Black Streaks in Molded Parts Case Two

Meter section with a spiral dam 6.35 4 The undercut of the spiral 

The lead length was 140 mm for the main flight of the screw. The main flight width and clearance were 12 and 0.13 mm, respectively, in all sections of the screw. The compression ratio was 2.4 and the compression rate was 0.0039. The ratio of the flight radii in the meter section to the meter depth was 0.2. The specific rotational flow rate for the screw was calculated at 6.4 kg/(h-rpm). 

As discussed in Section 11.12.2, several root causes exist for black streak contamination in molded parts. These root causes include degradation of the resin in the screw channels and nonreturn valve or runner system, degraded material entering with the resin feedstock, and poorly dispersed pigments in the color masterbatch. To determine if the color concentrate masterbatch was the source of the black streaks, the color concentrate was removed from the feedstock and only natural 

A high-performance screw was designed for the injection-molding press. This screw was designed with a much higher compression ratio and with large flight radii in all sections of the screw. The details of the screw are provided in Table 11.14. 

High-performance meter section 6.86 7.3 Double-flighted and average depth reported 

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