Based on the direction of rotation, twin-screw extruders can be divided into two types: co-rotating and
counter-rotating.
In a co-rotating extruder, both screws rotate in the same direction. In a counter-rotating extruder, the two screws
rotate in opposite directions.
Classification by Screw Axis Orientation
According to whether the screw axes are parallel, twin-screw extruders can be divided into parallel axis and
intersecting axis types.
Parallel axis twin-screw extruders have axes that run parallel to each other. Intersecting axis extruders are conical
in shape.
Meshing and Non-Meshing Types
Twin-screw extruders can also be classified as meshing or non-meshing.
Common Advantages of Parallel and Conical Twin-Screw Extruders
Both parallel and conical twin-screw extruders share the following advantages: a transfer mechanism for forced
advancement of plastics, good mixing and plasticizing ability, excellent dewatering capacity, and strong adaptability
to various material molding processes and plastic products.
Differences Between Parallel and Conical Twin-Screw Extruders
1. Screw Diameter
In a parallel twin-screw extruder, the diameter of both screws is the same throughout. In a conical twin-screw
extruder, the diameter at the small end differs from that at the large end.
2. Center Distance
In a parallel twin-screw extruder, the center distance between the two screws remains constant. In a conical
twin-screw extruder, the two axes are at an angle, so the center distance varies along the axis.
3. Length-to-Diameter Ratio (L/D)
For parallel twin-screw extruders, L/D refers to the ratio of the effective screw length to the outer diameter of the
screw.
For conical twin-screw extruders, L/D refers to the ratio of the effective screw length to the average of the large
end diameter and the small end diameter.
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