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