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

2nd. Workshop of COST Action E15

Drying of Black LocustWood

Marian Babiak

Technical University in Zvolen

Slovak Republic

Zvolen - location

Zvolen castle

Zvolen castleZvolen castle

Main squareMain square

University campusUniversity campus

Main building – ceremony hallMain building – ceremony hall

Another view of the University Another view of the University

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???

One of the traditional produtsOne of the traditional produts

•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

INCO-COPERNICUS Project No. PL 96-4114; Contract No.ERB IC15 - CT

960713Technology for High Quality Products

from Black Locust Robinia pseudoacacia „TEQUBLOC“

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

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

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

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

Dry bulb temperature - softDry bulb temperature - soft

Dry bulb temperature - hardDry bulb temperature - hard

Equilibrium MC - softEquilibrium MC - soft

Drying schedules: Hamburg – ON softDrying schedules: Hamburg – ON soft

Equilibrium MC - hardEquilibrium MC - hard

Drying schedules: Hamburg – ON hardDrying schedules: Hamburg – ON hard

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

Microwave kiln DIES 3-V

f=2,42 GHz, P=2kW

Microwave kiln DIES 3-V

f=2,42 GHz, P=2kW

Our experiments

Semivacuum kiln 30-40kPa

MW resonator – normal pressure

MW resonator – normal pressure

lowered pressure

HF heating

“Vacuum” kiln“Vacuum” kiln

Microwave “oven”Microwave “oven”

magnetron power 800 W, frequency 2450 MHz magnetron power 800 W, frequency 2450 MHz

MW in kilnMW in kiln

HF heatingHF heating

frequency 23 MHz, power 3,7 kW frequency 23 MHz, power 3,7 kW

MaterialMaterial

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)

Board for experimental evaluationBoard for experimental evaluation

Steaming diagram - 3x each cycle

pressure 0,35 MPa

 

Drying parameters for conventional

heating  

Slow Standard

Init. temp. 40 °C 50 °C

Final temp. 50 °C 60 °C

Init.RH 77,5% 72,5%

Final RH 30% 30%

Min. dr.rate 0,05 %/hour 0,1 %/hour

Results

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

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

Quality testing “vacuum” 30 mm

1 2 3 4 5 6 7 8 930 U SL 2,7 S L L S 0,07 285 31 1330 U ST 1,6 O M L U 0,11 281 38 10

30 S SL 1,8 S L L U 0,09 180 28 13

30 S ST 2,8 S L L U 0,13 137 28 12

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

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

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

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

Quality testing “vacuum” 60 mm

1 2 3 4 5 6 7 8 960 U SL 2,2 O L L S 0,04 871 47 1060 U ST 3 S M L U 0,07 290 31 1460 S SL 3 Q L L S 0,03 575 30 1260 S ST 4,2 Q M L U 0,07 249 30 15

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

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

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

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

  1 2 3 4 5 6 7 8 930_1M 1,9 Q L S U 3,26 6 36 1630_2M 1,7 Q L L U 1,86 11 35 1430_3M 0,2 O L S Q 1,58 15 31 860_1M 1,2 E L S Q 0,61 28 29 1260_2M 0,5 E L S Q 0,62 30 30 1160_3M 0,9 E L L Q 0,27 65 28 11

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

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 mmQuality testing microwaves 30, 60 mm

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

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

Drying curves(MWV,HF)

MC[%] vs time[h]

Drying curves(MWV,HF)

MC[%] vs time[h]

MC[%] distribution in layers - MWV-HFMC[%] distribution in layers - MWV-HF

 1 2 3 4 5 6 7 8 9

30_1 MV 1,2 E L S - 3,4 8 39 1230_2MV 0,4 O L M S 2,5 16 45 6,630_3MV 1,8 Q S S U 3,7 8,3 45 1330_3M 0,8 Q L L Q 2,4 11,3 41 13

60_1MV 2,1 Q L S U 0,88 21,2 36 1860_1M 1,5 Q L S U 0,69 26,2 37 18

60_2MV 1,2 S L S S 0,55 37 36 1560_2M 1,2 Q L M S 0,48 45,3 34 1430_1HF 1,7 Q L L S 1,26 24 44 1730_2HF 1,6 S L L S 1,04 31 47 1530_3HF 1,4 E L L U 0,89 26 36 12

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

Diffusion coefficient D[m2.s-1] “vacuum”Diffusion coefficient D[m2.s-1] “vacuum”

D[m2.s-1] MW (+V); HF D[m2.s-1] MW (+V); HF

Diffusion coefficient [m2.s-1] vs drying rate [%/h]

Diffusion coefficient [m2.s-1] vs drying rate [%/h]

y = 1E-09x - 4E-11 R2 = 0,9993 y = 1E-09x - 4E-11 R2 = 0,9993 

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

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 m2.s-1

ConclusionsMicrowave 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 m2.s-1

drawback - non-uniform distribution of energy

ConclusionsMicrowave+”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 m2.s-1

ConclusionsHigh frequency drying

drying rate slightly lower than microwaves

diffusion coefficients 1,4.10-9 to 2,5.10-9 m2.s-1

 

lesser risk to exceed temperature than microwaves

 

more uniform temperature distribution

Thank you for your attentionThank you for your attention

Zvolen 2000