Blow molding is a widely used manufacturing process that shapes plastic materials into hollow objects, such as bottles and containers. While this method offers many advantages, it is not without its challenges. Imagine the disappointment of discovering a batch of defective products after hours of production. These errors can be a significant setback. This guide aims to provide relief by identifying common problems and offering actionable solutions for blow molding troubleshooting. By understanding the root causes and implementing effective strategies, you can avoid costly rework and ensure consistent product quality.  

Blow Molding Troubleshooting
Learn about common issues in the blow molding process and effective blow molding troubleshooting solutions to optimize production and reduce downtime.

1. Blow Molding Process Overview

Blow molding is a manufacturing process used to create hollow plastic parts by inflating heated plastic into a mold cavity. The process begins by heating a plastic material, usually in the form of a tube known as a parison, until it becomes malleable. Air is then blown into the parison, forcing the plastic to expand and take the shape of the mold.

Once the plastic cools, the mold opens, and the final product is ejected. This technique is commonly used to produce bottles, containers, and automotive parts. Blow molding offers efficiency in producing lightweight and durable products at scale.

The global blow molding market was valued at USD 80.04 billion in 2023 and is projected to grow at a compound annual growth rate (CAGR) of 7.0% from 2024 to 2030, according to Grand View Research. Polyethylene (PE), polyethylene terephthalate (PET), and polypropylene (PP) are among the most common raw materials used in blow molding. These materials are chosen for their versatility, durability, and suitability for various applications.

There are five main types of blow molding operations:

  • Continuous extrusion blow molding: This is the most common type, where a continuous stream of molten plastic is extruded into a parison, which is then inflated in a mold.
  • Intermittent extrusion blow molding: The parison is extruded intermittently in this process, with breaks between each extrusion cycle.
  • Injection blow molding: In this technique, plastic is injected into a mold to form a preform, which is later blown into its final shape using air pressure.
  • Injection stretch blow molding: Similar to injection blow molding, this method adds a stretching step to improve material strength, and then inflating it to create a more complex shape, often used for making bottles.
  • Extrusion stretch blow molding: A combination of extrusion blow molding and stretch blow molding. In this process, the plastic is first extruded into a tube (parison) and then stretched and blown into the mold for shaping.

These types vary depending on the application and materials, but they all rely on the principle of shaping hollow plastic parts by blowing air into heated plastic.

2. What Is Blow Molding Used For?

Bottling and packaging represent the largest segment for blow molding, making up around 49% of the global market share. Blow molding is widely employed in creating plastic bottles, containers, and jars for industries such as foods, beverages, pharmaceuticals, and cosmetics. 

  • Containers: Bottles, jars, buckets, and canisters
  • Packaging: Food packaging, pharmaceutical packaging, and industrial packaging

Blow molding is also used to manufacture hollow plastic components in industries such as building and construction, consumer goods, and transportation. 

  • Automotive parts: Fuel tanks, radiator housings, air ducts, and bumpers
  • Toys: Balls, dolls, and action figures
  • Consumer goods: Household appliances, sports equipment, and medical devices
  • Building and construction: Plumbing, drainage systems, cable ducts, manholes, etc

Blow molding is a versatile process that can be used to create products with various shapes, sizes, and wall thicknesses, making it a popular choice in many industries. 

blow molding troubleshooting
Blow molding is widely employed in creating plastic bottles, containers, and jars for industries such as foods, beverages, pharmaceuticals, and cosmetics

3. Common Blow Molding Problems & Troubleshooting Solutions

Blow molding, like any manufacturing process, is not immune to challenges that can hinder production. Blow molding defects can significantly impact production efficiency and profitability for plastic product manufacturers. Some issues are specific to certain production methods or materials. To help you navigate these issues, we’ll highlight the common problems and provide effective blow molding troubleshooting solutions so that you can either prevent or swiftly address them when they occur.

Problem Causes Solutions
Rocker bottoms 

(Uneven container base)
  • Insufficient cooling in the mold bottom area: Clogged cooling channels, low coolant flow rate, or Incorrect coolant temperature 
  • Excessive parison thickness at the bottom: Variations in extrusion parameters like melt temperature and pressure, worn or damaged die head. 
  • Mold design issues: Lack of proper contour or ribs in the mold base design. 
  • Improve cooling: Clean and maintain cooling channels, adjust coolant flow rate and temperature. 
  • Refine parison profile: Monitor and adjust extrusion parameters, inspect and repair or replace the die head. 
  • Modify mold design: Add support features like ribs or a more contoured base.
Surface wall defects (Imperfections on container surface)
  • Contamination: Build-up of debris, residue, mold,  impurities…on the mold surface.
  • Material inconsistencies: Presence of moisture, foreign particles, or degraded resin in the melt.
  • Uneven cooling causing material flow issues: Insufficient cooling in some areas leading to uneven material distribution.
  • Implement a rigorous mold cleaning schedule: Regularly clean and inspect the mold surface, use appropriate mold release agents. 
  • Ensure proper material handling and filtration: Dry and filter the resin before processing, eliminate potential sources of contamination. 
  • Optimize cooling parameters: Adjust cooling channel design and flow rate for uniform temperature distribution.
Poor weld at pinch-off (Leakage at seal point)
  • Insufficient clamping pressure: Low clamping force at the pinch-off point during mold closure. 
  • Misaligned parison halves: Inaccurate positioning of the extruded parison halves before sealing. 
  • High material viscosity due to incorrect temperature: Processing temperature is too low, making the material too viscous to form a strong weld.
  • Increase clamping force at the pinch-off point: Adjust clamping pressure settings. 
  • Refine parison control system: Improve parison centering and alignment mechanisms. 
  • Adjust material temperature or consider alternative materials: Increase processing temperature within the recommended range, explore materials with lower viscosity at processing temperatures.
Blow-outs (Container ruptures during inflation)
  • Excessive air pressure during blowing: Air pressure used for inflation is too high, exceeding the container’s strength. 
  • Weak parison with defects: Thin spots, holes, or cracks in the parison due to extrusion issues.
  • Mold leaks or damage: Cracks, worn areas, or faulty seals in the mold allowing air leakage.
  • Reduce air pressure to the minimum level needed for proper inflation: Calibrate air pressure settings. 
  • Inspect and address parison weaknesses: Identify and adjust extrusion parameters to eliminate defects. 
  • Conduct thorough mold inspections and repairs: Locate and repair leaks or damage in the mold.
Uneven wall thickness (Variations in container wall)
  • Inconsistent parison wall thickness: Fluctuations in melt flow during extrusion, worn or damaged die head. 
  • Uneven cooling across different mold sections: Variations in cooling channel design or flow rate leading to uneven temperature distribution. 
  • Mold design limitations: The mold design may not provide sufficient control over wall thickness distribution.
  • Implement stricter controls on parison wall thickness during extrusion: Monitor and adjust extrusion parameters to ensure consistent melt flow, consider upgrading the die head. 
  • Optimize cooling channel design: Adjust cooling channels for uniform temperature across the mold. 
  • Evaluate potential mold design modifications: Explore options for improved wall thickness control, such as incorporating core pins or baffles.
Inconsistent, Incorrect Bottle Volume

(The bottles produced have varying volumes)
  • Inconsistent parison weight: Fluctuations in melt flow during extrusion, or uneven extrusion speed, worn or damaged die head.
  • Material shrinkage: Thermal contraction of the plastic material during cooling, variations in parison temperature can affect material distribution.
  • Mold clamping force variations: Inconsistent clamping pressure during the molding process, inconsistent air pressure during the blow process.  
  • Refine parison control: Monitor and adjust extrusion parameters to ensure consistent melt flow, inspect and repair or replace the die head.
  • Optimize cooling parameters: Adjust cooling channels and temperature to minimize shrinkage.
  • Maintain consistent clamping force: Calibrate and monitor clamping pressure settings, stabilize air pressure during the blow process to avoid fluctuations.

4. Conclusion

By understanding and addressing common blow molding defects, manufacturers can significantly improve product quality, reduce waste, and enhance overall efficiency. This guide has provided insights into key problems such as rocker bottoms, surface wall defects, and uneven wall thickness. By implementing the recommended blow molding troubleshooting solutions, you can optimize your blow molding process and achieve consistent, high-quality products.

Manufacturers facing blow molding troubleshooting challenges can benefit from high quality raw materials that contribute to a smoother and more efficient production process. EuP Egypt is a leading supplier of polyethylene (PE) and polypropylene (PP) fillers, crucial components in blow molding production. 

Our high-quality PE filler masterbatch and PP filler masterbatch offer excellent performance, enhancing product strength, durability, and cost-effectiveness. By incorporating EuP Egypt’s filler masterbatch into your blow molding process, you can optimize your product quality and achieve superior results.

Contact us today to learn more about our filler solutions and how they can benefit your business.