Many of the defects caused during the injection moulding and cooling of PET prefoms can be easily detected using the QCI 1 preform viewer.

Plane polarised light enables the operator to clearly observe the coloured polymer flow pattern ( molecular orientational strain ).

When a preform is held parallel to the viewing field as shown in fig.1 a coloured pattern known as an isochromatic fringe is visible.This indicates the magnitude of the stresses introduced during the moulding process.

When the preform is held at an angle of 45deg. as shown in fig.2 a black fringe known as an isoclinic can be seen.This indicates the direction of the stresses.

The correct interpretation of these flow patterns is of great value when detecting and reducing preform defects.