Flight starts

The mass generalized pressure-driven flow for screws with multiple flight starts from Eq. Ill is as follows ... 

As shown by Figs. 7.26 and 7.27, the correction factor decreases as the width ratio W/ZZj increases. Discontinuities occur between the number of flight starts. 

The Tj, factors correct for the non-Newtonian shear rheology effects that occur in the channel. The parameters that are used in the correction correlation include rheological and geometric factors power law index (n), aspect ratio of the channel [H/W], the ratio of the channel width to the screw diameter (W/Df), and the number of flight starts (p). 

Figure 14.4 Channel depths for a 114.3 mm diameter screw with a barrier melting section. The lead length in the feed and meter sections is 114 mm the lead length of the main flight in the barrier section is 172 mm. The barrier flight starts at the pushing side of the channel and ends near the trailing side. The barrier flight clearance is 1.2 mm...

Number of flight starts Pumping capability D ree offill Residence time Pressure build-up... 

The initial part of the barrier section is the same as the Maillefer screw. However, when the melt channel is sufficiently wide, the barrier flight starts to run parallel to the main flight. 

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