Sunday, May 15, 2011

Extruder heater with stainless steel tube...

I wanted to quickly test Nophead's comment in the previous post, that a stainless steel feeder tube to the heater might result in less heat conductivity away from the heater block, allowing the block to more easily reach a desired target temperature. This, as he suggests might be more successful due to stainless steel being a poorer conductor of heat than aluminium.

To test I took a 6mm stainless 'bolt'. It's actually another leftover element of the salvaged bearings from an old set of Rollerblades. I cut one end off and threaded it (M6 die), removed the aluminium tube and fitted the stainless one.

I then inserted the new tube into the heatsink passing through three vanes, giving sufficient contact for this test. I switched on the heater and observed what happened.
Without the fan running this was the result, with a target temperature of 200Deg C set in RepSnapper.
The heatsink was touch warm, but not hot which was an amazing difference in comparison to when the aluminium tube was used. With the aluminium tube you wouldn't keep your finger on the heatsink if the fan wasn't running. With the stainless tube and the fan running on the heatsink the max temperature I recorded was 178Deg C (readings from RepSnapper).

Note: I don't have any special temperature reading equipment. All the readings were taken from RepSnapper and are for relative comparison rather than specific calibrated temperature feedback purposes.

Conclusion: This was a satisfactory outcome, indicating the potential of a stainless shaft to be more effective as a structural connector between a cold-end mounted heatsink and the heater block (hot-end).

Deduction: This approach to extruder design would eliminate the need for more complex supporting side rods or PEEK T-bars. I will still entertain the idea of a PTFE liner inside the stainless tube.

Observing that some PLA that was on the nozzle had melted completely suggests to me that actual temperature on or near the nozzle may have been much hotter than my by now loosely constructed resister/thermistor arrangement was telling RepSnapper!



Photo showing melted PLA on the nozzle, after RepSnapper showed a reading of 190Deg C, an uncalibrated reading.

Thanks for viewing!

6 comments:

  1. That was quick!

    I really like the idea of it being self-structural as using PEEK and bolts takes up quite a bit of space at the hot-end, but that is a very long time to get to temperature.

    Do you have any isolation (PTFE Tape?) between the SS tube and the Alu Heatsink to help stop all the heat getting dumped? Mind you that will allow the SS tube to get hotter so it may need to be shorter.

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  2. Hi Rich,
    It was my first time timing the heating process and I agree it is a long time. Prob a number of factors when I think about it. My heater block is too large I realise now, and my resistor has come loose. I'm going to cut a new heater block following the heater block dimensions found here: http://www.reprap.org/wiki/Geared_extruder_nozzle

    I will attempt a resistor/thermistor transplant! :-)

    I don't have any isolation between the SS tube and the heatsink. In fact I want good contact there. I want the heatsink to keep the tube cool. The problem I was having with the aluminium was the heatsink was keeping it cool alright, but the aluminium tube was such a good it was sucking heat out of the heater block faster than the resistor could heat it.

    If I insulate where the tube attaches to the cold-end I might as well go back to inserting it to PEEK/PTFE type design.

    I'm after a single something that's structurally strong (no additional supports needed) but also a poor-ish conductor of heat. Open to suggestions! :-).

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  3. How about wood (oak?) wrapped in fibreglass tape /mesh (at the hot-end contact point) and maybe Copper or Aluminium on the outside if needed?

    When I run my machine again I will take some temperature readings of the PEEK support block and PEEK (PTFE lined) tube for reference, but I know the now thin PEEK tube is warm to the touch (under 50 degrees C, I guess).

    For reference, my set-up takes under 2 mins to fully heat up to 193 degrees C
    My resistor block is slightly smaller mass than the Geared extruder nozzle with a 6.8R resistor (12v supply)

    The PEEK support is reasonable mechanical solution and I'm now sure that I could make it much smaller sized now. The thinner PEEK+PTFE tube is also working well under vertical compression (no leaks yet), but it is tricky to make.

    I always wanted to try Ceramic for the mechanical support, but I can't see a better solution than PEEK+PTFE tube for the transition zone at the moment.
    I think Vic was going to try Bamboo and PTFE tube, that's worth trying.

    There is a very long Forum post about using Glass for both the nozzle and transition zone, I'm not sure is was ever proved to work constantly.

    And good luck with the transplant.

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  4. Hi Rich,
    I'm making a new smaller heater block and will test it's heating time while connected to the heatsink. If I don't have enough power in the resistor-heator for that set-up I'll probably revert to the more conventional RepRap design of insulated material supporting the hot-end. I've seen bamboo in some other post and tested it at the weekend. It's an excellent natural insulator (should post that test).
    I've PM'ed you more discussion points on RepRap Forum.
    Tks,
    No.6

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  5. this reminds me of lampmaker's all steel hot end on thingiverse:

    http://www.thingiverse.com/thing:3452

    he used a similar method of using a poor thermal conductor (steel) with a heat sink on top to help thermally insulate the pinch wheel mechanism from the hot end. i use a derivative, and it works great!

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  6. Hi Peter,
    Thanks for pointing that other all metal design out, and good to hear you got a derivative working also. I'm going to use an aluminium heatsink and aluminium heater block (resistor type heater). It's been coming together over over the past few evenings so I'm looking forward to seeing how well it works... or not! :-). I'll do a blog update soon.
    No.6

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