A blow molding machine is a type of plastic processing equipment used to manufacture hollow plastic products such as bottles, containers, drums, and tanks. It works by heating plastic until it becomes soft and then shaping it inside a mold cavity using air pressure. Blow molding is widely used in the packaging, automotive, and consumer goods industries because it produces lightweight, durable, and cost-effective products.

The Basic Principle of Blow Molding

Blow molding works on a simple concept:

1. Heat plastic until it becomes pliable.

2. Form a hollow tube or preform.

3. Use compressed air to expand the plastic against the walls of a mold.

4. Cool and solidify the product before removing it.

Main Types of Blow Molding Processes

1. Extrusion Blow Molding (EBM)

• Process:

1. Plastic pellets are melted in the extruder.

2. The molten plastic is extruded into a hollow tube called a parison.

3. The parison is clamped inside a cooled metal mold.

4. Compressed air inflates the parison, forcing it to take the shape of the mold.

5. The part cools and hardens, then is ejected.

• Applications: Bottles for milk, juice, detergent, automotive fuel tanks, and industrial containers.

2. Injection Blow Molding (IBM)

• Process:

1. Plastic is injection-molded into a preform (a test-tube-like piece with a neck finish).

2. The preform is transferred to a blow mold.

3. Air pressure expands the preform into the mold cavity.

• Applications: High-quality bottles with precise neck finishes, such as pharmaceutical and cosmetic containers.

3. Injection Stretch Blow Molding (ISBM)

• Process:

1. A preform is injection-molded.

2. It is heated and stretched both axially and radially inside the blow mold.

3. Compressed air forms the final shape.

• Applications: PET bottles for water, soda, and other beverages. Stretching improves strength, clarity, and barrier properties.

Key Components of a Blow Molding Machine

• Extruder or Injection Unit: Melts and plasticizes raw pellets.

• Die Head / Preform Mold: Shapes the molten plastic into a parison or preform.

• Blow Mold: Cools and shapes the inflated plastic.

• Air System: Provides the compressed air for inflation.

• Cooling System: Uses water or air circulation to harden the product quickly.

• Clamping System: Holds the mold halves together under high pressure.

Step-by-Step Workflow (Extrusion Blow Molding Example)

1. Feeding: Plastic resin pellets are loaded into the hopper.

2. Melting: Resin is heated in the extruder barrel to a molten state.

3. Extrusion: Molten plastic is extruded downward into a parison.

4. Clamping: The parison is captured between two halves of the mold.

5. Blowing: Compressed air inflates the parison to the mold’s shape.

6. Cooling: Mold chills the product until solid.

7. Ejection: Mold opens, and the finished product is removed.

8. Trimming: Excess plastic (flash) is cut away for a clean finish.

Advantages of Blow Molding

• High production efficiency for large volumes.

• Ability to create complex shapes and sizes.

• Cost-effective for lightweight hollow products.

• Compatible with many materials, including PET, HDPE, PVC, and PP.

Conclusion

A blow molding machine works by heating plastic, shaping it into a parison or preform, and then inflating it with air inside a mold to form hollow products. Depending on the method—extrusion, injection, or injection stretch blow molding—manufacturers can produce bottles, tanks, and containers with different properties and applications.