What is the first operation (1st op)?
When a seam is being formed, it goes through two processes:
The first operation starts the process using a first operation roll that pushes the end curl in and up in to the seam to form the cover hook while pushing the can flange down to form the body hook. After the first operation is done, the second operation roll comes in and compresses the seam.
80% of the seam is formed during the 1st operation. It is the more important of the two seaming operations and must be properly evaluated and controlled.
To check the first operation, may operators simply remove the second operation roll or disable it and the closed cans are only closed using the first operation. Any good seam inspection system should be able to check the 1st operation seam.
Typically, the countersink, seam thickness and seam width (AKA seam length or Seam Height) are measured and compared to the manufacturer’s recommended 1st operation standard.
What is a proper 1st operation seam?
- Cover hook is parallel to the body wall
- Correct 1st operation Seam Thickness
- Correct 1st operation Seam Height (Seam Length or Seam Width)
- Accurate Pin Height setting
- Proper lifter plate pressure
- Recommended: 1st operation Seam gap should be smaller than 0.03″ (0.076mm)
- No contact between Cover Hook cut edge and the can body wall (this indicates a tight 1st operation seam)
The images below can be used as a rough indication of normal, loose and tight 1st operation.