Intro to Wood Materials TED 126 ENGINEERING MATERIALS

Intro to Wood Materials TED 126 ENGINEERING MATERIALS AND PRODUCT DESIGN

Classification of Woods l A tree is usually defined as a woody plant which, when mature, is at least 20 feet tall, has a single trunk, unbranched for at least several feet above the ground and has a definite crown. l Trees are divided into two biological categories: softwoods and hardwoods. 2

Classification of Woods The terms softwood and hardwood do not refer to the hardness or density of the wood. Softwoods are not always soft, nor are hardwoods always hard. Mountain-grown Douglas fir, for example, produces an extremely hard wood although it is classified as a "softwood, " and balsawood, so useful in making toy models, is classified a "hardwood" although it is very soft. 3

Classification of Woods Hardwoods are biologically called angiosperms, which are trees that produce seeds enclosed in a fruit or nut. l The hardwood category includes the l l oaks, ashes, elms, maples, birches, cherry, walnut, beeches and cottonwoods. In contrast to softwoods, hardwood trees have broad leaves and nearly all North American hardwoods are deciduous, which means they drop their leaves in the fall. However, there are exceptions: holly, magnolia and live oak are hardwoods that retain their leaves year- round. 4

Classification of Woods In biological terms, softwoods are called gymnosperms, which are trees that produce "naked seeds. " l The most important group of softwoods are the conifers or cone-bearing trees, which have seeds that are usually visible inside opened cones. l All species of pine, spruce, hemlock, fir, cedar, redwood and larch are softwoods. l Nearly all softwood trees have another common characteristic: their leaves are actually needles or scales and they remain on the tree throughout the winter, which is why they are also called evergreen trees. Exceptions are larch (or tamarack) and cypress whose needles drop in the fall, leaving the tree bare during winter. l 5

Classification of Woods l Giant coast redwoods (Sequoia sempervirens) l The largest trees are over 300 feet (91 m) tall and 17 feet (5. 2 m) in diameter. They sprouted from seeds the size of oatmeal flakes nearly 2000 years ago, and grew into giants taller than the Statue of Liberty (from the foundation of pedestal to torch). 6

Classification of Woods Ancient Bristlecone Pine Bristlecone pines (Pinus longaeva and Pinus aristata) are one of the best sources of tree ring data because they live so long. As a result of the matching and overlapping of tree rings from different trees and sites, bristlecone pine chronologies exist that extend back to 9000 years ago. Earth's oldest living inhabitant "Methuselah" at 4, 767 years, has lived more than a millennium longer than any other tree. 7

Classification of Woods l Identification characteristic of woods: l Color – Most timbers show variation in color between species and within species. It can also vary within a single piece. Color descriptions usually relate to the heartwood of the species and may be significantly different from that of the sapwood. (Sapwood is always white to very light brown. ) Color can vary with use, age and by the application of finishes. Timber exposed to light will change color, and unprotected timber exposed to the weather will eventually become silvery grey in color. 8

Classification of Woods l Identification characteristic of woods: l l l Texture – of timber may be described as being coarse, fine, even or uneven. The differentiation between coarse and fine texture is determined by the size and arrangement of the wood cells. Softwoods are usually fine textured, while hardwoods may be either. For example, mountain ash is a coarse textured hardwood, but brush box is a fine textured hardwood. The main process affecting texture of the timber is the finishing applied during fabrication. Planing will produce a fine texture, sanding or brushing – a fine to coarse texture, rough sawing or splitting a coarse to uneven texture. Surface finishes will also affect the texture, high build, smooth coatings will give the finest texture. 9

Classification of Woods l Identification characteristic of woods: Figure – refers to the pattern produced on the surface of the timber. The pattern is determined by the type of grain, the arrangement and size of cells, color variations and sawing patterns. Designers can use these features to produce striking effects in different lights. Where particular grain patterns are required, this will need to be investigated very carefully with the supplier, and may require special milling. 10

Classification of Woods l Identification characteristic of woods: Grain – refers to the general direction, size and arrangement of wood fibers. Grain can be described as sloping, straight, spiral, irregular, wavy etc. 11

Classification of Woods l Identification characteristic of woods: Hardness – refers to the resistance of the timber to penetration. l This is an important parameter for flooring, with harder species wearing better and requiring less maintenance than softer species. l It may also be an important parameter for some cabinetry and joinery. l 12

Classification of Woods l Identification characteristic of woods: l l l Density – is influenced by cell structure and size, thickness of the cell walls and moisture content. The density of timber at a specific moisture content (usually 12%) is the amount of wood substance in a given volume, expressed as kilograms per cubic meter. Density is one of the most reliable indicators of stiffness, joint strength, hardness, ease of machining, fire resistance and drying characteristics. 13

Classification of Woods l Identification characteristic of woods: l l l Thermal properties – timber is a natural insulator. Air pockets within its cellular structure make timber a natural barrier to heat and cold. As thermal conductivity increases with density, lightweight timber is a better insulator than dense timber. Thermal conductivity also varies slightly with moisture content, and natural characteristics such as checks, knots and grain. 14

Classification of Woods l Identification characteristic of woods: l l l Acoustic properties – an important property of timber is its ability to damp vibrations. Its cellular network of minute interlocking pores converts sound energy into heat energy by frictional and viscous resistance within these pores and by vibration of their small fibers. Because of this high internal friction, wood has more damping capacity than most other materials. 15

Wood Structure l Cellulose (70%)… It forms the primary structural component of green plants. l l The primary cell wall of green plants are made of cellulose; the secondary wall contains cellulose with variable amounts of lignin. Lignin (25%) and cellulose, considered together, are termed lignocellulose, which (as wood) is argued to be one of the most common biopolymers on Earth. 16

Wood Structure Minerals, starches, oils, tannins, coloring agents fats and waxes. (5%) l All plants have tube or straw shaped channels ducts that run the direction of the plant called xylem. XYLEM, (pronounced ZIE-lem) is a tissue in plant stems and roots. l Xylem transports water and minerals upwards from the roots to the stem, via capillary action. l Xylem is strong and also provides support to the plant. l 17

Wood Structure l The two most troubling characteristics of juvenile wood are that: it shrinks and swells along the grain as moisture content changes, and l strength is lower, and in some cases much lower, than mature wood of the same tree. l This results in dimensional change not only in tangential and radial directions, but also along the grain when moisture is lost or gained. l 18

Wood Structure Seasoning of lumber l Green is wood that just been cut from a log l Once cut into individual boards they will be stored in either vertical or horizontal racks. 19

Wood Structure Basic Methods of converting a log l Plain sawn wood is the type most typically seen today. When the log is cut in to planks all the cuts are parallel to each other. 20

Wood Structure Basic Methods of converting a log l With Quarter sawn wood the log is first quartered (hence quarter sawn) and then diagonally from the center. l This results in a grain that is more vertical when looking at the plank end on. 21

Wood Structure Air Drying (AD) l To air dry, the lumber is arranged in layers, or courses, with l separating stickers, and built up into unit packages and piles l outdoors so that atmospheric air can circulate through the l piles and carry away moisture l Reduces moisture to about 15 percent. 22

Wood Structure Force Drying l l l In more complex drying processes, stickered packages of lumber are placed in closed buildings that have fans to recirculate heated air through the lumber piles. Both forced air dryers and predryers are commonly considered low temperature, forced-air circulation. 23

Wood Structure Kiln Drying (KD) To kiln dry, lumber is dried in a closed chamber by controlling l the temperature, relative humidity, and air circulation l until the wood reaches a predetermined moisture content. l Seven percent moisture – four to five days. l 24

Wood Structure Radio Frequency (RF) l Heat waves' unique technology utilizes electromagnetic waves from the l Radio Frequency spectrum to heat products within a vacuum controlled environment. l Heat waves' kilns use amplifier based power generators to create the radio frequency field which heats each load. l Amplifiers, as opposed to oscillators, allow for absolute control of the RF field which allows us to prevent any unwanted effects during the process. Usually for hardwoods – 24 hours. 25

Growth of a Tree A tree grows two times during the year. l Spring Growth – largest growth ring, the lighter colored ring l Summer Growth – smaller growth ring, darker colored ring. 1 light-colored ring + 1 dark-colored ring = 1 year. This is called a "growth ring. 26

Growth of a Tree Rings … the tree rings on the "Messiah" violin (photo © H. D. Grissino-Mayer). The wood used by Antonio Stradivari and all Cremonese violin makers for the violin top was Norway spruce (Picea abies). 27

Growth of a Tree Rings A cross section from an eastern hemlock (Tsuga canadensis) collected by Rex Adams near Ashland, Wisconsin (photo © H. D. Grissino-Mayer and R. K. Adams). The rings are extremely clear on this specimen. 28

Growth of a Tree Rings …. identify Heartwood Sapwood Cambium Outer Bark 29

Growth of a Tree Rings Thickness: How wide a ring is can tell you if the environment was good or bad for the tree to grow in. In years when the amount of rain and temperature were good a tree's rings are wider. In bad years a tree's rings are thinner. 30

Growth of a Tree Rings Shape: If rings start to become thinner on one side than the other it probably means the tree is leaning over to one side. High winds or a big storm can cause a tree to lean. 31

Growth of a Tree Things scientists study to learn about climate in the past include: l Ice cores from the Antarctic and Greenland. (They study bubbles of gas trapped in the ice. ) l Pollen from the bottom of lakes. l Fossil records of insects. l Growth rings of trees. 32

Growth of a Tree Dendrochronology: the study of tree rings Dendrochronology …means the measuring of time using trees – dendro = trees, and chronology = system of measuring time. 33

Growth of a Tree Extending a chronology based on living trees further back in time through crossdating. 34

Nature of Industrial Stock Yard Lumber – mainly softwoods Dimensional lumber is a term used in North America for lumber that is finished/planed and cut to standardized width and depth specified in inches. 1 x 12 Factory Lumber - Softwood lumber graded and used in the factory for the manufacture of such items as doors, sashes, moldings, and so on. Shop lumber - Softwood lumber graded and used in the factory for general cut-up purposes; similar to factory lumber but of a lower grade. 35

Nature of Industrial Stock Yard Lumber – mainly softwoods Structural lumber is light framing materials, such as 2 x 4 and widths up to six inches and wider for joist, rafters and framing uses. Rough Sawn Lumber – hardwoods and softwoods stock used for manufacturing fine quality wood products. Requires additional planing or surfacing. Chip Form – making of particle boards, wafer board and other sheet material. 36

Nature of Industrial Stock Yard Lumber…… OSB – Oriented Strand Board Masonite Hardboard – High Density Fiberboard MDF – Medium Density Fiberboard 37

Name of Industrial Stock Lumber Measurement The thickness of lumber is read in quarters of inches. four-quarters 4/4 five-quarters 5/4 six-quarters 6/4 eight-quarters 8/4 38

Name of Industrial Stock Lumber Measurement l In rough lumber (also called nominal thickness or size) that has not been surfaced (planed smooth). l 4/4 rough=1” board thickness l 5/4 rough=11/4” board thickness l 6/4 rough=11/2” board thickness l 8/4 rough=2” board thickness 39

Name of Industrial Stock Lumber Measurement l But surfaced lumber that has been planed smooth may vary slightly in thickness. l 4/4 rough=3/4” to 13/16” board thickness l 5/4 rough=1” to 11/8” board thickness l 6/4 rough=11/4” to 13/8”board thickness l 8/4 rough=13/4” to 113/16”board thickness 40

Wood Grades Classified accordingly to its quality. The grade of lumber refers to the appearance, strength and lack of defects in the wood stock. 41

Wood Grades l Softwood lumber is graded using the American Lumber Standards, which are based on the structural integrity of a board. l These grades consider the size and location of defects as well as the slope of grain in order to predict the load bearing capacity of the board. 42

Wood Grades Softwood lumber is graded using the American Lumber Standards, which are based on the structural integrity of a board. l These factors are used to determine the percentage of clear wood in the board that in turn determines the grade. Several of the most common grades and their clear wood requirements are: l l Select - at least 80% clear wood l Graded A to D. With A presenting the best quality surface appearance. 43

Wood Grades l Softwood lumber is graded using the American Lumber Standards, which are based on the structural integrity of a board. l Common - graded by number, ranging from 1 -4. With 1 being the best grade , no knots. l l l #1 Structural - at least 75% clear wood #2 Structural - at least 66% clear wood #3 Structural - at least 50% clear wood Construction Grade - at least 57% clear wood Standard Grade - at least 43% clear wood Utility Grade - at least 29% clear wood 44

Wood Grades Hardwood Grades l An FAS(First and Second) board must be at least 6" wide and 8' long. 83 1/3% of the board must be clear. l F 1 F (FAS One Face) If a board face is graded to FAS but the reverse face is not, the board drops in grade. If the reverse face of a board can be graded as #1 Common, the entire board is graded as F 1 F. l For example, if a board face grades to FAS but the reverse face only yields 82% clear the entire board is graded to at best F 1 F. l If a board reverse face cannot be graded to #1 Common the board is not F 1 F. 45

Wood Grades Hardwood Grades l Select l A select board is graded exactly like FAS. l The only difference is that the minimum size of a Select board is 4" x 6' (whereas an FAS board must be at least 6" x 8'). l The reverse face of a Select board can be either Select or #1 Common. 46

Wood Grades Hardwood Grades l #1 Common (Number 1 - 4) l A #1 Common board must be at least 3" wide and 4' long. 66 2/3% of the board must be clear. l The maximum number of imaginary cuts is one-third of the board measure plus one. Surface area after each imaginary cut must be at least 4" x 2' or 3" x 3'. l For example, a board 6" x 8' is 4 board measure. One third of 4 + 1 is 1. If a single imaginary cut in the board yields 66 2/3% clear where the uncut area is at least 4" x 2' or 3" x 3', the board is graded as #1 Common. l An additional cut in the board is allowed if the resulting clear yield is at least 75%. This applies to boards between 3 and 10 board measure. The reverse face of a #1 Common board is always #1 Common. 47

Wood Grades Hardwood Grades l #2 Common… #2 Common board must be at least 3" wide and 4' long, just like #1 Common. l The clear yield of a board can be as low as 50% after cuts equal to half of the board measure. Surface area after each imaginary cut must be at least 3" x 2'. l For example, a board 6" x 8 is 4 board measure and can be cut twice, half of four. The resulting clear area of the board must be at least 3" x 2' and at least 50% clear. l An additional cut is allowed in boards between 2 and 7 board measure if the yield is 66 2/3% clear. l The reverse face of a #2 Common board can be #2 Common or better. l If the reverse face of a board is #3 Common the entire board becomes #3 Common. 48

Wood Grades Abbreviations HDWD - hardwood M - thousand SAP - sapwood SD - seasoned S 1 E - surface one edge S 1 S - surface one side S 1 S 2 E -………. CLR - clear BTR - better 49

Wood Defects Bark Pockets - a patch of bark partially or whole …enclosed in the wood. Peck - a channeled or pitted area or pocket Decay - disintegration of wood fiber. Shake - a crack between and parallel to the rings of annual growth rings. Stain - a discoloration that penetrates the wood fibers. Wormholes - caused by insects or beetles. Knots - piece of sawed lumber which is either a portion of a branch or limb of a tree. Pitch - an accumulation of resinous materials. Wane - the presence of bark or absence of wood on corners of a piece of lumber. Warp - is any variation from a true surface. Bow - a curve along the face of a board that usually runs from end to end. Twist - warping in lumber where the ends twist in opposite directions. . Cup - warping along face of a board from edge to edge. Crook -warping along the edge from one end to the other. THE END 50