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Troubleshooting extrusion blow molding

To do well at troubleshooting, CPG companies need the right ammo.

Sterling Anthony, CPP
Sterling Anthony, CPP

Defective extrusion blow-molded bottles become more problematic the longer they go undiscovered.  When discovered at a CPG company’s facility, they can disrupt line operations.  When discovered in a CPG company’s distribution network, they add to costs because the filled bottles must be separated.  When discovered by the consumer, they can prevent repeat purchases.  It therefore benefits a CPG company to be proactive in its approach to troubleshooting.

The starting point should be the design of the bottle.  The 2/27/12 Packaging Insights article, Extrusion blow molding, identifies various design-related considerations that facilitate extrusion blow molding.  It’s a given that the bottle design must be replicated in the mold cavity; beyond that, the overall quality of the craftsmanship of the mold exerts a strong influence on the frequency and severity of bottle defects. 

A proactive approach extends to the selection of the supplier of the extrusion-blow molded bottles.  The justification is that quality-assurance not only involves the prevention of defects but also the quick, effective analysis and correction of defects; however, many CPG companies don’t factor in a supplier’s troubleshooting capabilities. The biggest reason likely is an uncertainty about how to evaluate those capabilities—before the advent of defects, rather than after-the-fact.

A CPG company needs to understand that defects can be categorized as either associated with the parison or with the formed container.  Thus informed, the company can ask any prospective extrusion blow-molder about how it troubleshoots, relative to each category of defects.   Since there are dozens of specific defects within each category, a CPG company should be wary of information overload.  To avoid that, a CPG company should emphasize that it’s interested in those defects that—were they to go undetected by the extrusion blow-molder—would cause that CPG company the most problems. 

 If, for example, the involved product is a liquid, it would be prudent for a CPG company to ask the extrusion blow-molder questions about the causes of leakers and about the associated troubleshooting.  One aspect that should arise is the integrity of the weldline (the center line that runs across the bottom of the bottle).  A bottle with a defective weldline is a sure leaker, but its cause(s) might not be obvious.  Possible causes might lie with the closing of the mold, the pinch-off of the parison, the trimming of the flash (excess plastic), something else, or a combination of the aforementioned.

 Distinct from defects that affect a bottle’s performance are those that affect a bottle’s aesthetics.  An example is decorative grooves that don’t come in as prominently as designed.  Another example is a surface that is supposed to be smooth emerging as rough.  A possible culprit is insufficient pressure with which the parison is blown to the contours of the mold (or even the time that the blown parison is held against the contours of the mold). 

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