Steady-State Mold Cooling

As has been mentioned in Sect. 7.3, the continuous injection-molding operation results in a cyclic heat transfer behavior in the mold, after a short transient period. The cycle-averaged temperature can be represented by a steady state heat conduction equation, i.e., Eq. 7.10. The mold cooling analysis can be greatly simplihed by solving the steady state problem. The boundary integral equation of ( 7.10) is 

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This section will illustrate the tools taught in the above sections in the form of examples applied to steady state problems. Example 8.3 applies the finite difference method to a simple one-dimensional fin cooling problem and illustrates the nature of the system of equations that is normally achieved. Example 8.4 present a 2D compression molding problem where an iterative solution method is introduced. 

Figure 9.39 Trace of normal stress for a compression-molded 73/27 HBA/HNA copolyester specimen (a) during sample loading at 320 °C, (b) during squeezing and cooling to 290 °C, (c) during temperature equilibration at 290 °C for 4 h, (d) transient and steady-state shear flows at y = 0.5 for 200 s, and (e) during relaxation after cessation of shear flow. An unrelaxed normal stress of 195 Pa was present in the specimen before being subjected to shear flow. (Reprinted from Han et al., Molecular Crystals and Liquid Crystals 254 335. Copyright 1994, with permission from Taylor Francis Group.)...

During the startup of an injection mold, some injection cycles will be needed to obtain a constant steady state situation. Once a mold is at steady state, one can assume that the heat balance of the mold will be the same during every cycle time. During every cycle time, the mold will be at transient solution heat flow , as temperature will change due to the cooling down of the plastic within the mold. 

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