Research Information System
European Food Research and Technology, vol.217, no.4, pp.365-368, 2003 (SCI-Expanded)
Non-destructive testing by the ultrasonic imaging method was evaluated to determine the heat seal quality of aseptically produced semi rigid cups, sealed at temperatures ranging from 150 to 200°C. Non-contact ultrasonic testing in pulse/echo mode using high frequency sound waves generated by a 20 MHz ultrasonic transducer was used to evaluate heat-seal quality. In order to relate ultrasonic response with the actual seal condition, various seal regions of a semi rigid container were sectioned for optical microscopic imaging and seal characterization. Results showed that ultrasonic signals could reflect the effects of the sealing process on the seal integrity. Change in the ultrasonic signals indicated an insufficient or non-uniform heat seal at sealing temperatures of 150-170°C, resulting in weak seals or discontinuities. Short seal width was observed at all sealing temperatures, indicating unparallel alignment of the sealing tool. Optical imaging correlated well with ultrasonic imaging. However, uniformity of heat seal did not correlate well with the magnitude of the ultrasonic signal, possibly due to non-uniform surfaces of heat seals. These results suggest that this non-destructive ultrasonic inspection system detects the quality of heat seals, which can eliminate potential failures and improve process control.