<p>Some plastics, and PC is quite bad about this, are hygroscopic, and will absorb water if they are not kept in a low humidity environment.</p>
<p>Usually the manufacturer of the plastic pellets has a data sheet that specifies a drying process that should be used to condition the pellets before they are melted.  Typically this consists of a baking process with a time/temperature profile, and can be incorporated into the pre-feed before it gets to the melt zone.</p>
<p>However, if the bake time is too long or your feed too fast, you may have to precondition them separately.</p>

CC BY-SA 4.0
2021-09-10T09:46:37.923Z
I dry the plastic for a long time and also bake in the pre-feed hopper. Could the feed/extruder ratios be causing this? What about the temperature of my heaters?
Husam Abu Zour
CC BY-SA 4.0
2021-09-10T11:09:03.203Z
Have you looked for the manufacturer's drying guidelines?  Possibly you aren't following them closely enough, maybe some of the temps are not right.
user10489
CC BY-SA 4.0
2021-09-10T11:18:16.323Z
Possibly baking it is not enough.  I've seen datasheets that indicate baking with humidity control as well.
user10489
CC BY-SA 4.0
2021-09-10T02:24:08.510Z
2021-09-26T14:22:29.117Z
2021-09-26T14:22:29.117Z
user10489
<p>I have a Kuka robot that I use to print large objects (output around 18 kg/hour). I am printing recycled polycarbonate pallets.</p>
<p>The problem I am having is that exploding air bubbles are appearing frequently. The extruder has four heaters with temperatures:</p>
<ul>
<li>210 °C (first heater)</li>
<li>230 °C</li>
<li>250 °C</li>
<li>260 °C (nozzle)</li>
</ul>
<p>The fan is turned off.</p>
<p>Any ideas what could cause this problem?</p>

CC BY-SA 4.0
2021-09-09T15:30:51.760Z
I would assume either the pellets have a manufacturing defect (air trapped in them) or the bubbles aren't air but water vapor, meaning the material has absorbed water. If you haven't dried it prior to use, you probably need to.
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2021-09-09T17:06:20.510Z
That's not air, that's water. Polycarbonate has water in between the molecules, it's part of the plastic. Heating it causes the water to boil.
user77232
<print-quality>
Exploding bubbles while printing polycarbonate
Husam Abu Zour
# Exploding bubbles while printing polycarbonate

(Asked by: username_0 on 2021-09-09)

I have a Kuka robot that I use to print large objects (output around 18 kg/hour). I am printing recycled polycarbonate pallets.

The problem I am having is that exploding air bubbles are appearing frequently. The extruder has four heaters with temperatures:

* 210 °C (first heater)
* 230 °C
* 250 °C
* 260 °C (nozzle)

The fan is turned off.

Any ideas what could cause this problem?

**Tags:** print-quality

> **Comments:**
> **username_1**: I would assume either the pellets have a manufacturing defect (air trapped in them) or the bubbles aren't air but water vapor, meaning the material has absorbed water. If you haven't dried it prior to use, you probably need to.  
> **username_2**: That's not air, that's water. Polycarbonate has water in between the molecules, it's part of the plastic. Heating it causes the water to boil.  

---

## 1 answers

### Answer by username_3 on 2021-09-10. Score: 1

Some plastics, and PC is quite bad about this, are hygroscopic, and will absorb water if they are not kept in a low humidity environment.

Usually the manufacturer of the plastic pellets has a data sheet that specifies a drying process that should be used to condition the pellets before they are melted. Typically this consists of a baking process with a time/temperature profile, and can be incorporated into the pre-feed before it gets to the melt zone.

However, if the bake time is too long or your feed too fast, you may have to precondition them separately.

> **Comments:**
> **username_0**: I dry the plastic for a long time and also bake in the pre-feed hopper. Could the feed/extruder ratios be causing this? What about the temperature of my heaters?  
> **username_3**: Have you looked for the manufacturer's drying guidelines?  Possibly you aren't following them closely enough, maybe some of the temps are not right.  
> **username_3**: Possibly baking it is not enough.  I've seen datasheets that indicate baking with humidity control as well.  

---

