TL;DR
Doctor blade streaking causes MD caliper streaks in tissue. Inspect blade loading pressure uniformity, blade holder alignment, and blade condition before replacing the blade.
What you might see
- MD streaks in creped tissue
- uneven creping across the machine width
- oscillating tissue caliper at one or more CD positions
- tissue tearing at consistent CD locations
Likely causes
Uneven blade loading pressure across the machine width
Doctor blade holder beam deflection or misalignment
Localized blade wear or nick at a fixed CD position
Foreign material embedded in the blade creating a lifted zone
Required tools
- Pressure gauges for blade loading beam
- Straightedge for beam alignment check
- Replacement doctor blade
- Heat-resistant gloves
Safety first
- The Yankee cylinder surface is above 100 deg C. Use heat-resistant gloves and avoid direct contact.
- Doctor blades are sharp. Use blade handling gloves and a blade changing tool, never bare hands.
Procedure
- 1
Stop tissue production and reduce Yankee speed to creep before inspecting the doctor blade area.
Warning: The Yankee dryer surface operates above 100 deg C. Use heat-resistant gloves and maintain safe distance from the cylinder surface. - 2
Check the blade loading pressure gauges across the beam width. Identify any zone where pressure deviates more than 0.1 bar from the adjacent zones.[1]
- 3
Inspect the blade edge along the full machine width from a safe position for visible nicks, deformation, or embedded particles.
- 4
Check the doctor beam alignment. Verify the beam is parallel to the Yankee surface within the tolerance specified in the maintenance manual.[1]
- 5
If a nick or particle is visible, stop the machine and replace the doctor blade. Nicks do not self-heal and worsen during operation.
- 6
Install the new blade with uniform loading across the beam. Start with lower loading and increase to setpoint gradually to condition the new blade.
- 7
Monitor CD caliper profile for the first reel after blade replacement to confirm the streak is resolved.
Sources
Valmet Valmet TurboDry Yankee Dryer general technical documentation, Valmet
Yankee dryer doctor blade maintenance and streaking diagnosis, general tissue machine practice (general)
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