Processing of Timber Flashcards
What are the two processes of processing timber
- cutting into visible sizes
- maximise yeild
what is the definition of conversion
cutting of freshly felled timber into usable sizes
cutting of freshly felled timber into usable sizes refers to
Conversion
what will determine the orientation and distribution of cells in sawn timber
cutting process
plain sawing produces a high
yield… but it’s properties differ from those of it’s neighbours
True radial sawing produces planks with…
identical properties…. but involves a high waste rate
what are the two types of growth defect
shakes and knots
shakes and knots are types of
growth defect
shakes are…
splits in the timber
knots are formed when…
branches grew out of the trunk
wane is a defect from the ….. process
conversion
wane is….
the presence of bark on the outer edge of the plank and has aggressive grain slope.
what is seasoning
this is the controlled reduction in moisture content
the controlled reduction in moisture content is also known as
seasoning
what is the equation for moisture content in timber
wet - dry / dry x 100
freshly felled or green timber can have a moisture content of
150%
timber must be dried to have a moisture content below 20% to eliminate
fungal attack
timber that is stacked in open sided sheds and allowed to dry naturally is know as
air seasoning
timber that is heated to expel moisture is known as
kiln seasoning
what is the fibre saturation point
this is when water is removed from the cell cavities, and the only remaining water is that contained within the cell walls.
drying beyond the fibre saturation point will result in
shrinkage and changes in mechanical properties
too rapid drying of the surface layers can lead to the surface experiencing tensile forces which will result in
splits and checks
timber is a …. material
anisotropic
how does shrinkage occur in timber
tangential - radial - longitudinal
timber below the fibre saturation point is a ….. material
hygroscopic
a hygroscopic material can
absorb water from moist air and lose moisture to dry air
timber is not truly elastic in its response to stress, it is…
viscoelastic
what is viscoelastic
it simultaneously manifests the properties of an elastic solid and a viscous liquid.
viscoelasticity is property associated with creep, under static loading timber undergoes…
instantaneous elastic strain followed by time dependent strain.
what are the major limitations to timber
variability in properties
anistropy
limited size availability at reasonable cost
