PTFE tube Air Injector / filament cooler for teflon bowden tubes

thingiverse

This is an air injector to achieve air flow through teflon (PTFE) bowden tubes for filament on 3D printers. It is designed to allow air flow only in direction of the extruder and not towards the filament roll. This is achieved by two factors: On the one hand the geometrical design inside of the air injector, and on the other hand by the use of different diameters of PTFE tubes. Towards the extruder you need to use a 3mm inner diameter/4mm outer diameter PTFE tube, and an 2mm inner / 4mm outer diameter PTFE tube towards the filament roll. The air injector is designed to be used with PC4-M10 pneumatic couplers for the PTFE tubes and also an M10 thread towards the air input hose connector. The PC4-M10 connectors to use are the ones where you can push the PTFE tube through (that is because the PTFE tube will be pushed into the air injector, to exactly center them and to allow hazzle-free filament loading). You only need 5-10cm PTFE tube with 2mm inner diameter to achieve sufficient air sealing towards filament roll. Because the PTFE tube with 2mm inner diameter also increases friction when filament is moving, take care if you want to apply long lenghts (for example coming from a filament dryer box). I would advice to add another coupler to go back to 3mm inner diameter after maybe 10cm towards filament roll for better filament movement inside the tube. Towards the 3D printer's extruder, you have to use a 3mm inner diameter PTFE tube (or larger), to allow sufficient air flow. In a setup as described above, I achieved about 1L/min air flow through a 50cm bowden tube, while filament is in there. The goal is to reduce filament temperature in the PTFE tube (e.g. for enclosed printers) and also to create some air flow into the top section of a direct extruder setup. Both aims at reducing the risk of heat creep and clogging and unwanted early filament softening. The most important thing to get that concept working is to have a good air pump that provides enough pressure (the more the better) and also sufficient air flow. I am using an Schego WS3 aquarium pump that provides 0.3 Bar (compared to cheap aliexpress ones with 0.15 - 0.2 Bar) and also about 5.8L/min (which actually is much more than needed at this pressure). The result is about 1L/min air flow through the tube, a filament temperature reduction of about 10-12°C at 60°C ambient temperature of the PTFE tube, and an air flow out of the end of the PTFE tube that can blow out a lighter flame at 15cm distance (while filament is inside the tube). This fast-flowing air out of the end of the PTFE tube can (additionally to the reduced filament temperature) help to blow at and reduce the temperature of the top section of the extruder. Besides the air pump you should also add an air dryer inline with the air feed hose, in my case I used some air tight plastic box and filled it with silica gel pads.This is to prevent moisture from the air to condensate on the filament, as you are using (slightly) pressurized air that expands at least when leaving the PTFE tube, but also already within the tube towars the end. You don't want water drops or moisture at your filament or in the extruder. I did not experience that issue, nevertheless it is a very good idea to have some silica gel to filter the air, as also some air pumps of worse quality than the one I used could also transport some oil drops or so together with the air. If you are using a good membrane pump that should not be an issue. Remember that the whole concept works better with higher pressure difference, so a weaker pump (especially in terms of pressure) will result in less performance of the cooling system. I measured an air outlet temperature of 47°C at 60°C ambient temperature around the PTFE tube (50cm length) and a filament temperature of 28°C at 45°C ambient temperature in the same setup. I measured about 1L/min air flow out of the end of the PTFE tube at an air pump pressure of 0.3 Bar (according to the pumps datasheet).