Blow molding is a process that uses gas pressure to inflate a plastic parison and fit it into a mold, creating a hollow product. It is widely used in beverage bottles, daily chemical packaging, pharmaceutical containers, automotive fuel tanks, and industrial barrels. With increasing international market demand for lightweight, consistent appearance, and durable products, blow molding defect control and raw material selection have become common concerns for both buyers and manufacturers.
As a professional supplier of plastic raw material pellets, we not only provide blow molding-grade materials with stable batches, low moisture content, and high strength, but also leverage our process experience to provide solutions to help customers reduce defects and improve yield. The following summarizes seven typical defects in the blow molding process, along with their causes and potential solutions.
1. Uneven Wall Thickness
Symptom: One side of the bottle or container is too thick, while the other is too thin, affecting appearance and strength.
Causes: Uneven heating of the parison, deviation in the die gap, unstable blow pressure, or insufficient melt strength.
Solutions:
-Adjust die design and temperature distribution;
-Optimize blow pressure and cooling water lines;
-Select high molecular weight or anti-sag grades.
Supplier Advantage: We provide high melt strength PE และ PP pellets to ensure uniform wall thickness and structural stability.
2. Bubbles and Voids
Symptom: Bubbles and holes appear on the surface or wall of the product, reducing mechanical strength and sealing.
Cause: Excessive moisture content in the raw materials, insufficient screw venting, or excessively high melt temperature.
Solution:
-Dry the raw materials thoroughly to control moisture content;
-Improve screw venting design;
-Lower the melt processing temperature.
Supplier Advantage: Our pellets are vacuum-packed and moisture content is tested to reduce the risk of bubbles and voids.
3. Weld Lines (Parison Lines)
Symptom: Visible seams appear on the surface or in the center of the product, resulting in a localized decrease in strength.
Cause: Uneven mold temperature, insufficient melt flow and convergence.
Solution:
-Optimize the mold heating system;
-Improve melt flow;
-Increase the melt mixing of the parison.
Supplier Advantage: We can provide materials with optimized flow properties to reduce weld line marks and improve product strength.
4. Bulging and Blow-Out
Phenomenon: Partial bulging or even cracking of the product during molding or storage.
Cause: Excessive blow pressure, insufficient melt strength, or thin wall thickness.
Solution:
-Rationally control blow pressure;
-Optimize product structural design;
-Select materials with good impact resistance and toughness.
Supplier Advantage: We provide impact-modified PE/PP grades to improve product toughness and reduce the risk of cracking.
5. Surface Streaks and Haze
Phenomenon: Ripples, flow marks, or haze appear on the bottle surface, affecting transparency and aesthetics.
Causes: Excessive mold temperature differences, poor masterbatch dispersion, and melt temperature fluctuations.
Solutions:
-Maintain a consistent mold temperature;
-Improve masterbatch dispersion;
-Stabilize the barrel heating system.
Supplier Advantages: We ensure batch stability and excellent masterbatch dispersion, helping customers reduce surface defects.
6. Deformation and Shrinkage
Symptoms: The bottle or barrel warps and collapses after cooling.
Causes: Uneven cooling rate, excessive material crystallinity, and poor mold temperature control.
Solutions:
-Optimize cooling channel design;
-Select raw materials with controlled crystallinity;
-Adjust cooling time and temperature.
Supplier Advantages: We provide granules with high thermal stability and controlled crystallinity to help maintain the product's shape.
7. Neck Cracking
Symptoms: Neck cracking occurs during capping, stacking, or transportation, affecting sealing and performance.
Causes: Localized stress concentration, insufficient cooling, and excessively thin wall thickness in the bottle neck area.
Solutions:
-Improve mold clamping accuracy;
-Enhance bottle neck cooling;
-Appropriately increase bottle neck wall thickness.
Supplier Advantages: We offer PE/PP with excellent stress crack resistance, extending product life.
8. Our Advantages
High-Quality Raw Materials: We offer blow molding-grade PE, PP, PETG, and other materials with low moisture content and batch stability.
Technical Support: We can recommend the appropriate material grade based on the product application.
Quality Control: We conduct factory testing for moisture content, melt index, and dispersion.
International Delivery: We have extensive cross-border logistics experience to ensure a stable supply chain.
บทสรุป
Preventing and correcting blow molding defects depends not only on process control and mold optimization, but also on raw material quality and supply stability. By selecting a reliable plastic raw material supplier, buyers and manufacturers can significantly reduce production defects, improve product consistency, and enhance market competitiveness.
If you are looking for a supplier of high-quality blow molding-grade plastic granules, we will escort your production and manufacturing with professional service, high-quality raw materials and global supply capabilities.
