Heat Breaks on Tool Changers

[CrazyIvan]

Does anyone know how heat breaks are managed on printers that tool-change hot-ends as per INDX (rather than whole head units like the U1)?

The heat break is an essential element of FDM printing. It effectively creates a seal, stopping the pressurised molten filament in the nozzle backing up the filament feed path. If anyone doubts this, I refer you to the mess that results when the nozzle isn't screwed into the heater block / heat break tightly enough and the molten filament finds its way through the thread (some hot-end assemblies have the heat break and nozzle combined, to avoid that problem).

The heat break would get nearly as hot as the nozzle, and unable to do its job, if it were not actively cooled. The hot end therefore has a fan to do this, and budget printers also use the same fan for part cooling.

So, the tool head comprises (as a minimum) the nozzle, a heater, a temperature sensor, a heat break, and a fan. It may also include a part cooling fan, and the extruder assembly. (If the extruder is not on the tool head, it will be at the far end of the Bowden tube.)

The idea of INDX is to minimise the replication of parts required across multiple tool heads, reducing cost and complexity. It is therefore logical that a parked INDX tool, now divorced from the tool head, has the minimum parts – just those which handle the filament directly, ie the nozzle and heat break, and probably the heater block (although I think I've seen something about non-contact heating using induction).

I was about to say that surely the parked nozzles need cooling as well, to prevent the heat breaks getting heat-soaked, but I think I might have answered my own question: If the nozzle is heated by induction, it will have much less thermal mass than a heater block, so if there is also adequate thermal isolation between the nozzle and the heat break, perhaps (when parked and therefore not actively heated) it is sufficient for the heat break to rely on passive cooling.

[designforlife]

Heat break is thermal isolation, not a seal. Parked INDX tools likely rely on passive cooling. Low thermal mass allows fast cooldown.

[CrazyIvan]

Heat break is thermal isolation, not a seal.

Well they are a seal actually, in operation, otherwise the huge pressure of melted filament in the heated zone would back up (as it does if a nozzle isn't screwed up tightly enough). When the melt reaches the heat break, it solidifies and seals around the solid filament.

Parked INDX tools likely rely on passive cooling. Low thermal mass allows fast cooldown.

That's OK if they are cooling down when unused, but isn't INDX the one with induction heating, as mentioned above? Other tool-changers have a traditional heater block.