Effect of Flight Flanks

If the channel width cannot be considered infinite, the equation of motion in the down-channel direction becomes  

The solution to this equation is more difficult than the solution to Eq. 7.194. The case of pure pressure flow was first solved by Boussinesq [130] in 1868. The solution to the combined drag and pressure flow was first published in 1922 [98] the authorship of this publication remains a question. Since the 1922 publication, numerous workers have presented solutions to this problem. Meskat [131] reviewed various solutions and demonstrated that they were equivalent. The velocity profile resulting from the drag flow can be written as  

The velocity profile resulting from the pressure flow can be written as  

The volumetric output can be conveniently expressed in the following form  

In the range of most extruder screws (H/W 0.6), the shape factors F and Fp can be quite accurately approximated with the following expressions  

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Clearly, the effect of calender clearance Is similar to the effect of flight flank angle. The effect of the radial flight clearance Is shown in Fig. 10.36 when AP° = 1E4. 

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