Take candy packaging as an example. The current method is to have two heated sealing bars clamp a film tube and partially melt the plastic composite, sealing the packaging. Once the candy is poured in, the tube is then clamped by the tools at the designated places and heat-sealed in the same manner. Finally, a blade separates it from the next unit. How well the seam holds depends above all on the temperature of the sealing bar surface: if it is too hot, the film burns; if it is too cold, the film sections are not fused tightly enough together. The result is the same in both cases: the package is not sealed properly. It is hardly surprising that manufacturers go to great lengths to detect such faults. For example, some spot checks are performed by placing the packaging in a water bath, and air bubbles rising to the surface indicate leaks.
An end to spot checks
There is, however, an alternative. “Because we apply the temperature sensors directly to the sealing bar, we receive direct information about every single packaging unit for each sealing process,” explains Gregor Wendt, scientist at Fraunhofer IVV in Dresden. If the temperature is too high or too low, it can be adjusted immediately at the machine – before large numbers of incorrectly sealed units of packaging start flowing off the line. The inline quality inspection method also reliably recognizes products that have become wedged in the packaging, such as a piece of candy that has slipped into the seam. This works as follows: when sealing bars seal films together, the films absorb some of the bars’ heat. Accordingly, the bars cool down a little. How far the temperature drops depends on the mass of the object wedged in the packaging. If a piece of candy has strayed into the sealing zone, it also absorbs some of the heat – the bars cool down faster than without wedged goods.
The highly sensitive system is even capable of detecting coffee powder in the seam – and of doing so faster and more accurately than the sensors that have been used in sealing processes up to now. For the sensor itself, the coating specialists use thermocouples manufactured in established thin-film processes. They vapor-deposit the various materials of the thermocouple in a vacuum directly onto the sealing bar. With a layer just a few hundred nanometers thick, the resulting sensor is extremely thin and has a very short response time. At Fraunhofer IWM, researchers are developing adapted protective coatings for specific industrial applications. Meanwhile, their colleagues at Fraunhofer IVV in Dresden are integrating sensor-fitted sealing bars into packaging systems and handling the ways in which sensors make contact. In tests on a laboratory sealing unit, the research team has already been able to verify that the sealing process with an integrated thin-film sensor functions properly. In further steps, the scientists are currently working on solutions to adapt this technology to the tools generally used in industrial manufacturing including the high number of cycles and wide variety of film materials this entails.
Take candy packaging as an example. The current method is to have two heated sealing bars clamp a film tube and partially melt the plastic composite, sealing the packaging. Once the candy is poured in, the tube is then clamped by the tools at the designated places and heat-sealed in the same manner. Finally, a blade separates it from the next unit. How well the seam holds depends above all on the temperature of the sealing bar surface: if it is too hot, the film burns; if it is too cold, the film sections are not fused tightly enough together. The result is the same in both cases: the package is not sealed properly. It is hardly surprising that manufacturers go to great lengths to detect such faults. For example, some spot checks are performed by placing the packaging in a water bath, and air bubbles rising to the surface indicate leaks.
Take candy packaging as an example. The current method is to have two heated sealing bars clamp a film tube and partially melt the plastic composite, sealing the packaging. Once the candy is poured in, the tube is then clamped by the tools at the designated places and heat-sealed in the same manner. Finally, a blade separates it from the next unit. How well the seam holds depends above all on the temperature of the sealing bar surface: if it is too hot, the film burns; if it is too cold, the film sections are not fused tightly enough together. The result is the same in both cases: the package is not sealed properly. It is hardly surprising that manufacturers go to great lengths to detect such faults. For example, some spot checks are performed by placing the packaging in a water bath, and air bubbles rising to the surface indicate leaks.
Take candy packaging as an example. The current method is to have two heated sealing bars clamp a film tube and partially melt the plastic composite, sealing the packaging. Once the candy is poured in, the tube is then clamped by the tools at the designated places and heat-sealed in the same manner. Finally, a blade separates it from the next unit. How well the seam holds depends above all on the temperature of the sealing bar surface: if it is too hot, the film burns; if it is too cold, the film sections are not fused tightly enough together. The result is the same in both cases: the package is not sealed properly. It is hardly surprising that manufacturers go to great lengths to detect such faults. For example, some spot checks are performed by placing the packaging in a water bath, and air bubbles rising to the surface indicate leaks.