APP – Fixing obvious extrusion issues (PEEK)

Once PEEK starts coming out of the nozzle for the first time, the settings adjustment process begins.

The first step is to fix the “obvious” extrusion issues.

At this stage, it is important to not spool the filament.

1. Cooling and pulling the filament

It is recommended to not spool the filament, but it should still be pulled by the automatic mechanism.

Cooling is key :

  • excessive cooling might result in PEEK solification inside the nozzle, causing a clogging. This is favored when the air in the room is humid and cold.
  • insufficient cooling will not result in a filament so hot it can melt the silicon puller wheel

The best way is too start with 50% fancooling and be prepared to make quick adjustments.

2. What are “obvious” extrusion issues ?

The obvious issues are the ones you can see with the naked eye. In general, they are easy to notice, understand, and fix.

The most common extrusion issue (thickness deviation) is not in this list. It has to do with the flow stability, which is a lot more difficult to manage and time-consuming. This will be the focus of the next finetuning step.

Fixing the first extrusion issues will result in a homogeneous, smooth output that comes out continuously and allows you to focus on the tolerance.

3. Troubleshooting each issue

Most extrusion issues can be fixed by tweaking the experimental process. Even though PEEK is a high performance polymer, certain grades are very unreliable and difficult to control.

Important note : When adjusting the settings, keep in mind that PEEK can irreversibly clog the barrel if it turns solid. The nozzle is of particular importance : this is the main spot where heat is lost, and also the spot that can be clogged easily. According to our trials, H1 should never be below 395-400°C.

Incomplete fusion (big punctual bumps in the filament)

This is usually a problem occuring in the first zones (H4, H3). It is good to experiment with all the heaters, and also focus on H4 and/or H3 separately.

  • Increasing the temperatures (steps of 5°C)
  • Decreasing the temperatures (steps of 5°C)

Note: increasing the temperatures does not necessarily mean that the material will melt more. Sometimes it is better to increase the friction, by decreasing them.

Weak flow (almost no material comes out)

This can happen when:

  • Ratholing or bridging is happening in the hopper. Then you can use the Feeder. (Only if the PEEK is in powder of flake form)
  • The material is too viscous. Then you can increase the temperatures.
  • The material is not viscous enough. This can happen with injection grades for example, or when the temperatures are too high, or when the material degrades (hydrolysis or another form of degradation)
  • There is not enough pressure to push the material. You can try to decrease H4 and H3 while increasing H1.
  • The barrel is partially or totally clogged. Purging the machine with Devoclean HighTemp might unclog it (around 400°C)

Bubbles

  • Lower the temperatures (small steps of 5°C)
  • Make sure the material has been properly dried.

Solidification/build-up at the tip of the nozzle

Certain polymers, especially the most crystalline ones, can solidify very fas upon exiting the nozzle, and stick to its tip. This issue becomes more likely when the temperature in the room is cold.

  • Make sure the magnetic plate is well-positioned on the hole around the nozzle
  • Angle the fans so that they blow as downward as possible (not horizontally nor straight toward the nozzle)
  • Increase the temperatures (especially H1)
  • Lower the fancooling percentage

Streaks on the surface

This refers to continuous streaks, or lines, carved into the surface of the filament.

Note: fibers can make the surface rough with lots of lines, so can bubbles, but those lines are not continuous.

  • A build-up of solid material at the tip of nozzle may cause this issue.
  • If the nozzle is damaged, then it should be changed.

Filament falling “like a snake”, not vertically down through the sensor

This can cause zeros in the reading, because the filament leave the reading angle of the sensor.

  • Decrease the fancooling

Filament sticking to the puller wheel

  • Increase the fancooling
  • Decrease the screw speed
  • Decrease the temperatures (especially H1)

Filament ovality

It is often due to the puller wheels. The filament is round when going down through the sensor, but gets flattened/crushed by the wheels. There are several solutions:

    • Increase the fancooling
    • Decrease the temperatures (especially H1)
    • Decrease the screw speed

Sensor reading zeros

If the filament sometimes moves out of the sensor’s reach, then this is normal (see “Filament falling “like a snake” ” above).

If not, it means the sensor reads zeros when it should not:

  • The sensor must be cleaned.
  • Light from the room is interefering with the optical sensor. Try to cover the opening of the sensor with a piece of tape.

4. What we did

The main challenge was to cool down the filament enough before it reached the puller.

For this we chose to :

  • Increase the fancooling to 70-100%
  • Decrease the screw speed to 4.5RPM
  • Decrease all temperatures down to 395°C (being very careful with H1, making small adjustments and keeping a close eye on the nozzle/output)

This allowed the PEEK filament to become solid just above the sensor. It is easy to tell because PEEK turns from dark translucent brown to little opaque brown upon crystallizing.