Page 358 - Biosystems Engineering

Food Package Engineering 335

Manufacturing Metal Containers
Cylindrical cans are the most frequent types of container made from
metal, although other shapes are also manufactured. These cans are
manufactured in three- and two-piece units. For manufacturing of
three-piece cans, a coil is cut into rectangular sheets, lacquered and
decorated as required, and then cut into strips of size based on desired
can dimensions. The slit strips are cut into body blanks and corners
are notched. The side edges forming the seams are bent to form hooks,
and then a strip is rolled to form the can’s body and side seam. The
seam area is then soldered with a mixture of 2 percent tin and 98 percent
lead. These days silver is used in place of lead for soldering due to
environmental concerns and lead toxicity. Welding is also done,
which offers a stronger side seam of narrow margin needing less
metal. A flange is then formed on each end of the can. One end, the
top or the bottom, of the formed body is then closed.
Two-piece cans are manufactured from both aluminum and tinplate
and have no side seam. A higher rate of production is achieved in
manufacturing two-piece cans compared to manufacturing three-piece
cans. Two processes—drawn and ironed (D & I) and drawn and redrawn
(D & RD)—are used to make two-piece cans (Figs. 11.6 and 11.7). In
the D & I process, a circular blank of metals fed into a cupping press
that stamps and draws shallow cups. The cup is then transferred to

1 2 3 4

5 6 7

FIGURE 11.6 Different stages of drawn and ironed can production. (1) Body blank,
(2 and 3) drawn and redrawn cup, (4 through 6) wall ironing and base formation,
(7) trim to required height. (Adapted from Ref. 1.)