How to control the processing temperature of an extruded feed extruder?

The temperature control principle of automatic fish food making machines relies on the dual effects of "mechanical shearing heat generation + external heating." Inside the barrel, feed ingredients are subjected to high-speed extrusion and shearing by the screw, generating a significant amount of frictional heat, which accounts for 30%-50% of the total heat. Simultaneously, external heating coils (resistive or electromagnetic) provide auxiliary heating, ensuring the temperature reaches the threshold required for ingredient puffing. The essence of temperature control is to coordinate the relationship between mechanical shearing heat generation and external heating through a PLC control system, maintaining temperature stability in each processing zone.

The difference in puffing temperature requirements for different raw materials is the core basis for temperature control. Grain raw materials such as corn and soybean meal require puffing temperatures controlled at 110-130℃, at which point the starch gelatinization rate can reach over 85%, forming a stable puffed structure. Animal protein raw materials such as fish meal and meat and bone meal require slightly lower puffing temperatures, around 100-120℃, to avoid excessive protein denaturation due to high temperatures. Meanwhile, coarse fiber raw materials such as straw and alfalfa require high temperatures of 130-150℃ to break down the fiber structure and achieve effective puffing. If the temperature is lower than the raw material requirements, it will lead to insufficient extrusion, high feed density, and poor palatability; if the temperature is too high, it will cause the raw material to carbonize, destroying vitamins and other nutrients.

The basic temperature control logic must follow the principle of "gradual heating and precise temperature compensation." From the feeding section to the discharging section, the temperature should gradually increase: the temperature in the feeding section should be controlled at 60-80℃, mainly to preheat the raw material and prevent cold material from clumping and clogging; the temperature in the compression section should be increased to 90-110℃ to initially plasticize the raw material; the extrusion section should reach the peak temperature (adjusted to 100-150℃ according to the raw material) to complete the core extrusion process; the temperature in the discharging section should be slightly reduced by 5-10℃ to avoid excessive charring of the feed. Simultaneously, temperature data for each section should be collected in real time by temperature sensors. When mechanical shearing heat generation is insufficient, the heating coils should automatically compensate for the heat; when shearing heat generation is too high, cooling fans or water cooling systems should intervene in time to control temperature fluctuations within ±2℃.

In addition, the moisture content of the raw material will also affect the temperature control effect. Raw materials with a moisture content of 14%-16% exhibit the highest mechanical shearing heat generation efficiency and require the least external heating power. Excessive moisture content leads to heat absorption, necessitating higher heating temperatures; conversely, insufficient moisture content generates excessive frictional heat, requiring enhanced cooling. Therefore, the moisture content of the raw materials must be tested before processing, and moisture or preset temperature parameters should be adjusted in advance to ensure precise temperature control.

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