The secret to matching blow molding machines with plastic materials: performance alignment and process optimization

Different plastics exhibit significantly varying processing characteristics, requiring tailored adjustments to equipment parameters for optimal molding.

Polyethylene (PE) Adaptation Solution
PE has a low melting point (110–130°C) and exhibits low melt viscosity. When extrusion blow molding, the barrel temperature should be set between 180–220°C, while the screw speed should be maintained at 50–80 rpm. Since PE is prone to melt fracture, the die pressure must remain stable within the range of 10–15 MPa. Additionally, the cooling air ring airflow should be adjusted to a medium-to-low setting to prevent rapid cooling of the film, which could lead to wrinkling.

Key parameters of polyethylene terephthalate (PET)
PET is highly hygroscopic and thermally sensitive, so it must be processed using a desiccant drying system, with the dew point of the dried material kept below -40°C. During injection blow molding, the barrel temperature is set in three zones: the feed zone at 250–260°C, the compression zone at 270–280°C, and the metering zone at 260–270°C. Additionally, the blow air pressure should be 0.2–0.3 MPa higher than that used for PE products, and the cooling time should be extended by 20% to ensure proper crystallinity levels are achieved.

Polypropylene (PP) Process Optimization
PP exhibits significant low-temperature brittleness, so an impact-modifying agent must be added during processing. The extrusion temperature should be set between 200°C and 230°C. Due to PP's low melt strength, the parison extrusion speed should not be too fast—ideally no more than 30 mm/s. Additionally, the blow-up ratio should be kept below 1:2.5, and the cooling water temperature should be raised to 25–30°C to minimize internal stresses in the final product.

When changing materials, thoroughly clean the screw and die. When switching from PE to PET, use PP as a transition material for cleaning to prevent mixing of different resins, which could lead to defects in the final product.