Twin screw counter-rotating

Figure 31.13 Shear viscosity as a function of the shear rate for the HIPS-TPP/clay blends. CR-TS, twin-screw counter-rotating extruder SS-SMD, single-screw extruder with the static mixing die SS-SMD-U, single-screw extruder with the static mixing die and sonication. Source Reproduced with permission from Sanchez-Olivares G, Sanchez-Solis A, Camino G, Manero O. Express Polym Lett 2008 2 569 [143]. Copyright 2008 BME-PT.

The TPO formulations were prepared using a Haake twin screw, counter rotating, 25-mm extruder, equipped with underwater pelletization. All of the ASTM test specimens were prepared by injection molding with an 85 ton, Cincinnati Milacron injection molding machine. 

Several studies have been performed to evaluate the mixing capabilities of twin screw extruders. Noteworthy are two studies performed by Lim and White [12,13] that evaluated the morphology development in a 30.7 mm diameter screw co-rotating [28] and a 34 mm diameter screw counter-rotating [3] intermeshing twin screw extruder. In both studies they dry-mixed 75/25 blend of polyethylene and polyamide 6 pellets that were fed into the hopper at 15 kg/h. Small samples were taken along the axis of the extruder and evaluated using optical and electron microscopy. 

Counter-Rotating Twin Screw Extruders. If the screws of a twin screw extruder rotate in opposite direction, it is called a counter-rotating twin screw... 

Comparison of single-screw, co-rotating and counter-rotating twin-screw extruders... 

Type Single screw Low speed type High speed type Counter-rotating twin screw... 

Most of the compounds were extrusion compounded in a conical, partially intermeshing, counter rotating twin screw extruder (Haake Reomix TW-lOO). The extruder speed was set at 50 rpm and the barrel temperature profile was set to produce a melt temperature of 260°C at the die. Samples were injection molded in a 31.8 MT Battenfeld press with a 59 cc shot size. Where noted, samples were compounded in a 60 cc Brabender internal mixer and compression molded. 

The industrial use of twin-screw extruders for this purpose revolves extensively, but not exclusively, around intermeshing co-rotating variants. Closely in-termeshing counter-rotating designs are widely used for profile extrusion of UPVC dry-blends since they permit close temperature control and exhibit a high conveying efficiency due to the positive displacement of material where the screws intermesh [150]. 

There seems to be considerable disagreement about co-versus counter-rotating twin screw extruders between different groups in the polymer processing industry and academic community. 

Figure 3.36 Number and weight average of polyamide 6 domain sizes along the screws for a counter-rotating twin screw extruder.

W.C. Thiele, Counter-rotating Intermeshing Twin Screw Extruders, in Plastics Compounding-Equipment and Processing, D. B. Todd, Ed., Hanser, Munich, 1998. 

J. W. Cho and J. L. White, Melting and Blending in a Modular Corotating/Counter-rotating Twin Screw Extruder, Int. Polym. Process., 11, 21-28 (1996). 

T. Li and I. Manas-Zloczower, A Study of Distributive Mixing in Counter-rotating Twin Screw Extruders, Int. Polym. Process., 10, 314—320 (1995). 

T. Sakai and N. Hashimoto, Application of Novel Counter-rotating Intermeshed Twin Extruder for Degassing Operation, SPE ANTEC Tech. Papers, 32, 860-863 (1986) also T. Sakai, N. Hashimoto, and N. Kobayashi, Experimental Comparison between Counterrotation and Co-rotation on the Twin Screw Extrusion Performance, SPE ANTEC Tech. Papers, 33, 146-151 (1987). 

K. J. Gadzenveld and L. P. B. M. Janssen, Scale-up of Counter-rotating Closely Intermeshing Twin Screw Extruders without and with Reactions, Polym. Eng. Sci., 30, 1529-1536 (1990). 

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.]...

Qi Leakage flow rate in a counter rotating intermeshing twin screw extruder... 

The desired self-cleaning function led to the development of the intermeshing twin screw. The counter-rotating screw was discarded, because it tended to get blocked by solids and was a poor mixer attention focused instead on the intermeshing, co-rotating extruder. 

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