1. Quality Drying of Hardwood 11.-13. September 2000 Sopron Hungary Quality Drying of Hardwood 11.-13. September 2000 Sopron Hungary 2nd. Workshop of COST Action E15

2. Drying of Black Locust Wood Marian Babiak Technical University in Zvolen Slovak Republic

3. Zvolen - location

4. Zvolen castle

5. Main square

6. University campus

7. Main building – ceremony hall

8. Another view of the University

9. Why Black Locust wood? Weedy species? Low quality? Small dimensions? Difficult to process (tool blunting)? Toxic??? Why Black Locust wood? Weedy species? Low quality? Small dimensions? Difficult to process (tool blunting)? Toxic???

10. One of the traditional produts

11. Ecological species – long natural durability Good mechanical properties Possibility to change the color by steaming Fast growing species Ecological species – long natural durability Good mechanical properties Possibility to change the color by steaming Fast growing species

12. INCO-COPERNICUS Project No. PL 96-4114; Contract No.ERB IC15 - CT 960713 Technology for High Quality Products from Black Locust Robinia pseudoacacia „TEQUBLOC“

13. Partners Institute for Wood Biology, University of Hamburg (coordinator) Department of Wood Science, West Hungarian University, Sopron Department of Wood Science, Technical University, Zvolen TNO Building and Construction Research, Delft Robinia Kft, Budapest

14. What we know? Czech,H.-Tamásy-Banó,M: Holz Zentralblatt above FSP max.temp.60°C < 30mm, 55°C > 30mm below FSP 65°C high thylosis – low permeability requires soft drying schedule tendency to form drying checks

15. Dry Kiln Operator's Manual, USDA, 1991 For thicknesses of 25 to 38 mm: recommended drying schedule: T6-A3 : For a thickness of 50 mm: recommended drying schedule is T3-A2 Slovak ON 49 0651 15-28 mm, 32-60mm, 75-100mm soft, hard

16. Drying steps 10-final8 15-107 20-156 25-205 30-254 40-303 60-402 Over 601 MC [%] (T6-A3)+(T3-A2) Steps 4-8 ON 49 0651 Steps 1-8

17. Dry bulb temperature - soft

18. Dry bulb temperature - hard

19. Equilibrium MC - soft

20. Drying schedules: Hamburg – ON soft

21. Equilibrium MC - hard

22. Drying schedules: Hamburg – ON hard

23. Klement,I. – Trebula,P.: Comparison of classic and MW drying Black Locust 50x150x3000 mm Schedule 15min…………P 105min…………P/2 180min…………0 MC 33%  10% MW 145 hours classic 408 hours

24. Microwave kiln DIES 3-V f=2,42 GHz, P=2kW Microwave kiln DIES 3-V f=2,42 GHz, P=2kW

25. Our experiments Semivacuum kiln 30-40kPa MW resonator – normal pressure lowered pressure HF heating

26. “Vacuum” kiln

28. Microwave “oven” magnetron power 800 W, frequency 2450 MHz

29. MW in kiln

30. HF heating frequency 23 MHz, power 3,7 kW

31. Material Specimen dimensions for drying (h = 30 w = 100-150mm ; h = 60 w = 150 - 200mm) Specimen dimensions for drying (h = 30 w = 100-150mm ; h = 60 w = 150 - 200mm)

32. Board for experimental evaluation

33. Steaming diagram - 3x each cycle pressure 0,35 MPa

34. Drying parameters for conventional heating SlowStandard Init. temp.40 °C50 °C Final temp.50 °C60 °C Init.RH77,5%72,5% Final RH30% Min. dr.rate0,05 %/hour0,1 %/hour

35. Results

36. Drying curves 30mm: MC[%]vs time[h]

37. MC[%] distribution in layers (1-6) 30 mm

38. Quality testing “vacuum” 30 mm 1 MC SD [%]; 2 Target MC; 3 End checking; 4 Internal checking; 5 Casehardening; 6 Average drying rate [%/h] 7 Drying time 8 Starting MC 9Final MC

39. Drying curves 60mm: MC[%]vs time[h]

40. MC[%] distribution in layers (1-6) 60 mm

41. Quality testing “vacuum” 60 mm 1 MC SD [%]; 2 Target MC; 3 End checking; 4 Internal checking; 5 Casehardening; 6 Average drying rate [%/h] 7 Drying time 8 Starting MC 9Final MC

42. Drying curves(MW) MC[%] vs time[h]

43. MC[%] distribution in layers (1-6; 1-7) - MW

44. 1 MC SD [%]; 2 Target MC; 3 End checking; 4 Internal checking; 5 Casehardening; 6 Average drying rate [%/h] 7 Drying time 8 Starting MC 9Final MC Quality testing microwaves 30, 60 mm

45. Drying curves(MWV) MC[%] vs time[h]

46. MC[%] distribution in layers (1-6; 1-7) - MWV

47. Drying curves(MWV,HF) MC[%] vs time[h] Drying curves(MWV,HF) MC[%] vs time[h]

48. MC[%] distribution in layers - MWV-HF

49. Quality testing microwaves + vacuum 30, 60 mm; high frequency 30mm

50. Diffusion coefficient D[m 2.s -1 ] “vacuum”

51. D[m 2.s -1 ] MW (+V); HF

52. Diffusion coefficient [m 2.s -1 ] vs drying rate [%/h] y = 1E-09x - 4E-11 R2 = 0,9993

53. Conclusions “Vacuum drying” 30 mm material - classification "standard" both standard and slow schedules 60 mm - slow schedule - lumber classified as "quality" frequently severe case hardening ("unacceptable") can be compensated by appropriate conditioning after drying

54. Conclusions “Vacuum drying” average drying rate 0,097%/h 30 mm 0,053%/h 60 mm diffusion coefficients 0,93.10 -10 to 3,64.10 -10 m 2.s -1

55. Conclusions Microwave drying substantially faster drying rate 20-fold for 30 mm and about 10-fold for 60 mm quality of dry material is good diffusion coefficients 5,2.10 –9 to 18,4.10 –9 m 2.s -1 drawback - non-uniform distribution of energy

56. Conclusions Microwave+”vacuum” drying drying rate under vacuum is higher than at atmospheric pressure for the 30 mm material this effect is more pronounced than for the 60mm material diffusion coefficients 6,4.10 -9 to 8,4.10 -9 m 2.s -1

57. Conclusions High frequency drying drying rate slightly lower than microwaves diffusion coefficients 1,4.10 -9 to 2,5.10 -9 m 2.s -1 lesser risk to exceed temperature than microwaves more uniform temperature distribution

58. Thank you for your attention Zvolen 2000