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Grain and flute direction in board and corrugated board
Board and corrugated board do not behave the same in every direction. The grain direction of the fibers and the direction of the flute affect how stable a package is and how it folds.
Grain direction: the direction of the fibers
During manufacture, the fibers of paper and board align mainly in the direction of the paper machine. This direction is called grain direction or fiber direction. In the grain direction, board is stiffer than across it. A crease line parallel to the grain is therefore easier to fold than one across it. When exposed to moisture, board expands more across the grain. For sheet-fed work, the terms short grain and long grain indicate whether the fibers run parallel to the long or to the short side of the sheet.
What the grain direction does for folding cartons
Grain direction affects how cleanly creases fold and how strongly side panels bow. It also affects how easily a carton can be erected and filled. A carton has creases in both directions. No grain direction is therefore ideal for all creases, and the choice is a trade-off. Which direction applies to your construction is determined by your printer. Record it in the inquiry and on the drawing rather than leaving it to chance.
Flute direction: the direction of the flute
Corrugated board consists of an outer liner, a flute and an inner liner. The flute direction is the direction in which the flutes run. If the flutes stand vertically, a carton carries more load in a stack. For that reason, the flute direction in shipping cartons is usually parallel to the height. Folding corrugated board parallel to the flute differs from folding it across. The allowances and reductions for folding are larger than for board and depend on the direction. In direct printing, the flute can also show through the printed image.
Grain direction and sheet layout
The direction limits how blanks may be placed on the sheet. A rotated up often yields more blanks on the same sheet. If it is rotated by 90 degrees, the grain direction in the finished carton is also different. If all cartons are to fold alike and be equally stable, all ups need the same direction. That may cost more material. The final sheet layout is determined by your printer, because it knows the machine, tooling and sheet format.
Direction in the material profile
In JetDieline, the grain direction belongs to the material profile, together with thickness, minimum values and crease compensation. The allowances and reductions also depend on the grain or flute direction. Sheet layout takes spacing, gripper margin and grain direction into account. Bundled profiles are starting values. They only become reliable once you build a test piece from your material and measure it. If you change the material or the direction, check the profile again rather than adopting the previous values without checking.
Step by step
- Set the material and material thickness.
- Ask your printer for the grain or flute direction.
- Enter the direction in the inquiry and on the drawing.
- Plan the sheet layout using permissible rotations only.
- Fold a sample from the intended material and check creases and stability.
Frequently asked questions
How can I recognize a board's grain direction?
Bend a sheet carefully in both directions. It yields more easily in one direction, and then the bending axis is parallel to the grain direction. The manufacturer's or your printer's specification is binding.
Must the flute always stand vertically?
No. For shipping cartons this is usual, because vertical flutes carry the stacking load. Trays, displays and inserts may have other requirements. The packaging manufacturer decides.
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