The Types and Characteristics of Extruder Screw

Ⅰ. Types and characteristics of extruder screw


The characteristics of the gradual extruder screw: the compression section is longer, accounting for 50% of the total length of the screw, the energy conversion is gentle during plasticization, and it is mostly used for PVC and other plastics with poor thermal stability.


The characteristics of the abrupt extruder screw: The compression section is short, accounting for about 5% to 15% of the total length of the screw, and the energy conversion is more intense during plasticization. It is mostly used for polyolefin, PA and other crystalline plastics.


General-purpose extruder screw features: relatively strong adaptability, can be adapted to the processing of a variety of plastics.


Ⅱ. The extruder screw segment description


In general, the extruder screw can be divided into feeding section, compression section, and homogenization section (also called metering section).


Description of feeding section: The screw groove of the extruder in this section has a fixed depth, and its function is to be responsible for preheating and plastic solid conveying and pushing. It must be ensured that the plastic begins to melt at the end of the feed section.


Compression section description: The screw thread of the extruder in this section gradually shrinks, and its function is to melt, mix, shear, compress and pressurize the plastic raw materials. The plastic will be completely dissolved in this section and the volume will be reduced. The design of the compression ratio is very important.


Homogenization section description: the screw groove of this section of the extruder has a fixed groove depth. Its main functions are mixing, melt conveying, and metering. It must also provide sufficient pressure to maintain a uniform temperature of melt and stabilize the flow of molten plastic.


Ⅲ. The materials commonly used to produce extruder screw elements


1. 38CrMoAla;


2. SACM645;


3. 42CrMo;


4. 9Cr18MoV;


5. SKD61;


6. Tungsten carbide alloy, tungsten carbide nickel-based alloy;


7. Fully hardened powder alloy (full alloy);


8. High temperature alloy.

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