unit 3 Performance characteristics of woods Flashcards
What are the stock forms of wood?
Rough sawn
Planed square edge (PSE)
Planed all round (PAR)
What is timber categorized into?
natural timbers - hard/softwoods and manufactured boards
how is a tree made to timber?
tree trunk is cut into standard sizes
Rough sawn timber will be sold off at this stage
Machines called planer thicknessers are used to trim rough sawn timber to PAR and PSE timbers
Rough sawn timber
cheapest stock form of timber
rough surface
used in saw mill and construction frames
planed timber
Planed timber is prepared using a planer and thicknesser
Material is wasted away, little by little, to achieve a 90° edge on one or more sides
What is PSE timber?
one square edge
around 3mm from surface
smooth
What is PAR timber?
square on all sides
smooth
3mm from surface
What is moulding?
machined profiles made for functional and aesthetic purposes
used for decorative features for products and interiors
What is manufactured boards?
sold as full or hall boards
available in range of thickness
What is good about softwoods?
low cost
fast growth
long straight shape
What are examples of soft woods?
Pine Spruce
Douglas fir Cedar
Redwood Larch
Pine
furniture and flooring
lightweight
good elaticity
resist to shrinking swelling
Redwood giants
rot and fire proof
Lightweight, soft, good strength to weigh ratio
Used for construction, decking and musical instruments
Flying Trees Spruce
was widely used in the construction of aircraft in World War I and II
Cedar
high oil content so resistant to decay
lightweight
knot free
fairly toxic
used for boats and paneling
Larch
strong stiff durable dense
fence posts, garden furniture and boats
Douglas Fir
toughest wood
cheap and strong
large scale projects such as housing frames
stable
smooth finish
rot and moisture resistant
What are hardwoods
slow growing and need more land, both these factors make them expensive
aesthetic qualities
dense and so are usually stronger and more durable than softwoods
What are examples of hardwood?
Oak Ash
Mahogany Birch
Teak Beech
Birch
Fine grain
Even texture
Ideal for veneers
Low cost
Resistant to rot
Beech
Hard and tough
Odourless
Close straight grain
Easy to work with
Flexible
Plywood
Strong in every direction
Can’t spilt along grain
Hard and smooth
Some knots
Flexible plywood
Aero ply and flexiply
Can be formed/curved
Aeroply
To form around frameworks and plane wings
Made from several birch veneers
Flexiply
consists of a thin central veneer with two softer outers
Used in lamination and fireworks covers
What is melamine formaldehyde laminates
Give protective and attractive finish to low cost timbers
Makes them hard
Resistant to heat moister and chemicals
Wood veneers
Stuck to surface and edges to improve aesthetics
grain pattern
markings that appear on surface of wood caused by growth rings
grain direction
the way the markings run along surface of wood strongest with the grain
surface defects
insect/fungal/desease/water/knots damage
warpage
caused by moisture contents it can change shape
shrinkage
as wood drys volume decreases
splitting
as wood dries fibres separate
joining
ability to join different materials together through joints/fixings
machining qualities
if the grain is tighter the wood will machine better as large chunks are less likely to break
wood grain
can affect cost and workability
end grain is the pattern which can be seen in the wood
wood structure
wood fibres are from hollow stew like cells held in lignin carry water and nutrients make wood strong
surface defects
knots-make wood shrink hard to work
machining-creates marks
woods damaged from insects
defects affect overall stability
distortions
must be seasoned to prevent
hygroscopic-absorbs moisture
air dried
stored under cover left to dry naturally
cheap
lots at a time
no energy needed
kiln dried
uses steam to artificially dry timber
quicker
expensive
shrinkage
wood swells and shrinks with seasons or with levels of moisture
a
b
c
a- square sections shrink to diamonds
b-boards tend to cup
c-uniform shrinkage
working properties of seasoned timber
stronger and more stable
less likely to decay
less likely to corrode metals
absorbs preservatives quickly
forming woods
consists of both additives manufacturing and wasting processes as well as manipulation
steam bending
uses heat and moisture to make wood pliable beech/ash steam well as they have an open pore structure
laminating
combines wood and adhesives for different purposes
resistance to decay
can be treated to increase resistance to decay through fungal and insect attack as well as rot
insect attack
beetles/termites are attracted to wood to the starches and sugars
fungal attack
damp or poor ventilated conditions make ideal environment to fungal attack dry wood has lower risk
toxic trees
tree sap and saw dust can cause health risks
regulations of COSHH
state that wood dust must be limited to 5mg per cubic meter
What is MDF?
fine wood dust particles bonded with resin
smooth finish and uniform density
Ideal for CNC milling
very resilient
What is PSE and PAR?
PSE - one square edge
PAR - square on all sides
pay more for less materials
What is a flat-pack
standardized components or knock down fittings used to enable quick assembly
What can woods be tested for?
strength
toughness
hardness
density
corrosion
malleability
elasticity
Tensile strength
tested by applying weight to test a piece and monitoring how much materials bend
Hardness tests
hit a centre punch into a material and measure the size of the dent created
Toughness tests
hold each test piece in a vice then hit hit each one in turn with the same force
how can tensile strength be measured
applying weight to a test piece and monitoring how much the material bends or defects
hardness
how easily materials resist abrasion and indentation
jaka hardness test
measures ability of wood to resist scratches or dents
ultrasonic tests
detects internal defects using sound waves
x ray testing
x ray beams are passed through a material and protect image on screen
preservatives
guard against insect attack
wood stain
doesnt need perservatives soaks into wood
teak oil
natural oils and solvents weatherproof
varnishes
liquid coatings sit on surface creates film
waxes
soak into surface makes it a little water resistant
paint
surface finish sits on top
