Thermal inspection uses an infrared camera to read the quality of the heat seal during the sealing process.
Imagine a foil seal on a PET yogurt cup. With a visual thermal system, the entire seal is clear – if part of the lid of a yogurt cup is tipped up, bent, or folded, you can see that in the image created by the infrared camera.
Some problems are obscured by the foil. One could be a “double seal”: two seals stuck together or on top of each other. In a thermal image, this part of the image will be “green”, meaning it’s so thick that the double-lid spot isn’t being properly warmed up by the heat-sealing process (i.e., it doesn’t get hot enough to seal because it’s too thick).
Images of the seal itself might show many colors, which could indicate varying levels of heat all over the product: some steps could be very warm, some spots could be cold. You, of course, need an even distribution of heat for there to be effective sealing. That means you should have a consistent image and consistent coloring in that image.
As you reduce the power, remember that all of these things are a reflection of how much heat is absorbed into the product. If the sealer head is raised above the product, there’s not as much transition of heat (which leads to weaker sealing). Conversely, if the seal is over-heated, the image will be white – indicating burning rather than even heating.
Remember, it’s all about relative heat. If the yogurt cup lid is imaged ten seconds after it’s sealed, and then one minute after it’s sealed, the coloring will be different.
However, it’s difficult for the infrared camera and software to have a repeatable approach because your sealing line starts and stops; or when you start the line in the morning, there’s no initial reference for the next few images. That makes this process more challenging for most people than the X-ray approach – which simply takes a picture.
For a more in-depth read about X-ray seal inspection, check out our article.