The co-rotating intermeshing twin-screw extruder has two types of low speed and high speed. The difference lies in the planning, operating characteristics and application fields of the two extruders. The former is mainly used for profile extrusion, while the latter is used for special polymer processing. The tightly intermeshing extruder is a low-speed extruder with a tightly intermeshing screw shape, during which the shape of the ridge of one screw closely matches the shape of the groove of the other screw, that is, the shape of the conjugate screw. The typical shape of the screw of a tightly meshed co-rotating (CICO) twin-screw extruder is shown in the following figure.
The shape of the conjugate screw seems to show an excellent seal between the two screws, but the cross section of the meshing area shown in Figure 3-10 shows a large open space between the grooves of the two screws (area II). Therefore, the conveying characteristics of the tightly engaged co-rotating twin-screw extruder is not as good as that of the tightly engaged counter-rotating extruder (CICT).
The tightly meshing co-rotating twin-screw extruder can theoretically be designed as a fully meshed screw groove horizontally sealed, but the longitudinal direction cannot be sealed, and it must be opened, otherwise the screw will not engage. It is necessary to design the width of the screw groove to be greater than the width of the screw edge, so the co-rotating twin-screw extruder has a sliding type of engagement.
When the material is added to a screw from the feeding port, it is dragged by the conflict and transported forward along the screw groove of the screw to the lower wedge-shaped area, and must be compressed. If the screw web has a large gap (Figure 3-12), the ridge of the other screw will not block the path of the material. Because the two screws in the wedge zone have a speed gradient of size and size and opposite directions, the material will not enter the meshing zone and continue to travel around the same screw, but is held up by the other screw and dragged by the conflict on the outside of the barrel. The screw groove of the other screw is transported forward, and the process is repeated when the material travels to the upper wedge-shaped area.