1. Paper Break
Refers to the sudden breakage of paper or original film during rotary printing.
Causes:
Damage or notching on the end face of the original film.
Holes in the middle of the original film.
Poorly executed joints.
Uneven tension (excessive).
If film breakage consistently occurs in a specific unit, it may be due to inconsistent air pressure in the impression cylinder of that unit.
Remedial Measures:
Carefully inspect the end face of the original film before winding. Remove or replace if damaged.
Re-thread the film after a break. If the film breaks twice in the same roll, replace the original film. Defective original films should be returned to stock.
Enhance personnel technical training.
Adjust tension appropriately (reduce it).
Have the maintenance department repair the impression cylinder of the unit, adjusting the pressure to ensure consistency on both sides.
2. Wrinkling
The occurrence of wrinkles in the original film during the printing process.
Causes:
The original film itself has wrinkles from winding, exacerbating wrinkles after passing through guide rollers.
Excessive printing pressure.
Improper printing tension.
Poor parallelism of guide rollers (including pressure rollers in the winding section).
Loosening of one side support roller of the guide roller.
Guide roller too dirty within the width range of the original film.
Lack of true roundness in the impression cylinder (uneven thickness).
Remedial Measures:
Replace the original film.
Appropriately reduce printing pressure.
Balance control of tension rollers.
Adjust or repair the parallelism of guide rollers.
Have the maintenance department repair the support roller of the guide roller.
Stop the machine to clean the guide roller, ensuring cleanliness within the width range of the original film.
Replace the impression cylinder.
3. Continuous Blade Lines
Lines that appear to move left and right with the swinging of the doctor blade, with varying thickness and sometimes appearing in parallel. Additionally, a special case involves scratches on the plate caused by the doctor blade holder, resulting in a continuous line that does not move left and right but remains relatively fixed.
Causes:
Damage to the doctor blade edge.
Debris (such as tape after cutting paper) stuck in the doctor blade holder.
Ink containing hard impurities.
Tape sticking to the plate after cutting paper.
Inadequate grinding of the plate or doctor blade.
Plate scratched by foreign objects.
Remedial Measures:
Wear cut-resistant gloves when grinding and replace the doctor blade.
Use a sharpened bamboo stick to remove debris (mild blade lines can be blown away with compressed air).
Filter the ink or replace it with fresh ink (the simplest method: use a stocking to filter at the ink pump outlet and ink tank drain).
Use a bamboo stick to remove tape stuck to the plate.
Re-grind the plate or doctor blade.
Replace the spare plate.
Special Note: Distinguish from the 20th abnormality "Scratches"; although the symptoms are similar, the meanings and causes are entirely different.
4. Intermittent Blade Lines (Also Known as "Gunshot")
Irregular, intermittent, vertical streaks of contamination on the printed material (unfixed position, variable length and thickness, irregular intervals).
Causes:
Wear of the doctor blade after passing through plate dot points.
Excessive pressure from the doctor blade.
Ink impurities (too dirty).
Lack of smoothness on the plate surface.
Ink itself is defective (lacks fatigue resistance).
Remedial Measures:
Grind or replace the doctor blade using a grindstone and sandpaper for thorough results.
Adjust the pressure of the doctor blade appropriately.
Use filtered ink or replace it with new ink.
Run the plate without inking before production and grind the plate at the doctor blade lines using 1000-grit sandpaper soaked in solvent. For intermittent blade lines during production, use "3M" scouring cloth (available on Taobao).
Replace the ink from another manufacturer.
Unconventional method: Add a small amount of water to the ink, with good results (generally, in a 20 kg bucket of solvent-based ink with a measured viscosity, you can add 100 ml of water. Do not add excessively, as it may cause ink clumping).
5. Blade Bone (Also Called "Knife Valley")
In the area where ink is transferred to the printed material, there are line-shaped blank spaces without ink that move left and right with the swinging of the doctor blade. Only one color is missing in the area of the blade bone, and it is not possible to have multiple colors missing simultaneously. If multiple colors are missing simultaneously, it is scraping caused by paper misfeed, not blade bone.
Causes:
Ink particles or debris adhere to the blade.
Ink is dirty: too dirty, with many impurities and coarse particles.
Remedial Measures:
Use a bamboo stick to remove or stop the machine to clean the doctor blade.
Use fingers or a cloth without hard impurities to dip slightly dry ink blocks and apply them to the blade bone on the front of the plate; this method works well.