Core Differences in Forming Principles: Mechanical Extrusion vs. High-Temperature, High-Pressure Extrusion. The core forming principle of wet fish feed pellet processing machines is "adhesive + mechanical extrusion," requiring no high temperature or pressure. A liquid binder causes the raw material particles to adhere and agglomerate, then they are extruded by pressure rollers. The entire process is controlled at room temperature to 60℃ (drying stage), a physical forming process that does not alter the nutritional structure of the raw material. In contrast, extruders (primarily twin-screw extruders) generate strong shear force through the meshing rotation of the screws, combined with steam heating to create a high-temperature environment of 120-160℃ and a high pressure of 3-6MPa within the barrel. This causes the starch in the raw material to gelatinize and the protein to denature. The material is then extruded after instantaneous pressure release, a synergistic physical and chemical process. This difference in principle results in wet pellet mills retaining more nutrients, while extruders have higher nutrient conversion efficiency.
Product Characteristic Differences: Density, Water Resistance, and Nutrient Retention. Wet floating fish feed machines produce high-density (1.2-1.5 g/cm³) pellets with a compact structure and no internal pores, classifying them as hard pellet feed. They have moderate water resistance (4-6 hours) and are suitable for bottom-dwelling fish and livestock. Because there is no high-temperature treatment, the retention rate of heat-sensitive nutrients (vitamins, enzymes) is over 85%, and pellet hardness can be flexibly adjusted (2-5 kg). Extruders produce low-density (0.6-1.0 g/cm³) pellets with a porous and loose internal structure. Floating, sinking, and semi-floating properties can be achieved through parameter adjustment, resulting in stronger water resistance (8-12 hours), making them suitable for mid-to-upper-level fish (bass, tilapia). Starch gelatinization reaches over 80%, increasing nutrient absorption by 20%-30%, but the retention rate of heat-sensitive components is only 70%-75%, and the pellet hardness is relatively lower (1-3 kg).
Differences in applicable scenarios: Complementary and adaptable to different aquaculture needs. Wet fish feed extruders are suitable for producing feed for young animals (piglets, fish fry), heat-sensitive feeds, and conventional livestock and poultry feeds. They are particularly suitable for scenarios with high requirements for pellet hardness and nutritional integrity. They have low equipment investment and low energy consumption, making them suitable for small and medium-sized feed mills. Extruders are suitable for producing feed for mid-to-upper-level fish, high-end aquatic feeds, and functional extruded feeds, meeting the needs of large-scale, high-quality feed production. They can improve nutrient absorption and reduce water pollution, but their equipment investment and energy consumption are higher than wet pellet mills. In actual production, some feed mills use a combination of wet pellet mills to produce basic pellets, followed by secondary processing with an extruder, balancing nutrient retention and extrusion characteristics to meet specific aquaculture needs.
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