Its main equipment is "screw extruder". The material is fed into the expander, and the screw propels the material to form an axial flow. At the same time, due to the mechanical friction between screw and material, material and barrel, and material interior, material is strongly extruded, stirred and sheared, resulting in further refinement and homogenization of material. With the gradual increase of pressure and the corresponding increase of temperature, under the conditions of high temperature, high pressure and high shear, the physical properties of materials change from powder to paste, starch gelatinization, protein denaturation, degradation and refinement of fibrin, killing pathogenic bacteria, improving hygienic indicators, inactivation of toxic components. When the paste material is ejected from the die hole, under the strong pressure difference, the material is expanded, dehydrated and cooled. The structure of the extruded product is loose, porous, crisp, and has better palatability and flavor.
2. Extrusion process and characteristics of extruded products.
(1)In the process of extrusion, the heat generated by mechanical friction, the direct steam fed into the expansion chamber, or the indirect steam fed into the jacket of the expansion chamber gradually increase the heating temperature and pressure. The material swells under high temperature and pressure, softens texture, collapses, refines and homogenizes under the action of mechanical force, breaks down cell wall, breaks up molecular structure, starch gelatinization and protein denaturation. The physical properties change qualitatively. Therefore, the screw extruder is also known as "continuous cooking machine".
(2)The maximum temperature of extrusion and extrusion in high temperature and short time sterilization and detoxification process can reach 130-160℃, while the time of material in high temperature period is very short, about 5-10 seconds. High temperature can not only kill pathogenic bacteria and improve health indicators, but also deactivate various harmful factors and enzymes and improve the quality of feed. Therefore, the extrusion process is also a high temperature and short-term process of sterilization and detoxification.
(3)The most effective way to improve the quality of materials is extrusion and extrusion processing, high temperature sterilization, and improve the hygienic indicators. Hydrothermal treatment can inactivate a variety of anti-nutritional and anti-feeding factors. High temperature and high pressure can change the physical properties of materials, improve the quality of feed and raise the feed price. Extrusion and puffing process makes raw meal become clinker, which is an epoch-making change in feed industry. Feed puffing technology, ideal protein system, biological system potency system, and the application of information network technology and molecular biology have brought feed industry into a new era of vigorous development.
.Basic Principle of Expansion Processing in Feed Production line：