Preform Strain Viewer ( Polariscope ) is an optical instrument designed to observe crystallization and other common defects which are invisible under natural light.

Residual stress in injection molding products can also detected .
It has been widely used in the quality control of various plastic rough processing products and finished products .

Objects of Polariscope
PET preform
resin plate , resin film , mold injection resin products

Measuring principle
The internal stress of plastic products has a birefringent characteristic. In other words, if there is stress inside of these types of products, light from he polarized lamp will be divided into different units, which produces optical interference phenomenon (ripple patterns) in turn.

When the plastic preform is placed on the sample plate at 0°or 90°, the colored birefringent stripes at the edge of the preform can be observed;

When the plastic preform is placed on the sample plate at 45°, black birefringence stripes in the central part of the preform will be displayed;