Problems and solutions encountered in the reconstruction of double paper paths

Paper Break

During the trial printing process, paper break is a common issue that can significantly affect efficiency and waste materials. When two paper paths are involved in double-sided printing, any paper break leads to the loss of both sheets. Various positions of paper breaks were analyzed, and the main causes include improper acceleration clutch pressure settings, incomplete clutch disengagement, paper cracking, brittle paper, insufficient tensile strength, and incorrect tension settings.

To prevent these issues, operators should closely monitor equipment performance, especially the acceleration clutch function. When the machine runs smoothly, it's important to recheck the paper and assess the roll by listening to sounds from both sides. Checking for flatness, inspecting the paper for cracks by running it through, and testing the edge by folding or tearing can help identify brittle paper. Adjusting the tension on both sides of the paper and tightening the tape as much as possible can reduce the risk of breakage. If cracks are found, they should be removed from the edge to avoid further breaks. Using crisper paper with reduced tension also helps minimize breakage.

Through multiple analyses, adjustments, and tests, the machine has gradually improved its operational stability. With proper rewinding and high tensile strength, paper breakage during the process is now rare.

2. Wrinkles at the Front of the Paper When Folding

Ensuring synchronization and stability in the folding of two paper paths is crucial. Unlike single-paper folding, where a central cutting knife is used, a skipping knife (also known as a flower wheel) is employed for double-paper folding. However, during post-press processing, wrinkles often appear at the front of the paper, sometimes even extending into the text of the book block, which looks unprofessional. This issue arises due to small skipping teeth, short cuts, and long connection points that trap air. The problem isn't obvious right after folding but becomes visible when the folded stack is placed on the stacking table.

To address this, our company modified the skipping cutter to increase the length of the cut, resulting in shorter connection points and effectively eliminating front paper wrinkling during double-paper folding.

3. Folding Instability

At the start of trial printing, the two paper strips were prone to shifting left, right, up, and down, causing instability. The outer paper strip was looser than the inner one, leading to inaccurate folding and misaligned page numbers. Even after adjusting the position using the machine’s switches, the adjustment range was too large to achieve precise alignment.

After analyzing the paper path, we implemented several solutions: adjusting the thickness of the outer printing roller, reducing the speed of the outer paper, ensuring both papers enter the folding mechanism simultaneously, adding guiding rollers for smoother movement, and using the device’s motor to adjust the paper’s left-right position. These changes greatly improved the stability of double-paper folding.

　　 The above content is selected from the 6th issue of “Printing Technology·Digital Graphic Arts” in 2013. For more journal content, please visit the journal channel.