Trailing flight

Figure 6.11 Schematics of the solid bed just prior to complete melting (a) the solid bed is pushed to the trailing flight with the Tadmor melting model and barrel rotation physics, and (b) the solid bed is a thin plate and positioned as in the diagram (screw rotation and observation). The cream color represents molten resin...

Figure 6.12 Schematic for the zones of the new melting concept Zone A is the solid bed. Zone B is the melt pool, Zone C is the melt film located between the solid bed and the barrel wall, Zone D is the melt film between the solid bed and the screw root, and Zone E is the melt film between the solid bed and the trailing flight. The cream color represents molten resin...

This functional form for the thickness next to the trailing flight can only be considered a first approximation. From an engineering point of view it does appear to provide results that are consistent with literature observations see Figs. 6.5, 6.6,... 

Notice that the dissipation term is four times as large as the one in Eq. A6.28. The barrel temperature is used here rather than the temperature of the trailing flight. In general, the temperature of the trailing flight is unknown. Derezinski [2] has shown, however, that the temperature of the flight is close to the local barrel temperature. The vectorial velocity in Film E is calculated as follows ... 

This is the velocity that is to be used in Equation A6.56. The film width at the pushing flight is calculated in a similar manner as the film thickness at the trailing flight surface. 

It is well know that melting occurs more rapidly if there is a positive pressure at the end of the transition zone. If Film B is considered to be large and if the pressure in the melt Film C is essentially zero at the trailing flight, a first order approximation of this pressure effect can be achieved by adding a pressure dissipation term to the rate of material loss in the y direction of the solid surface adjacent to the Film C ... 

The cross channel flow is derived in a similar fashion as the down channel flow. This flow is driven by the x-component of the velocity, which creates a shear flow in that direction. However, since the shear flow pumps the material against the trailing flight of the screw channel, it results in a pressure increase that creates a counteracting pressure flow which leads to a net flow of zero1. The flow rate per unit depth at any arbitrary position along the 2-axis can be defined by... 

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