Increasing the Rate of a Large Part Blow-Molding Process

7 Increasing the Rate of a Large Part Blow-Molding Process 

Blow-molding processes consists of five main operations plastication of the resin, formation of the parison, inflation of the parison, solidification of the part, and removal of the part from the tooling. The best process economics will occur with a part optimized for weight and a minimum cycle time. In order to have a minimum cycle time, the cooling operation must be the rate-limiting step. For the case study 

Lead length, flight width, and flight clearance were 131, 15, and 0.15 mm, respectively, in all sections of the screw. The specific rotational flow rate for the screw running PC/ABS resin was calculated at 13.2 kg/(h-rpm). The extruder had a smooth-bore feed section.  

The ET section and downstream channel sections were numerically simulated to determine if the screw could meet the target performance. The simulation was performed at a rate of 410 kg/h using the same barrel temperatures for the original screw and process and at an entry pressure and temperature of 7 MPa and 210 °C, respectively. The axial pressure and temperature profiles are shown in Fig. 13.15. The simulation indicates that 410 kg/h can be obtained at a screw speed of 24 rpm for a specific rate of 17.1 kg/(h-rpm) with a discharge temperature of 234 °C. Based on this simulation, the ET screw was fabricated. 

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