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MODE OF OPERATION
The system is based on the high peripheral speed of the mixing shaft tools of up to 50 m/s. The resulting centrifugal force forms a concentric ring layer of product along the drum wall. The product is moved through the mixing chamber in a plug-flow manner. The retention time depends on the filling level, speed, geometry and mixing tool adjustment as well as the throughputs but is extremely short compared with a continuous Ploughshare Mixer. The mixing chamber is divided into zones with different mixing tools enabling different shear intensity by selecting and adjusting the mixing tools according to each application. The friction of the product is increased through the high speed of the mixing tools but is still gentle enough due to the short residence time during the process.
LIQUID INJECTION
Liquid components (additives, coating agent) are introduced directly into the product ring layer – either via tangentially placed liquid pipes through the drum wall or via a hollow mixing shaft with specially perforated tools. However, moistening of the mixer wall and shaft is largely prevented. The liquid distribution is similar to a nozzle but avoiding any risk of clogging or disturbance of the spray. In this way, large liquid quantities can be easily added and mixed.
GRANULATION
A product is automatically granulated due to the bridging effect when liquids are added to products which turn sticky in contact with a liquid or if they contain binding agents. This granulation effect can be more or less pronounced. Usually the bulk density of the product is increased as soon as it is subsequently dried. In most cases, the resulting grain size is between 100 µ and 1.5 mm. In a certain extent, it can be controlled by adjusting the liquid quantity and the process parameters.
COATING
The coating of particles with, for example, molten fat, molten sulfur, is performed effectively using a ring layer mixer. The cooling and recrystallization has to be done in downstream equipment.