Ultrasonics opens up to more accurate sealing control

Machinery firms and end users are increasingly favouring ultrasonic welding over other technologies, most typically heat-sealing, because of its precise sealing control.

"With heat-sealing, you can set a temperature, but you can't really control the exact heat in the sealing jaws," explains Matthias Poth, packaging sales engineer at ultrasonics supplier Branson.

Ultrasound is effective even where there is contamination in the seal area, and is often selected for this reason. Other reasons include the drive for higher line speeds. The technology has reduced its footprint and cost over the past decade, Poth adds.

There is no direct application of heat. Instead, high-frequency electrical energy is converted into mechanical vibration. This in turn will plasticise certain polymers, and can be combined with pressure to create a join of a specific strength.

But Poth admits that heatseal can be cheaper. So for instance, beverage carton converters might use heat to join the base and side seals on the carton blank. They then use ultrasound for the inline, high-speed sealing of the carton top after filling, where contamination in the seal can be a factor. And like heat sealing, ultrasonics will only work with certain materials.

German machinery manufacturer Gerhard Schubert integrates ultrasound systems from another supplier into its TLM thermoform-fill-seal line. The firm underlines the benefit of being able to seal through a potentially contaminated join, and the importance of being able to validate the seal quality.

Md for polymer technology Sven Engelmann says: "We do the sealing and cutting in one short operation, so sealing is no longer a bottleneck. We have tested applications for easy-peel lidding, or where necessary we can provide a secure weld."

Ultrasonics is also a busy research area. Schubert is looking at reseal options, while Germany's Fraunhofer AVV research institute is examining the reasons why ultrasonic welding is only effective with certain polymers.

The TLM line will be shown in a confectionery application at the Pro Sweets trade fair in Cologne, Germany (February 1-4 2009).