In gravure printing, it's common for operators at flexible packaging factories to report abnormal failures without providing detailed descriptions. Instead of clearly explaining what's happening, they often just mention the symptoms. For example, an ink shortage can appear differently depending on the cause, and each cause requires a different solution. Understanding the specific reasons and how to address them is essential for effective troubleshooting.
1. **Ink shortage due to low ink in the tank** – This is one of the most frequent issues. The possible causes include: first, the ink pump stopping due to a malfunction; second, the ink tank shifting or sliding, which lowers the ink level; third, the ink level being too low because of rapid production speed. To resolve this, first, check and repair the ink pump to restore normal ink flow. Second, stabilize the ink tank to prevent it from sliding again. Third, adjust the ink level according to the production speed to maintain consistency.
2. **Ink shortage caused by dents on the impression cylinder** – This occurs when the magenta impression cylinder has pits or the printing plate has bumps. The solution involves increasing the pressure on the impression cylinder. If the issue persists, the cylinder may need to be replaced. Similarly, if the problem remains after adjusting pressure, the printing plate should be checked and replaced if necessary.
3. **Improper ink level causing ink shortage** – This happens when the ink tank is set too high during preparation, leading to residue buildup that touches the printing plate and damages the image. Another cause is long blocking paper on the scraper’s back side, which can curl and intermittently touch the plate, scraping parts of the design. To fix this, lower the ink level so the plate is only partially submerged (1–37.5 mm). Also, stop the machine and trim the blocking paper to prevent curling.
4. **Missing edges on text or patterns** – This typically results from clogged printing plate dots not being cleaned before starting the machine, improper use of ink or solvent, or incorrect ink viscosity. To address this, wipe the plate with a solvent-dipped cloth and cleaning powder before operation. If needed, wash the plate with a cleaning solution to ensure the dots are clear. Replace the ink or solvent if it's not suitable, and regularly check the ink viscosity to keep it within the correct range, avoiding any air disturbances around the press.
5. **Ink shortage caused by water droplets or oil stains** – This can occur when the humidifier produces excessive moisture, allowing water to drip onto the printing plate. A leaking cooling water pipe can also cause water to reach the plate, while a very low cooling temperature may lead to condensation build-up. These contaminants can interfere with ink transfer and damage the print quality. Regular maintenance of the humidifier and cooling system is crucial to prevent such issues.
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