Blow molding is a manufacturing process that utilizes compressed air to transform molten plastic into hollow objects. It is widely employed in the production of various containers, bottles, and other hollow products. The blow molding process can be broadly divided into three main stages:
- Material Preparation: Plastic pellets, typically made from polyethylene (PE), polypropylene (PP), or polyethylene terephthalate (PET), are fed into the hopper of an extruder.
- Melting and Mixing: The plastic pellets are conveyed through the extruder's heated barrel, where they are melted and homogenized to form a uniform molten polymer.
- Extrusion and Preform Formation: The molten polymer is forced through an extrusion die, shaping it into a tubular form known as a parison. The parison is then passed through a cooling ring to solidify its outer surface while maintaining the inner core in a molten state.
- Mold Clamping: The parison is transferred to a blow molding machine, where it is gripped between two halves of a mold. The mold halves are designed to form the desired shape of the final product.
- Air Injection and Inflation: Compressed air is injected into the parison through a pin located at the bottom of the mold. The pressurized air forces the parison to expand and conform to the shape of the mold cavity.
- Wall Thickness Control: The thickness of the blow molded product is controlled by adjusting the amount of compressed air used and the parison's cooling rate.
- Mold Opening: Once the parison has fully inflated and cooled, the mold halves open, releasing the molded product.
- Part Ejection: The ejected product may be automatically ejected from the mold by a robotic arm or manually removed by an operator.
- Final Cooling: The blow molded product is allowed to cool completely before being inspected, trimmed, and packaged.
- Parison: A tubular piece of molten plastic formed during the extrusion stage.
- Blow Mold: A two-piece tool that shapes the molten parison into the final product form.
- Mold Cavity: The interior space within the mold that defines the shape of the blow molded product.
- Core Pin: A central rod that supports the parison during the blow molding process.
- Air Injection Point: The location on the mold where compressed air is introduced into the parison.
- Blow Ratio: The ratio of the final product diameter to the initial parison diameter.
- Wall Thickness: The thickness of the blow molded product's walls.
- Cooling Time: The time required for the blow molded product to cool completely.
