Tuesday, October 15, 2013

Does insulating the heater block make a difference?

I was interested to examine what difference insulating the hotend heater block would make to hotend performance. I used some Teflon sheet material [ptfe] (sandwich toasting bags!), cut it to shape and then secured it in place with some kapton tape. I've done this in the past as you'll see from this post, but I've never done a graphed comparison of "before" and "after" insulation.
Photo above showing J-Head hotend with newly insulated heater block.

For comparison purposes I dug out a graph of temperature (Deg C) and power (%) over time (minutes) which I had recorded for the same hotend without insulation, while heating to an arbutrary target of 220 Deg C. The J-head was fitted to the printer and both fans running, one under-carriage fan, and the print cooling fan. This graph is below, Temperature over Time in Red, and % power to heater in Green, no insulation on heater block for this graph.

After insulating the heater block I repeated the graphing of the heating process and the tick-over at 220 Deg C which I allowed to run for a few minutes. Graph below...
Comparison and possible benefits of insulation:
Less power required to maintain a given temperature. For my setup, the same target temperature was maintained with <40% power in comparison to approx 50% power for the uninsulated heater block. This is beneficial since having capacity to deliver more heat may enable faster extrusion.

Insulation protects the heater block from stray cooling air. If you are running a cooling fan on PLA then air may also spill over and cool the hotend. It has to reacts by increasing power to maintain temperature. Insulating the heated block reduces the impact of the work cooling fan on the hotend. There is less conflict or fighting between heating and cooling needs when the heater block is insulated.

Slightly faster time to target temperature for insulated heater block. Not significant.

Reduced convective heat once the heater block is insulated. This a very positive benefit as it reduces the risk of insulator temperature rise and hotend jams. It can reduce the risk of x-carriage warping also, where PLA x-carriages are used.

Reduced radiated heat. If you can insulate most of the base of the heater block then there will be less heat radiated toward the printed work. This is good when printing narrow or detailed pieces, and when printing slowly. Often, you slow down when printing fine detail. Cooling of the printed work is essential at this stage to prevent distortion so insulation preventing radiated heat is of benefit.

Technical Notes:
This comparison was conducted with a 30 Watt, 15mm x 6mm, 12v Cartridge Heater in a J-Head Mk V hotend. The controller uses PWM, and PID control cuts in within 10 Deg of target temperature.
PID was retuned and new values set in the Marlin firmware following the insulation of the hotend heater block.
The temperature graphs are automatically plotted by Repetier Host software.
Both graphs were plotted while the printer was static (not printing).

Conclusions:
You could use a variety of materials to do this insulation, including silicon tape or glass tape, to potentially even better effect. It is a bit tedious a process but well worth considering.

There was no comparison made between print quality from an uninsulated versus insulated heater block. The advantages of an insulated heater block are more interms of increased power efficiency, more precision of temperature control, and reduced risk of hotend jamming, rather than print quality increase.

It would be interesting to see others publish such graphs for their printers so comparisons could be made between systems. It would also be good to see hot-end manufactures supply hotends pre-assembled and insulated (like Nophead), or at lease with some suitable and easy to apply insulation material included in hotend kits. I would see this as a selling advantage, even if at a marginal additional cost to the consumer.

Thanks for viewing!
NumberSix

6 comments:

  1. I have been using Makergear hotends forever, and it's standard practise for them to be insulated with a cool [sic] stretchy rubber coated fiberglass insulation. See http://www.makergear.com/products/plastruder-replacement-parts

    ReplyDelete
  2. Thanks Len. That's another good insulation example.

    ReplyDelete
  3. My two penneth ...
    Since Nophead added a self-amalgamating silicone tape 'wrap' to insulate the heater block, his Mendel90 kit builders have been recommended to use 185C as a starting point for Faberdashery PLA compared to the 220C figure which was recommended previously.
    If I understand things correctly, (and happy to be contradicted), this is because at a 185C extrusion temperature, the filament at the upper end of the JHead is 'solid' and able to provide more 'push' to the filament compared to the situation with an uninsulated block. Without the insulation and because of convected heat softening the filament at the top of the JHead, the PLA at this point imparts less force on the melted PLA. This gives rise to the requirement for a more fluid PLA at the business end, that is a 220C extrusion temperature.
    I have yet to try my M90 kit with silicone tape but I can confirm that for the last 11 months or so, I have been using 220C for PLA on an uninsulated JHead Mk5b.
    I've been getting good results by the way! However, I am about to add some silicone tape to insulate the heater block and can't wait to see if using 185C will (a) work and (b) improve what are already good looking M90 prints.

    Alan

    ReplyDelete
  4. Hi Alan,
    Thanks for chiming in. Always welcome.
    185 Deg C seems to be an established guideline temperature for extruding PLA but you might typically increase this if increasing print speeds to have a more fluid plastic I suppose, but this may be as much as providing a heat buffer to compensate for heat loss as plastic flows through more quickly. Different colours also seem to require slightly different temperatures to get the same flow consistency.

    The loss of ‘push’ due to filament softening in the upper filament path could lead to poorer print quality due to less sharp retraction between non-printing head movements. I might expect to see greater retraction and restart cycles in a printer where the upper part is allowed to get hotter, i.e. no active cooling or insulation on heater block. The sharp suck and prime behaviour would be diminished by a softened piston (the filament just above the melt zone). I can’t see how increasing the hot-end target temperature to 220 Deg C could compensate for this situation. If anything it would make things worse by making the plastic more fluid. I’m unclear why Nophead found 220 to work better.

    There are both conductive and convective effects at play in the hot-end as a unit, but Nophead’s key finding is that the primary transmitter of heat to the upper portion of a hot-end is convective heat rather than conductive heat, which he confirmed a long time back by running a hot-end sideways and observing temperatures along the length of the hot-end. This is at least in the J-Head case where the upper parts are made of poor conductors (PTFE and PEEK).

    I did notice that in the new M90 documentation, the Village Green PLA is now happy at 185 Deg C (p76) as against 220 Deg C in the previous revision (p74). :-) I'm wondering if this has more to do with the new silicon insulation keeping heat in the heater block, than anything else. Although I'm sure it is also preventing convective heat.

    The experiments documented in this post didn’t examine print quality vs insulated heater block, so I’d be interested in any print quality observations you may make after you fit the “self-amalgamating silicone tape”.

    I still recommend active cooling of the J-Head PEEK insulator, as well as insulating the heater block, for a full ‘belt and braces’ approach to jam prevention and efficient hot-end operation.
    NumberSix

    ReplyDelete
  5. Hi - its worth noting that Nophead also added a small hole in the main extruder fan. This hole provides airflow over the PEEK part of the JHead. while you typically would not have this fan on during the first layer of a print, you would also typically be printing slower so less likely to have issues with filament sticking due to the PEEK part being too hot. The combination of insulation and the small hole is enough to make PLA print fine - I have taken off the PEEK cooling fan on the printer I had fitted it on now.

    ReplyDelete
  6. Hi Tony,
    Thanks for your input, and highlighting Nopheads enhancement to the fan duct that surrounds the heater block (the small hole). I certainly agree that the smallest of air flow will disrupt the hot air and help keep things cool. My one concern is that without active cooling, there is a dependency on a cooling mechanism that has a different purpose. Also, when printing ABS the “Work Fan” is typically used a lot less, and the working temperatures of the extruder will be even higher, leading to a greater risk of too high a temperature rise in the upper section of the hot-end.
    I respect your perspective that there isn’t a need for active cooling of the PEEK insulator on the j-head, but it might be valuable to have more analysis and data on this sub-topic amongst the group (RepRappers). I’m happier to run active cooling on the insulator (PEEK), i.e. a second fan, always on.
    Thanks again for your input.
    NumberSix

    ReplyDelete