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  • Bark PROTECTIVE LAYER OUTSIDE IS DEAD - INSIDE ALIVE Cambium VERY THIN CREATES NEW CELLS Sapwood STORE NUTRIENTS & TRANSMITS SAP THICK - LIVING Heartwood DEAD WOOD PROVIDES STRUCTURAL STABILITY Pith EARLY YEARS GROWTH SMALL - WEAK
  • Primarily Hollow, Cylindrical Cells - “TRACHEIDS” Axis running parallel to the tree Tough Cellulose bond by Lignin IMAGINE A GROUP OF STRAWS Impact on the properties of wood PARALLEL WITH GRAIN (TUBE) STRONG PERPENDICULAR - WEAK
  • Springwood (earlywood) Faster growth Cells larger and less dense Summerwood (latewood) Slower growth Cells smaller and denser APPEARS DARKER HENCE - THE RINGS

ACH 121 Lecture 07 (Wood) Part 1 ACH 121 Lecture 07 (Wood) Part 1 Presentation Transcript

  • WOOD CONSTRUCTION Uses and Characteristics Types of Wood Manufacturing Process (milling & seasoning) Part 1 Professor Brandi R. Shepard© ACH 121-Materials and Methods 1
  • Sustainability in Wood Construction
    • Only major renewable structural material
    • Forestry Practices
      • Sustainable forestry
      • Clearcutting & replanting
    • Mill Practices – Lumber Recovery Factor (LRF)
    • Transportation
    • Embodies Energy Content
    • Construction Process
  • CHARACTERISTICS OF WOOD
    • Qualities of Wood
      • High strength relative to it’s weight
        • In compression & tension
        • Bending & resistance to impact
      • Easy to work with
        • Simple tools to create desired shapes
      • Highly durable
      • Excellent insulating qualities
      • Fastened quickly & economically
      • Recyclable
      • Biodegradable
      • Renewable Resource
  • CHARACTERISTICS OF WOOD
    • Undesirable Qualities of Wood
      • Not perfectly straight nor precise
      • Size & shape affected by moisture
      • Contains growth defects
      • Can spilt & warp
      • Burns easily
      • Decays
      • Susceptible to Insect Damage
  • USES OF WOOD
    • Structural
      • Light-wood framing
      • Heavy-timber framing
    • Non-Structural
      • Interior partitions (studs), blocking
      • Finished Carpentry
        • Flooring, panels, moldings, shelving
      • Architectural Woodwork
        • Cabinetry/Furniture, drawers, cornices, mantels
  • TYPES OF WOOD
    • Hardwoods
      • “ Leafy” (oak, cherry, etc.)
        • Deciduous (loses leaves)
      • Overall generally stronger
      • Grow slower
      • $$$$ cost more
      • Used for trim lumber
        • Flooring, cabinetry/furniture, interior paneling
  • TYPES OF WOOD
    • Softwoods
      • “ Needles” (evergreens)
        • Non-deciduous (does not lose leaves)
        • Called “conifer”, bears cones
      • Overall generally weaker
      • Grow quicker & Cost less
      • Used for framing lumber
        • Sheathing (roofing & exterior panels)
      • Types of trees
        • SPF (spruce-pine-fir)
        • Hem-fir (hemlock & fir)
        • Yellow pine
    • SOFTWOODS
      • 75% lumber in country
      • Fir, white pine, hemlock, cedar, aspen, spruce, cypress
    • HARDWOODS
      • Grows mostly in central region
      • Maple, birch, beech, ash, cherry, poplar, walnut, oak, hickory
  • PARTS OF A TREE (wood growth)
    • Pith: absolute center of tree
    • Heartwood: inactive cells that provide structural support for tree
    • Cambium layer: 3-5 cell thick zone of active cell growth just beneath the inner bark
    • Sapwood: carries sap (food) from roots to leaves
    Fig. 6.1-3
  • PARTS OF A TREE (wood growth)
    • Rays: run perpendicular to fibers and carry food across the grain; these produce the decorative grain effects
    • Inner bark: carries food (oxygen) from leaves to tree & roots)
    • Outer bark: dry, dead tissue; protects tree
    • Growth ring: made up by summer wood & spring wood; shows age of tree in years
  • Tree Composition
    • Bark
    • Cambium
    • Sapwood
    • Heartwood
    • Pith
  • Tree Cells
    • Primarily Hollow, Cylindrical Cells
      • Axis running parallel to the tree (grain direction)
      • Tough Cellulose bound by Lignin
    • Impacts the properties of wood
  • Professor Brandi R. Shepard© ACH 121-Materials and Methods 1
  • Tree Growth
    • Springwood (earlywood)
      • Faster growth
      • Cells larger and less dense
    • Summerwood (latewood)
      • Slower growth
      • Cells smaller and denser
  • GROWTH CHARACTERISTICS
    • Knots
      • Formed by branches
    • Shakes
      • Grain separation between growth layers
    • Pitch Pockets
      • Grain separation that contains solid or liquid resin
  • MANUFACTURING PROCESS
    • Sawing, edging and trimming logs into square or rectangular pieces of wood
    • Yard lumber
      • Boards
        • Sheathing, siding, flooring, paneling, trim, patterned millwork
      • Dimension Stock
        • Light framing, joists, planks, roof & floor decking
      • Timbers
        • Posts, beams, stringers
  • MANUFACTURING PROCESS
    • Trees are cut and transported to mill
    • Logs are cut into shorter lengths
      • Cut to fit machinery or to certain length
    • Logs are sent through debarker
      • Bark is removed by peeling, scraping or blasting using high-pressure water jets
    • Log is sent through a headsaw
      • Circular saw or band saw
  • MANUFACTURING PROCESS
    • Rough cants, timbers, planks & boards are sent through an edger
      • Removes rounded edges
      • Rips lumber into desired width
    • Lumber is then moved onto trimmer
      • Saws trim off rough ends & defects
    • Next step is green chain, where edged, trimmed lumber are sorted visually
      • According grade, species and size
  • MANUFACTURING PROCESS
    • Plainsawing:
      • Better yield from the log
      • Cheaper (better yield)
      • Uneven grain patterns
      • Uneven shrinkage (warps)
      • Used for framing lumber
    • Quartersawing:
      • Less yield from the log
      • Expensive (less yield)
      • Even grain patters
      • Even shrinkage (no warps)
      • Used for trim lumber
    Milling
  • Typical Sawing Method Typical Sawing of a Large Log
  • Typical Sawing Method
  • MANUFACTURING PROCESS
    • After sawmilling, lumber is seasoned.
      • Kiln-dried or air-dried
    • Drying Effects
      • Shrinkage
      • Reduced weight
      • Increase of strength and stiffness
      • More dimensional stable
  • MANUFACTURING PROCESS
    • Moisture Content:
    • Amount (percentage) of moisture (water) in the lumber
    • More moisture, more shrinkage!!
    Shrinkage creates problems!! A N D Seasoning
  • SEASONING- Shrinkage
    • Heartwood: oldest and strongest part of the tree
    • More shrinkage PERPENDICULAR to the grain
    • Lumber defects
      • Warps
      • Cracks in finish work
      • Checks
  • SEASONING- Shrinkage
    • Lumber Defects
      • Crook
      • Cup
      • Twist
      • Bow
      • Splits
      • Checks
    These are called seasoning defects
  • SEASONING- Moisture Content
    • Moisture content varies
      • 26-32% when cut
      • 19% MAXIMUM for framing-”kiln-dried”
      • 15% when shrinkage is a concern
    • Over 19% moisture content is considered “GREEN” (not good…)
  • MANUFACTURING PROCESS
    • Lumber is then sent to planing mill
      • Sizing and surfacing
      • Then graded, tallied and prepared for shipment
    Rough sawn (not surfaced)
    • Purpose for surfacing
      • Smooth
      • Dimensional precision
    • Surfacing typically performed after drying
  • Additional Resources The Encyclopedia of Wood by: Aidan Walker
    • Check out class WebCT site:
      • Articles from Fine Homebuilding Magazine
      • Website links