Page 359 - Biosystems Engineering

336 Cha pte r Ele v e n

1

2 3

4 5
FIGURE 11.7 Different stages of drawn and redrawn (D & RD) can
production. (1) Body blank, (2 through 4) drawn and redrawn cup,
(5) trimming and profi ling base. (Adapted from Ref. 1.)

an ironing press where it is pressed through series of dies (Fig. 11.6).
In this process, the wall thickness is reduced and the body height is
increased. The diameter of the bottom and the thickness of the sheet
remain the same during the ironing process. The bottom end is domed
to provide added strength, and the top portion is trimmed to the
1,2
desired height. The trimmed cans are chemically cleaned and
flanged. Cans intended for beverages are necked. In the D & RD pro-
cess, the final height and diameter of the container is produced by
sequentially drawing cups to a smaller diameter, keeping the thick-
nesses of the wall and the base as well as the surface area matching
the original blank (Fig. 11.7).
The metal containers are strong and provide an effective barrier
against gases and light and are resistant against high temperatures
during processing. The main disadvantages of metal cans are their
heavy mass, higher cost, and tendency to interact with contents and