TECHNICAL ARTICLE z A big step for foaming simulation
Bubble shrinkage becomes predictable
Barring Pai explains the strategic difference in results of Han and Yoo , and modified Han and yoo models of bubble growth dynamics in this technical piece .
Barry Pai
In the plastic foaming injection process , the supercritical fluid ( N2 or CO2 ) and the melt are firstly mixed into a uniform 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 change , and after the mold cooling and solidification , the products with cell structures are obtained .
By adopting the Han and Yoo model of bubble growth dynamics , we can simulate the process and dynamics of the bubble growth . However , when the product ’ s geometric appearance gets complicated , and various processes are applied , the in-mold pressure will not always be low . For instance , the melt pressure at the thin area is still very high , and even higher 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 release but may shrink because of the increasing in-mold melt pressure . Under the circumstances , the Han and Yoo model has limitations and is not able to accurately simulate the bubble shrinkage phenomena .
To improve the prediction capabilities of the original model , Moldex3D has collaborated with the Kanazawa University to develop the Modified Han and Yoo model . According to
Figure 1 The core-back process
Figure 2 The bubble shrinkage experiment
Figure 3 The comparison of the simulation and experimental results
20 Packaging South Asia 5 October 2021