Working Principle of Twin Screw Extruder

The structure of a twin-screw extruder is very similar to that of a single-screw extruder, but its working principle is very different. In a single-screw extruder, material transportation relies on the friction and viscous resistance of the material, so the residence time distribution is wider.

In contrast, the material conveying of the twin-screw extruder relies on the positive displacement of the screw, so the residence time distribution is narrower. The raw materials of the twin-screw extruder are fed through the feed port by a metering feeder. Some additives (such as glass fiber) need to be added through the feed port in the middle of the barrel and transported to the die head by the screw.

During this process, the movement of the material varies depending on the screw meshing method and the direction of rotation. This article will introduce the specific differences in their working principles from this perspective.

How does a twin screw extruder work?

First, we will take the application of twin-screw extruder in the field of plastics as an example to briefly introduce the working principle of twin-screw extruder. Then, we will specifically introduce their differences from the perspective of "different screw meshing methods and rotation directions".

The working principle of twin screw extruder is as follows:

1. After starting the twin-screw extruder, plastic granules or powder are first fed into the screw groove through the feeding system. The feeding system usually consists of a feeding port, a feeder, a hopper and a feeding screw. The plastic raw materials are evenly transported to the feeding screw through the vibration of the hopper or the rotation of the feeder.

2. After the plastic raw material enters the screw groove, the twin screw begins to rotate. By controlling the pitch and depth of the screw groove, the plastic raw material is pushed from the front end to the rear end. During the pushing process, the plastic raw material is squeezed by the outside of the barrel and the screw groove, generating shear force and friction. This causes high-speed friction and heating of the plastic raw material. The heating system provides additional heat energy to gradually melt the plastic raw material into a thermoplastic melt.

3. Extrusion process: When the molten plastic reaches a certain level, it enters the extrusion section of the barrel. This section usually consists of a widened screw groove and an extrusion die. In the extrusion section, the screw groove spacing gradually decreases, and the pressure generated is getting greater and greater, which further promotes the melting of the plastic. The extrusion die shapes the molten plastic into the required cross-section and length through specific structures and channels. The extrusion outlet is usually equipped with a cooling system to quickly cool and solidify the molten plastic.

The control system plays a vital role in the operation of the twin-screw extruder. Through the control system, parameters such as feeding, screw speed, temperature and pressure can be monitored and adjusted in real time to ensure the stability and controllability of the extrusion process. The control system can also adjust the screw speed, temperature and shape according to product requirements to achieve the ideal extrusion effect.

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