Bubble shrinkage no longer unpredictable
In the plastic foaming injection process, the supercritical fluid (N2 or CO2) and the cook are firstly mixed into a compatible single-phase fluid through the screw, and the homogeneous mixture leads to thermodynamic instability due to instantaneous pressure release during the injection process. It makes the supercritical fluid in the melt generate tens of thousands of tiny bubbles through phase alter, and later the mold cooling and solidification, the products with jail cell structures are obtained.
By adopting the Han and Yoo model of bubble growth dynamics, we can simulate the procedure and dynamics of the chimera growth. All the same, when the product's geometric appearance gets complicated, and various processes are practical, the in-mold force per unit area will not always be low. For instance, the melt force per unit area at the sparse area is still very high, and even college than the packing pressure. On the other hand, the core-back process (Figure 1) will also bring additional packing pressure. Thus, the in-mold bubbles will not continue growing due to pressure level release but may shrink because of the increasing in-mold cook pressure. Under the circumstances, the Han and Yoo model has limitations and is not able to accurately simulate the bubble shrinkage phenomena.
To amend the prediction capabilities of the original model, Moldex3D has collaborated with the Kanazawa University to develop the Modified Han and Yoo model. Co-ordinate to the bubble dynamic model proposed by Prof Taki from Kanazawa and the batch's experimental information [i], the bubbles will surpass the energy barrier to nucleate and abound as the pressure releases. If the pressure on the bubbling increases, the bubbles will gradually compress until they dissolve back into the melt (that is, it is back to the initial country of the mixture of cook and gas). If the pressure is released again at this time, the bubbles volition nucleate and grow at the same location. The experimental results also accept a very close trend with the bubble dynamic model, verifying the procedure of bubble shrinkage caused by the pressure imposed (Figure 3).
In the past, when the Han and Yoo model was used to simulate the sparse-function geometry, the procedure of bubble shrinkage could not exist accurately predicted. Therefore, the number of bubbles that disappeared due to the increasing pressure level was underestimated. Now, in the latest Moldex3D 2022 version, the selection of the Modified Han and Yoo model has been added (Effigy 4). Compared with the original Han and Yoo model, the modified one tin predict the shrinking bubbling more than accurately (Figure 5). Similarly, if nosotros utilize this modified model in the cadre-dorsum process, the required packing time for all the bubbles to dissolve back to the melt will exist obtained.
The foaming process is very various and complicated and is widely applied in diverse fields. Therefore, information technology is particularly of import to control the changes during the whole process. If we can accurately predict the bubble size through the microscopic model, information technology will exist helpful for farther prediction of many macroscopic properties such as heat transfer, mechanical strength, sound assimilation, and low dielectric constant. As a result, the product pattern and production efficiency will be significantly enhanced.
Reference
[1] K. Taki et al., "3D Numerical simulation and experimental observation of bubble growth and collapse in Nitrogen-gas saturated molten polymer for the core-back foam injection molding", ANTEC® 2022 – SPE.
Source: https://packagingsouthasia.com/active-and-intelligent-packaging/bubble-shrinkage/
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