Extrusion screw helix angle

Fig. 9.8 Curvature correction factor for drag flow for a Power Law model fluid. /v,. fl 0 denotes the ratio of drag flow between parallel plates to drag (Couette) flow between concentric cylinders at equal gaps and moving surface velocities. The subscript 6 — 0 indicates that in screw extrusion this correction factor is rigorously valid only in the limit of a zero helix angle. [Reprinted by permission from Z. Tadmor and I. Klein, Engineering Principles of Plasticating Extrusion, Van Nostrand Reinhold, New York, 1970.]...

One of the most demanding situations for controlling melt temperature is in foam extrusion. In the secondary extruder of a tandem foam extrusion line, the cooling screw is usually made with very deep channels to minimize viscous heating. Also, multiple (usually six) thin flights with a large helix angle are used to increase the heat transfer capability of the screw. 

The optimum screw geometry for melt conveying can be determined from extrusion theory. The optimum helix angle is dependent only on the degree of non-Newtonian behavior of the plastic melt it can be determined from the following expression ... 

Vo Die extrusion speed Eq. 9.130 (ps Helix angle screw surface Eq. 8.1... 

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