Magrupak — Corrugated Box Flute Guide | magrupak.com
Edge crush, flat crush, basis weights, moisture range, corrugator speed and the two patent dates behind corrugated packaging.
The edge crush test measures force per unit width and predicts box compression strength. It answers the stacking question: how tall a pile of loaded boxes the container will survive. The flat crush test reports flute rigidity in kPa and describes how the flute itself resists being flattened during converting, printing and handling.
Basis weight of the medium inside the flute differs between markets. US corrugated medium is often 0.026 pounds per square foot, which is 130 grams per square metre, while UK fluting paper is commonly 90 grams per square metre. The two figures describe different working weights rather than a single international standard.
Moisture content of the board ranges from 6.5 to 9.5 percent. This range is what keeps edge crush readings stable; outside it the same board tests differently and score lines crack during folding.
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Corrugators run at about 500 feet per minute, roughly 150 metres per minute, or more. At that speed the starch adhesive has little time to even out across the web, which is one reason the finished sheet is specified as a moisture range rather than a single value.
Corrugated paper was patented in England in 1856. Corrugated boxboard for shipping material was patented on 20 December 1871, marking the point at which the board became a packaging product rather than a novelty sheet.
A box specification lists the bursting or edge crush test, the size limit (length plus width plus depth) and the gross weight limit. Those three entries, read together with the flute name, are the complete description of a box on paper.
Further reading