Silver Streaks in a Clear GPPS Resin Injection-Molded Packaging Part

4 Silver Streaks in a Clear GPPS Resin Injection-Molded Packaging Part 

The injection-molding presses were 250 ton in size, and they were equipped with 63 mm diameter, 22 L/D plasticators. The screws were all identical and were conventional, single-flighted designs, and they had spiral dams positioned in the last 

3 diameters of the transition sections. The specifications for the screws are provided in Tabie if. 15, and a schematic of a spirai dam is shown in Fig. 11.37. These screws had a very low compression ratio of 2.4 and a compression rate of 0.0029. For GPPS resin and this application, a compression ratio near 3 and a compression rate of about 0.0035 is desired. The size of the flight radii in the metering section was relatively large compared to the depth of the channel. The specific rotational flow rate was calculated at 0.94 kg/(h-rpm). The resin had an MFR of 5.5 dg/min (200 °C, and 5 kg). 

Transition section with a spiral dam 8 The spiral dam was 3.3 diameters in length and it was positioned at the end of the transition section 

The lead length was 63 mm for the main flight of the screw. The main flight width and clearance were 7 and 0.06 mm, respectively, in all sections of the screw. The undercut of the spiral flight was 0.76 mm. The compression ratio was 2.4 and the compression rate was 0.0029. The ratio of the flight radii in the meter section to the meter depth was about 1.0. The specific rotational flow rate was calculated at 0.94 kg/(h-rpm).  

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