What happens to the temperature inside your nozzle?
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@zapta said in What happens to the temperature inside your nozzle?:
Copper coated by a harder material.
In which case, their claimed thermal conductivity is false.
This is from Trianglelab. They know 3D printing.
That's the funniest thing I've heard in a long time
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Interesting test. A couple of questions/thoughts. Did you take any steps to ensure that the sensor made good thermal contact with the material of the nozzle and that the same thermal contact was maintained for the different nozzles? Is the nozzle open to the air at the tip (and if it is what happens if you block it)? If the nozzle is open it could be that there is airflow through the nozzle (or even just inside the tip of the nozzle) that may be cooling the sensor/inner walls of the nozzle tip. If any direct air cooling like this is taking place it could be that it varies depending upon exact nozzle shape and/or the position of the sensor and wiring withing the nozzle.
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@gloomyandy I'm reasonable confident that the nozzle tip was in contact with the metal sides of the nozzle because of the way the temperature readings quickly changed as the fan was toggled between the off and on states. Had the probe tip been in free air, then I wouldn't have expected the readings to change as they did. The thermocouple protruded out of the hot block some 5 mm or so more than the length of the nozzle, so inserting the nozzle caused the wires to "buckle" and act a bit like a spring. But of course, I didn't have a camera inside the nozzle, nor do I have X ray eyes, so I can't be 100% certain.
Yes, the nozzle was empty and open. So it is possible that some deflected air could find it's way inside but bear in mind that it's only a 0.5mm diameter hole. But I think more important than air being blown into the nozzle, is that fact that (as I stated) in normal use, the nozzle would contain molten plastic rather than air (static or otherwise).
I was very careful about drawing conclusions. I think at best we can say that steel nozzles might be more susceptible to the quenching effect of part cooling air than brass nozzles. I have thought about fitting a thermocouple through the side of a nozzle, then one could measure the temperature of the actual filament inside. The problem for me is that the steel nozzles are made from Vanadium tool steel which is as hard, if not more hard, than any drills that I have.
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I wonder if filling the nozzle with thermal paste might help in both cases and also act as a filament substitute? Obviously it will not be flowing like molten plastic, but it might improve the thermal contact and will also prevent any airflow?
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@gloomyandy said in What happens to the temperature inside your nozzle?:
I wonder if filling the nozzle with thermal paste might help in both cases and also act as a filament substitute? Obviously it will not be flowing like molten plastic, but it might improve the thermal contact and will also prevent any airflow?
That's a possibility. I do have some Boron Nitride paste which I'm lead to believe is good thermal conductor but a poor electrical conductor. It sets hard and will be bugger to remove but in the interest of science.....
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Ouch, setting hard sounds bad! I'd hate you to ruin the thermocouple or the nozzles! I was thinking more of the heatsink compound used on PC heatsinks, which I don't think sets hard (but I have no idea if that can be used at the temperatures we are talking about here!).
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@gloomyandy said in What happens to the temperature inside your nozzle?:
Ouch, setting hard sounds bad! I'd hate you to ruin the thermocouple or the nozzles! I was thinking more of the heatsink compound used on PC heatsinks, which I don't think sets hard (but I have no idea if that can be used at the temperatures we are talking about here!).
I've got some of that too but I'm not sure if it's good for 200 degC. I also have copper grease which do know is good for those temperatures. I'm just not sure what happens to a bare wire t/couple if you cover it with thermal paste or copper grease though. Only one way to find out I guess (at least it'll clean off).......
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Thinking about it some more, I don't like idea of packing a nozzle with thermal grease of any sort. The main reason being that in general, filaments are poor thermal conductors. So if the grease/compound did make any difference, it still wouldn't be a fair representation of the true nozzle temperature when filament is loaded. But I'm sure I can find a way to block off the 0.5mm hole in the end.
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@deckingman said in What happens to the temperature inside your nozzle?:
bare wire t/couple if you cover it with thermal paste or copper grease though
if the copper grease is enough coppery to be conductive I suspect it'd mess up the readings. iirc the thermocouple works by the two dissimilar metals creating a tiny (temperature dependent) voltage potential at the junction where they're welded together; copper shorting out the two wires before the welded junction may add to the effect? idk, its all theory.
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@bearer similar thought process going on here...
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@deckingman I was measuring temp drop with the thermal camera and got "similar" results, but I was more interested in the temperature of the filament exiting nozzle so I concentrated on that (with ABS and aluminium nozzle the exit temp was ~8-12C lower then the heater temp - no fans). I did never came to useful conclusions that help in print quality difference so never revisited it. One thing from that time that I remember that might be interesting
I have no way to fit a thermocouple inside a nozzle which already has filament loaded.
I was thinking about this one and I actually found a solution that I never implemented at the end of the day but still might be interesting. We know that any two different metals will create a thermocouple. The probes we normally use are just selections of metals that give "more" and "linear" but any 2 will do. I tested following. The standard k-type is chromel-alumel wire, I cut a piece of the wire (I tried both chromel and alumel) and I weld it to the tip of the aluminium nozzle using battery of capacitors (around 1F 12V IIRC but maybe less voltage I don't remember.. one lead to aluminium nozzle other lead to the wire, touch wire near the tip of the nozzle and wire fuses to the nozzle). Measuring voltage now between aluminium and chromel or alumel wire gives temperature. I'm pretty sure this would also work both with brass and vanadium nozzles. The important thing is to not go too near the nozzle tip to not damage the hole itself.
There are two issues here that needs to be solved
- you need to connect to the nozzle with same/similar metal wire and get that to the "cold" joint position where you are measuring temperature. Aluminium wire is easy to get, brass nozzle I assume can work with copper wire but I'm not sure about vanadium wire
- some calibration temp table would have to be made by comparing reading from this "unknown" thermocouple and a known sensor put inside the nozzle
After those two are solved this could be used for super precise measurement of the tip temperature. My idea was to implement that but I never did.
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Not directly related to air flow, but this paper may be of interest:
https://link.springer.com/epdf/10.1007/s40964-019-00107-4
A friend of our hackerspace is co-author (he is a teacher in a engineer school fablab).
BTW, I use nozzle for Triangle Lab, which is drilled, and my thermistor is in this hole, nearly at the end of the nozzle:
https://fr.aliexpress.com/item/32843524186.html
I have silicone insulator around that portion, so almost no surface of the nozzle is exposed to air flow.
That way, the regulation is not done on the heat block, but on the nozzle itself. -
@deckingman think you have to stuff some filament through with the thermocouple tip drilled into the side of the nozzle so its in the flow as close to the tip as your machinery can do it!
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@T3P3Tony said in What happens to the temperature inside your nozzle?:
@deckingman think you have to stuff some filament through with the thermocouple tip drilled into the side of the nozzle so its in the flow as close to the tip as your machinery can do it!
Agreed - in an ideal world. But as I've said before, the steel nozzle I have is Vanadium tool steel, so it's harder than any drill bits that I possess.
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Ok everyone @deckingman is looking for some diamond tipped miniature drill bits, for science!
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drilling one brass and one "regular hardened steel" nozzle (not vanadium) might give enough data for conclusions?
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@T3P3Tony said in What happens to the temperature inside your nozzle?:
Ok everyone @deckingman is looking for some diamond tipped miniature drill bits, for science!
Or EDM
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...........Or alternatively, one of the multitude of nozzle\hot end\silicone sock manufacturers who happily relieve us of our hard earned cash, could pick up the batten and do the tests. I'm just a pensioner scratching about in his garage with very limited resources and getting bugger all in return.
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@deckingman said in What happens to the temperature inside your nozzle?:
Thinking about it some more, I don't like idea of packing a nozzle with thermal grease of any sort. The main reason being that in general, filaments are poor thermal conductors. So if the grease/compound did make any difference, it still wouldn't be a fair representation of the true nozzle temperature when filament is loaded. But I'm sure I can find a way to block off the 0.5mm hole in the end.
I absolutely agree with this. In fact, the thermocouple or thermistor itself has different thermal characteristics than any filament... but there's simply no other way to get a reading.
As an alternative to filament, what about a LOW temperature silicone? It might be the closest you'd be able to get to the thermal characteristics of molten plastic, yet still be easy to work with (and clean up) once it's cool.
Of course, even those results would be missing the variable of cold filament moving into the melt chamber, absorbing heat from the hot block and melting, and then the molten filament extruded (along with a significant amount of heat energy.) (Typing that last line, I'm reminded of how a HVAC heat exchanger works...)
Perhaps it'd be better to test the temperature of the filament actually being extruded instead of the nozzle temp? Afterall, the temperature of the block and even the nozzle is less important than the temperature of the molten filament. Would it be physically possible to test the filament as it's exiting the nozzle, but before the ambient air has had a chance to cool it? Is there any instrument that can measure a 0.5mm area without obstructing it?
To be fair, I don't think there's a really viable way to test this fully. As mentioned very early in the thread, your tests offer clues, but we might never really understand what's going on.
Personally, I love these kinds of threads, because they remind me of everything I don't know and make me question everything I think I do.
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@garyd9 said in What happens to the temperature inside your nozzle?:
Perhaps it'd be better to test the temperature of the filament actually being extruded instead of the nozzle temp? Afterall, the temperature of the block and even the nozzle is less important than the temperature of the molten filament.
I'd go as far as to say that the temperatures of the block and nozzle are completely irrelevant and that the only thing that matters is the temperature of the filament. In reality, until we find some other way to melt filament (and that comment could lead to whole new discussion), filament is heated by thermal transfer from the hot surfaces to which it is contact, so the hot block and nozzle temperatures will be close to that of the filament, but it's only the filament temperature that is important.
Would it be physically possible to test the filament as it's exiting the nozzle, but before the ambient air has had a chance to cool it? Is there any instrument that can measure a 0.5mm area without obstructing it?
I don't see why not. One would need a very small thermocouple. But a thermocouple is just formed by fusing the juntion of two different metals - I don't think there is any limit on the minimum size of those two metals. "Micro" temperature sensors probably exist (I don't have one laying around in my tool box though).
And of course to make life a bit easier, we could use a bigger nozzle - say 1.0 mm instead of just 0.5mm. But then having mentioned that fact, I can already see a whole new dimension to this testing - the effect of filament temperature as a function of nozzle diameter - which then leads to an investigation into the distribution of heat from the outer surface of the filament through to the core - and how this might be affected by different nozzle materials - all of which will be affected by filament flow rate through the nozzle - etc. There is enough there to form the basis of a higher education thesis I'd have thought
To be fair, I don't think there's a really viable way to test this fully. As mentioned very early in the thread, your tests offer clues, but we might never really understand what's going on.
Agreed. As I said in one of the opening statements of my blog. " In my opinion, it is not wise to assume that the temperature seen by the hot end thermistor is a true reflection of the temperature at the nozzle tip when there is some airflow passing over the nozzle". I think I have proven that statement to be true. I think also that I have shown that various nozzle materials react differently when subjected to some (inevitably) deflected part cooling air. But I haven't been able to demonstrate if this translates to a change in the temperature of filament, either inside the nozzle, or at the point of exit. We can still only guess (but maybe our guesses might be closer what truly happens, than they were before I did the tests).
