Since the 90’s, most of the inspection systems for seaming were destructive – a cross section is cut from the can and inspected using a seam inspection system.
However, the costs and implications of destructive testing have made non-destructive solutions a much more attractive options for can fillers. In some cases, X-ray solutions have been offered to provide similar solutions to their destructive counterparts.
There are essentially two major ways to do seam inspection using X-rays.
Cross section X-rays
The first is to model the units after their destructive counterparts, which typically yields similar looking images:
The main issue with this method is that of resolution. The image does provide all the critical dimensions (except wrinkle/tightness), but the results can be misleading due to de-focusing and resolution issues. In addition, the maintenance costs involved with the X-ray tubes over the cost of the system’s lifetime and the radiation implications meant there were very few actual installations of such systems in the field. These systems are completely impractical for food or aerosol cans, where material thickness and metal composition require a long period of exposure with higher radiation levels.
Top down approach
Some X-ray seam inspection systems work by projecting the X-ray in a top/down approach. In this case, the angled approach means lesser radiation levels, but the systems are still quite expensive, and are able to provide mediocre prediction of wrinkle rating. Typically, they cannot directly measure seam thickness, which is measured using either an add-on or using a “projected” approach which means that angled pieces touch the thickness are can be used to mathematically calculate the seam thickness.
These systems are relatively new, but are not very popular. The TCO (total cost of ownership) of these units is prohibitive and measurements are usually quite slow. These systems can be used on beverage or food cans, but their accuracy and popularity still need to be proven over the long run.
Additional alternatives exist to the X-ray seam method that focus on non-destructive methods:
- Pressure sensors: Seamer manufacturers sometimes place a pressure sensor on the seamer heads to allow them to detect sudden jumps in pressure. Some of these solutions are becoming more popular but have very limited success in detecting critical issues such as false seams that apparently are missed by these systems.
- 360 scanners: These systems scan, preferably using a non-contact or balanced method, measurements such as seam length and seam thickness around the can. It has been found that there is a strong correlation between issues inside the seam with problems in those two measurement values, provided that these are measured accurately and with many points around the can. It is critical that such systems provide and analyze the graphed correlation between these parameters in order to potentially detect serious issues such as false seams, wrinkle and other internal defects. Systems such as SEAM360 are able to do so and dramatically reduce the destructive tests that are necessary for most companies.
False seam as seen on the SEAM360 system: