PET Pre-Blowing System

The PSB® (Preform Stretch Booster) system is an innovative pre‑blowing solution developed by SIAPI for its SX1 and SX2 blow‑moulding machines, specifically designed to improve material distribution and performance in large returnable PET containers, such as 5‑gallon bottles with integrated handles. SIAPI is among the first companies worldwide to offer this PSB® technology on a 2‑cavity platform.

On SIAPI SX1 and SX2 platforms, preforms are first heated in multiple independently controlled heating modules. Accurate temperature management ensures that the preforms reach the correct thermal profile at each stage of the process, creating the ideal conditions for the subsequent PSB phase.

In conventional processes, container and neck dimensions, together with the target weight, define the preform design and stretching parameters. For large returnable bottles, this often leads to a radial stretch ratio above the optimal limit. The result can be inadequate handle encapsulation, poor definition of engraved areas, limited scratch resistance and sub‑optimal aesthetics. In addition, mechanical properties such as top‑load resistance, handle pull‑out strength and thermal stability during washing cycles may not fully meet the demanding requirements of multi‑rotation returnable applications.

The PSB® system addresses these critical points by introducing a controlled pre‑blowing phase that generates an intermediate preform shape before final blowing. After leaving the oven, the heated preform is transferred over the pre‑blowing unit. In Phase 2, this unit closes around the preform with specific shell. In Phase 3, compressed air is injected, expanding the preform to a defined intermediate geometry. This intermediate preform is then transferred to the blow mould (Phase 4), where it is blown to the final bottle shape.

SIAPIBy splitting the stretching into two steps, PSB® optimizes both axial and radial orientation of the PET. This leads to a more uniform wall thickness, better control of the material in the handle area and improved reproduction of any engraving or texture on the mould surface. The process is particularly effective when combined with SIAPI’s in‑mould handle insertion system, where the handle is automatically positioned in the blow mould just before preform entry, allowing full integration of handle loading and blowing in a single, fully automatic sequence.

Performance data show that the PSB® process can increase axial strength, with top‑load resistance improvements of around 20% compared to bottles blown without PSB®. Handle pull‑out resistance is also significantly enhanced, with increases of about 24%, ensuring secure handle anchoring throughout the bottle’s service life. From an aesthetic standpoint, PSB® eliminates whitening and stress‑cracking phenomena in critical transition areas, improves the definition of handle anchor points and mould engravings, and increases scratch resistance.

Thermal stability during washing cycles is another key benefit. Returnable 5‑gallon bottles must withstand repeated hot‑wash operations, typically between 55 °C and 70 °C. Tests show that bottles produced with PSB® exhibit substantially reduced volume shrinkage after 5 hours at these temperatures, with shrinkage reductions of up to 35% compared to standard bottles. This improved dimensional stability extends the usable life of the container and helps maintain consistent appearance and performance over many rotations.

In summary, the PSB® system on SIAPI SX1 and SX2 machines provides a robust answer to the challenges of large returnable PET containers. Through an intermediate pre-blowing step and precise thermal and process control, PSB® delivers superior material distribution, higher mechanical strength, improved handle performance, enhanced aesthetics and better thermal stability, making PET a highly competitive alternative to traditional PC jugs in demanding multi-rotation applications. Ultimately, the PSB® system on SIAPI SX1 and SX2 machines is not just an add-on, but a distinctive process architecture.