Reaction injection molding : analyzing the filling stage of a complex product with a highly viscous thermoset

Although numerical simulation has proved to be a useful tool to predict the filling behavior of injection molding products, few applications in reaction injection molding (RIM) have been reported. This is mainly due to the lack of appropriate descriptions of the material behavior, and to the lack of accurate material data. The analysis of the filling stage of the RIM process requires the determination of the cure kinetics and the rheological, pvT, and thermal behavior of the material, which in this study is a highly filled copolymer of ethylene and vinyl-acetate (EVA). Since this copolymer yields some viscosity anomalies, due to the amount of filler, the rheology of a similar EVA compound with low filler content was also investigated. The viscosity of this compound can be described by a Carreau model at low conversions levels

Simulation of three-dimensional polymer mould filling processes using a pseudo-concentration method

Mould filling processes, in which a material flow front advances through a mould, are typical examplesof moving boundary problems. The moving boundary is accompanied by a moving contact line at themould walls causing, from a macroscopic modelling viewpoint, a stress singularity. In order to be able tosimulate such processes, the moving boundary and moving contact line problem must be overcome. Anumerical model for both two- and three-dimensional mould filling simulations has been developed. Itemploys a pseudo-concentration method in order to avoid elaborate three-dimensional remeshing, andhas been implemented in a finite element program. The moving contact line problem has been overcomeby employing a Robin boundary condition at the mould walls, which can be turned into a Dirichlet(no-slip)! or a Neumann (free-slip) boundary condition depending on the local pseudo-concentration.Simulation results for two-dimensional test cases demonstrate the model?s ability to deal with flowphenomena such as fountain flow and flow in bifurcations. The method is by no means limited totwo-dimensional flows, as is shown by a pilot simulation for a simple three-dimensional mould. Thereverse problem of mould filling is the displacement of a viscous fluid in a tube by a less viscous fluid,which has had considerable attention since the 1960?s. Simulation results for this problem are in goodagreement with results from the literature

Simulation of three-dimensional polymer mould filling processes using a pseudo-concentration method

Mould filling processes, in which a material flow front advances through a mould, are typical examplesof moving boundary problems. The moving boundary is accompanied by a moving contact line at themould walls causing, from a macroscopic modelling viewpoint, a stress singularity. In order to be able tosimulate such processes, the moving boundary and moving contact line problem must be overcome. Anumerical model for both two- and three-dimensional mould filling simulations has been developed. Itemploys a pseudo-concentration method in order to avoid elaborate three-dimensional remeshing, andhas been implemented in a finite element program. The moving contact line problem has been overcomeby employing a Robin boundary condition at the mould walls, which can be turned into a Dirichlet(no-slip)! or a Neumann (free-slip) boundary condition depending on the local pseudo-concentration.Simulation results for two-dimensional test cases demonstrate the model?s ability to deal with flowphenomena such as fountain flow and flow in bifurcations. The method is by no means limited totwo-dimensional flows, as is shown by a pilot simulation for a simple three-dimensional mould. Thereverse problem of mould filling is the displacement of a viscous fluid in a tube by a less viscous fluid,which has had considerable attention since the 1960?s. Simulation results for this problem are in goodagreement with results from the literature

A 3-D finite element model for gas-assisted injection molding - simulations and experiments

To gain a better understanding of the gas-assisted injection molding process, we have developed a computational model for the gas assisted infection molding (GAIM) process. This model has been set up to deal with (non-isothermal) three-dimensional flow, in order to correctly predict the gas distribution in GAIM products. It employs a pseudo-concentration method. in which the governing equations are solved on a fixed grid that covers the entire mold. Both the air downstream of the polymer front and the gas are represented by a fictitious fluid that does not contribute to the pressure drop Fn the mold. The model has been validated against both isothermal and non-isothermal gas injection experiments. In contrast to other models that have been reported in the literature, our model yields the gas penetration from the actual process physics (not from a presupposed gas distribution). Consequently, it is able to deal with the 3-D character of the process, as well as with primary (end of gas filling) and secondary (end of packing) gas penetration, including temperature effects and generalized Newtonian viscosity behavior

Prediction of emulsion particle sizes using a computational fluid dynamics approach

For many food products emulsification processes play an important role. Examples are ice cream, spreads, sauces, etc. As is well known, droplet break-up and coalescence phenomena are the local processes underlying the control of particle size in an emulsion process. Quite a number of studies have generated scaling laws which can be easily applied and which are useful in the design of a process. However, the prediction of particle sizes in an inhomogeneous flow, where the flow velocity is changing spatially in strength and direction and with time, is not yet well established. For one-phase flows computational fluid dynamics (CFD) methodologies are in use to predict details on the flow with quite some success. This methodology has been extended to capture the dispersed phase in an efficient way. The essence is that break-up and coalescence processes determine source terms in a transport equation for the moments of the particle size distribution, while velocity vectors as obtained in the one-phase CFD simulation determine the convective term. This method allows particle size prediction in any equipment. The approach is illustrated for the particle size evolution of an oil-in-water emulsion, for a phase-separated biopolymeric mixture (a so-called water-in-water emulsion) and for the escape of the included oil droplets from a double emulsion of the type oil-in-water-in-oil. In all cases experimental results are compared with simulation results, which match very well. This shows the strength of the method