how to improve runnability in tissue paper machines

Improving runnability in tissue paper machines requires a holistic approach that balances mechanical precision, chemical stability, and operational discipline. Runnability is generally defined by the machine’s ability to operate continuously with minimal web breaks and consistent quality at high speeds.

1. Optimize the Creping Process (The Heart of Runnability)

The interaction between the Yankee dryer, the coating chemicals, and the doctor blade is the most critical factor in tissue runnability. If this interface is unstable, the sheet will break or wrinkle.

• Stabilize Yankee Coating: You need a coating that provides good adhesion (to hold the sheet for creping) but remains soft enough to prevent “chatter” (vibration).
  • Action: Use a base coat for protection and a release agent to control adhesion. Adjust the ratio based on sheet moisture; a wetter sheet requires a more water-resistant coating to prevent it from washing off.
• Doctor Blade Management: A worn or improperly set blade causes uneven creping and sheet breaks.
  • Action: Monitor blade wear patterns.¹ If you see “chatter marks” (horizontal lines on the dryer surface), change the blade immediately and check the holder alignment.
  • Action: Optimize the impact angle. A standard setup often uses a blade bevel of roughly 75–85 degrees, but this should be tuned to your specific grade (e.g., lower angles for higher softness, though this can risk runnability).

2. Manage Web Tension and Open Draws

Tissue paper is incredibly fragile, especially when wet or immediately after creping. “Open draws” (areas where the paper sheet travels unsupported between sections) are common break points.²

• Shorten Open Draws: The distance the sheet travels unsupported should be minimized.³
  • Action: Ensure the geometry between the press roll and the Yankee dryer is as close as mechanically possible.
• Tension Control: Fluctuations in speed between sections (draw) create stress.
  • Action: Use low-inertia guide rolls and precise drives to maintain constant tension. Even a 0.5% speed mismatch can snap a lightweight tissue web.
• Sheet Stabilizers: In the dryer section, moving air can cause the sheet to flutter and break.
  • Action: Install air foils or blow boxes that create a vacuum effect to hold the sheet flat against the fabric, preventing edge flutter.

3. Chemical Additives for Sheet Strength

Sometimes mechanical adjustments aren’t enough, and you need to chemically reinforce the web to survive the machine’s speed.

• Wet Strength Resins: These are crucial for runnability in the wet end. They help the wet web survive the transfer from the forming wire to the press felt.
• Dry Strength Agents: Additives like starch or polyacrylamides improve the internal bond of the fibers, reducing “linting” (dust) and preventing the sheet from disintegrating under tension.⁴
• Softener Application: While softeners make the product better, applying too much debonder weakens the sheet and kills runnability. Apply softeners via spray on the Yankee or converting line rather than in the wet end to preserve fiber bonding.

4. Press Section Dewatering

A drier sheet is a stronger sheet. If the sheet is too wet when it hits the Yankee dryer, it requires more energy to dry and is more likely to break.

• Felt Conditioning: Dirty or compacted felts cannot remove water efficiently.
  • Action: Use high-pressure showers and vacuum boxes to keep felts open and porous.
• Uniform Nip Pressure: Ensure the pressure profile across the press rolls is perfectly even. An uneven nip creates wet streaks, which become weak points that break later in the process.⁵

5. Monitoring and Maintenance

• Vibration Analysis: Install sensors to detect vibration in bearings and rolls. Vibration often precedes a mechanical failure that causes a web break.
• Cleanliness: Tissue production creates massive amounts of dust.⁶ Dust build-up on sensors or in the hood can fall onto the sheet, causing holes and breaks. Implement strict “blow-down” cleaning schedules.

Summary Checklist for Troubleshooting Breaks