BMT, a strategic technology provider for the global packaging industry, is showing how its Thermoscan preform temperature sensor helps manufacturers identify a key cause of inconsistency in PET production: variations in the thermal behavior of apparently identical preforms.
Even with the same stretch blow molding (SBM) recipes, differences introduced during injection molding can affect how preforms respond to heating, leading to inconsistencies in the final product. By making the true thermal profile of the preform visible, Thermoscan enables more consistent and stable outcomes.
Although the process may appear stable, variations in preform behavior can still lead to inconsistent results. As the use of recycled PET (rPET) increases and lightweighting tightens the process window, this variability becomes more difficult to manage.
Thermoscan measures both internal and external temperatures of preforms along their full length, capturing the complete thermal profile rather than relying on oven setpoints or surface readings alone. This makes visible the parameter that directly governs stretch behavior: how heat is distributed through the preform wall.
Standard process controls, such as oven setpoints, do not guarantee a consistent internal preform temperature. As a result, materials that appear identical in specification can enter the stretch process in different thermal states, creating variation that is not visible through conventional measurement methods.
“What matters in stretch blow molding is how the preform actually behaves during heating – not just the settings used to control it,” said David McKelvey, head of Product at BMT. “By measuring both internal and external temperature, Thermoscan gives manufacturers a clearer understanding of the temperature and helps them make more informed process adjustments.”
Injection differences, measurable impact on performance
In an illustrative use case, a PET bottle manufacturer operating a fixed and validated SBM process observed inconsistent performance linked to when preforms were produced. While the SBM settings did not change, preforms from one injection shift ran consistently, whereas those from another resulted in increased blowouts and greater instability.
Measurement with Thermoscan showed clear differences in temperature profiles between these preforms. These differences were traced back to subtle variations in injection molding conditions, including packing behavior, material history and cooling. Although all preforms met specification, they absorbed and distributed heat differently, resulting in different thermal states going into the stretch process.
Enabling consistent, stable production
By linking these upstream variations to downstream performance, Thermoscan enables manufacturers to move from reacting to instability to understanding its root cause. This reduces reliance on trial-and-error adjustments and supports better alignment between injection molding and stretch blow molding, helping to deliver more consistent outcomes.
