Numerical Comparison of Temperatures for Screw and Barrel Rotations

6 Numerical Comparison of Temperatures for Screw and Barrel Rotations 

Qmp = Qmd- The pressure gradient provided by Eq. 7.109 can then be used to estimate the temperature increase using Eq. 7.104 for screw rotation and Eq. 7.107 for barrel rotation. 

As indicated by Eig. 7.37 and Table 7.7 and as expected, the increase in melt temperature for a PC resin was always higher for the barrel rotation case as compared to screw rotation. If a very high die pressure was needed and the rate is reduced to 10 % of the rotational rate (T) = 0.9), the difference between discharge temperatures for the rotation cases was predicted at about 18 °C. In other terms, the temperature increase (47°C) for screw rotation was about 72% of the temperature increase (65 °C) for barrel rotation. The discharge temperature difference for the two rotation cases decreases to about 4 °C fora low die pressure case where the rate is 90% of the rotational flow rate (T) = 0.1). For this case, the melt temperature increase (6 °C) for screw rotation was about 60% of the temperature increase (10 °C) for barrel rotation. 

The predictions for a typical highly shear-thinning PS resin are shown in Fig. 7.38. The difference in predicted discharge temperature was not as dramatic for the different rotation cases. Like the PC resin and as expected, the melt temperature increase for the PS resin was always higher for the barrel rotation case. As shown by Fig. 7.38, the melt temperature increased by 22 °C for barrel rotation while it increased 19 °C for the screw rotation case. Thus, the melt temperature Increase for screw rotation was about 86% of the temperature increase for barrei 

---