The screw element is an important component in a screw extruder. The following will provide a detailed introduction from the dimensions of its classification, function, characteristic parameters, etc. Classification
Classification by Function
Conveying Elements: They are divided into forward conveying screw elements and reverse conveying screw elements. The forward screw elements have the same direction as the extrusion direction and are mainly responsible for conveying the material along the extrusion direction; the reverse screw elements, on the contrary, hinder the forward conveying of the material, which can extend the residence time of the material in the barrel, increase the filling degree and material pressure, and promote the mixing effect.
Shearing Elements: Mainly refer to kneading blocks, which are usually used in pairs or in series. There is an offset angle between adjacent kneading blocks, known as the stagger angle. Their function is to provide a high shearing force and have the ability to distribute and disperse the mixture, promoting the mixing and exchange of materials along the axis of the screw elements.
Mixing Elements: Generally refer to toothed elements, including straight teeth and helical teeth. The groove structure of the toothed elements can connect adjacent screw channels, promoting the mixing effect between materials, ultimately achieving melt homogenization and promoting longitudinal mixing of materials. At the same time, they can also generate a shearing force perpendicular to the flow direction on the material flow.
Classification by Structure
Single-Head Screw Elements: When the thickness is large, they can minimize material leakage. They have a smaller capacity than double-head screws but have the highest conveying efficiency.
Double-Head Screw Elements: They are the conventional conveying elements in co-rotating twin-screw extruders. They have less shearing force than three-head elements and are used for solid feeding, melt conveying, venting, and melt conveying. They have uniform heating and good self-cleaning performance.
Three-Head Screw Elements: They have higher shearing force and are mainly used for melting, dispersion, and mixing. They can make the pressure and temperature distribution of the material in the barrel more flexible and have a good exhaust and volatilization effect, but the output is lower.