Twin screw extruder machine consists of 2 identical co-rotating and intermeshing screws, hence the name “twin screw extruder”.According to function and screw arrangement, the screw is divided into three sections: Feed section, Cooking section, and forming section.
In the Feed section, raw ingredients are continuously fed from inlet into the barrel. The twin screws intermesh as they turn, mixing the ingredients thoroughly. Liquid, usually shortening, water or others, is injected through ports in the barrel according to technique requirement. In this section, the ingredients are worked into a continuous dough by the twin screw action.
In the Cooking Section, screw thread structure changes, pressure rises, and the external heating of the barrel and shear of the material between screws and screw/barrel, temperature of material rises and begins to melt until it is completely melted. The thread gap is further reduced, temperature and pressure of the material are increased, the starch in the raw material is fully gelatinized, fat and protein are denatured, texture is further homogenized, and reach to forming section.
In Forming section, the material flow is evenly distributed to the mold through flow divider. Now the pressure is usually 3～6Mpa (depending on the expansion requirements), and the temperature can reach 150～200℃. The high pressure in barrel exceeds saturated vapor pressure at the extrusion temperature, moisture will not evaporate quickly. When the material is extruded from dies, pressure is released quickly, free water evaporates rapidly, material expands, moisture is quickly lost from the material, product quickly cools to about 80 ℃, and get solidified and shaped , and will maintain its expanded shape.
