Screw Geometry Indices

C — for constant lead lengths in the feed and metering sections 

The compression rate for the transition section of the screw describes the rate of the channel depth change as the resin is transported through the transition section. The compression rate is calculated using Eq. 10.16. 

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Unfortunately, the optimum channel depth is dependent on many more variables than the optimum helix angle. The latter depends only on the power law index and reduced flight width. In addition to these variables, the optimum channel depth also depends on the screw speed, screw diameter, consistency index, and pressure gradient. This means that it is not possible to design a universally optimum screw geometry. Thus, one has to determine the most likely operating parameters that the screw is likely to encounter and design for those parameters. 

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