Stretch Ratio of PET Preforms

The stretch ratio of preforms plays a critical role in the blow molding process, mainly involving the circumferential and axial stretch ratios. The circumferential stretch ratio refers to the degree of stretching around the perimeter of the preform, while the axial stretch ratio refers to stretching along its longitudinal axis. For PET preforms, the circumferential stretch ratio typically ranges from 3.3:1 to 4.7:1, and the axial stretch ratio ranges from 1.4:1 to 2.6:1. The overall stretch ratio is usually 10:1 or higher, ensuring optimal bottle strength and gas-tightness.

Temperature distribution within the preform also has a significant impact on stretch ratios during blow molding. To achieve uniform temperature, the preform needs to be properly conditioned, with the inner wall slightly warmer than the outer wall. This facilitates better stretch blow molding and improves the mechanical properties of the final bottles, such as tensile strength and airtightness.