Melting Models for Barrier Screw Sections

Barrier melting sections are constructed by positioning a second flight (or barrier flight) in the transition section such that the solids are maintained on the trailing side and the molten resin on the pushing side. A schematic of a cross section of a barrier melting section is shown in Fig. 6.22. The resin is melted as discussed in Section 6.3.1 in the solids channel of the device. The resin that is melted near the 

As shown by Fig. 6.23, the channel geometry is relatively complicated for barrier flight melting sections. The geometric constraint on the channel widths are provided by Fq. 6.33. For most commercial designs, W is constant because the lead length of the primary flight is also constant. 

Two constraints are placed on the solids-conveying channel. That is, the sum of the widths and thicknesses for the components must equal the width and depth of the solids-conveying channel. Here, the melt film thicknesses 6t, and 6 for Zones B and D were found by difference  

As Stated above, both Ws(z) and are fixed by the geometry of the screw. A schematic representation of the solid hed in the channel is shown in Fig. 6.25 for a barrier section geometry similar to that of Fig. 6.23(a). This representation depicts how the four films change In dimension as the solid bed is consumed in the melting section of the screw. 

The axial pressure and temperature distributions for the molten resin in the melt-conveying channel are calculated using the control volume method outlined in Section 7.7.5. For this method, the change in pressure and temperature are calculated using the local channel dimensions, HJ z) and FK (z), and the mass flow rate in the channel using Eq. 7.54 for flow and the methods in Section 7.7.5.1 for energy dissipation and temperature. The amount of mass added to the melt chan- 

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