Co-kneader

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.

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. 

Although commercial twin-screw extruders can be as large as 300 mm size, capable of compounding up to 40 ton/hr, the acmal type and size of the equipment used depends on the type of the polymer blend and the production volume. Normally, for engineering polymer blends, twin-screw extmders of about D = 90 mm size (L/D = 30 to 40) and capable of compounding at 700 to 1000 kg/hr, are used. For blending PVC or elastomer blends other types of compounding equipment are used, e.g. Farrell continuous mixer (FCM), Buss co-kneader, or a batch mixer, such as Banbury. 

Elemans, P.H.M. (2009) Continuous equipment simulations - co-kneader, in Mixing and CompouruUr of Polymers ... 

Product development work is usually carried out in a pilot plant. Here one can use a small Banbury or a Brabender mixer for a batch process and a small twin-screw mixer or a co-kneader for development work on a continuous process. 

Co-Kneader (Ko-Kneader) having Reciprocating Scre v and Pin Barrel -Parrel Continuous Mixer -List Continuous Mixer -Ring Extruder. 

Most of the research on reactive extrusion is performed in twin screw extruders, although a single-screw co-kneader has definite advantages if micromixing plays an important role. Franz (24) gave an overview of applications of reactive extrusion with a Busskneader in a paper discussing the polycondensation reaction of silanoles to produce silicon oils. Aeppli (25)... 

A particular type of single-screw extruder that can be used as a polymerization reactor is the co-kneader. Traditionally this machine is often used for processing of rubbers and foods. Though discovered in 1945 and commonly used in industry, its application is far ahead of theoretical understanding. 

The temperature can be controlled by the thermostated barrel and screw. The large area-to-volume ratio as well as the radial mixing contributes to good heat transfer capacities. These characteristics make the co-kneader well suited for exothermic polymerization reactions, where... 

Other models to characterize residence time distributions are based on fitting the measured distribution to models for a plug flow with axial dispersion or for series of continuously ideally stirred tank reactors in series. For the first model the Peclet number is the characteristic parameter, for the second model the number of ideally stirred tank reactors needed to fit the residence time distribution typifies the distribution. However, these models should be used with care because they assume a standard distribution in residence times. Most distributions in extruders show a distinct scewness, which could lead to erroneous results at very short and very long residence times. The only exception is the co-kneader the high amount of back mixing in this type of machine leads to a nearly perfect normal distribution. 

C) Buss-Kneader PR46-11D Co-Kneader with 3.5D discharge screw 46 11 Kneading screw of 1 ID and discharge screw of 3.5D... 

Blends prepared in different mixing equipment showed some slight differences in blend morphology. The blends prepared with the Buss Co-Kneader-type extruder exhibited the finest dispersion of LCP phases. In contrast, the channeling effect and phase separation were most pronounced for the counterrotating twin-screw extruder, in particular for blends whose components had totally different melt viscosities. 

Direct-action impellers are needed for extremely high viscosity liquids and plastic masses. Such materials include bread dough, battery paste, saltwater taffy, carbon black mixed in rubber, and so on. Suitable mixers for such systems include the co-kneader, extruders, and the Banbury mixer. These are described in Chapter 16. 

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