TL;DR
A blanket smash from a double sheet or foreign object compresses the blanket and ruins print quality. Stop the press, measure blanket thickness, replace if smashed, and investigate the cause of the double sheet.
What you might see
- sudden print quality change, loss of coverage in a localized area
- indentation or low spot visible on blanket surface
- press stopping on double-sheet detector
- impression pressure alarm on control panel
Likely causes
Double sheet feeding through the impression nip compressing the blanket
Foreign object entering the press from the feeder pile
Over-impression from incorrect impression setting compressing the blanket gradually
Sheet jam in the impression causing the blanket to absorb excessive load
Required tools
- Caliper for blanket thickness measurement
- Replacement blanket and blanket bar bolts
- Torque wrench
- LOTO kit
Safety first
- Lock out the press before reaching near the blanket cylinder or impression area.
- Blanket bar bolts are under high tension. Follow the torque specification exactly to avoid uneven tension that can cause the blanket to pull during production.
Procedure
- 1
Stop the press immediately after a suspected blanket smash. Do not attempt to continue printing with a smashed blanket.[1]
- 2
Lock out the press before opening any guards or reaching near the blanket cylinder.
- 3
Visually inspect the blanket for indentations, wrinkles, or cut marks. A smashed area appears as a concave depression in the surface.
- 4
Measure blanket thickness at the suspected smash area and at an undamaged area with a caliper. A thickness loss greater than 0.1 mm indicates a smashed blanket requiring replacement.[1]
- 5
Remove and replace the blanket if the smash is confirmed. Torque the blanket bar bolts to specification.
- 6
Check and clean the double-sheet detector. Test it with a deliberately doubled test sheet to confirm it trips at one sheet overlap.
- 7
Inspect the feeder pile for wrinkled or stuck sheets that could have caused the double feed. Separate the pile before resuming.
Sources
Heidelberg Heidelberg Speedmaster XL 106 / CX 102 Offset Press (Sheetfed / Web) general technical documentation, Heidelberg
Offset press blanket smash detection, inspection, and replacement, general offset printing practice (general)
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