Differences and Characteristics of Single and Twin Screw Extruders

Introduction of single screw extruder

As the name suggests, a single screw extruder has a screw inside its barrel. Generally, the effective length is divided into three sections, which are determined based on the diameter, pitch and depth of the screw. Generally, the effective length is divided into one third of each section.

The first section: starts from the last thread of the material inlet, called the conveying section. The material is required not to be plasticized here, but to be preheated and compacted under pressure, which means that the material is compressed into a solid like a plug, its function is to complete.

The second section is called the compression section. The volume of the screw groove in this section gradually decreases from large to small, and the temperature must reach the degree of material plasticization. The material that has completed the plasticization enters the third section.

The third section: metering section. Here, the material maintains a plasticizing temperature, just like a metering pump, which accurately and quantitatively conveys the melt material to supply the machine head. At this time, the temperature cannot be lower than the plasticizing temperature, which is generally slightly higher.

Application of single screw extruder

Single screw extruder is mainly used for extrusion of pipes, sheets, plates, and profiles, as well as granulation of partially modified materials.

Introduction and application of twin screw extruder

Twin screw extruders include the following multiple systems. The screw system mainly completes the plasticizing and conveying processes of materials, and has a significant impact on the performance and quality of the finished product.

①Feeding system: including hopper, mixing motor, and feeding motor. It can prevent material accumulation and facilitate its smooth entry into the feed port. ②External heating system: mainly uses heating rods and cylinders to efficiently heat materials and promote plasticization. ③Cooling system: A heat exchange system composed of heat transfer oil or water is used to reduce the heat of the fuselage, thereby effectively controlling the temperature of the cylinder. ④ Hydraulic screen changing system: use replaceable filter screens to intercept impurities, improve the degree of plasticization, and ensure the uniformity and stability of the quality of the produced materials. ⑤Vacuum system: Extract water and other low molecular volatiles from the material. ⑥ Electric control system: responsible for monitoring and controlling relevant equipment of the main and auxiliary material systems. ⑦ Screw system: The most important component of an extruder, which can be divided into a conveying section, a melting section (exhaust port), a plasticizing section (vacuum port), and a discharge section.

Segmentation of twin screw extruder

The screw system of a parallel twin screw extruder is generally divided into four sections: the conveying section, the melting section (exhaust port), the plasticizing section (vacuum port), and the discharge section Conveying section: used to transport materials and prevent material return. ② Melting section: This section fully melts and mixes materials through heat conduction and friction shearing Plasticizing section: further melt and mix the various components of the material, with the function of distribution and dispersion mixing. ④ Discharging section: Conveying and pressurizing to form a certain pressure to make the material closer, while further mixing to achieve the purpose of extrusion granulation.

The difference between single screw and double screw extruder

(1)Single screw extruder with lower price.

Single screw extruder has simple structure and low price; Twin screw has a complex structure and high price.

(2)Single screw formula more simple

For operation, the difference between the two is not very large. However, the process and formula of a single screw extruder are relatively simple, while the process, process, and formula of a twin screw extruder are more complex.

(3)Twin screw with higher efficiency

Twin screw extruder has large output, fast extrusion speed, and low energy consumption per unit output, while single screw extruder is inferior. The efficiency of twin screw extruders is mostly about twice that of single screw extruders.

(4)Twin screw mixing has strong plasticizing ability

Simply put, a single screw is suitable for plastic extrusion of polymers and for extrusion processing of granular materials, such as molding, film blowing, injection molding, etc., with a wide range of materials used; Twin screw extrusion machines have excellent mixing and plasticizing capabilities, making them more suitable for modifying plastics. And a twin screw extruder can produce dual colors.

(5)Single screw for easy maintenance

In terms of maintenance, a single screw is simpler than a twin screw because its structure is relatively simple and easy to repair.

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