Black Color Streaks in Molded Parts Case One

2 Black Color Streaks in Molded Parts Case One 

Spiral-type mixer 2.5 Mixer provided distributive and dispersive mixing with a clearance between the flight and barrel wall of 3.5 mm 

The lead length was 157 mm for the main flight of the screw. The main flight width and clearance were 14 and 0.14 mm, respectively, in all sections of the screw. The compression ratio was 3.1 and the compression rate was 0.0049. The specific rotational flow rate was calculated at 9.5 kg/(h rpm). 

At the start of the trial, the target for the plant was to run a 65 s cycle time with a 1 % scrap rate or less due to all defects. The plasticator was running at 235 °C for 

Several mechanisms could cause the specific rate of the screw to be considerably less than the calculated specific rotational flow rate for the screw. These mechanisms include (1) normal operation for a screw with a very short metering section and a low-viscosity resin, (2) the screw is rate-limited by solids conveying, causing the downstream sections of the screw to operate partially filled, and (3) the entry to the barrier section is restricting flow (see Section 11.10.1) to the downstream sections of the screw and causing the downstream sections to operate partially filled. The goal was to determine which of the above mechanisms was responsible for the low specific rates for the plasticator. 

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