The “invisible” faults on PET preforms

  • Inspection system to detect watermarks, shrinkage and surface defects
  • The advantages of “grid inspection”
  • Patented SACMI system for inline and test lab applications

The company Sacmi has developed a “grid-type” inspection system can be installed on the entire PET preform vision system range, on both production lines (PVS 003 and PVS 024) and in test labs (PVS 2). The patented technology identifies, via a simple algorithm, preform defects that would otherwise be invisible to the human eye, and without any risk of encountering the errors induced by the image ”interpretation” that is necessary on traditional inspection systems which use polarised light.

Grid inspection

Grid inspection

The drawbacks of traditional inspection techniques

Traditional inspection techniques that use backlighting with a polarizer placed immediately behind the product make it difficult to execute easy detection of major defects (caused by, for example, on-resin stress during the cooling process and/or water in the moulds – the so-called watermark). These defects, in fact, generate patterns that then need to be interpreted by the operators. This requires skill and experience as the faults are tricky to translate into inspection algorithms.

Patented backlighting projects gridlines behind the preform

This is where the new Sacmi system comes into play: the polarised light has been replaced with a special patented backlighting unit that projects gridlines behind the preform. On flawless preforms the result is a series of straight parallel lines, on faulty areas these become wavy. Using the grid, even small defects are immediately identifiable.

Analysis of entire preform, body finish and bottom

The new technology is available as an option on the PVS range, thus allowing completion of the standard checks used to analyse defects on the entire preform, body finish and bottom. This supports the preform quality control department as it permits a very economic preform “X-ray” to be made that is error-free.

The PVS range will be exhibited at Sacmi on 15th September during the “Food & Beverage Plastic Day”, a special event organised to show customers and partners the latest technological developments in plastic containers and closures for the Food and Beverage markets.

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