6. Performance characteristics of wood Flashcards
What are the different stock forms of wood?
- rough sawn
- planed square edge (PSE)
- planed all round (PAR)
- natural wood
- manufactured boards
- mouldings
What is the rough sawn stock form?
- wood comes direct from seasoning
- has rough surfaces
- will have nominal sizes rather than accurate finished sizes
- cheapest to buy
What is the PSE stock form?
- wood only has one edge that is planed accurately
- the other edges are rough sawn
- planing removes about 3mm from the original nominal size
What is the PAR stock form?
- wood has sides and edges that are all planed square, straight and level
- smooth finish
- ready to use
- 3mm smaller all round than original nominal size
- most expensive to buy
What is the natural wood stock form?
- comes from trees
- available at only the maximum width of the tree
- natural planks would need to be joined to create a larger surface
- planks should be joined with the end grain going in opposite directions to minimise distortion
What is the manufactured board stock form?
- man-made
- produced in large sheets typically 1220mm x 2440mm
- wide surfaces can be produced from one sheet without the need for joining processes
What is the mouldings stock form?
- pre-made mouldings (e.g. skirting boards) are readily available in standard lengths up to 4 metres
What are the characteristics of wood?
- natural material
- will naturally biodegrade if left in landfill
- wood fibres grow along the length of the tree or branch (grain)
- wood expands and shrinks with changes in humidity
- strong in the direction of the grain and weaker across the grain
- wood is converted (cut from tree into useable pieces) and then seasoned (air or kiln) to remove excess moisture before use
What is air seasoning?
- traditional
- inexpensive
- wood is stacked in a shelter outside, protected from rain
- air circulates between planks to remove excess moisture
- slow process (up to a year)
- the wood is used for outdoor products
What is kiln seasoning?
- expensive
- uses controlled temperature and humidity levels
- wood is stacked on trolleys
- initially steamy in the kiln, then becomes hotter and drier
- quick process (up to a few weeks)
- wood is used for indoor products
Why is wood seasoned?
- gives greater immunity from decay
- increased resistance to rot
- increases strength and stability
- helps preservatives to penetrate
- makes wood less corrosive to metals
- helps prevent defects (twisting, warping, cracks, cupping, blowing)
How can the time taken to season wood be reduced?
- by felling trees in the winter
- grow less
- have less sap
- contain least moisture
What does the toxicity of wood depend on?
- the species
What is hardwood?
- wood from a deciduous tree
What is softwood?
- wood from a coniferous tree
What do both hardwood and softwood dusts have under the Control of Substances Hazardous to Health (COSHH) regulations?
- workplace exposure limits (WELs) of 5mg per cubic metre
What is hardwood dust listed as?
- carcinogenic
How can an employer ensure the WEL is not exceeded?
- by providing PPE
- make sure extraction and ventilation systems are used
What are hardwoods?
(examples)
- oak
- ash
- mahogany
- teak
- birch
- beech
What are the properties of oak?
- hard
- tough
- attractive grain
- good weather resistance
- contains tannic acid (corrodes steel screws or fixings)
What are the uses of oak?
- furniture
- flooring
- boat building
- cladding
- interior and exterior joinery
What are the properties of ash?
- tough
- attractive open grain pattern, making it more flexible
What are the uses of ash?
- tool handles
- ladders
- sports goods
- laminating
What are the properties of mahogany?
- can contain interlocking grain, making it more difficult to work
- rich, dark red colour
What are the uses of mahogany?
- indoor furniture
- shop fittings and cabinets
- veneers commonly used on manufactured boards
What are the properties of teak?
- hard
- tough
- straight grain
- natural oils resist moisture, acids and alkalis
What are the uses of teak?
- outdoor furniture
- laboratory benches
- traditional boat decks
What are the properties of birch?
- hard
- straight close grained
- resists warping
What are the uses of birch?
- furniture
- indoor panelling
- veneers used for birch-faced plywood construction
What are the properties of beech?
- tough
- close grained
- hard
- available in steamed (white colour) and un-steamed (pink tinge)
What are the uses of beech?
- chairs
- chopping boards
- tools (mallet)
- steam bent laminated furniture
- turned bowls
What are softwoods?
(examples)
- pine (European redwood)
- spruce
- douglas fir
- larch
- cedar
What are the properties of pine?
- straight grain
- knotty
- can contain resinous knots
What are the uses of pine?
- construction work
- roof beams
- timber frame construction
- interior joinery
What are the properties of spruce?
- straight grain
- resistant to splitting
What are the uses of spruce?
- indoor furniture
What are the properties of douglas fir?
- straight or slightly wavy grain
- few knots
- stable
- good corrosion resistance
What are the uses of douglas fir?
- veneers
- plywood construction
- joinery and construction work
What are the properties of larch?
- hard
- tough
- attractive grain pattern fades to silver upon exposure outside
What are the uses of larch?
- garden furniture
- cladding
- decking
- fencing
What are the properties of cedar?
- straight grain
- can corrode ferrous metals due to acidic nature
- low density
-good sound damping rot and insect resistant
What are the uses of cedar?
- exterior cladding
- sheds
- greenhouses
- beehives
- interior panelling
What are manufactured boards?
(examples)
- plywood
- marine plywood
- aeroply
- flexible plywood
- chipboard
- MDF
What are the properties of plywood?
- thin layers of wood are placed and glued at 90 degrees to one another and compressed to form the board
- good strength in all directions
- no grain weakness
- always has an odd number of layers
What are the uses of plywood?
- structural work
- desktops
- indoor furniture
- floorboards
What are the properties of marine plywood?
- similar construction to plywood
- but is gap and void free
- uses specialist water and boil proof (WBP) glue to provide resistance to moisture
- some higher quality is also resistant to fungal attack
What are the uses of marine plywood
- boat dashboards
- boat lockers and panelling
What are the properties of aeroply?
- plywood made from high quality timber (such as birch)
- available in very thin sheets
- lightweight
- easy to bend around a support frame
What are the uses of aeroply?
- gliders
- laminated furniture
- laser-cut projects
- jewellery items
What are the properties of flexible plywood?
- and odd number of layers glued together
- two outer layers made from open grained timber, allowing the sheet to flex
- bent and glued around a former to achieve a solid shape
What are the uses of flexible plywood?
- laminated furniture
- curved panels
What are the properties of chipboard?
- wood chips compressed with resin (such as urea formaldehyde)
What are the uses of chipboard?
- often veneered or covered with polymer laminate
- kitchen worktops and units
- shelving
- ‘flat pack’ furniture
What are the properties of MDF?
- compressed wood fibres
- sometimes urea formaldehyde is added as additional resin
- has two smooth faces
- available in either standard grade or veneered with a layer of timber
What are the uses of MDF?
- model or mould making
- furniture items such as bookcases, cabinets and desks
What are veneers?
- thin slices of wood less than 3mm thick
What are the uses of veneers?
- decorative coverings for manufactured boards
What are the properties of MF laminates?
- thin sheets of MF polymer
- hard
- tough
- chemical resistant
What are the uses of MF laminate?
- decorative coverings for chipboard for kitchen worktops etc
