Inspection of defects in the seal region of flexible food packages using the ultrasonic pulse-echo technique.

摘要

Container integrity is the major problem for flexible food packages. Current inspection techniques are not capable of detecting microscale defects in the seal region of these packages, which might compromise human safety. In addition to that, many of the techniques provide only statistical assurance, which does not guarantee the safety of untested package.; A nondestructive ultrasonic pulse-echo imaging method, Backscattered Amplitude Integral (BAI), was developed for seal defect detection. Channel defects (6--15 mum in diameter) and simulated food strands (20--60 mum in diameter) were fabricated within the seal region of both all-plastic and foil-containing retortable pouches. Results showed that 17.3-MHz pulse-echo BAI-imaging detected defects in both types of package materials.; In the second phase of the study, the contrast of the defect on the BAI-mode image was evaluated for various packaging materials, defect types and sizes. Channel (6--100mum in diameter) and inclusion defects (20--150mum) were fabricated in the seal area of all-plastic and foil-containing films. The 17.3-MHz pulse-echo BAI method was used to evaluate the contrast of defects. A linear relationship was observed between the defect size and the contrast value, DeltaBAI, and different defect types and packaging materials had a significant impact on the DeltaBAI value. The DeltaBAI for detecting defects is a useful and reliable sensing method for package inspection.; The BAI-mode imaging was poor for macroscale defects such as non-bondings, wrinkles, and bubbles when they were abundantly present in the seal region. The study indicated that the combination of the average and the coefficient of variation of BAI values would detect the macroscale defects and could provide a real-time, on-line control by being able to sense whether seal has achieved a proper state of fusion or not.; In conclusion, techniques developed in this study will provide safety assurance of the flexible food packages and make these packages more financially competitive by reducing inspection costs.