Determination of heat transfer coefficients at the polymer-mould-interface for injection molding simulation by means of calorimetry
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29th International Conference of the Polymer Processing Society
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Appropriate modeling of heat transfer from the polymer material to the injection mold is essential to achieve accurate simulation results. The heat transfer is commonly modeled using convective heat transfer and applying heat transfer coefficients (HTC) to the polymer-mold-interfaces. The set HTC has an influence on the results for filling pressure, cooling performance and shrinkage, among others.
In experimental studies, averaged HTC values in the range of 500 to 4500 W/(m²K) have been determined in heat flux measurements with multiple thermocouples [1,2,3]. These values correspond to HTC values recommended by simulation package suppliers. A critical aspect is crystallization heat. The lack of values at high cooling rates can lead to high inaccuracies . Another approach is based on parametric studies, fitting HTC to conform simulation and experiment . In this study, multiple effects (e.g. compressibility of the melt, surface roughness) are pooled in the determined HTC. Therefore, validity of the values is limited to the specific simulation package.
The current work, presents a new strategy to measure HTC in injection molding experiments using newtons law of cooling. The heat flux is calculated out of demolding enthalpy (measured by means of calorimetry), injection enthalpy (measured by means of an IR-sensor), cooling time and part mass. Cavity surface area, average mold surface temperature and average part surface temperature lead to the HTC. Several injection molding experiments have been performed to evaluate the influence of process setup on HTC.
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