurate way to measure temperature is to put a thermocouple in the nozzle, almost no one does this when they calibrate, so almost no one knows how accurate the thermistor is or isn't.

I planned to do this in order to see what temperature difference there was and adjust firmware/software as needed. use of the second hole in the hotend for a thermocouple could come in handy.

I bought this one from amazon http://www.amprobe.com/amprobe/usen/HVA ... ?PID=73400 it has two thermocouple inputs. maybe use one for heatbed and one for the hotend, maybe permanently mount the thermocouple, if you wanted to.

There is a second hole in the Al heater block and I've checked that with a thermocouple, all it tells you is if the thermistor is calibrated against it's spec sheet, unfotunately it doesn't tell you what the temperature difference between the location of the thermistor and various other parts of the hotend are.
If the heater were brass it would heat slower, but the thermistor temperature would probably be closer to actual because of the relatively large thermal mass, but Al cools so quickly, the difference in the distances between the resistors, the brass hotend and the thermistor will have some impact.