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Printing veteran teaches you how to eliminate the printing bar
Although the causes of bar defects are complex, careful analysis can reveal underlying patterns and help in identifying solutions.
a. Severe wear on the roller's driving gear or excessively large tooth gaps can lead to bars. Additionally, if foreign particles stick to the gear teeth or become lodged in the tooth gaps, they can cause similar issues.
Solution: Regular maintenance, cleaning, and removal of debris can significantly reduce or prevent such problems.
b. If the roller bearings are severely worn, it may result in a bar defect.
Solution: To mitigate this, you can add padding to the blanket to make the gripper pad trapezoidal, which helps reduce impact when the gripper closes. Alternatively, replace the bearing with a more wear-resistant one.
c. Excessive pressure between the plate cylinder and the rubber cylinder can cause large sliding friction, leading to dot deformation and ink buildup, resulting in bars.
Solution: Adjust the pressure between the two cylinders carefully instead of simply adding more backing paper to the rubber cylinder.
d. Inappropriate lining on the printing plate or rubber cylinder can create excessive sliding friction, causing the plate cylinder to be driven by the surface rather than the gear. This is particularly common in areas with low pressure and thickly lined rubber cylinders.
Solution: Reduce the linear velocity difference between the rubber and plate cylinders by adjusting the lining—reduce the rubber cylinder’s lining and increase that of the plate cylinder.
e. Improper pressure from the roller pillow in an offset press can also cause bars. The condition of the roller pillow affects gear meshing. If the pressure is incorrect, the gears may not mesh properly, leading to vibration and bar formation.
Solution: Re-adjust the roller pillow pressure according to the manufacturer’s guidelines.
f. Excessive pressure between the ink roller and the printing plate, or between the ink rollers themselves, as well as between the water roller and the plate, can cause bar defects.
Solution: Ensure that the contact width between the ink roller and the printing plate does not exceed 6mm, and between the ink rollers should be within 5mm. Also, reduce the pressure between the water roller and the plate.
g. Misalignment or wear of the ink roller gear and intermediate wheel, along with damaged ink roller bearings, can contribute to bar formation.
Solution: Replace the faulty components to resolve the issue effectively.
By understanding these causes and implementing the appropriate solutions, operators can maintain smooth operation and improve print quality. Regular inspection and proper maintenance play a crucial role in preventing bar defects and ensuring consistent performance.