Blow Moulding Technologies (BMT) is highlighting a persistent challenge facing PET preform producers: batches that meet specification but behave differently once they reach the stretch blow moulding process. Although dimensions, weight and polarised light testing are routine testing, these inspections do not directly assess how a preform will act once it arrives on the factory floor.

Preforms behave unpredictably from labs to factories

Traditional inspection methods identify geometric and material-related issues. However, two preforms can meet the same specifications, pass visual inspection and still exhibit significantly different heating and blowing behaviours. 

Due to the disconnect from labs to reality, tangible problems arise, such as increased machine profiling, greater troubleshooting effort, more operator interventions and reduced stability, with variations only appearing after preforms have been shipped and introduced to the bottle manufacturing process, by which point lines have already inherited the problem. The result can be increased troubleshooting, production inefficiencies and valuable engineering time spent diagnosing issues that originated long before the preform reached the bottle line.  

Measuring temperature profiles in identifying PET bottle imbalances

Blow moulding performance is heavily influenced by preform temperature behaviour. If a preform heats differently, it will stretch differently. And if it stretches differently, the bottle performance changes too.

Earlier this year, an investigation using BMT’s THERMOSCAN solution resurfaced just how difficult these issues are to identify. In this scenario, a bottle production process that had previously operated successfully began to experience quality variations, despite having equipped the same recipe and oven settings as before. Further research into this lapse revealed that variations originating within the injection moulding process itself had influenced thermal behaviour, and were in turn creating an inconsistent blowing performance. Therefore, the bottle line was not the root cause. The preform was.

In another case, a manufacturer experiencing issues with a problematic material batch required an expert process technician to visit site six times within two months to resolve production challenges. Previously, the same manufacturer had required only six visits across the entire year. In addition to the cost of specialist support, the issue also resulted in production downtime while the source of the variation was identified and addressed.

The investigation demonstrated how difficult these issues can be to diagnose once production is underway, often leading manufacturers to focus on downstream equipment when the source of variation exists much earlier in the process.

As manufacturers introduce higher levels of rPET, bio-based materials and other sustainability-focused innovations, understanding how preforms will behave during heating and blowing is becoming increasingly important. Small variations can influence processing performance, making early validation critical before committing to full-scale production trials. As the industry works to reduce material usage, lower carbon emissions and incorporate alternative feedstocks, manufacturers face growing pressure to introduce change without compromising production stability.

Tackling the problem: evaluating variations in preform quality

To help manufacturers identify these variations before they reach production, BMT developed BLOWSCAN, which assesses heating and inflation behaviour, as well as overall blowing consistency.

Today's quality systems indicate whether a preform meets specification. BLOWSCAN helps determine whether it will perform to specification. This additional layer of quality assurance is designed to reduce downstream disruption, improve process stability and strengthen confidence in preform performance.  

"Despite extensive quality checks, manufacturers can still encounter batches that perform differently during blowing," said Josh Turner, Delivery Manager at BMT. “The challenge is that these differences often only become apparent once production has started. By comparing blowing behaviour against a validated reference, manufacturers can identify variation earlier and gain greater confidence that every batch will perform as expected.”