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Seal Quality Inspection with Airborne Ultrasound Technology

Airborne ultrasound is a referenced technology in the new USP <1207> Chapter Guidance as a deterministic test method for seal quality testing.

A pouch seal is a structural element that joins flat film material, and a component designed to close a pouch airtight. Traditional test methods e.g. peel strength or burst, can measure the joint strength of the seal, using destructive methods. However, this type of testing is often unreliable. A strong seal is not necessarily an airtight one, and the flow of gas or liquid through the seal (leak) is just one type of seal defect. As such, there is a fundamental challenge to any leak testing method, whether it is a fish tank-bubble, vacuum deferential, or helium test: none of these methods detect non-leaking seal defects.

PTI's Seal-Scan® and Seal-Sensor are non-contact airborne ultrasonic testing technology.  In order to use ultrasonic inspection effectively, it must be possible to place the seal in a direct line between a pair of transducers and move it (or move the transducers) along the seal. The ultrasound is transmitted and reflected at the transition from one media to the next. The greater the acoustic difference between mediums (most evident at a gas to solid transition) the more sound is reflected and the less sound transmitted through. The variation of the material thickness has only a minor effect.

Any material fold, foreign media inclusion and even a microscopic air gap between layers of pouch material causes the significant reflection, so transmitted signal is lower. A small cut, abrasion or missing layer in a material causes the less reflection, so transmitted signal is higher. Therefore, the level of a signal received after passing through the seal is a function of the seal quality. Various types of defects, visible and invisible, leaking and non-leaking, process-related and random, are detectable.

Seal-Scan® technology has been proven in the field with several online and offline units installed. PTI's ability to adapt this technology into various production constraints and environments make it an excellent solution for flexible packaging systems. It has been established as one of the most effective methods for non-destructive testing of flexible packages.  In 2013, ultrasound technology was awarded the ASTM Test Method F3004-13.


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