How's Corrugated Boxes Made?

Corrugated board is manufactured on large high-precision machinery lines called Corrugators running at 500 lineal feet per minute or faster.

The corrugated medium is usually a 26 lb/1000 sq ft (127 g/m^2) paperboard; higher grades are also available. It arrives to the corrugator on large rolls. At the single-facer, it is heated, moistened, and formed into a fluted pattern on geared wheels. This is joined to a flat linerboard with a starch based adhesive to form single face board. At the double-backer, a second flat linerboard is adherred to the other side of the fluted medium to form single wall corrugated board. Linerboards are often kraft paperboard (of various grades) but may be bleached white, mottled white, colored, or preprinted.

Common flute sizes are "A", "B", "C", "E" and "F" or microflute. The letter designation relates to the order that the flutes were invented, not the relative sizes. Flute size refers to the number of flutes per lineal foot. For example, "B" flute is approximately 1/4 inch from the top of one flute to the next, or 50 flutes per foot. "C" Flute is 5/16 inch from flute to flute or 42 flutes per lineal foot. "E" flute is 1/8 inch flute to flute or 90 flutes per lineal foot. Board thickness is an unreliable metric, due to various manufacturing conditions. However, a rough guide is: "C" flute=5/32 inch thick, "B" flute=1/8 inch thick, "E" flute=1/16 inch thick. The most common flute size in corrugated boxes is "C" flute.

Corrugated board is often graded by the basis weights of the linerboards, burst or mullen strength, edge crush test, or flat crush test. TAPPI [[1]] and ASTM test methods for these are standardized.

The choice of corrugated medium, flute size, combining adhesive, and linerboards can be varied to engineer a corrugated board with specific properties to match a wide variety of potential uses. Double and triple-wall corrugated board is also produced for high stacking strength and puncture resistance.


Box Manufacture
Boxes can be formed in the same plant as the corrugator. Alternitively, sheets of corrugated board may be sent to a different manufacturing facility for box fabrication.

The corrugated board is creased or scored to provide controlled bending of the board. Most often, slots are cut to provide flaps on the box. Scoring and slotting can also be accoplished by die-cutting.

The "Flexo Folder Gluer" is a machine that in one single pass prints, cuts, folds, and glues flat sheets of board to convert them to boxes for any application, from storing old family pictures to shipping the biggest of plasma TV sets to the global market. The most advanced of FFG's can run at speeds of up to 26,000 boxes per hour.

The most common box style is the Regular Slotted Container. All flaps are the same length and the major flaps meet in the center of the box.


Box blank showing score lines, slots, and manufacturer's jointThe manufacturer's joint is most often joined with adhesive but may also be taped or stitched. The box is shipped flat (knocked down) to the packager who sets up the box, fills it, and closes it for shipment. Box closure may be by tape, adhesive, staples, strapping, etc.