drying hardwood lumber

Download Drying Hardwood Lumber

Post on 12-Apr-2015

28 views

Category:

Documents

2 download

Embed Size (px)

TRANSCRIPT

United States Department of Agriculture Forest Service Forest Products Laboratory General Technical Report FPLGTR118

Drying Hardwood LumberJoseph Denig Eugene M. Wengert William T. Simpson

AbstractDrying Hardwood Lumber focuses on common methods for drying lumber of different thickness, with minimal drying defects, for high quality applications. This manual also includes predrying treatments that, when part of an overall quality-oriented drying system, reduce defects and improve drying quality, especially of oak lumber. Special attention is given to drying white wood, such as hard maple and ash, without sticker shadow or other discoloration. Several special drying methods, such as solar drying, are described, and proper techniques for storing dried lumber are discussed. Suggestions are provided for ways to economize on drying costs by reducing drying time and energy demands when feasible. Each chapter is accompanied by a list of references. Some references are cited in the chapter; others are listed as additional sources of information. Keywords: drying, hardwood, lumber, warp, kiln

Units of MeasurementIn this manual, measurements are expressed in both English (inchpound) and SI units. The following provides SI equivalents for lumber thickness sizes, dimension lumber, board foot volume, and other units.

SI equivalents for lumber thickness sizes 3/4 4/4 5/4 6/4 8/4 10/4 12/4 14/4 16/4 19 mm 25 mm 32 mm 38 mm 51 mm 64 mm 76 mm 89 mm 102 mm

SI equivalents for dimension lumber Nominal (in.) 2 by 4 2 by 6 2 by 10September 2000

Standard (mm) 38 by 89 38 by 102 38 by 165

Denig, Joseph; Wengert, Eugene M.; Simpson, William T. 2000. Drying hardwood lumber. Gen. Tech. Rep. FPLGTR118. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 138 p. A limited number of free copies of this publication are available to the public from the Forest Products Laboratory, One Gifford Pinchot Drive, Madison, WI 537052398. Laboratory publications are sent to hundreds of libraries in the United States and elsewhere. The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin. The use of trade or firm names is for information only and does not imply endorsement by the U.S. Department of Agriculture of any product or service. The United States Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or familial status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact the USDAs TARGET Center at (202) 7202600 (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, 1400 Independence Avenue, SW, Washington, DC 202509410, or call (202) 7205964 (voice and TDD). USDA is an equal opportunity provider and employer.

SI equivalents for other units board foot ft3 a

2.36 10 m3

3

0.0283 m

3

ft/s ft/min lb lb/in lb/ft F temperaturea 2 3

0.305 m/s 0.005 m/s 0.454 kg 6.895 kPa 16.0 kg/m 0.56C TC = [TF 32]/1.83

The conversion factor for board foot is used to convert gross volumes of lumber. It does not take into account any variation between actual and nominal sizes but rather is based on the volumetric ratio between 1 cubic meter (1 m 1 m 1 m) and 1 board foot (1 in. 12 in. 1 ft).

Drying Hardwood LumberJoseph Denig Associate Professor North Carolina State University, Raleigh, North Carolina Eugene M. Wengert Professor Emeritus University of Wisconsin, Madison, Wisconsin William T. Simpson Research Forest Products Technologist Forest Products Laboratory, Madison, Wisconsin

PrefaceFor hardwood lumber producers, drying is an opportunity to add value to products and to enter new, previously inaccessible markets. For most hardwood users, such as furniture manufacturers, lumber drying is an essential procedure in the manufacturing process. As with any part of the manufacturing process, costs must be controlled. Costs can be magnified by improper drying techniques that cause degrade, resulting in quality losses; mistakes can be made that cause problems in subsequent manufacturing processes; and considerable amounts of energy can be wasted. As hardwood lumber prices escalate, ensuring that the highest yield is obtained from the hardwood resource becomes critical in controlling overall costs. Fortunately, drying techniques and systems are available that can produce a quality hardwood lumber product at minimum cost. Drying Hardwood Lumber is an update of a previous Forest Service publication, Drying Eastern Hardwood Lumber by John M. McMillen and Eugene M. Wengert. Both publications contain information published by many public laboratories, universities, and associations, as well as that developed at the Forest Products Laboratory and other Forest Service units. The updated version includes much basic information from the original publication and new information relevant to new technology and the changing wood resource.

iii

ContentsPage Chapter 1 Overview......................................................... 1 Quality Requirements and Cost of Degrade .....................1 Basic Drying Concepts .....................................................1 Drying Methods................................................................3 Moisture Content..............................................................5 References ....................................................................... 6 Chapter 2 Drying Mechanisms of Wood........................ 7 Wood Characteristics That Affect Drying ........................7 Environmental Factors....................................................12 Rate of Drying ................................................................18 Stages of Drying.............................................................21 References .....................................................................24 Chapter 3 Stock Preparation and Stacking ................. 25 Protection of Logs ..........................................................25 Sawing Procedures .........................................................25 Protection of Green Lumber...........................................26 Prevention of Surface Checks.........................................27 Prevention of End Checks ..............................................27 Color Enhancement Through Steaming..........................28 Other Lumber Pretreatments ..........................................28 Sorting ............................................................................29 Stacking..........................................................................30 Additional Ways to Control Warp..................................33 References ......................................................................33 Chapter 4 Air Drying .................................................... 35 Advantages and Limitations ...........................................36 Utilization of Air Movement ..........................................36 Other Factors That Affect Drying Rate and Degrade .....37 Drying Time and Final Moisture Content.......................40 Air Drying and Shed Drying Operating Costs ................43 Quick Guide for Improving Air Drying..........................43 References ......................................................................44 Chapter 5 Drying Sheds .................................................45 Open Sheds.....................................................................45 Fan Sheds .......................................................................46 References ......................................................................47 Chapter 6 Accelerated Air Drying and Predrying...... 49 Accelerated Air Drying ..................................................49 Warehouse Predrying .....................................................50 References ......................................................................56 Chapter 7 Conventional Kiln Drying .......................... 57 Dry Kiln Designs............................................................57 Dehumidification Drying................................................58 Basic Kiln Operating Philosophy ...................................60 Kiln Samples ..................................................................60 Recording of Drying Date ..............................................71 Basic Hardwood Kiln Schedules ....................................72 Page Tropical Hardwoods.......................................................78 Kiln Start-Up Procedures ...............................................79 Equalizing and Conditioning ..........................................86 Sterilization ....................................................................88 Drying Time ...................................................................88 Operational Considerations ............................................90 References ......................................................................91 Chapter 8 Advanced Kiln Drying Procedures............. 93 Modifications to General Hardwood Schedules .............93 Special Hardwood Schedules .........................................94 Adjustment of Moisture Content of Kiln-Dried Wood...95 Alternative Schedules for Some Species ........................96 Kiln Operational Techniques..........................................97 References ....................................................................102 Chapter 9 Drying Defects............................................ 103 Checking...........

Recommended

View more >