Transcript Document

Wood and Plastics
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Major Topics
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Classification of Wood
Hardwood
 Softwood
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Growth of Wood
Wood Defects
Wood (Lumber)
Seasoning/Kiln Drying
 Moisture Content
 Cutting
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Major Topics con’t
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Wood (Lumber)
Decay/Insects
 Grading
 Sizing (Nominal vs. Actual)
 Joints
 Fasteners
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Prefabricated Wood (Gluelaminated)
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Major Topics con’t
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Plywood
Other Panels
Waferboard
 Composite
 Particleboard
 OSB (Oriented Strand Board)
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Plastics
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Classification of Wood
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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
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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
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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
Wane – irregular rounding caused
by cutting too close to outside of log
Knot
Resin Pocket
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Lumber
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Broad term that applies to all finished or
semi-finished wood shaped with parallel
longitudinal surfaces
Nominal piece sizing includes:
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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
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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
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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
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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
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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
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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
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Waterborne
Oil-borne
Creosote
Fire-retardant solutions
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Grading
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Depends on the appearance ( # of
defects) and strength
Lumber pieces are marked with a grade
stamp
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Typical stamp includes
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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)
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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
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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
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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
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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 GluLam
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Douglas Fir
Alaska Cedar
Spruce-Pine Fir
Southern Pine
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Plywood
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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
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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
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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
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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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Thermoplastics
Chemical
Name
Properties
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
Tough, wear- and stain-resistant
Poly-Vinyl
Chloride (PVC)
Tile & sheet/Floor & wall
tile, sheet covering;
Coated glass fiber/
window screen; Plumbing
Parts
Polyamides
(Nylon)
Cast/Rollers & Bearings
Tough, hard, wear-resistant,
expensive
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Thermosetting
Chemical
Name
Properties
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
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