Technical Datasheet Walkthrough (2/3)
So you have the datasheet…
If you have read this article (Technical Datasheet part 1/3), you know that a Technical Datasheet (TDS) is a valuable resource when trying to manufacture 3D printing filament, for it gives information about the expected final properties of the material, but also about how to process it. It is quite simple and quick to read through a TDS and start extruding. If you know what information you should be looking for.
When preparing an extrusion experiment, only a small fraction of the datasheet is of great importance. It mostly consists in the thermal properties of the material.
If some of the data is not available in the datasheet, it is recommended to contact the supplier of the material to ask for additional information, or to estimate the missing information using the datasheet of a similar grade of polymer.
1- Melting temperature of the material
This can be a temperature or a range. This is the most useful piece of information.
The goal of extrusion is to melt plastic, and for this you need the melting temperature.
Some plastics are amorphous, and therefore only have a glass transition temperature, no melting point.
For those plastics, you can generally calculate a theoretical metling point:
convert Tg to Kelvin, multiply by 1.5, convert back to Celsius.
2- Melt Flow Rate (MFR) or Melt Flow Index (MFI)
It represents how much molten material can be pushed through a standardized hole, at a given temperature, under a given weight, in 10min.
A high MFR means the plastic is very fluid. A low one means it’s viscous.
This cannot be used as it is, but it will tell you if the grade is appropriate for extrusion.
- MFR < 10g/10min = extrusion grade
- MFR ~ 10g/10min = general purpose grade
- MFR > 10g/10min = injection grade
- MFR > 20-30g/10min = injection grade, extremely difficult to extrude
3- Drying instructions
This only concerns hygroscopic materials – materials capable of absorbing moisture.
Hydrophobic materials, such as polypropylene, do not need to be dried prior to extrusion.
Drying instructions are:
- drying temperature
- drying duration
- sometimes a recommended target moisture content
4- Processing temperatures and processing recommendations
Those are not always available.
They are indications which the polymer manufacturer indicates, about how the material can be processed, generally. Because these settings were used on completely different extruders, they can serve as guidelines, but must not be set by default on your own extruder.
! ! TRAP : Here in the picture, ‘Melt Temp.’ refers to the temperature of the melt, or molten plastic. It is different from the temperature you set as parameters in your process. This ‘Melt Temp.’, sometimes called other names, does not refer to the temperature at which the plastic melts.
Limitations to the TDS
It is crucial to keep in mind that all the information available in a datasheet was obtained under very specific circumstances, and that it remains valid under certain conditions. This is especially true for the typical material properties, which are given with a reference to a certain test method, usually an ASTM or ISO standard. This means that for each of these values, the corresponding norm should in theory be read to understand the validity of the value. The appropriate and simpler approach is to keep in mind that none of the values should be taken “as granted”, but they can be considered good estimations.
It takes a bit of experience to translate the data from a TDS into extrusion settings.
You can find a complete practical guide about how to start an extrusion experiment after the quick reading of a TDS here.