Extrusion Process of Co-rotating Parallel Twin-screw Extruder

In general, the extrusion process experienced by the material in the twin-screw barrel generally includes: feeding, melting, melt conveying, mixing, homogenization, exhausting, metering, and the like.

Extrusion process

(1) Feeding

After the material is added to the screw below the feeding port of the barrel, the screw groove is not fully filled. The screw of this section is basically composed of forward conveying threaded elements, but the thread lead can be changed from large to small to improve the filling degree of the material to the screw groove.

(2) melting

Under the action of the heat transmitted by the barrel heater to the barrel and the heat generated by the extrusion and shearing of the material by the screw, the material begins to melt, and after passing through this section, it basically becomes a melt.

The filling degree of the material in this section is higher than that of the solid conveying section, and the pressure is generated, which consumes a large amount of energy.

(3) Melt conveying

The residual solid phase conveyed from the melting section is melted into a melt. The screw of this section is composed of large-lead forward conveying screw elements, the filling degree of the material is low, and the pressure is not established, so the additives or fillers to be added can be added in this section.

(4) Mixing

Auxiliaries or fillers added in the melt conveying section enter the mixing section composed of kneading blocks together with the melt for mixing (distribution mixing and dispersive mixing).

(5) Homogenization

After the material enters the homogenization section, the components of the mixture are homogenized under the shearing action of the kneading block (mainly distributed mixing, but the components that have not been dispersed are also continued to be dispersed and mixed), so that the components are mixed uniformly.

(6) Exhausting

The screw of the exhaust section is composed of a large-lead forward conveying screw element. The filling degree of the mixed material to the screw groove is low, which is conducive to exhausting. Adding vacuum assistance can further enhance the exhausting effect.

(7) Metering

In the metering section, since the lead of the screw becomes smaller, the filling degree of the melt to the screw groove becomes larger, so the pressure is established to extrude the mixed material from the die for granulation.

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