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Tissue creping training

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Tissue creping training

  1. 1. Tissue Machine Operator Training
  2. 2. Why Crepe Tissue? <ul><li>Increase sheet bulk </li></ul><ul><ul><li>Sheet thickness </li></ul></ul><ul><li>Increase sheet softness </li></ul><ul><ul><li>Bulk </li></ul></ul><ul><ul><li>Flexibility (limpness) </li></ul></ul><ul><ul><li>Extensibility (extension under a specific load) </li></ul></ul><ul><ul><li>Surface smoothness (roughness and coefficient of friction) </li></ul></ul><ul><li>Increase sheet absorbency </li></ul><ul><li>Increase sheet stretch </li></ul><ul><ul><li>Elongation at sheet failure </li></ul></ul>
  3. 3. What is Percent Crepe? <ul><li>Percent Crepe = Yankee Speed - Reel Speed X 100% Yankee Speed </li></ul><ul><li>Percent Crepe is one way of measuring the stretch(su căng ra) in tissue </li></ul>
  4. 4. What Happens During Creping? <ul><li>The sheet is held against the dryer by the coating (crepe aid) </li></ul><ul><li>The sheet is pulled off the dryer by the reel </li></ul><ul><li>The sheet is “blown apart” (debonded) at the creping blade, losing >50% of its strength </li></ul>Doctor Blade Yankee Dryer Paper Soft Coating (Blue) Hard Coating (Green)
  5. 5. Why Apply Coating and Release? <ul><li>Protect the Yankee dryer surface against damage from the creping (doctor) blade and cleaning blade </li></ul><ul><li>Hold the sheet against the dryer during creping- the coating acts as an adhesive (glue) </li></ul><ul><li>Help build a good roll at the reel </li></ul>
  6. 6. Creping Mechanics <ul><li>A = Cutting angle </li></ul><ul><li>B = Blade bevel angle </li></ul><ul><li>C = Blade angle </li></ul><ul><li>D = Take off angle </li></ul><ul><li>R = Reel speed </li></ul><ul><li>Y = Yankee dryer speed </li></ul><ul><li>% Crepe = Y - R X 100% R </li></ul>Yankee Dryer Creping (Doctor) Blade A B C D Y R
  7. 7. Stages in Coating Formation Pressure roll Spray bar Creping Blade Yankee Dryer CROSSLINKING CURED GLASS TRANSITION REWETTING DOCTORING SETTING
  8. 8. Coating Layers Dryer Surface: Iron Dryer Surface: Metallized coating Inorganic Substrate Cured (Hard) Organic Coating Soft (Modified) Organic Coating Paper Sheet Creping Blade
  9. 9. Factors Influencing Creping <ul><li>Furnish: Hemicellulose content </li></ul><ul><li>Water: Hardness/pH/chlorine </li></ul><ul><li>Wet end additives (especially wet strength and surfactants) </li></ul><ul><li>Dryer surface </li></ul><ul><ul><li>Cast iron vs. metallized </li></ul></ul><ul><ul><li>Physical damage </li></ul></ul><ul><li>Blades </li></ul><ul><ul><li>Cleaning blade loading </li></ul></ul><ul><ul><li>Oscillation </li></ul></ul><ul><ul><li>Beveling </li></ul></ul><ul><ul><li>Uneven wear </li></ul></ul><ul><li>Dryer surface temperature </li></ul><ul><ul><li>Steam pressure </li></ul></ul><ul><ul><li>Uneven condensate removal </li></ul></ul><ul><li>Moisture profile </li></ul><ul><ul><li>Uneven sheet basis weight </li></ul></ul><ul><ul><li>Press section: uneven showering, filled/damaged press felts </li></ul></ul><ul><ul><li>Uneven crepe/release shower bar coverage </li></ul></ul><ul><li>Moisture content </li></ul><ul><ul><li>Sheet solids at pressure roll </li></ul></ul><ul><ul><li>Crepe/release spray bar water volume </li></ul></ul>
  10. 10. Common Problems <ul><li>Too much coating </li></ul><ul><li>Sheet picking at the creping blade (excessive dust and/or sheet holes) </li></ul><ul><li>Sheet can’t release from the dryer (sheet breaks) </li></ul><ul><li>Severe creping (low sheet strength and stretch) </li></ul><ul><li>Too little coating </li></ul><ul><li>Not enough creping (low softness and bulk) </li></ul><ul><li>Corrugated roll </li></ul><ul><li>Carbon marking of the sheet </li></ul><ul><li>Yankee dryer damage </li></ul>
  11. 11. How to Adjust Crepe & Release Aids <ul><li>1st priority: protect the Yankee dryer surface </li></ul><ul><li>2nd priority: build a good roll at the reel </li></ul><ul><li>3rd priority: attain sheet specifications </li></ul>
  12. 12. Protecting the Yankee Surface <ul><li>Look for a hazy coating on the Yankee; the metal surface should not look like a mirror when a flashlight is shined on it </li></ul><ul><li>Increase the coating feed rate until a hazy coating is present </li></ul><ul><li>Make sure the coating is even across the dryer; if not: </li></ul><ul><ul><li>Make sure the Yankee spray bar gives even coverage </li></ul></ul><ul><ul><li>Compare the basis weight profile with dryer streaks </li></ul></ul><ul><ul><li>Compare press felt streaks with dryer streaks </li></ul></ul><ul><ul><li>For narrow streaks (<1cm across): if they move, check needle showers; if not, the problem may be poor condensate removal </li></ul></ul>
  13. 13. Building a Good Roll at the Reel <ul><li>When increasing the creping aid (coating) or decreasing the release aid feed rate: </li></ul><ul><ul><li>Look for (feel for) pin holes in the sheet </li></ul></ul><ul><ul><li>Make sure the holes are “dry end” holes </li></ul></ul><ul><ul><li>If you find “dry end” holes, there is too much coating on the dryer </li></ul></ul><ul><li>When decreasing the creping aid (coating) or increasing the release aid feed rate: </li></ul><ul><ul><li>Watch for roll corrugation, carbon marks, or sparks on the Yankee </li></ul></ul><ul><ul><li>Check for the odor of burning metal </li></ul></ul><ul><ul><li>If you find any of the above, there is not enough coating on the dryer </li></ul></ul>
  14. 14. Attaining Sheet Specifications: Strength <ul><li>Mechanical Options </li></ul><ul><li>Increase refining (brushing, not cutting)- up to a point </li></ul><ul><li>Increase wet pressing </li></ul><ul><li>Decrease calendering </li></ul><ul><li>Reduce headbox consistency (to improve sheet formation) </li></ul><ul><li>Use a beveled creping blade </li></ul><ul><li>Use more long fiber pulp </li></ul><ul><li>Chemical Options </li></ul><ul><li>Increase release aid feed rate </li></ul><ul><li>Decrease coating feed rate </li></ul>
  15. 15. Attaining Sheet Specifications: Stretch <ul><li>Mechanical Options </li></ul><ul><li>Increase % crepe </li></ul><ul><li>Use a beveled creping blade </li></ul><ul><li>Chemical Options </li></ul><ul><li>Increase release aid feed rate </li></ul><ul><li>Decrease coating feed rate </li></ul>
  16. 16. Attaining Sheet Specifications: Bulk <ul><li>Mechanical Options </li></ul><ul><li>Decrease refining </li></ul><ul><li>Decrease wet pressing </li></ul><ul><li>Decrease calendering </li></ul><ul><li>Use more short fiber pulp </li></ul><ul><li>Chemical Options </li></ul><ul><li>Decrease release aid feed rate </li></ul><ul><li>Increase coating feed rate </li></ul>
  17. 17. Attaining Sheet Specifications: Softness <ul><li>Mechanical Options </li></ul><ul><li>Decrease refining </li></ul><ul><li>Decrease wet pressing </li></ul><ul><li>Decrease/increase calendering (depends if you need more bulk or smoothness) </li></ul><ul><li>Use more short fiber pulp </li></ul><ul><li>Decrease headbox consistency (to improve sheet formation) </li></ul><ul><li>Use a square creping blade </li></ul><ul><li>Chemical Options </li></ul><ul><li>Decrease release aid feed rate </li></ul><ul><li>Increase coating feed rate </li></ul><ul><li>Use a softening agent </li></ul>
  18. 18. Coating/Release Feed Strategies <ul><li>Add coating/release to the wet end </li></ul><ul><li>Add coating/release to the felt-supported sheet </li></ul><ul><li>Add coating/release to the Yankee dryer </li></ul>
  19. 19. Wet End Addition <ul><li>Advantages </li></ul><ul><li>Simple, low cost equipment setup </li></ul><ul><li>Product addition is fairly even across the sheet width (depends on basis weight profile) </li></ul><ul><li>Disadvantages </li></ul><ul><li>Product is not applied outside the sheet edges, leading to dubbing of the dryer </li></ul><ul><li>High feed rates (around 10 times as much as through a spray bar) </li></ul><ul><li>Longer lag time when adjusting coating/release ratio </li></ul>
  20. 20. Felt-Supported Sheet <ul><li>Advantages </li></ul><ul><li>More cost effective than wet end addition </li></ul><ul><li>Minimal lag time when adjusting coating/release ratio </li></ul><ul><li>Independent of basis weight profile </li></ul><ul><li>Disadvantages </li></ul><ul><li>Product is not applied outside the sheet edges, leading to dubbing of the dryer </li></ul><ul><li>Requires a spray boom (more expensive equipment setup) </li></ul><ul><li>Possibility of uneven product application (worn/plugged nozzles or poor shower design) </li></ul>
  21. 21. Yankee Surface <ul><li>Advantages </li></ul><ul><li>More cost effective than wet end addition </li></ul><ul><li>Treats the entire Yankee surface, not just the part that contacts the sheet </li></ul><ul><li>Minimal lag time when adjusting coating/release ratio </li></ul><ul><li>Independent of basis weight profile </li></ul><ul><li>Disadvantages </li></ul><ul><li>Requires a spray boom (more expensive equipment setup) </li></ul><ul><li>Possibility of uneven product application (worn/plugged nozzles or poor shower design) </li></ul>
  22. 22. Typical Yankee Application Setup Quick Disconnect For Pressure Equalization of Home Made Shower Bars- Not Needed for Professionally Engineered Shower Bars Quick Disconnect (or Flush Line) Double Coverage Shower Bar Static Mixer Fresh Water Source Crepe aid Release aid Filter
  23. 23. Creping Trial: Overall Trial Plan Initial feed rates need to be determined for each trial individually; double click on the chart at left to determine crepe aid flow
  24. 24. Protect the Yankee Surface
  25. 25. Build a Good Roll at the Reel- Coating/Release
  26. 26. Build a Good Roll: Coating/Modifier/Release
  27. 27. Attain Sheet Specifications
  28. 28. Yankee-Applied Softener Trial

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