Structural Features of Co-rotating Twin-screw Extruder

Combined screw

The most notable feature of the co-rotating twin-screw extruder is that both the screw and barrel adopt a "building block" design. The screw consists of several components mounted on the mandrel, such as threaded components, kneading blocks, toothed mixing discs, retaining rings, etc. The barrel also consists of different barrel parts (fully enclosed, with exhaust port and feed port). According to the specific materials, formula and performance requirements of the mixture to be prepared, different types and quantities of screw elements and cylinder elements are combined in a certain order through scientific combination to efficiently complete the set mixing task. By changing the combination sequence of screw and barrel, the best use effect of different materials and formulas can be achieved, achieving the purpose of one machine with multiple uses. In addition, another advantage of the building block design is that worn threaded and barrel elements can be partially replaced, thus avoiding the scrapping of the entire screw or barrel and significantly reducing maintenance costs.

Combined barrel

The modular design of the barrel can be connected by flange or tie rod. The barrel is usually embedded with a bimetallic liner to improve the wear resistance of the inner surface of the barrel. In order to achieve precise temperature control, each barrel section has its own heating/cooling design, thus achieving the best combination of cooling and heating functions.

By combining various threaded elements, the co-rotating twin-screw extruder has the functions of feeding, melting, mixing, exhausting, pressure holding and conveying, realizing various process such as material conveying, plasticizing, shearing, exhausting, pressure holding and extrusion.

1) Forced transport.

The two screws move in opposite directions in the meshing position. One screw pulls the material into the meshing gap, while the other screw pushes the material out of the gap, causing the material to transfer from one screw groove to another, and the material is forced to be transported to the machine head along the screw in an "∞" shape.

2) Homogenization and mixing.

The co-rotating twin screws have a small gap at the meshing position, and the speed directions of the screw ribs and spiral grooves are opposite, so the shear speed in the meshing area is high, the shear force is large, and the mixing effect is very good.

3) Self-cleaning.

The co-rotating twin-screw extruder has a very high shear rate, which can scrape off any accumulated material attached to the screw, and has a very good self-cleaning effect, so the residence time of the material is very short and it is not easy to cause local degradation.

4) Plasticization of materials.

The screw gap has a great influence on the plasticization quality of the material. The smaller the gap, the greater the shear force, but the amount of material passing through is reduced; the larger the gap, the greater the amount of material, but the shear force will decrease.

5) Feeding method: The co-rotating twin-screw extruder requires uniform quantitative feeding, and adopts the metering weight loss feeding method.

6) Exhaust. A large lead screw conveying element can be used to keep the spiral groove unfilled and in a zero pressure state, so that an exhaust section can be set.

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