Operating point of a single-screw sheet extruder: the intersection of the screw characteristic curve and the die characteristic curve. Plasticization: the process of heating solid polymers to produce a uniform, non-volatile, and highly plasticized fluid. Clamping force: the force applied during the holding phase of injection molding.

The injection machine exerts a separating force on the moving and fixed molds due to the molten material within the mold cavity, and this force is transmitted to the mold. Flow diverter: A streamlined metal block located inside the barrel or die of an extruder or injection molding machine. Its function is to force the flowing melt into thin layers, enhancing heat transfer and thereby improving plasticization efficiency. “Three highs”: The phenomenon where the transverse thickness of an extruded product is uneven—thicker in the center and at both ends, while thinner near the center and along the sides. Jet flow: The gate thickness is much smaller than the part thickness, and the melt flow rate is very high (resulting in unstable flow and easy melt fracture). Stagnant flow: The gate thickness is less than the part thickness (leading to melt fracture). Holding pressure: Applying a specific pressure to the melt in the mold cavity to compensate for its cooling‑induced shrinkage.

Back pressure: Plasticizing pressure is the force exerted on the molten material at the tip of the screw as the screw rotates and retracts.

Injection pressure: The pressure exerted by the screw tip on the molten plastic.

Shrinkage rate: the amount by which the dimensions of the molded part are reduced relative to the dimensions of the injection mold cavity.

Supercooling: the difference between the material temperature and the mold temperature.

Reaction Injection Molding (RIM): Two or more low-viscosity, low-molecular-weight liquids—monomers or prepolymers—are injected into a closed mold under high pressure, where they are impacted and mixed, triggering a chemical reaction within the mold.

Compression molding: A process in which a specified amount of molding compound—whether in powder, granular, or fibrous form—is placed into a metal die and cured under specific temperature and pressure conditions to form a finished part.

Non-uniform shrinkage: asymmetric thermal contraction caused by uneven cooling of the part; non-uniform planar and volumetric shrinkage; anisotropic behavior arising from induced orientation; and differential thermal‑strain flow resulting from geometric effects.

Measures:

1. Appropriately reduce the injection and holding pressures;

2. Increase material flow and mold temperature;

3. Increase the screw back pressure;

4. The product design is well‑thought‑out. Pressure‑holding and solidification: Under sustained molding pressure, thermoplastic materials transition from a flowable state to an insoluble solid, continuing until they are fully cured.

Additives for single-screw sheet extruders are chemical substances added to resin formulations to facilitate smooth molding and processing and to achieve the desired performance characteristics. Geometric dispersion: a process in which two or more components are brought into close proximity—reducing interparticle distances within the same component and between different components—through a reduction in geometric dimensions; it is categorized into simple mixing and dispersed mixing. Extrusion stability: the degree of fluctuation in flow rate, pressure, temperature, composition, and the quality of the extrudate during the extrusion process. Aggregated-state structure: the spatial arrangement of individual polymer chains, stabilized by intermolecular interactions. Free volume: the difference between a material’s specific volume and the volume occupied by its molecules, characterized by randomly distributed voids of varying sizes within the material. Draw ratio: the ratio defined by the die and the core die.