How to Prevent Defects in Blow Molding Products and Ensure Part Quality

How to Prevent Defects in Blow Molding Products and Ensure Part Quality

Minimize costly product defects with these five expert insights.

By Shell Polymers on Jun 16, 2020

Producing blow-molded products that aren’t consistent can cause unnecessary downtime and disrupt supply chains, costing companies valuable time and resources. Typically, inconsistent product quality isn’t caused by a single issue. Although it’s common to hunt for a quick fix that solves the problem instantaneously, it’s crucial to realize that defects and quality issues in blow molding applications are usually the result of multiple variables and should be addressed accordingly.

Avoid common causes of defective products with these five blow-molding best practices

1. Establish Routine Maintenance

Routine mold maintenance is critical for high-quality products. A poor or worn cavity surface finish will hinder proper venting and result in inadequate product surface appearance. To avoid air entrapment, it’s also important to maintain the vents. Since entrapped air prevents good contact between the parison and the cavity surface, keeping the vents free of obstructions such as plastic accumulation will allow for a better final product and help maintain efficient cooling.

Additionally, proper preventive maintenance of the neck ring and blow pin will assure that these components are not worn out and cause defective products.

2. Maintain a Healthy Heating System

Blow-molded products are very sensitive to fluctuations or inaccurate heating control. When exposed to inconsistent temperature, the process is frequently adjusted to counteract them, which results in an overall smaller process window and the possibility of lower efficiency.

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3. Maintain a Healthy Air Control System

Having a healthy air control system is especially crucial in blow molding applications because it enables repeatable pre-blow and blow pressures, which translates to consistent and repeatable product quality. For example, too high a blow pressure can blow-out the parison, while too little blow pressure will cause end products to lack the necessary surface detail.

Additionally, keeping the air entrance channel in good condition, such as ensuring that there are no obstructions to the opening, is critical. A blocked entrance channel could cause the blow time to be too long or the blow pressure to be unable to produce the surface details of the mold.

4. Size Head Tooling Appropriately

Properly sizing the head tooling for the intended application is paramount to achieving consistent, high-quality final products. Running head tooling that is too small can result in a final process that relies more on pre-blow to achieve the proper parison size, making the final product more susceptible to inconsistencies and defects.

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5. Use the Recommended Heat Profile

Believe it or not, running cooler is not always better. Using a material supplier’s recommended heat profile is critical to how the material behaves and how it will process. Running a colder heat profile generates more stresses in the polymer that can translate into processing inconsistencies and mechanical failures.

Blow molders have been manufacturing products in the same way for a very long time. Current research and technological advancements have disproved common theories and processes, resulting in new, science-based best practices. For example, Industry 4.0 technologies are being applied to help converters obtain and monitor processing data. This data is then used to help the operator to maintain high standards of process quality, control, and productivity.

Stay up-to-date on the latest advancements by partnering with a polyethylene supplier that keeps its fingers on the pulse of the industry to help converters experience more profitable production of high-quality products.