Problems and solutions encountered in the reconstruction of double paper paths

Paper Break

During the trial printing process, paper breakage is a common issue. When double paper feeding is involved, any break in the paper results in waste from both paper paths. Different causes can lead to this problem, such as incorrect acceleration clutch pressure settings, improper separation of the clutch, paper cracking, overly brittle paper, insufficient tensile strength, and misadjusted tension parameters.

To prevent these issues, operators should carefully monitor the equipment’s performance. It’s crucial to check if the acceleration clutch is functioning properly. When the machine is running smoothly, they should also inspect the paper by listening to the sounds on both sides of the roll. They can assess the flatness of the roll and check for cracks by running the paper through. Folding or tearing the edge of the paper can help determine its brittleness. Adjusting the tension on both sides of the paper and tightening the tape as much as possible is essential. If cracks are found, tearing them from the edge can help avoid further breaks. Using crisper paper and reducing tension can also lower the risk of paper breakage.

Through multiple tests and adjustments, the team gradually mastered the proper equipment settings. As a result, when using rewound paper with high tensile strength, paper breakage became very rare.

2. Wrinkles at the Front of the Paper During Folding

To ensure synchronization and stability during the folding of two paper paths, a skipping knife (also known as a flower wheel) is used instead of a central cutting knife like in single-paper folding. However, during post-press processing, wrinkles often appear at the front of the paper, sometimes even extending to the text of the book block, which looks unattractive. This issue is caused by small skipping teeth, short cuts, and long connection points that prevent air from escaping. The problem isn’t obvious right after folding but becomes visible when the paper is stacked.

To address this, our company modified the skipping knife to increase the length of the cut, making the connection points shorter and effectively solving the issue of front paper wrinkling during double-paper folding.

3. Folding Instability

In the early stages of trial printing, it was observed that the two paper strips moved unpredictably during operation, leading to instability. The outer paper strip was looser than the inner one, causing misalignment and misplaced page numbers. Even after adjusting the position using the machine's switches, the range was too large for precise control.

After analyzing the paper path, we implemented several solutions: adjusting the thickness of the outer printing roller, slowing down the outer paper feed, and ensuring both paper strips enter the folding mechanism simultaneously. Adding guiding rollers helped maintain smooth paper movement, and using motorized adjustments allowed for more accurate positioning. These changes significantly improved the stability of the double-paper folding process.

　　 The above content is selected from the 6th issue of “Printing Technology·Digital Graphic Arts” in 2013. More journal content please pay attention to the journal channel.