Extruder multiple-screw operation

It is also possible (as mentioned earlier) to have extruders that use twin or multiple screws. Such extruders are utilized in certain operations because they offer specific advantages. These include (1) increased output at low screw speed, (2) improved pumping control over a wide range of operating conditions, (3) decreased viscous dissipation and internal heat generation, (4) ability to handle materials that are difficult to feed, and (5) lower power requirements (see Fig. 7-9). 

Solids feeders are composed of single or multiple screws that rotate inside a sleeve. Granules and additives from the feed and additive tanks are conveyed to the homogenizer by the feeders. Most solids feeders are single screws that deliver solids at a specific rate. Granules leave the feed tank continuously when the extruder is in operation. Figure 10-13 illustrates how a solids feeder operates. 

Screw extruders are also used, however, to produce pelleted materials, either as a final product or for further processing, in the food, ceramics, chemical and other industries. Many orifices in a die plate form a multiplicity of extruded rods which are cut into pellets by rotary cutter blades. The extrusion operation is frequently the final step in a sequence of processes which may include binder/lubricant addition, mixing, heating, cooling or vacuum degassing. 

For the tests of preparing dynamic vulcanizates in the continuous process of reactive extrusion a twin-screw mixer-extruder DSK 42/6D manufactured by Brabender was used. The vulcanizates were produced dynamically in the process of one-stage or two-stage extrusion process, setting the favorable operating parameters for the device, which had been determined based on multiple tests distribution of temperatures in each heating area... 

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