Container Manufacturing Processes - In-Depth Notes

Overview of Container Manufacturing Processes

Blow Molding Overview
  • Definition: A manufacturing process for shaping hollow plastic parts.
  • Processes:
    • Extrusion Blow Molding (EBM)
    • Injection Blow Molding (IBM)
    • Injection Stretch Blow Molding (ISBM)
Extrusion Blow Molding (EBM)

  • Process:

    • Hollow tube (parison) extruded downward into the mold.
    • Mold closes, injecting air to inflate the parison.
    • Cycle consists of:
    • Extrude parison
    • Close mold
    • Inject air
    • Cool part
    • Open mold
    • Eject part
    • Trim excess material (flashing).

  • Key Terms:

    • Flashing: Excess material formed due to off-center finishes or handles.
    • Self-trimming molds: Finish bottle comes directly from the mold.
    • Spin Trimming: Uses a hot knife for trimming the bottle neck.

  • Materials: Typical materials include LDPE, HDPE, PVC, PET.

Injection Blow Molding (IBM)

  • Process:

    • Preform is injected into the mold, then expanded by air.
    • Cycle avoids secondary operations, reducing scrap material.

  • Typical Materials: PET, LDPE, HDPE, PP, PVC.

  • Advantages:

    • High precision neck finishes.
    • Optimal production for small containers.
    • Thicker walls and superior dimensional stability.
Injection Stretch Blow Molding (ISBM)

  • Process:

    • Preform conditioned, stretched, and blow molded in the same cycle.
    • Comprises single stage (directly from preform) and two-stage (pre-molded preform).

  • Key Points:

    • Widely used with PET for bottles requiring clarity and strength.
    • Allows for detailed control of production parameters leading to fewer defects.
Glass Container Processes

  • Annealing Lehr: Gradually cools glass to relieve internal stresses; a critical process post-forming.

  • Surface Treatments:

    • Hot-End Coating: Applied at high temperatures to enhance durability and adhesion.
    • Cold-End Coating: Further protection applied after molding.

  • Glass Molding Processes:

    • Blow and Blow: More variability; used for hollow bottles.
    • Press and Blow: Better control, efficient use of higher volume glass production.
Compression Molding
  • Process: Solid pre-weighed polymer is placed in a heated mold where it cures into shape.
  • Benefits:
    • Uniform part formation, resistance to solvents, good fatigue strength.
  • Negatives:
    • Expensive, difficulty with recycling, and limited color options.
Rotational Molding
  • Definition: Material dispersed on heated mold walls through rotation.
  • Uses: Typically large, hollow items such as tanks and kayaks.
  • Key Steps:
    • Load polymer
    • Heat and rotate mold
    • Cool and remove part.
Welding Techniques
  • Spin Welding: Uses frictional heat from rotational movement to create joints; efficient and energy-saving for round parts.
  • Ultrasonic Welding: Uses ultrasonic vibrations to bond materials under pressure; effective for joining thermoplastics, albeit expensive.
Material Considerations
  • Common Materials: HDPE and PET are predominant in bottles; polypropylene (PP) for closures.
  • Reprocessing and Regrind: Mixing recycled materials with virgin resin to maintain properties and reduce costs.
  • Co-Extruded Bottles: Multi-layer production that can enhance barrier properties but adds complexity to recycling.