Calculation of the Specific Rotation Rate

The compression ratio for a high-performance screw is typically based on the axial distance-averaged depth, while the compression rate is based on the channel depth at the entry to the section. The screw described above has a feed section with a depth of 10.9 mm, and thus the compression ratio is about 2.5. 

Method and Apparatus for Refining and Separating Plastic Materials, U. S. Patent 3,375,549 (1968) 

and Barr, R.A., Energy Efficient Extruder Screw, U.S. Patent 4,405,239 

Somers, S.A., Spalding, M.A., Dooley, and Hyun, K.S., An Experimental Study of the Flows in an Energy Transfer Screw, SPE ANTEC Tech. Papers, 48, 307 (2002) 

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