During the creasing process, improper techniques can lead to issues such as longitudinal paperboard tears and uneven double folds. The following sections will summarize the root causes of these problems and propose corresponding solutions. It is important to note that, even after implementing appropriate measures, operators must still conduct regular, random inspections during routine operations to promptly identify defective paperboard and take corrective action without delay.

Causes of Longitudinal Fracture

(1) The longitudinal rolling pressure is too high.

When the cardboard enters the creasing roller operation, the roller can crush the cardboard, causing the liner or face paper to tear along the corrugation direction. To resolve this issue, operators must adjust the pressure of the longitudinal creasing roller according to the cardboard thickness; under normal conditions, the ideal penetration depth for a three-ply cardboard is 2–3 mm. However, during routine production, operators should further fine-tune the pressure based on the quality of the base paper, ensuring that the paper is not crushed while remaining easy to fold.

(2) The press wheel is improperly designed.

The most commonly used method in cardboard creasing is the male–female die configuration. Due to variations in paper type, production environment, and board thickness, the design of the creasing rollers also differs accordingly. The key parameters are ensuring that the widths of the upper and lower rollers are appropriately matched, and that the transition fillets on the rollers are adjusted based on the desired crease depth and the specific type of board being processed. In general, the thicker the board, the wider the crease should be; for three-ply board, a roller with a curved surface may also be employed. There is no standardized design for creasing rollers, so operators must select the appropriate roller configuration based on actual conditions.

Solution:

(1) Improve the structure of the wire-pressing roller. By adjusting the roller’s design, the radius of the step transition arc on the roller can be appropriately increased.

(2) Adopt the pre-compression failure method by performing a preliminary compression prior to the formal crimping. The drawback is that it leaves relatively obvious crimp marks.

(3) The base paper must be of high quality; for cardboard with stringent requirements, higher-quality face and liner papers should be used.

(4) The moisture content of the base paper and cardboard must be appropriate. The poorer the quality of the base paper and the drier the cardboard, the higher the likelihood of crease-line cracking.

(5) Appropriately control the depth of the creasing. Adjust the gap between the upper and lower creasing rollers according to the thickness of the cardboard being processed, ensuring that the cardboard receives proper creasing.

(6) Ensure that the centerlines of the upper and lower presser wheels are aligned to prevent misalignment.

(7) For cardboard with exceptionally poor base paper quality, use a line-matching machine to align the edges.

(8) If the crease line cracks due to insufficient moisture in the cardboard, water spraying can be used to increase the cardboard’s moisture content.

The reason why the reverse fold does not show a double line

Under normal circumstances, when a manually operated creasing line produced by a creasing machine (also known as a scoring machine) is folded toward the face stock, it should appear as a double line. If it does not form a double line, it means the fold is not straight, the creases from the two knives are either faint or uneven, resulting in the absence of a true double line. The causes include: first, uneven wear of the two knives leading to inconsistent pressure at the ends and in the middle; second, misalignment of the lower embossing bar, which shifts the crease and causes the fold to be offset, thereby preventing the formation of a double line; and third, improper adjustment of the equipment itself, resulting in unequal pressure at the two ends—one side receiving more pressure than the other—and consequently an uneven fold that fails to produce a double line.

Solution:

(1) Based on the wear condition of the two cutting edges, perform grinding promptly to maintain balance between the two sides and the center.

(2) Based on the double-line reverse-fold condition, promptly adjust the lower convex strip to restore it to its normal state;

(3) Based on the equipment’s operating condition, have maintenance personnel or operational technicians adjust the equipment to ensure it is in optimal working condition.