Friday, August 17, 2012
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.