Empirical Model To Correlate Press Drying Time of Lumber To Process And Material Variables


  • William T. Simpson
  • Yi-fu Tang


Drying, press drying, southern pine, warp


Loblolly pine lumber was press dried with thickness and platen temperature as variables. Drying times ranged from about 20 to 85 minutes, depending on thickness and platen temperature. The dried lumber was free of collapse and surface and internal checking, although some surface darkening was noted at the highest platen temperature. A heat-transfer-based empirical model that relates press drying time of lumber to certain process and material variables was developed and tested. The potential use of the model is for a segregation system that will group boards of similar drying times so that they can be dried together, thus reducing variability in final moisture content and taking fullest possible advantage of the warp suppression benefits of press drying. The model relates drying time to several board characteristics that can be measured at production line speed so that an immediate grouping decision can be made on each board just before drying. The model predicts the expected consequences of changing the process and material variables and has potential as the base for a segregation system.


Ashworth, J. C. 1980. Design of drying schedules for kiln drying of softwood timber. Drying '80, developments in drying, vol. 1. Hemisphere Publishing Co., New York.nBramhall, G. 1979. Mathematical model for lumber drying. Wood Sci. 12(1):14-31.nComstock, G. L. 1971. The kinetics of veneer jet drying. Forest Prod. J. 21(9):104-111.nForest Products Laboratory, Forest Service. 1987. Wood handbook: Wood as an engineering material. Agric. Handb. 72, rev. 1987. U.S. Department of Agriculture, Washington, DC.nHart, C. A. 1981. Simsor: A computer simulation of water sorption in wood. Wood Sci. 13(1):46-71.nKollmann, F. F. P., and W. A. Côté. 1968. Principles of wood science and technology: I. Solid wood. Springer-Verlag, New York.nRosen, H. N. 1983. Recent advances in the theory of drying lumber. Proceedings of the Wood Drying Working Party at the International Union of Forestry Research Organizations Division 5 Conference, Madison, WI.nSimpson, W. T., J. D. Danielson, and R. S. Boone. 1988. Press drying plantation grown loblolly pine 2 by 4's to reduce warp. Forest Prod. J. 38(11/12):41-48.nSpolek, G. A., and O. A. Plumb. 1980. A numerical model of heat and mass transport during drying. In Drying '80, Proceedings of the Second International Drying Symposium, Montreal; Hemisphere Publishing Co., New York.nStanish, M. A., G. S. Schajer, and F. Kayihan. 1986. A mathematical model of drying for hygroscopic porous media. AIChE J. 32(8):1301-1311.nTschernitz, J. L. 1985. Empirical equations for estimating drying times of thick rotary cut veneer in press and jet dryers. Res. Pap. FPL 453. U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, WI.n






Research Contributions