Core Structural Differences: Number of Screws and Transmission System. The single-screw floating fish feed extruder machine uses a "single screw + extrusion chamber" structure as its core. The screw is an integral design, with the screw groove depth gradually decreasing from the feed section to the discharge section. It is equipped with only one drive motor and reduction system, resulting in a simple and compact structure with a footprint of only 15-30㎡. The twin-screw pet food extruder, on the other hand, uses a "two-screw + closed extrusion chamber" structure. The screws are either meshing (co-directional or anti-directional) or non-meshing, requiring a synchronous transmission system to ensure that the two screws rotate at the same speed. It has more auxiliary equipment (such as a forced feeding device and a precise temperature control system), and its footprint reaches 50-100㎡, 2-3 times that of a single-screw extruder. For example, a single-screw extruder with a capacity of 150kg per hour requires only one 15kW drive motor, while a twin-screw extruder with the same capacity requires two 20kW motors, significantly increasing the complexity of the transmission system.
Working Principle Differences: Material Conveying and Heating Mechanisms. Single-screw fish feed processing machines rely on the friction and axial thrust generated by the rotating screw to convey materials. The material flows in a "dragging" state within the screw channel, and its conveying efficiency is greatly affected by the material's flowability. Heat is primarily generated through frictional heat, with external heating only as an auxiliary method, resulting in significant temperature fluctuations (±10℃). Twin-screw pet feed extruders achieve forced conveying through the meshing rotation of two screws. The material flows in a "shear-mixing-pushing" composite flow state within the screw gap, resulting in stable conveying efficiency unaffected by material flowability. Heat is generated through a combination of frictional heat and precise steam heating, and equipped with a multi-stage temperature control system, allowing temperature fluctuations to be controlled within ±3℃. For example, when processing low-flow, high-fiber raw materials, single-screw extruders are prone to conveying interruptions, while the forced conveying of twin-screw extruders ensures a continuous and stable flow of material into the extrusion chamber.
Differences in Extrusion Mechanisms: Pressure Control and Material Modification Effects The extrusion pressure of a single-screw floating fish extruder is formed by die throttling, resulting in large pressure fluctuations (±0.5MPa) and uneven material residence time in the extrusion chamber (3-5 seconds), leading to significant variations in the puffing and modification effect. In contrast, a twin-screw extruder, through precise control of the screw meshing gap, achieves stable extrusion pressure (±0.2MPa), uniform material residence time (5-8 seconds), and can achieve deep modification of raw materials through shearing action, resulting in a more uniform puffing effect. For example, when producing highly puffed pet snacks, the puffing ratio of a twin-screw pet pellet making machine fluctuates by only ±0.2 times, while that of a single-screw extruder fluctuates by ±0.5 times.
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