4.2 b Flashcards
natural timber
wood cut directly from the tree, cut into boards of diff sizes
difference between hardwood and softwood is in…
in how the fibre and pores work
where is tensile strenght greater in timber
along the grain (fibre) than across the grain (matrix)
damp resistance of timber
timber absorbs moisture from the air during humid periods and releases moisture during dry periods
hardwoods
wood from decidious trees (lose their leaves) that bear fruit. slow growing (take up to 150 years) => considered non renewable
softwoods
wood from coniferous (keep their leaves) trees – cone bearing ones
generally mature in 40 years
softwoods features, in comparison to hardwoods
grow faster
have lower density, hence lower mechanical strength and lower durability
more likely to absorb water
less tensile strength
more lightweight
easier to work with
catch fire easier
hardwoods examples
oak
mahogany
balsa
softwood examples
pine
spruce
rosewood
wood grain patterns
flat grain
vertical grain
end grain
hygroscopic
absorbs moisture of surrounding environment
equilibrium moisture content
when the tree is in a stable environment, not gaining or losing moisture
define seasoning + how long it usually takes
drying of timber to reduce the moisture content of wood
between 1 and 5 years, depending on type of wood and what its intended to be used for
seasoning methods
kiln seasoning
air drying
define kiln seasoning
using controlled heat and air circulation in chambers to dry timber more quickly and bring moisture content to desired level
define air drying
stacking timber outside as air slowly dries it
kiln seasoning adv
speeds up process
insects killed off
moisture content can be brought to a specific level
kiln seasoning disadv
expensive
skilled person needed
energy use
air drying adv
no need for expensive equipment
reduced labour costs
little energy use
air drying disadv
longer time needed
less control
timber defects
warping – material bending bcs of uneven drying
bowing – warping along length of face of wood
cupping – warping across width of face of wood
twisting – warping where two ends of material dont lie in the same plane
knots – imperfections caused by growth of branches in the tree
warping
bowing
cupping
twisting
knots
characteristics of man made boards + how theyre produced
produced by gluing strands/fibres of wood together eg MDF or plywood
tensile strength
resistance to damp environments
aesthetic properties
longevity
lamination
covering the surface with a thin sheet of another material
why is lamination typically done
protection, aesthetic reasons
Treating and finishing timbers
improving the timber’s resistance to heat, attack by insects and fungus, its durability is enhanced/aesthetic properties are enhanced
treatment
additive preservative to improve the timber’s resistance to attack from fungi and insects
wood preservers soak into wood fibres rather than sit on the surface
finishes
applied to the surface to improve material’s natural beauty, but also to protect it from impact, heat, or moisture
recovery and disposal of timber
1 reforestation
2 wood recycling (turning waste timber into usable products)
3 wood waste (feedstock, animal bedding, biomass etc)
