In actuality, this is the visual part of a simpler defect called “false seam“. False seams occur when the seam formation is not done correctly, typically due to incorrect 1st operation setup. This issue is particularly nasty as it means that the entire closure is compromised, typically meaning that the can will lose internal pressure, leak as well as expose its contents to potentially harmful outside influences (e.g., pestisides, toxic materials, erosion).
This problem must never occur on a normal production line!
Steps to detect Vee:
- Sectioning of the seam
- Visual inspection of the can
- Non-destructive 360 degree scanning of the can
Possible reasons for a Vee:
- Product entrapment
- Damaged 1st operation roll
- Incorrect setup of 1st operation
- Weak springs in seaming roll levers (check spring tention)
- Incorrect body thickness or cover thickness.
- Seamer timing is set up incorrectly.
- Damaged cover curls (Ensure that the ends are not damaged when placed into the seamer).
This is what the defect looks like in a non-destructive scanner – note the “humps” at the bottom Length graph indicating the defect.