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.

Cellulosic Ethanol

IN FEBRUARY 2007, the Department of Energy selected six cellulosic ethanol projects to receive up to $385 million in grants. Authorized by the Energy Policy Act of 2005, the funding was part of an effort by the Bush Administration to end the U.S.'s "addiction to oil" and enhance the nation's energy security.

The money was intended to further two of President George W. Bush's goals: to make ethanol out of nonfood biomass, including billions of pounds of agricultural waste, at a cost competitive with gasoline by 2012 and to increase the use of renewable and alternative fuels to 35 billion gal per year by 2017. In all, more than $1.2 billion was to be invested in the six biorefineries.

Two years later, none of the projects has been built, although one is under construction. Two were canceled right out of the gate. Hitches in the plans have turned up in numerous places. From securing feedstock to financing construction to finding a ready market, the experiences of the awardees illustrate that the nascent cellulosic ethanol industry faces several daunting hurdles.

The chosen projects represent technologies including enzyme hydrolysis, acid hydrolysis, and gasification. They were to be located in the Midwest, Southeast, and West and were planning to use feedstocks ranging from corncobs to wood chips. The companies advancing the projects had little in common other than having a plan to turn cellulosic waste into ethanol.

The designers of the DOE program envisioned that the grant money would be invested over four years, with the companies contributing 60% of the plant costs. When fully operational, the six facilities were expected to produce more than 130 million gal of cellulosic ethanol per year.

B.C.T. compression load of a corrugated board box

When a corrugated board box manufacturer tries to develop a new box, one of the design problems he runs into is selecting the correct cross section of the corrugated board. This includes the type of paper and the shape and number of the different layers. The board should meet different design requirements such as the maximum number of stacked boxes. Sometimes the capacity of a box to resist the vertical loads derived from stacking is expressed in terms of the so called "Box Compression Test" (BCT).

From a designer's standpoint, it would be very useful to have a predictive tool that allowed the computation of the BCT number of a box, from the geometry of the box and the cross section of the boards, without the need to make a prototype. Such a tool would speed up the design process and would produce boxes close to the optimum for each particular application. The difficulties in developing a tool like this come from the anisotropic nature of paper, together with the geometrical nonlinearities of an assembly of thin sheets of paper.

The BCT is obtained by simulation of the compression test, with a speed of 10-13 mm/min in the press.

In our methodology, we work at two levels: the global (complete box) level and the local (board) level. The local level analyses the micromechanics of the board and produces macromechanical properties for the study of the box at the global level.

The flowchart describes our methodology. We have created a library with the macromechanical behaviour of different board configurations (different thicknesses and geometries). Using this library, we assign to each box prototype the properties of a corrugated board, so we can easily obtain the BCT number of the prototype.