New Insights into Gap Forming of Lightweight Containerboard

Transcription

1 New Insights into Gap Forming of Lightweight Containerboard Frank Swietlik, Jukka Muhonen, Ari Puurtinen, Hannu Turpeinen, Teuvo Virkkunen Metso, Paper business line PaperCon 2011 Page 345

2 Concepts for forming PaperCon 2011 Page 346

3 Gap former with two-layer headbox High-open volume forming roll design PaperCon 2011 Page 347

4 Gap former with two-layer headbox Dewatering elements Forming roll Multifoil shoe Forming shoe Curved suction box Couch roll Support foil Flat suction box Transfer suction box Flat suction box (2 ch.) PaperCon 2011 Page 348

5 High-performance two-layer headbox Fluidized state in headbox slice jet Turbulence generator and slice channel area with wedge technology Homogeneity of board structure Fluidized state in headbox slice jet Dilution principle Side/edge flows Shape-optimized header Even profiles Board samples PaperCon 2011 Page 349

6 Formation comparison Advanced former concept to conventional gap former designs Norm. formaton [%] Conventional gap formers Advanced gap former Basis weight (gsm) PaperCon 2011 Page 350

7 New high-performance two-layer headbox Layer coverage Poor fluidization, non optimized geometry (extra steps, parrot beak slice lips etc.) and speed difference between layers destroy layer coverage Optimized technology of the new highperformance two-layer headbox delivers good layer coverage without disturbing streaks PaperCon 2011 Page 351

8 Rigid separating element two-layer headbox Literature references concerning - Two-layer rigid separating element headbox and strength properties - Higher strength properties (geom. tensile strength, SCT CD, RCT CD) achieved if the outer layer runs at a higher speed than the inner layer Geom. Tensile Strength index = ( tensile index tensile ) MD index CD The outer layer runs at a higher speed than the inner layer. PaperCon 2011 Page 352

9 Main strength properties Test with rigid separating element two-layer headbox PaperCon 2011 Page 353

10 Other strength properties Test with rigid separating element two-layer headbox Poor Good PaperCon 2011 Page 354

11 Gap former configuration for containerboard Forming zone PaperCon 2011 Page 355

12 Forming roll drainage process PaperCon 2011 Page 356

13 Produced board grades, machine speeds and production rates Table 1 Grade [g/m²] Reel speed [m/min] Production rate [t/m*h] , , , PaperCon 2011 Page 357

14 Effect of lower headbox consistency on board properties Table 2 Property Pumping costs Retention Tensile and burst strength Internal strength Effect of lower headbox consistency Increase Decrease No effect below 1.5 % Decrease PaperCon 2011 Page 358

15 Effect of total headbox consistency on in-plane tensile strength PaperCon 2011 Page 359

16 Effect of total headbox consistency on in-plane burst strength PaperCon 2011 Page 360

17 Effect of forming roll wrap angle on drainage Forming roll dewatering [%] 90 % 85 % 80 % 75 % 70 % 65 % 60 % 90 g/m2 120 g/m2 150 g/m Forming roll wrap angle [ ] PaperCon 2011 Page 361

18 Effect of machine speed on the proportion of forming roll dewatering with 90 g/m² Forming roll dewatering [%] 100 % 95 % 90 % 85 % 80 % 75 % 70 % 65 % 60 % Basis weight 90 g/m² Forming roll wrap [angle [ ] 1250 m/min 1550 m/min 1750 m/min PaperCon 2011 Page 362

19 Effect of machine speed on the proportion of forming roll dewatering with 120 g/m² Forming roll dewatering [%] 100 % 95 % 90 % 85 % 80 % 75 % 70 % 1250 m/min 65 % Basis weight 120 g/m² 1550 m/min 60 % Forming roll wrap angle [ ] PaperCon 2011 Page 363

20 Internal strength as a function of forming roll wrap angle Internal strength [%] g/m2 120 g/m2 150 g/m Forming roll wrap angle [ ] 15 g/l 13 g/l PaperCon 2011 Page 364

21 Geometrical tensile index as a function of forming roll wrap angle Geom. tensile index [%] %-units higher filler content Forming roll wrap angle [ ] 90 g/m2 120 g/m2 150 g/m2 Burst strength index [%] %-units higher filler content Forming roll wrap angle [ ] 90 g/m2 120 g/m2 150 g/m2 PaperCon 2011 Page 365

22 Effect of forming roll wrap angle on beta formation Poor Norm Beta fomation [%] Good g/m2 120 g/m2 150 g/m Forming roll wrap angle [ ] PaperCon 2011 Page 366

23 Typical power demand distribution of a high speed containerboard machine Production machine data PaperCon 2011 Page 367

24 Dryness increase versus dwell time Forming section Dryness P 1 < P x < P 2 P 2 P x Outlet dryess P x P 1 Outlet dryness P 1 Inlet dryness Dwell Time T 1 Dwell Time T x Time PaperCon 2011 Page 368

25 Optimized scaling of suction box vacuums Containerboard machine, production data Dryness P 1 < P 2 < P 3 P 3 P 2 P 1 T 1 T 2 T 3 Suction Box 1 Suction Box 2 Suction Box 3 Time PaperCon 2011 Page 369

26 Suction box vacuums in test Gap forming concept, 100 g/m2 linerboard, 100 % recycled fiber-based furnish, production data Test point number Multi foil shoe [kpa] Form ing shoe 1 [kpa] Form ing shoe 2 [kpa] Form ing shoe 3 [kpa] Curved box 1 [kpa] Curved box 2 [kpa] Suction box [kpa] Transfer box [kpa] Suction box 1/1 [kpa] Suction box 1/2 [kpa] Suction box 2/1 [kpa] Suction box 2/2 [kpa] Ref PaperCon 2011 Page 370

27 Dryness level development of a gap former Containerboard machine, production data Before couch roll 19 Sheet dryness % After turning roll After forming shoe 7 5 REF PaperCon 2011 Page 371

28 Suction box drainage in a twin wire zone Containerboard machine, production data PaperCon 2011 Page 372

29 Development of drive power and dryness before the couch roll Containerboard machine, producttion data Power % Dryness % Power Dryness 80 REF PaperCon 2011 Page 373