Maintaining Lumber Quality in Press Drying by Manipulating Sawing Patterns
Keywords:Drying, press drying, high-temperature drying, rapid drying, oak, drying defects, honeycomb
Lumber is traditionally dried in kilns by processes that often take several weeks to complete. Considerable research has been conducted on more rapid processes. Press drying can dry common 25-mm-thick lumber in 1 to 2 hours instead of several weeks. However, little success has been achieved with this technique because intolerable drying defects usually accompany such rapid drying. This paper reports on a press-drying technique that offers considerable promise in avoiding honeycomb that usually develops. In this technique the sawing pattern of boards from logs is changed from the usual flatsawn pattern to quartersawn. The honeycomb that usually develops occurs at interfaces of ray tissue and the surrounding tissue and is caused by internal tensile forces that develop during drying. With flatsawn boards the wide face, which makes contact with the platens during drying, is parallel with the critical internal tensile forces. By using a quartersawn pattern, the direction of the critical internal tensile forces is effectively rotated by 90 degrees. The critical internal tension is then perpendicular to the wide face of the board.
The hypothesis of the study was that the compressive pressure of the press therefore opposes the internal stresses and prevents honeycomb. In this study honeycomb in press-dried quartersawn red oak was significantly less than in press-dried flatsawn red oak. Small compressive forces of the platens were less effective than large forces in reducing honeycomb in quartersawn oak, thus verifying the hypothesis.
Bello, E. O., and H. Kubler. 1975. Shrinkage-strain-control(S-S-C)—A new approach to the process of kiln drying wood. Wood Sci.7(3):191-197.nChen, P. Y. S. 1978. Press-drying black walnut wood: Continuous drying versus step-drying. For. Prod. J.28(1):23-25.nChen, P. Y. S. 1980. Press conditions affect drying rate and shrinkage of hardwood boards. For. Prod. J.30(7):43-47.nChen, P. Y. S., and F. E. Biltonen. 1979. Effect of prefreezing on press-drying of black walnut heartwood. For. Prod. J.29(2):48-51.nHaygreen, J. G., and K. Turkia. 1968. Technical and economic considerations in the platen drying of aspen sapwood and paper birch cut-stock. For. Prod. J.18(8):43-50.nHittmeier, M. E., G. L. Comstock, and R. A. Hann. 1968. Press drying nine species of wood. For. Prod. J.18(9):91-96.nMcMillen, J. M. 1955. Drying stresses in red oak. For. Prod. J.5(4):71-76.nRosen, H. N., and R. E. Bodkin. 1978. Drying curves and wood quality of silver maple jet dried at high temperature. For. Prod. J.28(9):37-43.nSchmidt, J. 1967. Press drying of beechwood. For. Prod. J.17(9):107-113.nSimpson, W. T. 1980. Radio-frequency dielectric drying of short length of northern red oak. USDA For. Serv. Res. Pap. FPL 377.nWang, J.-H., and F. C. Beall. 1975. Laboratory press-drying of red oak. Wood Sci.8(2):131-140.nWard, D., and R. C. Anderson. 1964. Dry wood parts in minutes. Woodworking Digest66(9):45-48.nYoungs, R. L. 1957. The perpendicular-to-grain mechanical properties of red oak as related to temperature, moisture content, and time. For. Prod. Lab., Rep. No. 2079.n
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.