Closely intermeshing co-rotating twin screw

Closely intermeshing co-rotating twin screw extruders occupy a dominant position among extruders and are used in a wide variety of applications. They are not only used extensively in the production, compounding, and processing of plastics, but also employed in large numbers in other branches of industry, e.g., the rubber and food processing sectors. 

Fig, 5.25. Geometry cross section for closely intermeshing co-rotating twin screw extruders... 

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

To really control the mixture and dispersion of additives, or to do reactive extrusion, a twin-screw extruder is necessary. Twin-screw extruders are available in several different configurations, but for the work of compounding the most often used is a closely intermeshing co-rotating extruder, with a specially designed screw for the particular task. In order to accomplish this with the least amount of machining. 

The iow speed extruder has ciosely intermeshing screw geometry where the flight profiie fits ciosely into the channel profile, i.e., a conjugated screw profile. A typical screw geometry of the closely intermeshing co-rotating (CICO) twin screw extruder is shown in Fig. 10.3. 

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]. 

Counterrotating intermeshing twin-screw extmd-ers have the narrowest residence time distribution followed closely by co rotating intermeshing twin-screw extmders. Counter rotating nonintermeshing twin-screw extruders have the broadest residence time distribution. 

Screw Elements for Co-rotating, Closely Intermeshing, Twin-Screw Extruders... 

From the time they were first developed, co-rotating, closely intermeshing twin-screw extruders have proven to be highly effective for the continuous treatment of viscous products and they have successfully replaced many discontinuous technologies. They will certainly continue to be successful in other markets in the future, facilitating new production processes. 

The machines mainly used for compounding plastics, chemicals and food are co-rotating, closely intermeshing twin-screw extruders. Some 30 000 such extruders are in use worldwide, about 1/3 are ZSK from Coperion Werner Pfleiderer, Stuttgart. In the chemical industry increasingly more and more batch mixers are being replaced by continuous twin-screw knea-ders. 

A new process has been developed for the production of PLA using reactive extrusion polymerization based on a new catalytic system, which not only enhances the ROP kinetics of L-lactide but also suppresses side and degradation reactions such as intermole-cular transesterification reactions. Co-rotating closely intermeshing twin-screw extruders have often been used for polymerization reactions, but in any case, the reaction time was sufficiently smaller than the residence time in the extruder. In the case of ROP of lactide, the extraordinary effect of triphenylphosphine on the efficiency of Sn[Oct)2 as a catalyst was the key point to ensure further enhancement of the polymerization reaction. Thus, it was feasible... 

Thanks to their residence time distributions, co-rotating, closely intermeshing twin-screw extruders have assumed a dominant market position. Other machines, such as single-screw and counter-rotating extruders are used only for special tasks. Fig. 4.7 [35]. 

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