In the conveying section, the material enters the barrel from the hopper, and with the rotation of the screw, it is transported forward along the direction of the screw groove, and is gradually compacted. After entering the compression and melting section, the pressure rises due to the changes in the spiral structure, and due to the heating of the barrel itself and the material between the two screws and the strong stirring, mixing and shearing of the screw and barrel, the temperature of the material rises High, start melting until all melt. As the space of the spiral groove is further reduced, the material is further heated and pressured to obtain cooking, so that the raw starch is fully gelatinized, and fat and protein are denatured. A series of complex biochemical reactions, such as tissue, are further homogenized to reach the uniform section. The material from the expansion cavity is evenly distributed to the template. At this time, the pressure is usually 3 ~ 6Mpa (depending on the expansion requirements), and the temperature can reach 150 ~ 200 ° C. Because the high pressure in the closed sleeve exceeds the extrusion temperature Under the saturated vapor pressure, the moisture will not evaporate quickly. When the material is instantaneously squeezed out from the die hole of a certain shape, the pressure is released quickly, the free moisture evaporates rapidly, and the material expands accordingly. It is quickly cooled to about 80 ° C, so it is cured and shaped, and maintains its expanded shape.