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Box Construction
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The strength of a corrugated box starts with its material. A corrugated sheet
consists of two major components - linerboard and medium. Linerboard is the
flat paper that covers both sides of the sheet and the medium is the "fluted"
or arched paper found between both liners. The flute, when anchored to the
linerboards with a starched-based adhesive, resists bending and pressure
from all directions. When placed vertically on its ends, the flutes form
vertical columns, capable of supporting considerable amounts of weight.
Flutes come in five basic heights and shapes - the most common are "B-Flute"(used
for die-cut boxes) and "C-Flute (used for RSCs). B-flute is compressed and
appears thinner, but don't be fooled. It is made with more paper to provide
stronger side-wall protection from blows and punctures. C-flute is taller,
with more air space, but offers enhanced stacking strength. For excellent
graphic reproduction, consider E-flute. |
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The amount of virgin pulp fibers and the length of those fibers in a corrugated
sheet substantially contribute to box strength. For example, the difference
between a 200# test box and a 275# test box is that the latter has more pulp
fibers in its corrugated linerboard. The 200# test box is rated to hold up
to 65 lbs. of box and contents while the 275# box can hold up to 95 lbs. A
350# test box is rated to hold up to 120 lbs. of box and contents.
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Flute Designation
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Flutes per Linear Foot
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Flute Thickness (in.)
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Flute Cross Section
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A Flute
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33±3
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3/16
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B Flute
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47±3
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1/8
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C Flute
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39±3
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5/32
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E Flute
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90±4
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1/16
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