Faygo Plast

The thermomechanical cooking is of course the main stage in extruding aquafeeds. A co-rotating twin screw extruder is a positive displacement pump (Figure 1), thanks to the interpenetration of the screws. This allows handling viscous, oily, sticky or very wet materials, with the same level of pumping efficiency. There is an extended choice of raw materials when using a corotating TSE. A TSE has a high tolerance to lipids in raw materials and formulations.
In a co-rotating twin screw extruder, throughput and screw speed are decoupled. Then, for a given formulated feed mix, a co-rotating TSE is characterised by multiple operating points and screw profiles can vary extensively to modulate the mechanical energy input.
In a co-rotating TSE very intense mixing is observed in the intermeshing zone of the screw extruder where macromixing and micromixing occurs (Figure 2). Consequently, heat transfer coefficient in the fully filled sections is high. Homogeneous melts can be obtained with very good lipid binding. Die expansion develops consistently, which leads to constant product density,
texture and shaping as well as a uniform product colour.
Single screw extruder is a process of thermomechanical cooking, with the two main energy inputs being temperature and mechanical energy. To optimally use these inputs the design of the TSE is of importance regarding screw diameter, screw length/diameter ratio and screw profile. Operating conditions that influence the cooking process are mix feed rate, water flow rate, steam flow rate, screw speed and temperature profile. The final product then is determined by die texturisation, which is managed by the shape of the inserts, the opening section, air gap and die plate design.