Blow molding is a key process for manufacturing hollow plastic products and is widely used in the production of bottles, cans, barrels, boxes, as well as industrial components such as automobile fuel tanks and ventilation ducts. Its core equipment – blow molding machine, can be divided into three main types according to the different molding methods of the parison: extrusion blow molding machine, injection blow molding machine and stretch blow molding machine. Each type has its own unique working principle, advantages and characteristics, and applicable fields.

Extrusion Blow Molding Machine: Extrusion blow molding machine is the most common and widely used form of blow molding, which is characterized by the parison being a continuously extruded tubular plastic melt.

● Extrusion: Plastic granules are heated and melted in the extruder, then extruded through the die head and mouth into a vertically downward hollow tubular parison.
● Mold Closing: When the parison reaches the desired length, the blow mold quickly closes, clamping the parison and sealing its bottom.
● Air Blow Molding: A blow needle is inserted into the top of the parison, injecting high-pressure air into the interior, forcing the soft parison to adhere to the mold cavity wall, where it cools and sets into shape.
● Mold Opening and Part Removal: The mold is opened, the molded product is removed, and trimming is performed.

Extrusion blow molding machines are mainly used to produce hollow containers that do not require very high dimensional accuracy, such as bottles, barrels, cans, toys, automobile air ducts, fuel tanks, etc. of various specifications.

Injection Blow Molding Machine: The characteristic of the injection blow molding machine is that the parison is made by injection molding and is a complete preform with bottle neck thread.

● Molten plastic is injected into the preform mold, where it cools to form a tubular preform with a bottle mouth and a bottom. This preform is placed on a core rod.
● The turntable rotates, moving the core rod with the preform into the blow mold. After the mold is closed, high-pressure air is introduced through the core rod to inflate and shape the preform.
● After the molded product cools, the mold opens, and the turntable rotates to the demolding station to eject the finished product from the core rod.

Injection blow molding machines are mainly used to produce small, thin-walled containers with large batches and high dimensional accuracy requirements, especially medicine bottles, cosmetic bottles, daily necessities bottles, etc.

Stretch Blow Molding Machine: The stretch blow molding machine stretches the parison axially and inflates it radially before blow molding after the parison is made by injection molding or extrusion, thereby significantly improving the mechanical properties and barrier properties of the product.

● First, a transparent, bottomed preform is created through injection molding. Its shape and dimensions differ from those of the final product.
● The cooled preform is reheated to a temperature suitable for stretching (high elasticity).
● The heated preform is placed in a blow mold, where it is mechanically stretched axially using a stretch rod while simultaneously inflated radially by the injection of high-pressure air.
● After cooling and finalizing, the mold is opened and the part is removed.

Stretch blow molding machines are almost exclusively used to produce PET plastic bottles, such as mineral water bottles, carbonated beverage bottles, cooking oil bottles, soy sauce bottles and other packaging containers that require high barrier properties or high transparency.

In summary, the selection of blow molding machines depends entirely on the requirements of the final product. Whether it is the pursuit of cost-effectiveness and flexibility of extrusion blow molding, the pursuit of high precision and high-quality bottle neck injection blow molding, or the pursuit of ultimate performance of stretch blow molding, each has its irreplaceable application stage.