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Drying Eastern Hardwood Lumber DRYING EASTERN HARDWOOD LUMBER By JOHN M. McMILLEN and EUGENE M. WENGERT Forest Products Laboratory Forest Service U. S. Department of Agriculture (Maintained at Madison, Wisconsin, in cooperation with the University of Wisconsin) AGRICULTURE HANDBOOK NO. 528 September 1978 Library of Congress Catalog No. 77-600073 MCMILLEN, JOHN M. and WENGERT, EUGENE M. 1977. Drying eastern hardwood lumber. U.S. Dep. Agric., Ag- ric. Handb. 528, 104 p. Presents recommendations based on recent research and industry practice for drying eastern hardwood lumber, in- cluding dimension items. Accent is on comparing methods for energy-saving management decisions, but practical guid- ance is also given to wood drying personnel. Air drying, accelerated air drying, and kiln drying are covered. KEYWORDS: Hardwoods, drying, air drying, kiln drying, forced-air drying, high-temperature drying, steaming, de- humidifier drying, cost accounting, energy saving, degrade reduction. ABOUT THE AUTHORS . JOHN M. MCMILLEN is a forest products technologist who has specialized in the drying of wood for more than three decades at the Forest Products Laboratory. EUGENE M. WENGERT, formerly a member of the wood dry- ing group at the Laboratory, is now extension specialist in wood technology at Virginia Polytechnic Institute and State University, Blacksburg, Va. For sale by the Superintendent of Documents U.S. Government Printing Office Washington, D.C. 20402 Stock Number 001-000-03761-7 ii PREFACE Interest in broader utilization of hardwoods has been spurred by shortages of softwoods and an apparent surplus of hardwoods. However, to greatly increase use of hardwoods will require simplified drying procedures. At the same time, the better grades of hardwoods must be seasoned by methods less wasteful of both material and the energy required to dry it. These facts make this publication desirable. The handbook is confined to eastern hardwoods because most of the hardwood timber grows in the Eastern United States. Much of the general methodology will apply to western hardwoods, but some species have special problems and some localities have severe air drying weather; western hardwood users should consult local authorities on specific questions. Without supplanting the two existing handbooks on kiln drying and air drying lumber, this handbook combines improvements in practice with new research findings to provide savings in costs and energy. It assembles scattered technology on accelerated air drying and presents new facts and interpretations on air drying. Kiln drying information is concentrated here, and other methods of drying are discussed. An overall guide is also provided to combine various drying procedures most economically for various product requirements. This publication should be of the greatest value to operating and managerial personnel responsible for hardwood lumber processing in hardwood mills, custom drying operations, and furniture plants. It should also help individuals dry small quantities of lumber inexpensively without sacrificing quality. Teachers and students should find this handbook helpful in career development programs. The authors acknowledge the assistance of Val Mitchell, State Climatologist, University of Wisconsin, Madison in supplying and interpreting some of the climatological information needed for this publication. Other vital contributions were made by many Forest Service colleagues and coworkers in industry. Particular recognition goes to Walton Smith and Paul Bois for photographs, to Kenneth Compton for specific information on steaming of walnut, and to members of the U.S. Forest Products Laboratory research unit on improvements in drying technology. For all these forms of assistance, we are most grateful. JOHN M. MCM ILLEN E UGENE M. WENGERT Use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval of any prod- uct or service by the U.S. Department of Agriculture to the exclusion of others that may be suitable. iii CONTENTS Page Page Drying Hardwoods . 1 Chapter 6.—High-Temperature Drying . 56 Chapter I.—Comparison of Drying Basic Concepts . 56 Methods for Hardwoods . 2 Research and Practice to Date . 57 Basic Drying Concepts . 2 Drying Times and Species Methods . 2 Potentialities . 58 How Dry is Dry Enough . 4 Apparent Process Requirements . 59 Literature Cited . 4 Literature Cited . 60 Chapter 2.—Stock Preparation and Chapter 7.—Special Predrying Stacking . 5 Treatments . 61 From Logs to Lumber . 5 Steaming . 61 Sorting . 7 Chemical Seasoning . 65 Stacking . 8 Polyethylene Glycol Process . 65 Further Warp Control . 8 Surface Treatments to Prevent Literature Cited . 10 Checking . 66 Other Pretreatments . 66 Chapter 3.—Air Drying . 11 Literature Cited . 67 Advantages and Limitations of Air Drying . 12 Chapter 8.—Other Methods of Utilizing Air Movement . 13 Drying . 68 Other Factors Relating to Drying Heated Room Drying . 68 Rate and Defects . 13 Dehumidifier Drying . 68 Drying Time and Final Moisture Solar Drying . 70 Content . 19 Press Drying . 71 Deterioration of Lumber While High-Frequency and Microwave Air Drying . 21 Heating . 71 Air Drying Small Quantities Solvent Seasoning . 72 of Lumber . 21 Minor Special Methods . 72 A Quick Guide for Improving Air Literature Cited . 73 Drying Efficiency of Hardwoods 22 Literature Cited . 22 Chapter 9.—Storage of Dried Lumber . 74 Chapter 4.—Accelerated Air Drying 23 Air-Dried Lumber . 74 Research Basis . 23 Kiln-Dried Lumber . 74 Types of Dryers and Procedures . 24 Advantages and Disadvantages of Chapter 10.—Economics and Energy 76 Accelerated Air Drying . 31 Typical Costs for Various Drying Drying Times . 31 Procedures . 76 Literature Cited . 33 Degrade Costs and Causes . 77 A Cost Accounting Approach . 78 Chapter 5.—Conventional Kiln Energy Considerations . 81 Drying . 34 Literature Cited . 83 Drying Procedures . 36 Operational Considerations . 52 Appendix A.—Species, Thicknesses, Drying Times . 54 Drying Schedules, and Literature Cited . 55 Comments . 84 iv CONTENTS (Con.) Page Page Appendix B.—Mixed Drying of Some Appendix D.—Lumber Names, Tree Species by Simplified Species, Seasoning Types, and Schedules . 87 Botanical Names Mentioned in This Handbook . 92 Appendix C.—Special Kiln Schedules for Special Purposes . 89 Glossary . 94 Requests for copies of illustrations contained in this publication should be directed to the Forest Products Laboratory, Forest Service, U.S. Department of Agriculture, P. O. Box 5130, Madi- son, Wis. 53705. LIST OF TEXT TABLES Table Title Page Table Title Page 1 Expected average interior 7 Approximate Canadian relative humidities and low-temperature kiln recommended moisture schedules for 4/4 maple content values for most and birch . 30 wood items for interior uses . 4 8 Suggested low-temperature kiln schedule for rough- 2 Estimated time to air dry sawed 4/4 red and green 1- and 2-inch hard- white oak . 30 wood lumber to approxi- mately 20 percent average 9 Accelerated air drying times moisture content . 18 for common hardwood items in slightly heated 3 Forced-air dryer sched- forced-air dryers (low- ules for selected eastern temperature kilns) . 32 hardwoods . 27 10 Grouping species for basic 4 Index of forced-air drying kiln schedules . 36 schedules . 28 11 Alphabetical index of 5 Low-temperature kiln species and basic kiln schedules for selected schedule table numbers . 37 eastern hardwoods . 29 12 Basic kiln schedules for 6 Index of low-temperature red and white oak, south- kiln schedules . 30 ern lowland . 38 v LIST OF TEXT TABLES (Con.) Table Title Page Table Title Page 13 Basic kiln schedules for red 22 Basic kiln schedules for oak, northern or upland . 38 basswood, aspen (sap- wood or box lumber). 42 14 Basic kiln schedules for white oak, northern 23 Accelerated kiln schedule or upland . 38 for northern or upland red oak 4/4, 5/4 with 15 Basic kiln schedules for rock a high initial moisture elm, dogwood, persimmon, content (some risk of and similar woods . 39 slight surface checking) . 45 16 Basic kiln schedules for 24 Approximate kiln-drying American and slippery elm, times for 4/4 hardwood holly, and black walnut . 39 lumber in conventional internal fan kilns . 54 17 Basic kiln schedules for beech, sugar maple, 25 Eastern hardwood species and pecan . 40 for which high-temperature kiln-drying potential has been 18 Basic kiln schedules for indicated, and estimated white ash, yellow birch drying time for 1-inch cherry, sweetgum lumber . 59 and similar woods . 40 26 Amount temperature must 19 Basic kiln schedules for be raised above average magnolia, paper birch, outdoor temperature for butternut, normal cotton- various equilibrium mois- wood, and similar woods . 41 ture content values in heated-room drying . 68 20 Basic kiln schedules for yellow- poplar and cucumber-tree . 41 27 Energy consumption and cost estimates in kiln 21 Basic kiln schedules for drying hardwood lumber . 81 black tupelo (black gum) and sweetgum sapwood (sap gum) . 42 Mention of a chemical in this handbook does not constitute a recommendation; only those chemicals registered by the U.S. Environmental Protection Agency may be recommended, and then only for uses as prescribed in the registration—and in the manner and at the concentration prescribed. The list of regis- tered chemicals varies from time to time; prospective users, therefore, should get current information on registration status from Pesticides Regulation Division, Environmental Protection Agency,
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