Going back to my Spare Parts Printer, I was really surprised at the anemic fans put on a Creality CR-3/CR-10 hot end (I was using a genuine cooling shroud originally) and I wanted to really understand how necessary a high flow fan is in regards to keeping the overall heat sink temperature down (with a focus on the top of the heat sink).
So, I created a simple mount for the Creality CR-3/CR-10 hot end with a small (30mm) fan to test its operation. I put the fan on a PWM control rather than on the basic 24V always on so I could control it on or off. The mount is printed in ABS and has a 40mm blower installed because of the other side of the hot end was open to minimize printing time and I expected that in a printer, this side would have a nozzle cooling fan/blower.
I should point out that I’ve been amazed at people who have designed 3D printed hot end holders and used materials like ABS and PETG. It honestly didn’t seem reasonable to me as I would expect things to get hot enough to melt the mount.
The CR-3/CR-10 has a Mk 8 nozzle, a 40W cartridge (with 100k NTC thermistor) and I took out the interior PTFE tube and the M10 PTFE tube lock. I did leave on the silicone rubber insulator with the idea that if heat was going to escape, I wanted it to go up towards the heat sink, rather than out into the open air. This is really the worst case scenario as I continually read that the filament inside the PTFE tube inside the heat sink absorbs heat within the heat sink and passes it to the heater block/nozzle.
Too measure the temperature, I used my 64x64 sensor thermal imaging camera and tried to get the target point (the cross hairs in the middle of the image) on the heat sink itself.
With everything at ambient, the thermal view looks like:
No surprises, everything is at roughly the same temperature.
I next set the heater to 100C and waited for things to warm up.
After one minute:
After five minutes:
After seven minutes:
In this series of images, you can very clearly see the heat sink temperature rising up into the heat sink (as would be expected).
Next, I turned on the fan while keeping the nozzle temperature at 100C.
After 2 minutes:
After 7 minutes:
After 20 minutes (I got a call that interrupted me):
Note that the heat sink temperature drops over time while the maximum temperature (which is noted with the square box) remains constant.
I then ran the nozzle temperature up to 150C and checked the heat sink temperature.
After 5 minutes:
and after 10 minutes:
There is a bit of a rise in the heat sink temperature but its much lower than the worst case where the fan was off.
Next, was at 200C.
After 2 Minutes:
After 5 Minutes:
You can see that there’s definite heat creep up the heat sink. When I put my finger to the heat sink itself, it felt cool to the touch, it seems like the heat was coming from the central pillar of the heatsink and does not extend out to the fins.
Finally, I put the temperature up to 250C.
At 5 minutes:
I ended the experiment here with the nozzle heater set to 0C and the fan left running.
After a couple of minutes:
A few things I would do if I were to repeat this experiment:
- Mount the thermal camera on a tripod so I am always looking at the same spot on the heat sink.
- Use a thermal touch sensor to validate what my uncalibrated fingers are telling me about the temperature of the fins.
- Repeat the experiment with one of my 3D printers with a commercial heat sink fan/duct work.
Regardless, I think this was a useful experiment and I may want to repeat it with filament running through the hot end.
My conclusions from this experiment are:
- A fan is necessary to keep the hot end’s heat sink at a reasonable temperature.
1.1. I should probably move the fan downwards by 5mm or so - most of the air coming from the top of the fan’s annulus is blowing against the top of the heat sink and not through the fins lower down on the body of the heat sink - I suspect that much of the airflow is wasted and could provide more efficient cooling.
- The heat sink fan can be very modest.
2.1. I should point out that the heat sink had 5mm of free space around it with nothing impeding or directing the airflow.
- The heat sink temperature measurement/image from my thermal camera seems to be dominated by the central pillar of the heat sink.
3.1. I’m noting this because it’s important to keep the temperature of the filament in the PTFE tube in the heat sink at a reasonable temperature so the hot end doesn’t get clogged.
- It’s very reasonable to design a hot end holder out of ABS/PETG and maybe even PLA as long as there is a fan ensuring that it keeps cool.
- After printing, keep the heat sink fan running until the hot end is under 50C. This is to minimize problems due to heat creep.
5.1. Looking at the heat progression with the fan off, I would think that there could be an issue here if power was shut off with a hot end at 200C or more - but with making sure the temperature goes below the melting point of any filament, that shouldn’t be an issue.
Comments from anybody?