When talking about Corrugated protection, Flute is one of the things you might hear to describe the type of corrugated, to you it might sound like an musical instrument, but rather, it means a fluted corrugated sheet with flat linerboards on either side of it. The most commonly used Flute, is the C Flute, see below the measurement are for all the flute sizes.  Corrugated sheets are widely used to manufacture corrugated boxes and protective sheets or rolls.

Manufacture of Corrugated Board

Corrugated board is manufactured on large high-precision machinery lines called corrugators, usually running at 500 lineal feet per minute or faster. These machines over time have become very complex with the objective of avoiding some common problems in corrugated board production, such as warp and washboarding.

The manufacturing process begins with pulping, the separation of wood (hardwood and sapwood) into individual fibers, as accomplished by mechanical methods or chemical treatment.

In the classical corrugator, the paper is softened with high-pressure steam. After the board is formed it is dried in the so-called dry-end. Here the newly formed corrugated board is heated from the bottom by hot plates. On the top, various pressures are applied by a load system on the belt.

The corrugated medium is often 26 lb/1000 sq.ft basis weight in the U.S. 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 adhered to the other side of the fluted medium to form single wall corrugated board. Linerboards are test liners (recycled paper) or kraft paperboard (of various grades). The liner 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, although the actual flute dimensions for different corrugator manufacuturers may vary slightly. Measuring the number of flutes per lineal foot is a more reliable method of identifying flute size than measuring board thickness, which can vary due to manufacturing conditions. The most common flute size in corrugated boxes is “C” flute.

Corrugated fiberboard can be specified by the construction (single face, singlewall, doublewall, etc), flute size, burst strength, edge crush strength, flat crush, basis weights of components (pounds per thousand square feet, grams per square meter, etc), surface treatments and coatings, etc. TAPPI 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.

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