Working principle of twin-screw extruder
The structure of the twin screw extruder and single screw extruder is very similar, but its working principle is different. In a single screw extruder, the material transport depends on the friction and viscous resistance of the material, so the residence time distribution is wide.
In contrast, the material transport of the twin-screw extruder relies on the positive displacement transport of the screw, so the residence time distribution is narrow. The raw material of the twin-screw extruder is fed by the metering feeder through the feeding port. Some additives (such as glass fiber) need to be added through the feed port in the middle of the barrel and transported by the screw to the die head.
In this process, the movement of the material varies depending on the screw engagement mode and rotation direction. This paper will introduce the specific differences of its working principle from this point of view.
How does the twin-screw extruder work?
First of all, we take the application of twin-screw extruder in the field of plastics as an example, briefly introduce the working principle of twin-screw extruder. Then, we will specifically introduce their differences from the perspective of "screw engagement and rotation direction is different".
Twin screw extruder
It works as follows
1. After starting the twin-screw extruder, plastic particles or powder are first fed into the screw groove through the feeding system. The feeding system is usually composed of a feeding port, a feeder, a hopper and a feeding screw. Plastic raw materials through the hopper vibration or the rotation of the feeder evenly to the feed screw.
feeding
2. After the plastic raw materials enter the screw groove, the twin screw begins to rotate. By controlling the spacing and depth of the spiral groove, plastic raw materials from the front-end to back-end. During the propulsion process, the plastic raw material is squeezed by the outside of the barrel and the spiral groove, resulting in shear force and friction. This leads to a high-speed friction and heat plastic raw materials. The heating system provides additional heat energy and gradually melts the plastic raw material into a thermoplastic melt.
Screw rotation process
3. The extrusion process: when the molten plastic after reaching to a certain extent, part into the barrel of the extruder. This part usually consists of a widened spiral groove and an extrusion die head. In the extrusion section, the spiral groove spacing is gradually reduced, resulting in increasing pressure, which further promotes the melting of the plastic. Extrusion molds shape the molten plastic into the desired 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.
Extrusion process
The control system plays an important role in the operation of twin-screw extruder. Through the control system, feed, screw speed, temperature and pressure parameters 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 the product requirements to achieve the ideal extrusion effect.
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