Self-wiping co-rotating twin screw extruders

S. Bawiskar and J. L. White, Melting Model for Modular Self Wiping Co-rotating Twin Screw Extruders, Polym. Eng. Sci., 38, 727 (1998). 

The concept of a self-wiping co-rotating twin-screw extruder dates to the beginning of the twentieth century (Figure 1.14) [77, 78]. However, an intermeshing co-rotating t vin-screw extruder was not commercialized until 1939. This was initiated by Roberto Colombo [79] and Lavorazione Materie Plastische (LMP) in Turin, Italy. 

Figure 1.14 Wunsche 1901 self-wiping co-rotating twin-screw extruder.

CICO is closely intermeshing co-rotating twin screw extruder (low speed) CSCO is closely self-wiping co-rotating twin screw extruder (high speed)... 

Figure 9.21 Early self-wiping co-rotatIng twin-screw extruder of Wunsche [98] (1901)...

Bourry, D., F. Godbille, R. E. Khayat, A. Luciani, J. Picot, and L. A. Utracki, Extensional Flow of Pol3mieric Dispersions, Polym. Eng. Set, 39, 1072-1086, 1999. Denson, C. D., and B. K. Hwang, Jr., The Influence of the Axial Pressure Gradient on Flow Rate for Newtonian Liquids in a Self Wiping, Co-Rotating Twin Screw Extruder, Polym. Eng. Set, 20, 965-971, 1980. 

The enormous flexibility and variability of the system was possible thanks to the constant development of the process related components, such as the barrels and screw elements and new geometry variants being developed continuously. The initial aim of the design, to maintain the self-wiping function of the screw elements, is sometimes abandoned, in part or in whole, to permit innovative geometries. This enabled the co-rotating, twin-screw extruder to carry out the most diverse processes and handle the most diverse products with this single machine system. 

Fig. 4 Self-wiping in the two and three lobed co-rotating twin-screw extruders. (Courtesy of Coperion Corporation.) (View this art in color at www.dekker.com.)...

Material transport in intermeshing, co-rotating twin-screw extruders is generally dependent on drag flow. The screws pick up the material as they rotate and, where the two screws meet, a complete transfer of the material from one screw to the other takes place, see Fig, 4. The tip of one screw wipes the flanks and roots of the other screw, resulting in a self-wiping action. As the material is transferred from one screw to the other, the direction of material flow is changed and new material surfaces are created with each screw revolution. 

Once the tip angle and the number of flights are selected, the centerline distance and the root diameter are fixed in a self-wiping co-rotating extruder. This imposes a considerable design constraint on co-rotating twin screw extruders. 

Generally, continuous mixers are superior to batch mixers. The compounds are more uniform have superior mechanical properties and much shorter residence times [135, 136]. The major continuous mixers used commercially in 2009 for compounding and blending are modular co-rotating self-wiping twin-screw extruders. 

Extrusion was conducted on a Werner and Pfleiderer ZSK30 twin screw extruder (Werner and Pfleiderer, Ramsey, NJ) equipped with two co-rotating self-wiping screws. Commercial hard red wheat flours (Bay State Milling Co., Minneapolis, MN) were extruded under puffing conditions according to conditions described by Schaich (1), Rebello (2), Koh et al (3), and Wang ( 4). 

Figure 6.9 Schematic of the screw profile of a co-rotating self-wiping twin screw extruder (D = 30 mm,...

Twin-screw extruders have an important role in the compounding industry. There are various possible geometries for twin-screw extruders. These include directions of screw rotation and level of intermesh. Two screws can rotate in the same direction (co-rotating) or in opposite directions (counter-rotating). The screws may be separated, tangential, intermeshed and fully intermeshed and self-wiping. 

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