What happens to the temperature inside your nozzle?
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@zapta said in What happens to the temperature inside your nozzle?:
I would think that the thermal mass will affect transitions but for the steady state the heater will need more energy to compensate for the energy loses from the deflected air cooling.
I think you need to look again at the results https://somei3deas.wordpress.com/2020/05/21/the-effect-of-deflected-part-cooling-air-on-brass-and-steel-nozzle-temperatures/
With regard to your assumption, the important thing to note is that, after the fans were turned on and after the initial temperature drop of the hot block, it very quickly recovered. So the control system reacted to the temperature drop and adjusted the PWM value accordingly. If the heater had insufficient power, then the control system would go to 100% PWM (fully on) but the temperature would not recover to the set point.
But there are far too many variables to assume that would be the case for every hot end. The surface area of the hot block, the amount of air flowing over that area, and the size (wattage) of the heater would all play a part. But it's easy to check if the heater is sufficiently powerful. Simply turn on the fans and see if the hot end temperature recovers to the set point. If it doesn't, then before compensating by fitting a more powerful heater, consider mitigating the problem by insulating the hot end (fit a silicone sock), or adjust the part cooling air flow (volume and/or direction).
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Hi @deckingman, I made a quick experiment on my printer, measuring the the effect of the material cooling fan and nearby bed on the PWM of the hotend, results are below.
Invariants: 200C, with silicon sock, brass nozzle, no filament, heatsink fan on. A picture of my setup is at the bottom here.
Variables: material fan on/off. Bed close/far from nozzle.
Measurement: average current to the heater, using a Uni-T DC clamp. This is a linear proxy of the PWM. With 100% PWM (during initial heating) the current is 1.23A which is ~30W at 24V. All measurements are in steady-state, not during transitions.
Results:
#1. fan off, bed far, 0.39A
#2. fan on, bed far, 0.55A
#3. fan on, bed close, 0.75A.Observation: Bringing the bed close to the nozzle ('deflecting'), increases the power by ~25%. This is to compensate for the extra cooling of the nozzle.
I would guess, based on your results, that with a steel nozzle, the #2 -> #3 power increase will be smaller due to the lower thermal conductivity fo the nozzle, which means that the tip of the nozzle will be cooler as you shown. This assumes that most of the deflected cooling is on the nozzle (?).
BTW, Aliexpress (Trianglabs) has this chart. It suggest that 'copper plated nozzle' is even better in this regard and the ruby is better than steel.
My setup:
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@zapta As I said, every hot end configuration and part cooling fan combination will behave differently but I guess you have answered your question about whether your heater will be sufficiently powerful for your particular set up (which it is).
A couple of observations if I may. I note that the ends of your heater cartridge are exposed (not covered by the sock). So much of the required increase in power may be due to cooling air being deflected over the heater cartridge ends, rather than purely as a result of being deflected over the nozzle tip.
I take anything published by Chinese cloners with a huge pinch of salt. What do they mean by "Copper Plated Nozzle"? Do they mean the base material is copper which is plated with something else, or do they mean the base material is something else which is plated with copper? They've quoted the thermal conductivity of copper but used a hardness value of medium steel. So it either has a hard coating with low thermal conductivity, or it has a soft(is) coating with higher conductivity. The specification shows the best of both but that can't be true in reality.
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Yes, that's correct, some of the deflected air heat loss is not from the nozzle. I don't have a steel nozzle to compare with the PWM with that of bronze.
@deckingman said in What happens to the temperature inside your nozzle?:
I take anything published by Chinese cloners with a huge pinch of salt. What do they mean by "Copper Plated Nozzle"
Copper coated by a harder material. The other way around wouldn't have much benefit. This is from Trianglelab. They know 3D printing.
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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?
