Stress-Based Kiln Drying of Gmelina arborea Roxb. Lumber

Wency H. Carmelo1, Ramon A. Razal2*,
Chrysline Margus N. Piñol3, and James Fuller4

1Forest Products Research and Development Institute,
College, Laguna 4031 Philippines
2Department of Forest Products and Paper Science, University of the Philippines Los Baños
 College of Forestry and Natural Resources, College, Laguna, Philippines
3Institute of Mathematical Sciences and Physics,
University of the Philippines Los Baños College of Arts and Sciences,
College, Laguna, 4031 Philippines
4Fuller Drying Labs, Orange, Virginia 22960 USA

*Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

The study evaluated the kiln drying of 25-mm thick Gmelina arborea Roxb. lumber using conditions based on changing shrinkage rates following the procedure developed by Fuller under US Patent No. 5,873,182 dated 23 February 1999. For comparison, a separate kiln drying run was done following conventional, moisture content (MC)-based drying schedule. To monitor shrinkage, a linear variable differential transducer was mounted across a sample board that was coupled to a data acquisition system. Real-time shrinkage data was processed and the graph of dynamic shrinkage versus time provided information on peak stress, stress reversal and reduction of shrinkage rates. These transitions were taken as signals to advance kiln drying conditions to the next step prescribed in the MC-based drying schedule, which allowed prompt changes in kiln settings. The early transition in internal kiln drying conditions resulted to reduction in kiln drying time by 30 to 36%. The quality of the dried lumber was evident in the more uniform final moisture content distribution of the dried boards, less steep moisture gradient, and the absence of residual stresses in the boards dried in a kiln where changing shrinkage rates were used as basis for operation and control.


Drying is one of the most important steps in the processing of wood.  The quality of finished products depends to a large extent on the moisture present in the wood at the time of manufacture.  For fast wood drying with minimal drying degrade, proper kiln settings as well as appropriate kiln drying schedules (KDS) must be followed. . . . . read more


ALLEGRETTI O, SCANZONI R, BAGOLINI A, MARGESIN B. 2003. In-situ measurement of wood stress during drying process. eProceedings, DOI No.: 10.1142/9789812702944_0090.  Sensors and Microsystems. World Scientific Publishing Co. Pte. Ltd.
ALLEGRETTI O, BAGOLINI A, MARGESIN B, TRAVAN L. 2005. A sensor to measure wood stress during the drying process. In: Proceedings of the 9th IUFRO International Wood Drying Conference IUFRO International Wood Drying Conference, Nanjing, China. 161-165.
ALLEGRETTI O, FERRARI S. 2008. A sensor for direct measurement of internal stress in wood during drying: Experimental tests toward industrial application. Drying Technology 26:1150-1154.
CHAPRA SC, CANALE RP. 1998. Numerical methods for engineers: with programming and software applications, 3rd ed. The McGraw-Hill Companies, Inc., USA, 629-632.
CARMELO WH. 2003. Design, Construction and Evaluation of a 0.12 m3 Capacity Furnace type Lumber Dryer. Project Terminal Report.  FPRDI, College, Laguna.
FERRARI S, PEARSON H, ALLEGRETTI O, GABBITAS B. 2010.  Measurement of internal stress in Radiata pine sapwood during drying using an improved online sensor. Holzforschung 64:781-789.
FORTIN Y, ILIEVA M, CLOUTIER A, LAFOREST P. 1994. Potential use of a semi-ring extensiometer for continuous wood surface strain measurement during kiln drying. 4th IUFRO International Wood Drying Conference, Rotorua, New Zealand: 329-334.
[FPRDI] Forest Product Research and Development Institute. 2003. Technical Information on Yemane (Gmelina arborea Roxb.) Forest Products Research and Development Institute, Department of Science and Technology, College, Laguna.
FULLER J. 1999.  Kiln control based on changing shrinkage rate.  Free Patents Online.  US Patent No. 5,873,182.
FULLER J. 2000. Determining the source of changing shrinkage rates during kiln drying. Drying Technology 18(1&2):261-278.
NATIONAL INSTRUMENTS INC. 2006. Measurement and Automation Catalog: 23.
PERRE P, CANTERI L, MARTIN M. 1994.  Surface strain measurements during convective drying at high temperature as a quality criterion.  4th IUFRO International Wood Drying Conference, Rotorua, New Zealand: 465-466.
RASMUSSEN EF. 1961. Dry Kiln Operator’s Manual. United States Department of Agriculture Forest Service, Forest Products Laboratory 1 Madison, Wisconsin. Edited by William T. Simpson. Revised August 1991.
REITZ R.1955. Accelerating the kiln drying of hardwoods, Southern Lumberman 181(2262):43-54.
UETIMANE JR. E, ALLEGRETTI O, TERZIEV NM, SÖDERSTRÖM O. 2010. Application of non-symmetrical drying tests for assessment of drying behaviour of ntholo (Pseudolachnostylis maprounaefolia PAX). Holzforschung 64:363-368.
YOUNGS R, BENDTSEN B. 1964.  Tensile, compressive and shearing stresses developed in red oak as it dries.  Forest Products J 14(3):113-118.