Properties of Wood (2)

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Author:
Marciaho
ID:
277291
Filename:
Properties of Wood (2)
Updated:
2014-06-21 06:45:58
Tags:
Properties Wood
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Properties of Wood
Description:
Properties of Wood
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  1. Moisture content
    Equation
    Mwet - Mdry/M dry x 100
  2. What is EMC
    Equilibrium Moisture Content
  3. Hygroscopic materal
    Absorbs and evaporates until it reaches equilibrium with the air. EMC Equilibrium moisture content
  4. Fibre Saturation Point
    • Cells empty but cell walls fully saturated. 
    • 25-30%
    • Changes in free water does not lead to significant changes in volume
    • Below FSP there is reduction in volume (shrinkage)
  5. Shrinkage and degree in each direction
    • Greatest in tangential direction
    • Then radial direction (2/3 tangential)
    • Little in longitudinal
  6. Different distortions (4)
    Bow, Twist, Crook, Cup
  7. Three types of board cut and degree
    • Flat sawn (45 degree)
    • Worst quality with defects
    • Rift sawn (45-80)
    • Quarter sawn, perpendicular
  8. Lumber Process
    • Step 1: Harvest when trunk reaches 400-800 mm diameter, Radiata Pine (24-35 yrs) Douglas Fir (35-50yrs)
    • Step 2: Sawing
    •    Live (plain sawing) - rapid and economic
    •    Quarter Sawing - max amount of prime vertical cuts, better quality
    •    Combination- most typical
    • Step 3: Seasoning (drying) Greenwood 30-200% MC to 12-15% when it leaves the mill
    • Step 4: Surfacing - takes approximately 2-5mm from each side
  9. Types of drying
    • Air drying
    • Kiln Drying
    • Combination
  10. Features of Sawn Timber
    • Natural wood growth
    • Seasoning too dast
    • Wood diseases
    • Animal parasites
    • Faulty processing
  11. Problems with wood (7)
    • Knots- result from wood grain flowing into branches
    •    Loss of load carrying cross section
    •    Fibres in knot area distorted
    •    Checking and splitting around knots
    •    Greatest impact on tensile strength
    • Sloping Grain- grain disturbed locally due to branch
    •    Board sawn parallel to pith but had significant taper
    •    Will reduce stiffness and strength, largely affects tensile strenght
    • Corewood (juvenile wood)- first 5-10 growth rings
    •    Less dense and contains small knots
    •    More cellulose
    • Reaction wood - compression wood in softwoods lower leaning side of trunk 30-40% denser
    • Checks - unavoidable in larger pieces of timber
    • Shake - seperation between annual growth rings
    • Wane- lack of wood on corner of board
  12. Grading for structural Timber
    (2)
    • Pre sorted- sorted to pre established rules
    • Strength class- strength catergories, mill chooses method for segregating into different classes
  13. 4 Types of Machine Grading
    • 1. Constant Load plank grader
    • 2. Constant deflection grader
    • 3. Joist Grader
    • 4. Accoustic Grader
  14. Fungal Decal- spread by_____
    Secrete ____ that _____ cellulose
    • Spores
    • Enzymes 
    • Depolymerise
  15. Fungal Decay - types (4) and its effect on strength
    • Moulds 
    • Stainers - both discolour and dont really affect strength
    • Soft rot fungi
    • Wood rotting busidiomycetes - can cause strength loss
  16. Fungi needs
    • Moisture
    • Air
    • Favourable Temperature
    • Food
  17. Fungi produces _____
    water
  18. Termites need what conditions and feed off what? 
    What can you do to prevent them
    • Moist warm conditions
    • Feed off cellulose
    • Block off access and apply preservative
  19. Wood borers like what waters
    What can you do to prevent?
    • Salt and brackish
    • Pressure heat wood
  20. Fire retardants work by:
    • Reducing amount of flammable gas released
    • Reducing amount of heat released in inital stages
  21. Two Primary methods for fire resistance
    • Pressure impregnation with insoluble salts
    • Fire retardant chemicals painted on surface
  22. Chemical attack- reacts with
    Iron oxide
  23. UV Light does what to the surface?
    Oxidises, changing to soft grey
  24. Wood preservatives does what?
    • Makes wood toxic to fungi and eliminates food
    • 5-10 time service life
  25. The effectiveness of wood preservatives depend on
    Preservative retention and depth
  26. Chromated Copper Arsenate CSA
    • Copper primary fungicide
    • arsenic secondary
    • Applied in water solution
  27. Alkaline Copper Quaternary ACQ
    • Alternative to CCA
    • Copper primary 
    • Quarternary Ammonium compound secondary
  28. Wood preservatives list
    • CCA 
    • ACQ
    • Borates
    • Creosote
    • Tin Compounds
  29. Composite benefits (5)
    • Dimensional Stability
    • Durability
    • Plane stiffness
    • Mechanical Stiffness
    • Resource utilisation
  30. Composite Draw backs
    • Emissions
    • Mechanical properties
    • Moisture/ Temperature effects
    • Manufacturing energy
    • Resource competition

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