A double seam is a sealed closure of a can – made by folding (or rolling) the end/lid’s curl with the can’s flange. To ensure that the closure is sealed, a tight double seam is required, which has to have sufficient overlap between the body and cover.
The interlocking seam is sealed by the lining compound, which was prepared on the lid’s curl and which turns the entire seam into a hermetically sealed gasket.
Ultimately, these all decide how sealed the seam will be. A properly sealed double seam should look like this image.
A double seam is essentially the folded end curl with the can’s flange – with compound in between them, preventing leaks and any outside influence on the can’s contents.
For a double seam to be closed, it first goes through the “first operation” and then the “Second operation”.