Screw pushing side

Fig. 20. Photographs taken through a transparent barrel section in a twin-screw extruder showing the presence of bubbles at an extraction pressure of 8 Torr (MacKenzie, 1979). The polymeric solution is heptane-poly(dimethyl siloxane). (a) Screw rotational speed is 15 min . Note how bubbles are dispersed on pushing side of flight. Flow is from right to left, (b) Stationary screw. Note how the bubbles shown in (a) coalesce when the screw is stopped. 

Recalling the discussion earlier in this chapter, in most cases melting in the channel typically occurs at all four edges of the solid bed, with the majority of the melting occurring at the solid bed-melt film interface located between the solid bed and the barrel wall, as shown in Eig. 6.2. The newly molten resin from this location is then conveyed by the motion of the screw to a melt pool located at the pushing side of the channel. Eor very special and sometimes unpredictable conditions, the melting process can occur by a different mechanism. In these cases, the... 

Figure 6.30 Photographs of the conventional melting of a commercial PP resin in an experimental extruder with a glass barrel. In both photographs a melt pool forms near the pushing side of the channel. The screw was rotated at 15 rpm and the barrel temperature was 90 °C. The ruler Is In Inches...

Figure 14.4 Channel depths for a 114.3 mm diameter screw with a barrier melting section. The lead length in the feed and meter sections is 114 mm the lead length of the main flight in the barrier section is 172 mm. The barrier flight starts at the pushing side of the channel and ends near the trailing side. The barrier flight clearance is 1.2 mm...

This shows how the fluid from the center region is cut by the offset flight and pushed to the screw surface at the pushing side of the flight and to the barrel surface at the trailing side of the flight. It is clear that a considerable axial distance is necessary to bring about the redistribution of the material. 

Figure 6.6 Melting profiles for a 63.5 mm diameter extruder running an ABS resin at 60 rpm for screws with a 8.89 mm deep feed channel, 6 diameters of feed section, and a metering channel depth of 3.18 mm (C = 2.8) (a) 8 diameters of transition section for R = 0.00342, and (b) 4 diameters of transition section for R = 0.00684 [13, 14]. The pushing flights are on the right side of the section photographs...

Figure 11.14 Flight radii and tangent points in a screw channel. The pushing flight R, in this case is estimated at 0.5 the depth of the channel (H) while the radius R2 at the trailing side of the channel is estimated at 1.5 times the channel depth...

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