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PAPER AND PAPERBOARD PACKAGING
271
Figure 8.20 Production of corrugated fibreboard (courtesy of The Institute of Packaging).
paper is conditioned with heat and steam, and pressed between large rolls, with
a gear wheel shaped surface, to produce the corrugation (Fig. 8.20).
Several standard flute configurations are available varying in the pitch
height and number of corrugations per unit length, characterised by letters
A (coarse), B (fine), C (medium) and E (finer than B). B-flute has a high flat
crush resistance and is used for packing cans and bottles where the contents
themselves contribute to the stacking strength. C-flute is used where the contents do not support the case because C-flute has a higher compression strength
at the same board weight. It is also used for glass bottles where its higher flute
height may provide more cushioning and higher puncture resistance.
In addition to box compression, cushioning, flat crush resistance and puncture resistance other performance features which have to be taken into consideration are print quality, efficiency of cutting and the scoring and bending
characteristics. Printing is carried out either after corrugating or, where higher
print quality is required, before corrugating. The latter is referred to as pre
print.
It is sometimes more appropriate for the packer to purchase an unprinted
standard sized case and print, or label, on demand. This approach may be
applied where seasonally cropped fresh fruit and vegetables are being canned
and it is difficult to estimate the eventual size of the crop and therefore the
number of printed cases required. If the estimate is above the eventual requirement, printed cases are left in stock until the next packing season occurs, and if
underestimated there is a need for urgent deliveries of additional printed cases.
Box compression strength can be calculated from the weight of contents,
stacking geometry, and atmospheric conditions of storage. The manufacturers
of corrugated packaging have mathematical models based on their standard