Extruder tangential twin-screw

Fig. 1. Process flow sheet for the continuous conversion of latex in a counterrotating, tangential twin-screw extruder as it might be arranged for the production of acrylonitrile-butadiene-styrene polymer (Nichols and Kheradi, 1982). Polystyrene (or styrene-acrylonitrile) melt is fed upstream of the reactor zone where the coagulation reaction takes place. Washing (countercurrent liquid-liquid extraction) and solids separation are conducted in zones immediately downstream of the reactor zone. The remainii zones are reserved for devolatilization and pumping.

R. J. Nichols, Pumping Characteristics of Counterrotating Tangential Twin Screw Extruders, SPE ANTEC Tech. Papers, 29, 130-133 (1983). 

Howland, C. Erwin, L. Mixing in counter rotating tangential twin screw extruders. SPE Antec Proceedings, Chicago, IL, May 2-5, 1983 113-116. 

Nichols R. and Kheradi, G., Melting in Counter-Rotating Tangential Twin Screw Extruder, SPE ANTEC, 134, May 1983. 

Non-intermeshing. These are sometimes referred to as tangential twin-screw extruders and are effectively two single-screw extruders but with a single barrel. This type of machine is of little use for mixing. 

Howland, C. and L. Erwin. 1983. Mixing in Counter Rotating Tangential Twin Screw Extruders. 41st SPE Annual Technical Conference, Chicago, IL, 29,113-116. 

Tangential twin-screw extruders (c and d) are not closely intermeshing they can be envisaged as a parallel connection of two single-screw extruders with... 

Counterrotating, Tangential, Nonintermeshing Twin Screw Extruders... 

We now discuss the elementary steps of processing as they occur in the twin screw segment of the CRNI tangential extruders melt pumping in the single screw segment was covered in Chapter 9. 

A. Kiani and H. J. Samann, The Influence of Curvature on the Simulation of Flow in a Tangential Counter-rotating Twin Screw Extruder, SPE ANTEC Tech. Papers, 39, 2758 (1993). 

Fig. 11.15 RTD cumulative functions of a single screw tangential counter-rotating twin-screw extruder (TCTSE) under matched and staggered conditions, and the back-mixed extruder reactor. [Reprinted by permission from Y. Lu, Ph.D Dissertation, Department of Chemical Engineering, Stevens Institute of Technology, Hoboken, NJ, 1993.]...

In the most simplistic view, the counter-rotating non-intermeshing twin-screw extruder could be viewed as two tangential single-screws sitting side by side in a barrel with an open apex area between them, see Fig. 10. Unlike intermeshing twin-screws, the non-intermeshing... 

White, J.L. Modular counter-rotating twin screw extruders intermeshing and tangential. In Polymer Mixing Technology and Engineering White, J.L., Coran, A.Y., Moet, A., Eds. Hanser Munich, 2001 167. 

Twin-screw extruders can be co- or counter-rotating, intermeshing or tangential, cylindrical or conical. Co-rotating screws are very efficient mixers for high viscosity fluids due to the axially and cross-wise open... 

Figure 1.12 Fuller Welding Engineering modular tangential counter-rotating twin-screw extruder [71].

Tangential (Non-intermeshing) Counter-rotating Twin-Screw Extruder This extruder is used more for latex coagulation, recovery, devolatilization of polymer solutions, and for reactive extmsion. 

Secor [41] presented an intermeshing model for devolatilization in co-rotating twin screw extruders that incorporates the major characteristics of fluid motion. These characteristics were experimentally observed in a twin screw extruder with a transparent barrel. The observed flow pattern consisted of alternating rotation in the tangential direction with the screw and axial forward motion at the entrance to the intermeshing region see Fig. 10.61. 

It is critically important that the screw channel under the vent port is only partially filled with plastic this is true for single as well as twin screw extruders. Figure 67 shows a cross section of a partially filled screw channel. The vent opening has a tangential design this is beneficial in minimizing accumulation of plastic melt in the vent port. 

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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