Core Process Analysis of Plastic Blow Molding: Comprehensive Control from Raw Materials to Finished Products

The stability of the blow-molding process directly determines the quality of the final product. Although the process routes vary slightly depending on the type of blow molding machine, the core stages can be summarized into four major phases: raw material pre-processing, plasticization and molding, blow inflation and cooling, and post-molding handling—including demolding and finishing.

Raw Material Preprocessing
Raw materials must be scientifically selected based on the requirements of the final product. Polyethylene (PE) boasts excellent chemical resistance, making it ideal for detergent bottles; polypropylene (PP), with its high rigidity, is commonly used in food packaging; and PET stands out for its exceptional transparency and barrier properties, making it the top choice for carbonated beverage bottles. Moisture-sensitive materials like PET must undergo treatment in a desiccant dryer, dried at 160–180°C for 4–6 hours to ensure the moisture content remains below 0.02%, thus preventing bubbles from forming during molding. Additionally, color masterbatches or antioxidants—among other additives—should be added proportionally, ensuring these additives exhibit excellent compatibility with the base material.

Plasticization and Molding Stage
Extrusion Blow Molding: The screw heats the raw material to a molten state (PE around 180–230°C, PET approximately 270–290°C). The molten material is then extruded through a die to form a tubular parison. The thickness of the parison is precisely controlled using Axial Wall Control (AWC) and Radial Wall Control (RWC) systems, with up to 30 to 128 control points available for fine-tuning.
Injection blow molding: The injection system feeds molten material into a parison mold, forming a preform with a threaded bottle neck. A transfer mechanism then moves the preform to the blow-molding station, where compressed air at 0.3–0.8 MPa is introduced to tightly conform the preform against the mold cavity.

Cooling and Post-Processing
The mold requires temperature control via evenly distributed cooling channels, with the cooling water typically set at 15–25°C. Cooling time accounts for 60%–80% of the overall production cycle. After demolding, the extrusion blow-molded products must undergo trimming to remove excess parisons, and some items also require sealing tests and surface printing.