A roll is a tooling that comes either as 1st operation or 2nd operation variant. The first operation roll is designed to start the process by rotating around the can and creating the first operation seam. The second operation roll will then rotate around the can and complete the seam’s formation by “ironing” it and pressing it into a completely closed seam – thus ensuring that the can is hermetically sealed and pressurization is maintained.
The configuration of the roll in a typical seamer head is one chuck (holding the end), a lifter plate (lifting the can and its contents into position) and two rolls. However, there are seamers with more rolls (e.g., 4 rolls per head).
A roll (The two objects on the right and left) has a small groove in it, which actually does the work and the design of that groove (shown in the image inside the red square) determines the operation. The image above shows the first operation roll on the left (with a more circular open profile shape) and a tighter 2nd operation roll (with a profile shaped as shape of the final seam).