Granulation screw mixer-extruders

Granulation Techniques Involving Use of Screw Mixer-Extruders. . . 168... 

Standard production lines for obtaining granulated aminoplast by the use of screw mixer-extruders are shown in Fig. 14a, b. The production line illustrated in Fig. 14a is the Buss line for obtaining crushed material35 ... 

The following ways of incorporating are used (a) thermoplastic powders are blended with flame retardants in a fluid or turbine mixer, extruded by means of a twin screw extruder, and pelletized (b) previously pelletized thermoplastics are mixed with powders of flame retardants in a Banbury mixer then the mixture is transferred to a roll mill and into a belt granulator ... 

A number of thermal stability tests arc available, some of which have developed into national (DIN) or international industrial standards (ISO). Pigments in thermoplastic systems, for instance, are studied under heat extrusion conditions [110]. The colorant to be tested, possibly together with titanium dioxide, is dispersed in the thermoplastic, using a mixer and a granulating extruder (Sec. 1.8.3). The pigmented test pellets are then fed into a screw extruder which ejects a standardized test specimen with defined dimensions [111]. Starting at the lowest possible temperature level, the extrusion temperature is increased by intervals of 10 or 20°C between samples. 

The third type of compounding device is the extruder. Next to its use for fabrication (which will be dealt with in 11.4.2), it is applied as a mixer. In essence, it is a screw pump, in which the mass to be mixed is transported in a heated cylinder by a screw, or, with twin-screw extruders, by two parallel screws. During this transport melting and intensive mixing take place. At the end of the screw the blend is pressed through a number of openings and cooled down in most cases the strands thus obtained are on-line cut into granules. 

There are systems, which provide a dedicated mixing system. The use of mixing within a co-rotating twin-screw extruder system is described by Kleinebudde et al. (13). This system also claims the ability to be able to adjust the water content to the appropriate level and because it acts as both mixer and extruder, reduces the number of items of equipment required. This system is not widely employed in screen extruder systems, which without careful formulation can generate considerable heat that could be detrimental to heat sensitive formulations. Hellen et al. (14) describe the use of a granulator (Nica M6L, Nica systems AB, Molndat, Sweden) that functions with a high speed turbine to mix the powder with the water prior to extrusion. 

A feed hopper and a mixer continuously feed resin pellets (and carbon black batch pellets if necessary) and a certain amount of granulated edge trimming from the running geomembrane production into the extruder (Fig. 2.5). The main part of the extruder is the extrusion screw, which rotates in a heated barrel (Fig 2.6). Typical process temperatures for HDPE... 

An extruder screw functions as a feeder, a conveyor and a mixer. The screw must take plastic granules and melt and mix them, before the material is conveyed out through the die. Different screw... 

FIG. 6 Flow sheet of a compounding unit of PP with fillers (clay, calcium carbonate, kaolin, etc.) and other additives. (1) Compounding extruder. (2) Nonfluxing mixer. (3) PP powder. (4) Metering screw. (5) Hopper. (6) Degasing. (7) Granulating device. (8) Switcher. (9) Water separator. (10) Dryer for granules. (From Ref. 47.)... 

---