What happens to the temperature inside your nozzle?
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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).
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Great work. Since I joined the Duet community at the start of the year I have learned so much. But I always felt like there were chunks of information missing.
The point of "we know what makes a print work, and we use it, but we might not know why it works" comment is so true. Seeing unexpected results comes from these chunks of missing information.
I have been using A2 machine steel nozzles exclusively for over a year. Not because I print with abrasive materials, but because I figured they were more durable, and I could replace them less. I never really put temperature into the equation. I knew that hardened steel is less heat conductive, and I have tended to use higher temperatures because of this. But seeing your results as certainly opened my eyes wide, and I am going to go back to using high quality brass nozzles.
But on top of that, it makes me think greatly about the impact of cooling near the nozzle. Maybe the cooling ducts that are popular are thought to be great, but over doing their job and causing heat loss in unexpected ways.
It opens up a new direction of thought when thinking of some of the consistency issues I have been having.
CR10S, August 2018
Anycubic Photon S December 2019
Ender 5 Feb 2020
Ender 5 Plus May 2020
Anycubic Photon Mono X Nov 2020
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https://3dimensiongames.com/ -
These nozzles allows to measure and/or stabilize the temperature closer to the tip.
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@RyanP said in What happens to the temperature inside your nozzle?:
................ But seeing your results as certainly opened my eyes wide, and I am going to go back to using high quality brass nozzles.
It was never my intention to put people off using hardened steel nozzles. They still have their place - with certain filament types, I'd say they are essential. But just be aware of what part cooling air might do to the filament temperature. It may be that you can still print that part which needs to be made from an abrasive material, without any part cooling?
But on top of that, it makes me think greatly about the impact of cooling near the nozzle. Maybe the cooling ducts that are popular are thought to be great, but over doing their job and causing heat loss in unexpected ways.
Exactly so. In my opinion, it is impossible to blow cooling air over a part that is being printed a fraction of a mm below the nozzle, without some of that air passing over the nozzle itself - either directly from the fan ducts, or indirectly by being deflected back from the part being printed. What might come close would be a sort of reverse Berd air system - a small annular tube around and close to the nozzle, but with holes pointing away from the nozzle.
It opens up a new direction of thought when thinking of some of the consistency issues I have been having.
That's great. I wonder too how many people have been suffering with what appear to be extruder issues (grinding filament, missed steps etc) which happen to coincide with switching to a metal nozzle?
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@ All. For info - I'll shortly be running those tests again with a home made silicone "sock" around the nozzle. And I'll be detailing a very cheap and quick method to make such a sock.
I'm calling it a "nozzle trainer sock". A sock (as in item of clothing) covers the foot and ankle, but here in the UK, one can buy "trainer" socks, which cover just the foot but not the ankle. This sock covers the nozzle but not the hot block - hence "nozzle trainer sock".
I'll do another blog post and put a link on this forum in the next couple of days or so.
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Certainly I never took your test or your post as a slag on metal/steel nozzles, simply realizing that I am not necessarily using the best nozzle for my current printing needs.
When I first got into 3D printing with my Creality CR10S, I frequented its reddit sub. Over time the answer being shared around bothered me because every problem can't be "under extrusion".
Since I converted my now three printers two Duet board and started participating in this forum, I have learned so much, especially volumetric flow rates and their place in printing. Focusing on nozzle pressure made so much sense to me.
With this information that you have provided compliments that info. I still don't know exactly how the correlate, but if a certain amount of volume pressure in the nozzle is needed to maintain the quality of print, then exact nozzle temperature would need to be a highlighted aspect of that.
@zapta These nozzles look great. I will certainly look into these.
