Quality Drying of Hardwood September 2000 Sopron Hungary Quality Drying of Hardwood September 2000 Sopron Hungary 2nd. Workshop of COST Action E15

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

Zvolen - location

Zvolen castle

Main square

University campus

Main building – ceremony hall

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 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 ; Contract No.ERB IC15 - CT Technology 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 mm, 32-60mm, mm soft, hard

Drying steps 10-final Over 601 MC [%] (T6-A3)+(T3-A2) Steps 4-8 ON Steps 1-8

Dry bulb temperature - soft

Dry bulb temperature - hard

Equilibrium MC - soft

Drying schedules: Hamburg – ON soft

Equilibrium MC - hard

Drying 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 lowered pressure HF heating

“Vacuum” kiln

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

MW in kiln

HF heating frequency 23 MHz, power 3,7 kW

Material Specimen dimensions for drying (h = 30 w = mm ; h = 60 w = mm) Specimen dimensions for drying (h = 30 w = mm ; h = 60 w = mm)

Board for experimental evaluation

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

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

Results

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

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

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

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

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

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

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

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

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

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

MC[%] 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-HF

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

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

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

Diffusion coefficient [m 2.s -1 ] vs drying rate [%/h] 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, to 3, m 2.s -1

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

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, to 8, m 2.s -1

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

Thank you for your attention Zvolen 2000