Optimizing for Plasticating

For optimization of just the helix angle or the channel depth, the results from the Newtonian flow rate equation with correction factors for pseudo-plastic behavior, Eq. 8.54, are more accurate than the results from the modified Newtonian analysis, Eq. 8.36. It should again be noted that simultaneous optimization only makes sense for relatively large positive pressure gradients. When the pressure gradient is negative, the output increases monotonicaiiy with channel depth. In this case, there is no optimum channei depth. 

The term A, in Eq. 8.55 is the compression in axial direction. Aj is related to the compression in down-channel direction A by  

The results shown in Fig. 8.15 are predictions for a 50-mm extruder running at a screw speed of 100 rpm with an output of 100 kg/hr. the barrel temperature is set 50°C above the melting point of the polymer. The channel depth in the feed section is 5 mm, the axial compression Aj = 0.008, and the number of flights p = 1. The following polymer properties were used  

Axial melting length versus helix angle 

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Baesso, R., Salvador, M., Lucchetta, G., Filling Balance Optimization for Plastics Injection Molding, Proceedings of Advanced Manufacturing Systems and Technology, 617-624 (2005). 

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