A normal or correctly formed 1st Operation Seam.
When the 1st Operation Seaming Roll Profile forms material in the cover curl and can body flange as seen here, 2nd Operation Seaming Roll Profile will successfully compress and form an ideal final seam.
1st Operation Seams must be formed correctly in order for 2nd Operation Rolls to finish the seam. The 1st Operation is a major key in controlling the Cover or End Hook, which in turn partly controls the can Body Hook formation, Countersink depth, and degree of Wrinkles in the Cover or End Hook.
1st Operation seam formation will also control, to a degree, the final seam Width. A narrow 1st Roll Profile will result in a narrow 2nd Operation seam Width.
The width and thickness of the 1st Operation seam will be a variable depending on tin plate weight, diameter of the can, and Seaming Roll groove profiles. The can manufacturers will have standards with allowable tolerances that should be adhered to as closely as possible.
A useful rule of thumb is to closely observe the bottom portion of the 1st Operation seam. The cover curl should form a smooth radius and come as close to contacting the can body wall as possible. Maintaining a smooth radius, witout flat spots or a sharp break into the can body will assure you of a good 1 st Operation Seam. When the ideal conditions are
In an initial set-up of a seamer or closing machine, or when installing new seaming rolls or re-adjusting to correct a malformation in a seam, you should always back off 2nd Operation Seaming Rolls or turn the Seaming Cam to the Off Seam position to check 1st Operation seams only. Without a properly formed 1st Operation seam it is difficult, if not impossible, to obtain a correct or acceptable finished seam.