The term
residence time in injection moulding operations refers to the time that a
plastic pellet takes from entering the injection moulding barrel until entering
the injection mould. It relates to the amount of polymer material present in
the cylinder of the injection unit, the shot weight and the total cycle time.
Often, residence time is also referred to as Hold-Up Time (HUT).
Melting of
plastics for processing is usually attained by bringing the plastics over a
certain temperature, i.e., glass transition temperature for amorphous
thermoplastic polymers and glass transition temperature as well as crystalline
melting temperature for semi-crystalline thermoplastic polymers. For both types
of thermoplastics longer than necessary heat exposure, especially in the
presence of oxygen (air), may induce chemical degradation. Therefore, the residence
time in injection moulding at polymer-sensitive melt temperatures needs to be
optimal. In this context, residence time is especially important for polymers
such as, for example, PVC, POM, ABS, PBT and PET.
Melt
temperatures have to be chosen in a way that the material’s thermal stability
during processing is ensured [1, 2]. Guidance about optimal residence time and
residence time for different polymers is given by material manufacturers in processing
and design guides. In practice, tools
for accurately calculating the melt residence time depending on the utilized
machine and processing conditions are usually not available. This prevents
processing engineers from making quick process assessments. For this reason, I
have created an online tool to calculate the residence time of your injection
moulding operation. This can be used online or downloaded. The calculation is
based on the formula below [3].
 |
| Formula for calculating the residence time in injection moulding |
Here, number 8 represents the volume of the molten polymer in the barrel.
This is the ratio between flight height and screw length, which for most injection
moulding machines is approximately 8. Part A gives the number of shots in the
barrel and Part B represents the cycle time to produce the part.
Finally, keeping the residence time at an optimum level will help you keeping materials’ degradation to a minimum and, consequently, the mechanical properties of your final moulded part to a maximum.
Successful moulding and thanks for reading!
Finally, keeping the residence time at an optimum level will help you keeping materials’ degradation to a minimum and, consequently, the mechanical properties of your final moulded part to a maximum.
Successful moulding and thanks for reading!
Till next time!
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
[2] GE Plastics - Injection Moulding Guide
[3] Christoph Jaroschek - Spritzgießen für Praktiker
[4] https://www.wittmann-group.com/sites/default/files/2021-05/wiba_prnews_plasticizing-screws-article-series-part2_04-2020_en.pdf
[4] https://www.wittmann-group.com/sites/default/files/2021-05/wiba_prnews_plasticizing-screws-article-series-part2_04-2020_en.pdf
of blogs. Thank you so much for sharing this blog. Thank you. China Injection Molding Company
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