Unclogging the Hotend using the Cold Pull method

If you've got full or partial blockage in the hot zone of your hotend, the Cold Pull method is here to save the day.  It is an effective means of removing debris and residue from the inside of your hotend. This method is easy, reliable, and requires no disassembly of the printer.

Note: A cold pull clears blockages deep down inside the hot portion of the hotend. It is not useful (and cannot be performed) on hotends with blockages high up in the barrel "cold end" of your hotend.

-This guide applies to all three hotends used by Printrbot: Ceramic, Ubis13, and Ubis13s.

- Printrbot considers hot end tips as a "consumable" and recommends installing a replacement every 3-6 months when under heavy use, especially when abrasive filament is used.  i.e. carbon fiber

How the cold pull works:

  • Filament is allowed to cool inside the hotend, causing whatever debris may be inside the heated chamber and nozzle area to be encased within plastic filament.  The hotend is then heated and the filament is manually extracted from the hotend at the lowest possible temperature.  Because the plastic is still in a solid or semi-solid state when extracted, the debris comes out with the plastic.

coldPullExamples.jpg

Supplies:

  • Filament - BEST CHOICE: Taulman Nylon (because it's slippery, has a high melt temperature, and is somewhat transparent)
  • Filament - 2ND CHOICE: Clear PLA  (Clear filament helps you see impurities that are extracted, which is helpful to indicate if you're making progress.)
  • Filament - Any PLA

Detailed steps:

  1. Raise your Z axis to about 3cm above the bed.  This allows any excess extruded plastic room to accumulate on the bed instead of accumulating around the nozzle tip.
  2. Heat the hot end to 230C using the manual controls inside your software.  
  3. With your left hand, depress the extruder pinchwheel lever.  With your right hand, feed filament manually into the hotend as far as it will go.  If you only have a partial blockage you'll see filament come out of the nozzle tip, which is a great indicator that the hotend is completely full of plastic.  If you have a full blockage you probably won't see anything come out, so just press filament into the hotend as far as it will go. 
  4. Set the hotend temperature to 0c. 
  5. While the hotend cools, continue to push filament down into the nozzle to ensure that it remains primed full of plastic.  As the hotend cools down below melting temperature, you will no longer be able to extrude plastic by hand and that's exactly what we want.  A 100% full hotend is critical for an effective Cold Pull.  Hotends tend to "ooze" plastic when heated, which is why we need to continually feed filament to ensure the hotend is 100% full of plastic once cooled.
  6. Wait until the temperature has reached 40c.  This ensures the plastic is completely cool and hard.
  7. Set the hotend temperature to 230c and get ready to pull filament out.
  8. While the hotend is heating, depress the extruder pinchwheel lever and try to pull the filament out.  We want to pull that filament out at the lowest possible temperature where the filament will release from the inside of the hotend.  (The exact minimum temperature this occurs at will depend on your choice of filament.)  As mentioned in the "supplies" section, Nylon is absolutely the best choice of material for this.  It's slippery, strong, and has a high melting temperature.  It won't stretch when we pull it at a low temperature. These attributes make it an ideal filament for staying solid during this extraction process.  We don't want the filament to be molten for this step - it needs to be as firm as possible to keep a good grip on the garbage.
  9. When the filament pops free, inspect it visually for contaminants.  You might see a flake of metal or some black charred residue.  You can repeat this process until the nozzle is as clean as you like.  Generally, 4 pulls with Nylon will be sufficient.

 

 

 

 

 

 

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