Hello and welcome to a new Rule of Thumb post. Today we discuss the importance of melt temperature and residence time of engineering polymers. Here the link to the residence time of high performance polymers.
Melt temperature - injection moulding
In general, melt temperature and residence time of the polymer melt are strongly linked and have a high impact on reaching the mechanical properties of your part. It is best to follow the recommendation of the material supplier for the optimal melt temperature. For example, if you decrease the melt temperature 10 Kelvin, starting from the recommended optimum value, tensile strength and elongation can drop 25 %. Reason are unmolten particles which enter the final part during moulding and cause a drop in mechanical properties. On the other side, a 10 Kelvin increased melt temperature is not as critical as the lower temperature profile. The final part still will have 95% of the mechanical properties. The polymer melt can handle short increases in temperature which in turn leads to a better flow profile too.
Residence time of engineering polymers - injection moulding
Next to the temperature is the residence time. The biggest impact on the residence time has the size of your plasticizing unit and its optimal selection. If you have a high metering stroke, residence time is low. If you have only a small metering stroke, residence time will be up and you have to check if you are not above the maximum residence time of the polymer. It can encounter this by using an increasing temperature profile on your plasticizing unit. Figure 1 shows the maximum residence levels of different engineering polymers. POM and TPE can have high residence times (up to 30 minutes) and Polyesters (PET, PBT, PC) should not be much above 6 minutes in total residence time (including hot runners if applicable).
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| Figure 1: residence time (minutes) of most used engineering polymers. |
I created also calculation tools which allows you to estimate the residence time for injection moulding and extrusion - here the link.
Thanks for reading and #findoutaboutplastics
Greetings,
Herwig Juster
Interested to talk with me about your polymer material selection, sustainability, and part design needs - here you can contact me
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Literature:
[1] Kunststoff Taschenbuch - Hanser
[2] Serie Kunststoffpraxis Teil 12: Verweilzeit und Temperaturprofil - Plastverarbeiter
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