Counterrotating Screws

Screw compressors use two counterrotating screw-like shafts (Figure 13.11a). Lubricating oil is required in some designs to lubricate the rotors, seal the gaps... 

This TSE consists of two parallel counterrotating screws, as shown in Fig. 6.53. The distance between the screw centers is L < Db, where Db is the barrel diameter thus, there is an open axial slit along the barrel. This type of extruder has advantages for the feeding of particulate solids (e.g., powder), venting, and devolatilization of the molten polymer. 

Fig. 10.20 Axial location of the two planes perpendicular to the counterrotating screws, where velocity fields were calculated. Plane (I) is at the middle of the side, and plane (II) at the middle of the calender gaps. [Reprinted by permission from T. Katziguara, Y. Nagashima, Y. Nakano, and K. Funatsu, Numerical Study of Twin Screw Extruders by 3-D Flow Analysis - Development of Analysis Technique and Evaluation of Mixing Performance for Full Flight Screws, Polym. Eng. Sci., 36, 2142 (1996).]...

The pumping ability of the thin-flighted, filled co-rotating screw is about 1.4 times that of the counterrotating screw. The side-gap flow with the counterrotating screw is 90% of the... 

The partially filled counterrotating screws advance the free-flowing particulates against the region of the pushing flights by metal-particulate frictional forces. The... 

The back-mixed extruder is a variant of the conventional nonintermeshing (tangential) counterrotating TSE represented on Fig. 11.13(a) both counterrotating screws in this LCFR create a dominant downstream flow with no back mixing and with some mixing screw-to-screw flow. By contrast, the two counterrotating screws of the back-mixed reactor... 

Figure 2. (A) Vector diagram of a counterrotating screw (B) Cross section of counterrotating screws.

Several types of multiple-screw machines are available, including intermeshing corotating screws (in which the screws rotate in the same direction, and the flight of one screw moves inside the channel of the other), intermeshing counterrotating screws (in which the screws rotate in opposite directions), and... 

In ICRR the roll-off process between the screw crest and screw root and between the screw flanks simulates the action of a calender. The necessary shear velocity required to wipe the boundary layers is proportionately lower because of the low relative velocity. Counterrotating screws require greater clearances between them since their mode of action is rather like a two-roll mill, passing material through the nip between them (Schoengood 1973). The material is drawn into the roller gap and is squeezed onto the surface. Consequently, ICRR has less efficient self-cleaning action. 

Figure 12.31 Schematic of counterrotating screws defining location of high and low pressure regions.

Figure 13.8. Diagrammatic representation of the principie of an extruder with two counterrotating screws.

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