wood and plastics
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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Wood and Plastics
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Major Topics
Classification of Wood Hardwood Softwood
Growth of Wood Wood Defects Wood (Lumber)
Seasoning/Kiln Drying Moisture Content Cutting
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Major Topics con’t
Wood (Lumber) Decay/Insects Grading Sizing (Nominal vs. Actual) Joints Fasteners
Prefabricated Wood (Glue-laminated)
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Major Topics con’t
Plywood Other Panels
Waferboard Composite Particleboard OSB (Oriented Strand Board)
Plastics
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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
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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.
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Wood Defects
Common defects include: knots, stain, pitch pockets, decay, and cracks.
These defects will impact the visual “grading” of wood products
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Examples of Defects
Knot
Wane – irregular rounding caused by cutting too close to outside of log
Resin Pocket
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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
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Lumber Measured in “Board Feet”
http://www.woodzone.com/tips/board_feet/board_feet.htm
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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)
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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%
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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]
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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
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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
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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)
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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”
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Joints
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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]
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Nails
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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)
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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
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Species of Lumber Used for Glu-Lam
Douglas Fir Alaska Cedar Spruce-Pine Fir Southern Pine
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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”
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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
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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
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APA – Engineered Wood Products
APA – American Plywood Association – key organization for plywood information
Website link:
http://www.apawood.org/
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Other Panels
Waferboard Composite Particleboard OSB (Oriented Strand Board)
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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
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Chemical
NameProperties Forms/Uses
Acrylics
(Plexiglas)
Transparent, hard, weather-resistant, shatter resistant, easily scratched
Cast sheets/Window & skylight glazing
Polyethylene Flexible, tough, translucent, low cost, easily scratched; Film thickness measured in “Mils”
Film & sheet/Vapor barriers, building enclosing ; Open mesh/ window screen
Polystyrene
(Styrofoam)
Hard, clear, brittle, water- and chemical-resistant, low cost; good insulating properties
Tile & sheet/Wall covering & tile
Vinyls
Poly-Vinyl Chloride (PVC)
Tough, wear- and stain-resistant Tile & sheet/Floor & wall tile, sheet covering; Coated glass fiber/ window screen; Plumbing Parts
Polyamides
(Nylon)
Tough, hard, wear-resistant, expensive
Cast/Rollers & Bearings
Thermoplastics
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Thermosetting Chemical
NameProperties Forms/Uses
Alkyds Weather-resistant, tough, good adhesive properties
Liquid and solid/Surface coatings such as paints, enamels, molded products
Melamines Hard, durable, abrasion-resistant, chemical- and heat-resistant
Sheets/Decorative laminates, high-pressure laminates, countertops
Polyesters Weather- and chemical- resistant, stiff, hard
Corrugated and flat translucent laminates, woven glass reinforced/ Window glazing & skylights
Epoxy Resins Applied by using brush, trowel, or spraying equipment
Waterproofing, joint sealers, protective coatings, adhesive