Common types of screw barrels

I. Classification by the number of screws
(I) Single screw barrel
Single screw barrel is a more common type. It consists of a screw and a corresponding barrel. The single screw barrel has a simple structure and relatively low cost. In plastic processing, single screw extruders are often used to produce some simple plastic products, such as some ordinary pipes and profiles. When the single screw barrel is working, the screw rotates to push the material forward. The material goes through different areas in the screw groove of the screw, such as the feeding area, compression area and metering area, and gradually completes the material conveying, plasticizing and other processes. For example, when producing ordinary PVC pipes, the single screw barrel can meet the basic material conveying and plasticizing requirements, plasticize the PVC raw materials into a uniform melt, and then extrude them into pipes through a mold.

(II) Twin screw barrel
Parallel twin screw barrel The two screws of the parallel twin screw barrel are placed in parallel in the barrel. This type of screw barrel has better mixing performance because the synergistic effect of the two screws can make the material more fully stirred and mixed in the barrel. In plastic processing, parallel twin-screw barrels are often used to produce products with high requirements for mixing uniformity, such as the production of plastic alloys, filled modified plastics, etc. For example, when producing modified plastics filled with PP and calcium carbonate, parallel twin-screw barrels can fully mix PP and calcium carbonate powder, so that calcium carbonate is evenly dispersed in the PP matrix, and the performance of plastic products is improved. Parallel twin-screw barrels have various specifications, such as the common twin-screw barrels with different diameters such as Φ50/2 and Φ65/2.

Conical twin-screw barrel The screw of the conical twin-screw barrel is conical, and its characteristic is that the screw diameter is larger at the feeding end, and the screw diameter gradually decreases as the material is transported forward. This structure makes the conical twin-screw barrel have a larger volume when feeding, and can better adapt to materials of different shapes and sizes. Conical twin-screw barrels are often used in some occasions with high requirements for material adaptability in plastic processing, such as processing some irregularly shaped recycled plastic particles. For example, when recycling waste plastics to produce plastic products, conical twin-screw barrels can effectively process waste plastic particles of different shapes and sizes, and re-plasticize them into new plastic products.

2. Classification by function and structural characteristics
(I) Venting screw barrels
The venting screw barrel is provided with an exhaust port on the barrel. During the plasticization process of the material, volatile substances such as moisture and air in the material can be discharged. This is very important for the production of some plastic products that have high requirements for product quality and cannot contain bubbles or moisture. For example, when producing transparent plastic sheets, if there are bubbles in the material, it will affect the transparency and quality of the sheet. The venting screw barrel can effectively solve this problem.

(II) Barrier screw barrels
The screw of the barrier screw barrel is provided with a special barrier structure. This structure allows the material to flow and mix more specifically in the screw groove of the screw, enhancing the plasticization effect of the material. For example, when processing some high-viscosity plastics, the barrier screw barrel can improve the plasticization uniformity of the material, reduce the presence of unplasticized particles, and improve the quality of plastic products.

(III) Pin-type screw barrel
Pin-type screw barrels have pins on the inner wall of the screw or barrel. These pins can disrupt the flow direction of the material and increase the shear and mixing effect of the material. When producing some plastic products that require the addition of multiple additives or pigments, pin-type screw barrels can make the additives and pigments more evenly dispersed in the plastic matrix, thereby improving the performance and appearance quality of the plastic products.