Base paper fibers are arranged in either the cross direction (CD) or the machine direction (MD). Currently, papermaking typically uses a longitudinal orientation, with the paper web direction being the cross direction and the paper length direction being the machine direction (ring compression tests are typically conducted in the cross direction, i.e., 12.7mm parallel to the paper width and 152.4mm parallel to the paper length). In color box manufacturing, the fiber direction of the color surface should intersect the flute direction of the mounting paper. The vertical and horizontal directions can be identified using the following methods:
① Visual observation: Most fibers run in the longitudinal direction.
② Cut into small squares and wet: The axial direction of the natural curl is parallel to the longitudinal direction.
③ Hand stiffness: The stiffest direction indicates the longitudinal direction.
④ Observe the tear direction during tear resistance testing: The tear direction should be parallel to the cross direction.
⑤ The direction with the highest fold strength or the highest number of folds indicates the longitudinal direction.
