How to Detect the Defects in Performs using Polarized Light

How to Detect the Defects in Performs using Polarized Light

Today, the PET containers that are manufactured in PET & Preform Industries are extraordinarily thriving in the packaging market, especially in food industry and pharmaceutical industries to pack food & beverages and chemicals which make the performs economically efficient and that offers the wide range of possible PET containers. But there are some defects that are usually encountered by the manufacturers in the PET bottles and Preforms at the time of production. These defects can be occurred at the time of injection molding, during filling, due to inappropriate weight and dimensions, due to the different quality of resins that are used to manufacture a Preform.-

What are the Major Defects that are usually found in Preforms?

There are numerous factors that explains the quality and the defects of the Preforms like its shape, percentage of material used, incorrect geometrical dimensions, quality of the tightness of the seal, standardized dimensions, micro holes at the injection point, long injection points, any type of damage in the rings like burnt rings, moisture rings, presence of small particles, chromatic variations, bubbles, transparency and the strains in the performs.

Role of Polarized light in detecting the preform defects

Many of the defects are found with Preforms and PET containers that can be detected easily with the help of polarized light. Preforms that are viewed in Polarized lights exhibits different colored birefringence patterns. The birefringence is a result of the polymers flow lines that shows molecular orientation strain that produces the lines and strains at the time of injection molding process. The pattern of colors or strains can be observed with Preform when observed from an angle of 450 i.e. the angle of the polarizing axis is known as an isochromatic fringe that signifies the amount of birefringence.

When a Preform is placed parallel to the polarizing axis, it reflects the black isoclinic rays that depict the molecular orientation defect or strain in the Preform. To detect the defects in a Preform efficiently, one must need to interpret the flow patterns correctly. To view the test specimen from the most convenient angle, the operators need to adjust the design of the angle. And with the help of testing equipment having best platform area and wider viewing area, more performs could be placed and viewed at the same time.


The strains in the Preform can be detected easily with the help of a testing instrument known as Polariscope. The instrument produces polarized light to observe the test specimen efficiently. The instrument helps to view even the slightest defect or strain in the PET containers and Preforms. The instrument offers highly precise and stable test results.

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