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Wood and Plastics

Wood and Plastics. Major Topics. Classification of Wood Hardwood Softwood Growth of Wood Wood Defects Wood (Lumber) Seasoning/Kiln Drying Moisture Content Cutting. Major Topics con’t. Wood (Lumber) Decay/Insects Grading Sizing (Nominal vs. Actual) Joints Fasteners

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Wood and Plastics

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  1. Wood and Plastics

  2. Major Topics • Classification of Wood • Hardwood • Softwood • Growth of Wood • Wood Defects • Wood (Lumber) • Seasoning/Kiln Drying • Moisture Content • Cutting

  3. Major Topics con’t • Wood (Lumber) • Decay/Insects • Grading • Sizing (Nominal vs. Actual) • Joints • Fasteners • Prefabricated Wood (Glue-laminated)

  4. Major Topics con’t • Plywood • Other Panels • Waferboard • Composite • Particleboard • OSB (Oriented Strand Board) • Plastics

  5. Classification of Wood • Hardwood – trees which are deciduous (shed broad shaped leaves annually) ex: Birch, Ash, Maple, Oak • Softwood – trees which are evergreen (needle-like leaves) ex: Southern Pine, Fir, Spruce, Redwood

  6. Growth of Wood • Growth is formed from core (pith) in rings. The # of rings and spacing between rings show age and growing conditions of tree. • Wood is made of hollow tubular cells running parallel to the long axis of the tree.

  7. Wood Defects • Common defects include: knots, stain, pitch pockets, decay, and cracks. • These defects will impact the visual “grading” of wood products

  8. Examples of Defects Wane – irregular rounding caused by cutting too close to outside of log Knot Resin Pocket

  9. Lumber • Broad term that applies to all finished or semi-finished wood shaped with parallel longitudinal surfaces • Nominal piece sizing includes: • Board -- 11/2” or less thick and 2” or more wide • Dimension – 2” to 5” thick and >2” wide • Timbers -- 5” or more thick and wide

  10. Lumber Measured in “Board Feet” http://www.woodzone.com/tips/board_feet/board_feet.htm

  11. Seasoning/Kiln Drying • Seasoning- the process of reducing moisture until a suitable level is achieved (causes shrinking in lumber size) • May be seasoned in the air (2-6 months for softwood and may take 4 years for some hardwoods) or by using a kiln • A chemical (hygroscopic) may be applied to the wood to keep surface moist to reduce shrinkage cracks (checks)

  12. Moisture Content • The strength of wood increases as the moisture content (m.c.) decreases • M.C. varies depending on the conditions (geographical region & indoor/outdoor) in which the lumber will be used • Typically, m.c. does not exceed 19%

  13. Cutting • Plain-sawed (flat sawed) – lumber which is cut in parallel slides [less waste & cheaper; warps & splits] • Edge-sawed – lumber which is cut perpendicular to the exterior of the tree • Quarter-sawed – lumber in which the log is 1st cut into quarters and then cut on the diagonal [produces the most attractive wood grains]

  14. Decay-Insects • Termites – destroy wood by chewing it (chemical or physical barriers should be used to deter them) • Fungi – feed on wood fibers leaving wood weakened with rotting • Avoid placing untreated wood directly in contact with concrete

  15. Pressure-Treated Lumber • Must meet all EPA (Environmental Protection Agency) requirements • CCA (Chromated Copper Arsenate) is the most common treatment used today • 4- EPA approved wood preservatives include • Waterborne • Oil-borne • Creosote • Fire-retardant solutions

  16. Grading • Depends on the appearance ( # of defects) and strength • Lumber pieces are marked with a grade stamp • Typical stamp includes • Grading body (WWP – Western Wood Products • Mill identification • Grade name (Const – construction) • Moisture content • Type of wood (D-Fir – Douglas Fir)

  17. Sizing (Nominal vs. Actual) • Lumber is referred to by nominal size but the actual size is less (see handout) • 2”x4” actually measures 1/1/2” x 3 ½” • 1” x 8” actually measures ¾” x 71/4”

  18. Joints

  19. Fasteners • Nails, screws, bolts, staples, anchors, and joist hangers are common fasteners • Sizes, styles, and finishes (coatings) depend on the intended application • Length of nails designated in “pennies” [d]

  20. Nails

  21. Prefabricated Wood • Because of the limitations of size of sawn wood – the gluing of smaller pieces together will enable structural members of virtually any length, cross-section, and desired curves to be made • Glu-lam members are widely used in areas of construction using arches (must comply with ANSI 190.1)

  22. Glu-Lam • Individual laminations are placed so that: • Weak spots are separated from each other to avoid concentration of weakness • Appearance flaws in wood are hidden within the member • End joints between lams are separated from each other to avoid a plane of weakness • The strongest wood is placed where stresses are highest

  23. Species of Lumber Used for Glu-Lam • Douglas Fir • Alaska Cedar • Spruce-Pine Fir • Southern Pine

  24. Plywood • Plywood is a type of glued, laminated wood. Thin wood layers of laminations are arranged with the grains of each layer perpendicular to the adjacent one. • Veneers – the actual laminations consisting of face & back, crossbands, and the inner (core) [see fig 6-20, pg. 176] • Usually an odd number of veneers (3-5; may be up to 11) • Thickness may range from ¼” – 1 ¼”

  25. Advantages of Plywood vs. Sawn Lumber • Has great transverse strength which aids in strengthening/bracing entire structure when used over studs, joists, and rafters for wood frame construction • Less warping and change due to moisture changes • Is more easily bent to form curves for concrete forms or curved wood construction • Fabricated in large sheets (4’x8’, typical) which covers larger areas more quickly • Can be worked closer to the edges without splitting • Desired appearance can be obtained by using thin veneers of high quality wood where they are visible

  26. Grades/Types of Plywood • 5 basic grades from best to less desirable finished appearance: A, B, C, C plugged, & D • 5 species groups (according to stiffness and strength): Group 1 is the strongest/stiffest • Types of plywood: interior and exterior • Interior- made with glue suitable for indoor use; available in any grade • Exterior – made with hot, phenolic resin glue which is unaffected by water & resists weathering; no veneers below C grade used

  27. APA – Engineered Wood Products • APA – American Plywood Association – key organization for plywood information • Website link: http://www.apawood.org/

  28. Other Panels • Waferboard • Composite • Particleboard • OSB (Oriented Strand Board)

  29. Plastics • Usually contain synthetic resins. May also contain plasticizers, fillers, and colorants • 2 basic classes of plastics; thermoplastics (no chemical change during heating/cooling) & thermosetting plastics (change chemically when heated and solidify while still hot) • Plastic products are strong, light in weight, formable, and resistant to corrosion

  30. Thermoplastics

  31. Thermosetting

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