Extrusion For Snacks

Principle and working principle of extruder
The raw material is fed into the screw, which then conveys the material. The smaller screw blades located below the barrel limit the volume of the material and enhance the resistance of the material to movement. As a result, the material is squeezed and fills the gap between the barrel and the screw blades. As the material is pushed upward in the barrel, it is kneaded by the screw to form a semi-solid plasticized material. Extrusion cooking refers to the process of heating the material to more than 100 degrees Celsius (or hot extrusion). During this process, the temperature rises rapidly due to friction heat and any additional applied heating. Higher operating temperatures promote the gelatinization of starch components and promote the stretching of expandable components in the presence of water. After pausing the powder conveying, the pressure and shear force of the barrel section with the least screw blades increase.

At the discharge end of the barrel, the powder finally passes through one or more restrictive holes (die heads), is extruded under pressure, expands to the final shape, and cools rapidly as the water flashes in the form of steam. Low-pressure extrusion, with temperatures below 100 degrees Celsius, is used to produce fish paste, fish glue, pet food, etc. The operating parameters of an extruder include:
 Temperature
 Pressure
 Die aperture
 Shear rate
Classification of extruders
Based on operation:
1) Hot extruders
2) Cold extruders
Based on construction:
1) Single screw
2) Twin screws
 Counter-rotating extruders
 Co-rotating extruders