Double seam
Canning process
A double seam is a canning process for sealing a tin can by mechanically interlocking the can body and a can end (or lid).
Originally, the can end was soldered or welded onto the can body after the can was filled. However, this introduced a variety of issues, such as foreign contaminants (including lead and other harmful heavy metals). The double seam was later developed as a cheaper and safer alternative and quickly replaced the welded seam.
The double seam is made using a double seamer, which can have just one or a number of heads or seaming stations. The double seam is formed by mechanically interlocking five layers of material together: three layers of the can end and two layers of the can body. Each seaming head typically consists of two rolls, a first operation roll and second operation roll, and a chuck. Some seaming machines have two first operation rolls and two second operation rolls and a few machines use a method called "rail seaming" which requires no rolls. During the seaming operation, the can end is lowered on to the filled can body and held down by the chuck, which acts as an anvil to the seaming operation. The first operation roll then engages the can end against the can body thereby folding the end curl around the flange of the body.
“Double seam” enters the record as canning process. Crown Archives preserves that source wording while asking what Double, seam and Canning can confirm, complicate or overturn.
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