The metering section is the downstream zone of an extrusion screw, following the melting/compression section. Its primary function is to homogenize the molten polymer, eliminate pressure fluctuations, and deliver a consistent volumetric flow rate to the die. It ensures uniform product dimensions and quality by maintaining steady pressure and temperature.
In extrusion screw design, the metering section is critical for achieving consistent output. It features a constant, shallow flight depth that creates shear and backpressure, further homogenizing the melt and removing any remaining solid particles. The geometry is designed to generate the pressure required to force the material through the die, ensuring predictable pumping and pressure generation.
Typical parameters for this component include screw diameter (20–150 mm), metering section length (4–6 D), channel depth (2–8 mm), flight width (0.08–0.12 D), radial clearance (0.1–0.4 mm), surface roughness (Ra 0.2–0.8 µm), hardness (56–62 HRC), operating temperature (180–400 °C), operating pressure (10–40 MPa), screw speed (20–120 rpm), throughput (5–500 kg/h), and weight (5–200 kg). Material grades such as 38CrMoAlA (per GB/T 3077) are referenced for wear resistance.
When selecting or verifying a metering section, confirm model-specific values with the legal manufacturer or supplier. The listed ranges are directory references and must be validated for the actual application. Standards, if any, serve as procurement references, not proof of certification or compliance.
Maintenance signals include increased pressure fluctuations, reduced output, or visible wear on flight surfaces. Failure boundaries may involve excessive wear to leakage flow, or thermal degradation due to high shear. Proper installation and alignment with the screw and barrel are essential for performance.
The metering section features a constant, shallow flight depth. As the screw rotates, the molten material is dragged forward by the screw flights. The shallow channel creates shear and backpressure, which further homogenizes the melt, removes any remaining solid particles, and generates the pressure required to force the material through the die. The constant geometry allows for predictable pumping and pressure generation.
