文档介绍：Metering Function 29
Conduction Melting
As the solid bed continues to melt along the screwthe solid pieces
Ⴠ High feed temperature
Ⴠ Low melting point
Ⴠ Small heat capacity for melting
Metering Function
When all pellets are molten toward the end of a screw, the rest of the screw functions as a
metering pump to pump the polymer melt out of the screw through the die. As the screw
rotates, some of the melt adheres on the screw and rotates with the screw. Some of the
melt is held back or dragged by the stationary barrel and comes out of the screw because
of the helical geometry of the screw channel. Because the movement of the melt rotating
with the screw is diffi cult to visualize, it is customary to assume that the screw is stationary
and the barrel rotates in the opposite direction of the screw rotation. In this way, the
movement of the melt relative to the screw can be easily observed through a transparent
barrel. Figure shows a stationary unwrapped rectangular screw channel with a moving
++ 2299 110:01:490:01:4930 2 Physical Description of Single-Screw Extrusion
barrel. Th e forward fl ow caused by the drag of the moving