Watermarks, shrinkage and surface defects: the “invisible” faults on PET preforms

| Quality & Diagnostic | Sacmi | Imola

The advantages of “grid inspection”, the innovative patented SACMI solution that can be installed on the entire range of preform inspection systems, both on line and in test labs

A formula plus patented technology to identify, via a simple algorithm, preform defects that would otherwise be invisible to the human eye, detecting them easily, economically and – above all – without any risk of encountering the errors induced by the image ”interpretation” that is necessary on traditional inspection systems which use polarised light. This innovative Sacmi-developed “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).

Traditional inspection techniques that use backlighting with a polarizer placed immediately behind the product make it difficult to execute easy, economic 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 able to be used by a vision system.