COUNTER-ROTATING EXTRUDER

Machine Type single screw extruder, twin screw extruder (co-rotating), twin screw extruder (counter-rotating), multi screw extruder, buss co-kneader, internal mixer, static mixer. 

Metal-to-metal wear can also occur in intermeshing twin screw extruders. Counterrotating twin screw extruders are more susceptible to metal-to-metal wear than co-rotating twin screw extruders. Counter-rotating twin screw extruders, therefore, generally operate at rather low screw speeds. Unfortunately, co-rotating extruders also can experience serious metal-to-metal wear problems. 

Items Single- Screw Extruder Co-Rotating Twin Screw Extruder Counter- Rotating Twin-Screw Extruder... 

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

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. 

A study was made of nucleation in PE foams produced in a counter-rotating extruder using talc powders and masterbatches as nucleating agents and CFG and HCFC blowing agents. The results indicated the importance of shear force in nucleation, as proposed in the lump cavity nucleation model and demonstrated by melt temperature effects observed in these experiments. It was shown that shear enhancement via lump break-up was not a vital mechanism in nucleation. 6 refs. 

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]. 

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. 

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.

Fig. 10.27 Devolatilization of a 42% polychloroprene-58% CCI4 in a JSW TEX 65 counter rotating, intermeshing TSE. (a) The effect of increasing the number of vent ports at Q = 30 kg/h and N = 125 rpm. (b) The effect of decreasing Q/N ratio, at constant Q. [Reprinted by permission from T. Sakai and N. Hashimoto, Application of Novel Counter-rotating Intermeshed Twin Extruder for a Degasing Operation. SPE ANTEC Tech Papers, 32, 860 (1986).]...

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). 

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... 

Fig. 13.1. Different types of extruders, a) single screw b) co-kneader c) non-intermeshing, mixing mode d) nonintermeshing, transport mode e) counter-rotating, closely intermeshing f) co-rotating, closely intermeshing g) conical counter-rotating h) self-wiping, co-rotating.

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. 

The same data, determined by not too complex means, can also be used to answer further questions, e. g., relating to the efficiency of the pressure build-up. Figure 2.26 illustrates the product stress (the reciprocal value of the pump efficiency) comparing counter-rotating and co-rotating extruders [40], i.e., two substantially different machines. 

The market for counter-rotating twin-screw (TS) extruders is basically dominated by two designs. One has cylindrical screws called parallel TS extruder and the other TS extruder is fitted with conical screws. Performancewise, the superiority of the conical principle to parallel does not only appear in the theoretical comparison, but in practice as confirmed by users. Flexibility of conical turns out an extrudate of consistent quality at both low and high output rates which are not sensitive to raw material fluctuations. It appears that the parallel have reached their efficiency limit unless a means of drastically increasing the... 

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