COSC 253 EXAM 2 (Simms) || All Correct.
MasterFormat Division 6 correct answers Wood, Plastics, and Composites
Tree Structure correct answers Bark: Outermost protective layer (A: dead, B: living)
Cambium layer (C): Source of new cells
Sapwood (D): Living cells that store and transport nutrients
Heartwood (E): Dead cells that contribute to structural strength
Pith (F): Innermost, first year's growth
Annual growth rings (G): Result from differences in rate of tree growth and density of cells,
from spring to summer
Softwoods correct answers - from cone-bearing (coniferous) trees
- simple cell structure
- generally, plain grain structure (or figure) - pattern of grain and surface features
- primarily originate from North American forests
- fast-growing, plentiful, relatively in-expensive
- generally soft, easy worked
- used for structural wood products, finish trim, shingles, siding, flooring
- note: not all softwoods are soft! For example, Douglas Fir is harder than some hardwoods
Hardwoods correct answers - from broad-leaf (deciduous) trees
- more complex cell structure
- often more interesting grain structure/figure
- harvested from around the world
- slower growing, generally more expensive than softwoods
- denser, with greater variety of color and figure
- for fine trim, paneling, flooring, fine cabinet work, furniture
Environmentally Certified Wood correct answers - comes from largest forests that are managed
to meet certain standards
- Forest Stewardship Council (FSC) certification program
-- Chain of Custody Certification
-- FSC Controlled Wood (less stringent)
- Chain of Custody Certified Wood eligible for points in the LEED rating system
Sustainability of Wood correct answers - wood is the only major structural material that is
renewable
- in North America, annual tree growth exceeds the volume of harvested trees
- manufactured wood products efficiently use waste (chips, strands,
sawdust, scraps, etc.)
- if the wood frame of a building is kept dry, it can last indefinitely
Sawing correct answers - plainsawn: growth rings roughly parallel to wider face of board
- quartersawn: growth rings close to perpendicular to wider face of board
, Plainsawn Lumber correct answers - most economical sawing method
- produces maximum yield of useful pieces
- lumber experiences greater distortion (crook, bow, cup, twist) during drying process
Quartersawn Lumber correct answers - requires more handling of the log during sawing
- not as efficient, generates more waste
- lumber is more dimensionally stable
- produces more pleasing grain figure
Seasoning correct answers - after lumber is sawn, it is seasoned (dried), either in air or in kilns
- kiln drying usually preferred over air drying
- kiln drying uses more energy but is faster and produces more stable, uniform lumber
- seasoned lumber is lighter, stronger, and stiffer than green (unseasoned) lumber
Seasoning (moisture content) correct answers - Moisture Content (MC) - amount of water
present in wood
- Determining MC = (Wet Wt. - Dry Wt.)/Dry Wt. x 100
- standard framing lumber is seasoned to MC 19 at the mill
- decay causing fungi cannot survive in wood with a moisture content (MC) below ~20%
- MC of growing wood can vary from 30 percent to 200 percent
Seasoning (shrinkage) correct answers - wood does not shrink/swell uniformly with changes in
MC
- shrinkage along the length of the log (longitudinal) is minimal
- radial shrinkage is larger
- tangential shrinkage is larger again by half or more and causes radial cracks called checks
- Difference between rates of tangential and radial shrinkage cause distortions in shape,
especially in plainsawn lumber
- as wood dries below approximately 30 percent MC, it shrinks, mostly in cross section, and only
slightly in length
- wood eventually dries to equilibrium with the surrounding air, reaching its equilibrium
moisture content (EMC)
-- EMC for exterior uses: ~ 12%
-- EMC for interior uses: ~ 8%
Surfacing correct answers - lumber is surfaced to make it smooth and more dimensionally
precise
- Framing lumber: usually surfaced four sides (S4S)
- Finish lumber: may be S4S, or surfaced two sides (S2S), the other
sides to be sawn and surfaced by the woodworker
- Surfacing after seasoning (S-DRY) most common: removes some drying distortions
- Surfacing before seasoning (S-GRN): sometimes more economical; best for wood species that
don't distort excessively as they dry
- Construction planking: unsurfaced; Plank is stronger (no material has been removed) and more
slip-resistant
