Wood Btech2

8/6/2019 Wood Btech2

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Its importance: wood has so many uses toman, not only shelter but also for food, heat,

clothing, etc. Builders are mostly concernedwith the uses of tiber for building purposes.Our local lumber is decidedly superior inmany respects to those other places, and

there is an abundant supply. This supply maylast forever if we know how to take care ofour forest. We have all kinds of varieties forinnumerable purposes.


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We have hardwood for structural purposes suchas Ipil, Yakal, Guijo and many others. Forfurniture we have Narra, Dao.

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or interiorfinish almost any local wood can be used. In thebeauty of grains and color it is also superior toany in the world. What seems to be the defect inour lumber industry is the bad treatment thelumber receives. First there is indiscriminatecutting of logs. Immature trees are choppeddown just to have quantity.


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Then some irresponsible and none too honest lumberpeople pass inferior kinds for the right ones. In sawingthe logs into lumber saw mills seldom cut it to actual

commercial specified size, as for example one inch(1) flooring is not actually one inch but 7/8 inchesprocessing the furnished lumber, the lumber peopledo not supply real good planed and smooth products.

In other words there appears plenty of rooms forimprovement both in logging and processing. Everwith the structural lumber if we do not carefully checkthe deliveries about 5% to 10% is not usable forpurpose it is ordered.


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This is due either to defects in sizes, knots,shapes and other imperfections, there seems tobe no desire to improve the quality of the

product. All of these add up to the cost of thebuilding. And if the builder does not care orworst yet does not know how to improve thesebadly prepared lumber in the course of his

construction then we can only expect poorquality building, not only in strength anddurability but also in beauty. The improvementin this line of the building industry cannot beemphasized.


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1. Structure and Appearance - Lumber isgenerally known by its appearance. However,

some lumber are similar to other kinds thatother means are restored to in order todetermine accurately the identity of thespecies. Color, weight, smell and resonance

are hopeful, but the structure of the wood isthe most reliable means of identifying thewood.


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The growth of wood is by layers deposited allover the trunk and branches between the

bark and the old wood. If one examinescarefully the cross-section of the log he/shecan see concentric bands called AnnualRings. As the tree gets older the inner layers

become checked with the concretionarysubstances and will become useless as sapcarriers. They will serve only as the support ofthe tree.


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Therefore, there are two kinds of wood in a tree,the dense and the strong Heart Wood (usuallydarker in color than the sap wood) and the

cutter, more porous Sap Wood although thecontrast is not always very marked. Theproportion of the sap wood varies considerablyin various parts of the same tree. In order trees

to sap wood is weaker, freer from knots, andmore susceptible to decay that the heat wood.While in comparatively young timber thedifference in strength between heart wood andsapwood is not very much.


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The comparative width of annual tree rings,the direction and the arrangement of the cells

and fibres are the causes of the grain of thewood. Thus, trees of rapid growth havingwide annual rings produce coarse grainedwood, while those of slower growth producewood of narrow rings of fine grain. If thegrains of the wood straight grained.


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Sometimes the grains are twisted around the axis ofthe tree thus producing spiral grain. Some trees haveseveral rings of fibres run obliquely to the axis of the

tree in one direction, while the next layer are obliquein the opposite direction: such wood are called cross -grained. Guijo, Yakal and some species of lauan fallunder this. Wavy grain is caused by large undulations

in wood elements, generally on the radial surfaces,and curly grain by small undulations. In selecting wood for structural purposes care should

be exercised so as to avoid failures due todisadvantageous runs of the wood grains.


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Besides irregularities in the character of thegrain there are, structurally speaking, trees

important classes of defects in timbernamely:


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Wood is essentially an organic substance madeup of a skeleton ofcellulose impregnated withlignin.

Cellulose is whitish, like starch incomposition, highly resistant to alcoholicfermentation.

Lignin is a carbohydrate compound, butmore soluble in acid than cellulose.

Chemically - dry wood contains 49% carbon,44% oxygen, 6% Hydrogen and 1% ash.


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The deterioration of wood is caused by thefollowing: (a) natural decay, (b) attack of

insects, (c) attack ofmarine borers, (d)attack by woodpeckers, (e) mechanical

abrasion or wear, (f) fire.


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A. Natural Decay - is caused b the action ofcertain forms of plant life called fungi,

consisting of very fine, thread - like filamentswhich penetrate the wood in all directions,feeding upon the cells and breaking downtheir structure.


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There are four (4) requirements for the growth of fungi, namely,air, moisture, food, and favourable temperature. Of course if anyof these is excluded, as for example air by emerging woodcontinuously under water, no fungi can exist thus the wood will be

preserved for a very long time. Also if the wood cells which servesas food of the fungi being impregnated with poisons, the fungi cannot live. Such poisoning is accomplished by the use of commercialpreservatives such as coal tar, creosote and zinc chloride. Paintingdry wood will keep out dampness and prevent the development offungi.

The high temperature of drying kilns, will also kill the fungi aswell as expel the moisture, so that well seasoned lumber is lesslikely to decay if properly protected, than green lumber.


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B. Attack by Insects - timber with bark iseasily attack by insects, such as the following:

1. Powder post insect (bok-bok) 2. Pole borer - reddish brown beetle 2/5 20

4/5 inches long. 3. Termites, namely (a) subterranean and

(b) dry wood variety.


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(a) The subterranean variety inhabits dark, damp tunnelsbelow surface of ground and extends runaways to thewood for food.

(b) Dry wood variety - do not require humid earth forhabitat. The first warning of the presence of termites is theappearance of a swarm of flying alates (young termiteswith wings). Ravages of termites can be prevented by (a)building light concrete foundations, (b) keeping untreatedtimber out of contact with the ground, (c) providing metal

shields for sills, foundations timber and other preventivemeasures, (d) wood that is partly attacked can be save bytreating it with finely powdered Paris green or sodiumflousilicate.


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C. Marine Borers: (a) mollusc and (b) crustaceantypes. Protection from these borers: (1) Creosoting,(2) encasing in concrete jackets, (3) chlorine gas.

D. Other deteriorating influences:(a) Mechanical abrasion or wear as say, wood ties,mine props, wharf timbers, stairs; maybe preventedby putting iron plates.

(b)F

ire by burning: maybe burning by the preventionof the start of the fire: by saturating with soaksolutions (5-10%) of Ammonium Sulphate orAmmonium Phosphate.(c) Wood peckers.


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The moisture content of green lumber isreduced by exposure to air or by heating in

kilns. The former process is called seasoningand reduces the moisture content from 30%to 35% down to 12% to 20%.


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(1) to decrease shrinkage after placement inthe structure; (2) to increase its resistance to

decay; (3) to reduce its weight (4) to improveits strength and mechanical properties; and(5) to prepare it for preservatives treatment.To air dry lumber it is stocked in a yard undercover (not exposed to elements, sun and rain)and separation of about 1 strips are placedbetween to have a free circulation of air.


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For ordinary purposes 3-4 months seasoning isenough. However, for interior finishes or flooring kiln -drying is recommended. In kiln drying the lumber is

placed in air tight chambers and subjected to aconstant current of hot air of about 150to 180F forabout 10-12 days, or until the moisture content isreduced from 3-8%. Kiln dried lumber will absorbmoisture quickly so that it should be well protected indelivery and while it is not yet nailed in place. It is bestorder kiln dry finishing lumber after the roof is inplace. For exteriors or exposed surfaces it isrecommended to cover same or paint it right away.


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It has been found that well seasoned lumber is strongerand stiffer and more durable than green lumber. However,if lumber is over dried in kilns, that is, if too much moistureis eliminated, it becomes brittle and weak.

To construct such a member the first lamination isbent over from and firmly secured. Adhesive is spread overthe first piece, and next lamination, with the adhesivespread over both faces, is placed in position and securelyclamped with devices that produce uniform pressures of

100 to 200 psi. The remaining pieces are added similar,when the pieces are not long enough to extend the fulllength of the joint is about twelve times the thickness ofthe piece.


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The construction of laminated membersmust be performed in a shop which the

pressure and temperature can be controlledand where equipment, experience and skillare available.


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The methods employed in laminating haveresulted in interesting curved forms, rigidframes, etc. Bowstring trusses with 250-ft. spans

have been built with glued laminated chords.The minimum radii for bends are generally givenas 125 to (preferably) 150 times the thickness ofthe lamination. Waterproof glues of theresorcinol and phenol types are used for exposedexterior work; in interior work the non-waterproof casein glues with mold inhibitors areemployed.


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Uses of glued, laminated wood: 1.Stringers of circular stairs

2. Roof beams, trusses and rafters for widespan and creator overhangs.

3. Built-up or composite girders. 4. Floor finishing, furniture making and

doors. 5. Aircraft manufacture.


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Glues used for woodworking are: 1. Casein glue

2. Blood-albumin glue 3. Animal glue (untreated)


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A. for waterproofing season wood to render ifresistant to the attack of fungi which can notthrive with out moisture: (a) rude oil, (b) Paints(linseed oil turpentine and some inorganicmatter (c) stains having a cresote base.

B. To poison food supply of fungi and insects:(a) creoste oil, (b) inorganic salts (zinc chloride,mercuric chloride and copper sulphate).


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The structure of wood plays a very importantpart in determining the case with which

preservation may be injected in to wood. Thetimber must be porous and as possible shouldhave radial cannals for better penetraions.


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The best time to cut timber is during the wetseason, to avoid fungus growth or insect attacks

and to avoid checking due to rapid drying. Thebark should be removed at once to preventinsects and fungus growth. Penetration ofpreservatives into woods lacking open radialducts is improved by incising timbers by toothedrollers to a depth of 1/2"-3/4:. All timber to betreated should be thoroughly seasoned tofacilitate absorption.


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This can be accomplished by: (a) air-seasoning, (b) exposure to saturated steam

(timber is placed in a large treating cylinderand subjected to live steam at a pressure of20-40 lbs. per sq. in. for 2-10 hours, afterwhich the timber is ready for treatment)

sometimes timber is soaked in creosote oilwhich is gradually heated to a temperatureabove boiling point of water, to cause thewater or moisture to vaporize.


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When the amount of timber to be treated is small, when haulingor lifting is not practical, or when the treatment is to be done byminimum cost:

(a) Brush Treatment- creosote, paint, oil and whitewash.Creosote is to be heated to 200oF before application-minetimbers,poles, and posts.

(b) Dipping- the timber is dipped into the preservatives andallowed to soak for a few minutes.- Fence posts and poles.

(c) Charring- a very old and inexpensive method is charring theouter fibers by fire, thus converting the surface of the timber intocharcoal which, devoid of food elements, is not attacked by fungi-structural members where beauty or appearances is noconsideration.


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The preservative is drawn into the wood by absorption or itsforced by atmospherice pressure.

(a) Open -tank process:- The timber is placed in a tank andcovered with preservatives; it is then heated just above boiling

point of water, to expel air and moisture; after about one hour ortwo the timber is allowed to cool with the preservative and isinjected by atmospheric pressure, this method maybe used forcreosote, zinc chloride or crude oil.

(b) Kyanizing:- well seasoned lumber is immersed in a 1%solution of bichloride of mercury for several days. (the number ofdays equals thickness of timber in inches plus 1 (+1), with depth ofpenetration of 1/4"). The salt is very poisonous hence great careshould be taken in using this process. Treated lumber should notbe used where it is likely be licked by animals.


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(c) Boiling Process:- Same as Bethell process, out timber, eithergreen seasoned, is first given a conditioning treatment in creosoteoil. Boiling may injure the strength of the wood.

(d) Rueping Process:- This is sometimes called empty-cellprocess with creosote. Air-dried or steamed lumber is placed in acylinder and the wood cells are filled with compressed air underpressure of about 75 lbs. per square inch. Oil is then admitted at aslightly higher pressure until the wood has been immersed, andthen the pressure is raised to 150 lbs. per square inch. After properamount of oil is absorbed, the creosote is forced out of thecylinder and the pressure released. As the pressure is withdrawnthe

compressed air within the wood expels the excess oil into thecylinder. This process is about 2/3 as much as the full-cell method.


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(e) Lowry Process:- Air-dry timber is placed into the cylinder andsubmerged in creosote oil at 200oF. Pressure is then applied untilthe timber has been filled with oil. After withdrawal of oil avacuum is drawn until the surplus oil in the wood cells has been

removed. (f) Card Process:- The main feature of this process is to lessen thecost by using mixture of 15 to 20% creosote with a 3 to 5% solutionof zinc chloride. Air-seasoned lumber is given a vacuum treatmentfor about an hour. Next is immersed in the preservative at atemperature of about 180oF. A pressure of about 125 lbs. persquare inch is then applied for several hours. The oil and zincchloride is continously stirred. When it is finished the preservativeis drained off to remove surplus oils. This cost about 1/2 as muchas the Bethell process.


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Market Sizes of LUmber:1. Structural lumber, and 2.Finishing lumber (sidings, flooring, etc.) For structural

such as posts, girders, girts, joints, beams, trussmembers, studs, jambs, heads, sills, etc.

CrossSections:

4"x4" 2"x2" 3"x3" 4"x10" 6"x6" 2"x4" 3"x4"4"x12 8"x8" 2"x6" 3"x5" 4"x14 10"x10"2"x8" 3"x6" 12:x12 2"x10" 3"x8 2"x12"3"x10 2"x14" 3"x12 3"x14"


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8"-0" to 18"-0 For finishing lumber we have different kinds of sidings such as (a) Rizal

sidings (b) T. & G. tongue & grove (c) V-cut (e) Corrugated. Any of thesemay be obtained at 3/4" or 1" thick by 4", 6" or 8" wide and a length of

10"-0" to 14'-0". Special sizes may be obtained but usually an extracharge of 5-10% is asked.

1. Knots are classified as sound,loose, encased, and rotten. They arethe beginnings of branches which have been surrounded by the parentstem.

2. Checks are radial cracks produced by unequal stresses set up in thelumber during seasoning process.

3. Shakes or sometimes called ring shakes are separations betweenadjacent annual rings. They are thought to be due to the bending of thetree by the wind. However, unless we use the whole log as structuralmember we need not to worry about these defects because they arealmost automatically eliminated when the log is sawn into boards.Besides our local timber seldom show these defects


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