Friday, August 17, 2012

Initial testing of a thermally fused concept nozzle.


I finished machining a concept nozzle for the J-Head Mk VI-B this evening.  Since some people have had the PEEK nozzle holder melt after the hot-end exceeded 248 degrees Celsius, for one reason or another, I decided to try a hot-end with a thermal fuse wired in series with the heater resistor.

For this purpose, thermal fuses were purchased with a "Rated Functioning Temperature" of 240 degrees.  Unfortunately, I didn't realize that 240 degrees was the upper temperature limit and that the "Holding Temperature" was really 200 degrees and that is the temperature, above which, the circuit is broken.



In order to test the thermal fuse concept, the hot-end was suspended, from the ceiling, and hooked up to a Sanguinololu board.  At 185 degrees, the fuse holds fine.  When the temperature was set to 230 degrees, however, the hot-end didn't quite reach 210 degrees before it started to cool.  The thermal fuse opened up and shut the heater resistor down as it was supposed to do.

I am planning on mounting it in a printer and testing it with PLA in the near future.  However, until a higher temperature thermal fuse is available, it clearly would not be able to print ABS unless the heater resistor is wired without the thermal fuse.

As it appears that the thermal fuse manufacturer is testing thermal fuses, with "Holding Temperatures" up to 230 degrees, maybe this concept will be more useful at some point in the future.

10 comments:

  1. Hi Brian,
    I run your hot ends up to 255C with maybe up to 5C initial overshoot, no sign of anything melting. Where does 248C come from?

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    Replies
    1. Hello,

      McMaster has PEEK listed with a temperature range of -20 degrees F to 480 degrees F (248.9 degrees C). While I haven't melted one myself, I've had customers report that the nozzle pushed out at 250 degrees. Since some PEEK manufacturers don't specify and exact high temperatures, I'd rather err on the side of caution and specify 248 degrees.

      I have a suspicion that the exact high temperature could vary slightly from manufacturer to manufacturer. PEEK, from different manufacturers does vary slightly and machines a little differently.

      Regards,

      Brian

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    2. I think the main problem is some of the thermistor tables are wildly out. I picked the Epcos 100K table in Marlin and it was +30C.

      I do worry about the resistor you supply though as that is only rated for 250C and it gets hotter than the brass. Have you had any failures?

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    3. Hello,

      I have not been aware of any recent failures of the resistor at this time. I do remember one being reported and it was mentioned that the resistor was a little loose in the hole.

      Regards,

      Brian

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  2. Hi Brian,
    Were the failures with the J-head Mk V specifically or also with the older J-head Mk IV?
    Did you note whether those with failures had fans running on the PEEK or not?
    Regards,

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    Replies
    1. Hello,

      This sort of failure occurs with all hot-ends that use PEEK and not necessarily J-Heads alone. I did not note whether a fan was used.

      In one case, however, a customer reported that his hot-end melted and that the filament vendor specified a high temperature of 250 degrees. So, he set his hot-end to 250 degrees and the brass nozzle came right out.

      Regards,

      Brian

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  3. I was running mine on temps like 270C slightly colour changes but none melting, so I think it peek manufacturer problem )

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  4. When you said "At 285 degrees, the fuse holds fine." Did you mean to say "At 185 degrees, the fuse holds fine."? Or am I missing something?

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    Replies
    1. Hello,

      I meant 185 degrees. Thanks for catching that. I just updated the blog entry to 185.

      Regards,

      Brian

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  5. Nice to see the result of the testing.
    To inform the 'crowd', I had a discussion with Brian, but not related to a meltdown of a J-Head if there was a way to protect it against a sudden overheating by $failure. This resulted in this test.
    So one can say ( as I do ) here is someone who not only innovates, but has a keen eye on customer-demand.

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