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Conflict of Interest: In relation to this article, we declare that there is no conflict of interest.

Publication history: Received October 9, 2002
Accepted February 20, 2003

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/bync/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Prediction of Gas Flow Directions in Gas Assisted Injection Molding When Cavities and Runners Are Involved

Kwang-Hee Lim^† Eun Ju Lee

Department of Chemical Engineering, Daegu University, Kyungsan, Gyeongbuk 712-714, Korea

khlim@daegu.ac.kr

Korean Journal of Chemical Engineering, May 2003, 20(3), 592-599(8), 10.1007/BF02705571

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Abstract

In the prediction of gas flow-direction for gas-assisted injection molding (GAIM), the statement “Gas goes to the direction of the last area to fill with resin” has been accepted as a correct one. When there exists more than one area to fill with resin, a mold design engineer for GAIM technologies has to determine to which direction gas goes that commercial software for GAIM (e.g., Moldflow) may be utilized for its mold design. However commercial software is generally expensive and is sometimes hard to become familiar with. As a rule of thumb, it is suggested that the resistance to the initial velocity of melt polymer at the nearest geometry to a gas injection point should be used as its criterion since gas goes in the direction of least resistance to initial resin-velocity. Neither the flow rate nor the resistance to flow rate can be a criterion in the prediction. Thus the statement “Gas goes to the direction of the least resistance to flow rates” should be corrected to “More flow rate goes to the direction of the least resistance to flow_x000D_ rates.” The rule of thumb suggested in this paper was verified by using commercial software, Moldflow, in the prediction of gas flow directions in GAIM under geometries where cavities and runners were involved. When the ratio of initial resin-velocity is so close to unity it is proposed as the adapted rule of thumb to calculate new emerging resinvelocities and resistances to resin-velocity at the first coming change of diameters in series of pipes and to compare those for upper and lower sides each other to predict the gas direction. Thus the judgment as to which point is the point where gas starts to choose a preferred direction is very important in the prediction.

Keywords

Gas Assisted Injection Molding Rule of Thumb Preferred Direction of Gas The Least Resistance to Initial-Resin Velocity

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