The single-screw extruder has a single screw within the barrel. Generally, the effective length is divided into three segments, and the three effective lengths are determined in accordance with the diameter of the screw, the pitch, and the depth of the screw thread, and are typically evenly divided at one-third each.
Conveying segment: Beginning from the final thread at the material inlet, it is termed the conveying segment. the material is required not to be plasticized here, but to be preheated and compressed;
Melting segment: The compression segment. The volume of the screw groove in this segment gradually reduces from large to small, and the temperature needs to attain the plasticizing degree of the material. Compression occurs here (the volume being 3 in the conveying segment, and it can be compressed to volume 1 here. This is called the compression ratio of the screw - 3:1. Some machines might also vary), and the plasticized material proceeds to the third segment.
Metering section is the metering section, where the material maintains a plasticizing temperature to supply the head, which is generally slightly higher than the plasticizing temperature.
The twin-screw extruder has twin screw within the barrel.The screw system of parallel twin screw extruder is generally divided into 4 sections: conveying section, melting section (exhaust port), plasticizing section (vacuum port), discharge section.
Conveying section: the function is to transport materials and prevent feedback.
Melting section: This section through heat conduction and friction shear, so that the material is fully melted and mixed.
Plasticizing section: the components of the material are further melted and mixed, with distribution and dispersion mixing function.
Discharge section: conveying and pressurizing, forming a certain pressure, making the material closer, while further mixing, to achieve the purpose of extrusion granulation.
Difference between Single and twin screw extruder
|
Item |
Single screw extruder |
Twin screw extruder |
|
Screw diameter ratio |
More shorter,most ratio is 7:1~11:1,but also has 18:1 |
More longer,12:1~16:1 |
|
Screw section shape |
Rectangle |
arc-shape |
|
Screw structure |
Simple |
Complex |
|
Degree of equipment maintenance |
Normal |
Difficult |
|
Temperature control |
Temperature control is easy |
Temperature control is not easy |
|
Convenience level of changing granules |
More convenient |
Normal |
|
Formulation |
Simple |
Complex |
|
flexibility |
more rigid,can not be combined |
can be freely combined |
|
Efficiency |
The efficiency is just half of twin-screw extruders |
Large output, fast extrusion speed, low energy consumption per unit output,due to its better mixing and heating of raw materials, the products produced are more uniform and of higher quality |
|
Price cost |
Lower |
Higher |
|
Plasticizing capacity |
Single screw is suitable for plasticizing polymer extrusion, suitable for extrusion processing of granular materials, such as molding, blowing film, injection molding, etc., |
The twin-screw extruder has a good mixing plasticizing ability and is more suitable for the modification of plastics. And twin-screw extruder can produce two colors. |
|
Applied materials |
PP,PE,PS,ABS,PMMA,PVC |
HDPE,PE,PP,ABS,PC, EVA+ CaCO3,Talc ,TiO2 and etc. |
|
Application scenarios |
Single screw extruders are widely used in the production of plastic pipes, plates, films, and profiles; |
Twin screw extruders are mainly used for the production of composite and polymer materials, and their capabilities are usually more powerful than single screw extruders. |
|
Sensitivity to metallic foreign bodies in materials |
Relatively sensitive, it is not easy to process recycled powder |
Less sensitive |
How to Choose Plastic Extruder?
Single screw extruder and twin screw extruder each have their own advantages and disadvantages. The advantages of a single screw extruder are low cost, easy maintenance and operation; The disadvantage is that the production efficiency is relatively low, and it cannot produce high-end products required by the system. The twin-screw extruder has high production efficiency, good product quality, but high cost, complex equipment, and difficult operation.
It is very important to choose the appropriate extruder according to raw materials. Understanding the differences and advantages and disadvantages between single screw extruders and twin-screw extruders can help enterprises choose production equipment .