Barrier flight extruder screws

Hyun, K. S., Spalding, M.A., and Powers, J.R., Elimination of a Restriction at the Entrance of Barrier Flighted Extruder Screw Sections, SPEANTEC Tech. Papers, 41, 293 (1995)... 

The inventor of the barrier flight extruder screw is Maillefer, a pioneer in the field of extrusion. He first appiied for a patent in Switzerland on December 31, 1959 [23], and later applied for patents in various other countries. Patents were granted, among other countries, in Germany [24] and in Engiand [25]. Maillefer filed a patent application in the U.S. on December 20,1960. However, Maillefer did not obtain a patent in the U. S. because of a particular provision in U. S. patent law. Geyer from Uniroyal filed a patent application for a barrier screw on Aprii 5, 1961, several months after Maillefer s filing date [26]. 

Campbell, G.A. and Spalding, M.A., Numerical Analysis of the Melting Process for Barrier-Flighted Single-Screw Extruders Using Screw Rotation Physics, SPE ANTEC Tech. Papers, 56, 418 (2010)... 

Obviously, all barrier-type extruder screws (see Section 8.6.2) impart some degree of dispersive mixing to the polymer because all the polymer has to flow over the barrier flight to leave the extruder. Thus, every polymer element is exposed to a brief but relatively intensive shearing in the barrier clearance. Simulation of fluted mixers is discussed in Section 12.4.3.4 see also Fig. 12.43 and Fig. 12.44. 

Mixing screws based in elongational mixing devices and without barrier flights result in minimal MW reduction. These screws have little melt temperature and pressure variation, can disperse gels, and achieve a high quality product with minimal dimensional variation. As a result, such extruder screws are attractive in medical extrusion operations where MW reduction has to be minimized and dimensional control and product quality maximized. 

Figure 12.3 (A) Melting mechanism of single-screw extruders as determined by Maddock. (B) Schematic diagram of barrier screw cross section showing separate solids and melt channels separated by the barrier flight as defined by Barr.

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