Detecting Different Types of Defects in PET Preforms

In many of our previous posts we have discussed the properties the PET, which are making it one of the most common and useful form of packing for different industries. PET is manufactured from preforms, they are small structures in which hot air is blown to mould them into desired shape. If the preforms have defects, it is very natural that final product will have defects. As a reputed product manufacturer, you cannot afford to produce defective pieces. Also, these defects help in analysing the faulty production. 

 

Due to external stress, there develops internal strain in the structure. This internal strain not only spoils the appearance but also impacts the strength of the preform. To identify such defects, polariscope is used. This instrument comprises of an incident light and polarised lenses. When this incident light passes through the specimen, the light passes through it without any refraction. On the other hand, when incident light encounters a strain, the light tends to refract doubly and thus creating birefringence patters. These birefringence patterns are matched with defect chart to identify the cause of strain.

Polariscope is a bench top model and set in very small space in the QC labs. The specimen is tested at two angles, 45° and 90°. With the advancement in technology, manufacturers are now offering software enabled models. The defective image is captured by the computer and matched with the pre-loaded images. The best match is chosen and defect type, its reasons and remedies are presented in front of the operator. Based on the information provided, the production process is reconsidered. 

It is another important analysis to get the right coloured products. The PET containers available in different colours have colour preforms. To get the right appearance, the colour values are predefined. It is very important that preforms are coloured very appropriately. Colour measurement devices like tp800 spectrophotometer are used widely. These devices are capable of quantifying the colour into numerical values. Colour managers are well versed in comprehending values obtained in L*a*b and ∆E format. 

 

In this test, the eccentricity of the preform is tested. Sometimes due to defect in the production process, the preforms are not perfectly circular. This may defect may affect the final product. Thus, to control the shape of the preforms before starting the mass production eccentricity tester is used.

Presto is the leading manufacturer and supplier of PET preform testing instruments like tp800 Spectrophotometer, polariscope and many more. Contact our experts today to explore the complete range.