Differences between plastic recycling twin-screw extruder and single-screw extruder differences

The difference between twin-screw extruders and single-screw extruders is mainly reflected in two aspects: the way the material is conveyed and the flow field of the material. This article will briefly explain the differences between twin-screw extruders and single-screw extruders in plastic recycling from these two aspects.

Here is the list of contents

Material transfer method

The flow field of the material

Applications of plastic recycling twin-screw extruders

Material transfer method

In a single-screw extruder, the solid transfer part is the frictional resistance and the melt transfer part is the viscous resistance. The frictional properties of the solid material and the viscosity of the melt material determine the conveying behavior. If the frictional properties of certain materials are poor, feeding to the single-screw extruder is more difficult without solving the feeding problem. In twin-screw extruders, especially meshing twin-screw extruders, the conveying of material is to some extent a positively displaced conveying, and the degree of positive displacement depends on the proximity of the screw prongs of one screw to the relative screw grooves of the other screw. The screw geometry of a tightly meshed anisotropic rotary extruder produces a high degree of positive displacement conveying characteristics.

The flow field of the material

The flow velocity distribution of the material in a single-screw extruder has been fairly well described, while the flow velocity distribution of the material in a twin-screw extruder is quite complex and difficult to describe. Many researchers have analyzed the velocity field of the material without considering the flow of the material in the engagement zone, but the results of these analyses differ significantly from the actual situation. This is because the mixing characteristics and overall behavior of a twin-screw extruder depend mainly on the leakage flow that occurs in the engagement zone, which is however quite complex. The complex flow profile of the material in a twin-screw extruder exhibits macroscopic advantages that cannot be matched by a single-screw extruder, such as adequate mixing, good heat transfer, high melt capacity, and high leakage capacity, as well as good control of the material temperature.

Applications of plastic recycling twin-screw extruders

Glass fiber reinforced, fuel barrier pelletizing (e.g. PA6, PA66, PET, PBT, PP. PC reinforced flame retardant, etc.)

Highly filled materials pelletizing (such as PE, PP filled with 75% CaCO.)

Heat-sensitive material granulation (such as PVC, XLPE cable material)

lntense color masterbatches (e.g. 50% filled with color powder)

Antistatic masterbatch, alloy, coloring, low-fill co-blended granulation

Cable material granulation (e.g. sheathing material, insulation material)

XLPE pipe material granulation (e.g. masterbatch for hot water cross-linking)

Thermoset plastic blending extrusion (e.g. phenolic resin, epoxy resin, powder coating)

Hot melt adhesive, polyurethane reaction extrusion pelletizing (such as EVA hot melt adhesive, polyurethane)

K resin, SBS de-volatile pelletizing

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