How to Identify a Crushed Blanket
Where the blanket is pressed down, the same position is faint on every sheet, and the repeat length equals the circumference of the blanket cylinder. It is not missing ink: the dots are still there, just light. Do not add ink first; adding ink will only muddy the surrounding area while the low spot remains faint. Add a shim or replace the blanket.
Where the blanket is depressed, every sheet is weak at the same position, and the repeat length equals the blanket cylinder circumference. It is not that ink is not being applied: the dots are still there, just light. Don’t add ink first; adding ink will only muddy the surrounding area, and the low spot will still be weak. Shim it with a sheet or replace the blanket.
How to tell it from a missing print
A missing print means that area has no ink at all and bare paper shows through. With a damaged blanket, the ink is still there, the dots are smaller and lighter, and the edges are blurry. Feel the blanket with your hand; the low spot is often a dent caused by a paper wad, a wrench, or a dried ink lump. Because the blanket passes the same spot every revolution, the weak spot stays in the same position on every sheet.
Measure the distance from this weak spot to the same weak spot on the next sheet. If it equals the blanket cylinder circumference, it is on the blanket. If it equals the plate circumference, only then check the plate or plate cylinder.
What to check first
| Symptom | Repeat length | Action |
|---|---|---|
| An area is weak, dots still present | Blanket cylinder | Shim or replace the blanket |
| An area shows bare paper | Plate cylinder | Check the plate, not shim the blanket |
| The whole image is weak | No fixed position | Check overall pressure; don’t look for one particular dent |
Do this first
- Magnify to confirm the dots are still there and just light.
- Measure the repeat length, and match it only against the blanket cylinder.
- If it matches, stop the press and inspect that spot; don’t add ink first.
