working with woods, plastics and polymers Flashcards
fabrication
joining together of component parts to make a product
what is laminating ?
when thin veneers or flexible plywood are glued together to make a permanent curved profile
-former helps apply uniform pressure to the layers whilst the adhesive cures
even costing of glue between layers
wastage
removal of material
forming
changing the shape of a material
addition
material is added in order to create a form
what might be considered when choosing a joint?
-angle and strength
-time
-skill required
-aesthetic
-cost
dovetail and comb joints +ve -ve
-create repeated aesthetic patterns
-difficult to ensure consistency
-takes a lot of time
-not designed for disassembly
-requires lots of skill
-difficult to transport
methods of joining with components
-wood screws
-nuts and bolts
-coach bolts
-knock down fittings
what’s a coach bolt
-used in wooden structures
-square section embeds into wood and prevents bolt spinning during assembly
-once installed it’s impossible to remove from the head
what’s a KD fitting
-strong but collapsible joint
-glue free so good for disassembly
-easy to install
-reduces manufacture costs
how is a vacuum bag used?
-laminate is placed on a one part mould and encapsulated in a heavy duty polythene bag
-pump sucks air out of bag
-resulting atmospheric pressure forces it into position
positives of vacuum bag?
-low cost
-low skill
negatives of vacuum bag?
-time consuming
-bag could get punctured
how does steam bending work?
-steam box heats up and softens the wood fibres so they bend
-wood can be bent in all directions to form complex bends and twists
how does the steam box work?
-it’s made up of a vented container and steamer
-steam must be able to circulate and excess steam and water need to be able to leave
-steamed wood must be mover quickly to a robust former
3 hand processes
-chisel
-gouges
-planes
4 examples of machine processes
-turning between centres
-turning with a chuck and faceplate
-milling
-routing
how does turning on a lathe work?
-it holds and spins the work piece while cutting tools are used to create waste
what’s turning between centres used to create and how does it work ?
long cylindrical forms
-the prepared stock is secured in lathe at both ends which gives extra stability
-rotation speed is changed depending on diameter of wood
how does a chuck and faceplate work?
-material is secured at one end only
-secures larger work more easily
-work piece is either screwed to faceplate or clamped in chuck
what’s a milling tool made from and how does it move?
tungsten carbide
-moves up and down work laterally
how can 3D statues be created?
-milling machines fitted with robotic arms
why are finishes applied to wood?
to improve aesthetics and performance
how do finishes protect the wood
improve moisture resistance and guarding against insect and fungal attack
how do you prepare wood for finishes?
-timber must be sanded smooth along the grain
-rub down timber with methylated spirit which removes surface dust and freeze
-finishes are applied with a brush, cloth, roller or spray
polyurethane varnish
-extremely tough and hard wearing
-highly resistant to heat, water and chemicals
-sold as matt, satin or gloss finish
-used on boats and wooden flooring
pros of polyurethane varnish
-gives lustrous finish
-water based are better for environment and safer to use
cons of polyurethane varnish
-makes wood look plastic and fake
-solvent based have a long drying time and pose a greater risk to health
-yellows over time
-not resistant to uv
pros of acrylic varnish
-fast drying time
-doesn’t yellow with age
-adds durability if put on top of paint
-hard wearing
-non toxic
-odour free
good for interior use
cons of acrylic varnish
-less resistant to solvents and heat
-can’t be used exteriorly
pros of water based paints
-available in any colour
-can be watered down for a translucent look
-little odour
-low levels of volatile organic compounds(VOC)
-hardwearing, quick drying, easy to use and clean up
what are waterbased paints used for
-woodwork and furniture
what are stains?
-a finish you apply to wood that apply colour whilst keeping the natural grain
pros of stains
-aesthetic
-available in bright colours and natural tones
con of stains
no protection against decay
pros of wax finishes
-easy to apply and gives natural finish that prevents moisture getting in
-food safe and non toxic
con of wax finish
-will need to be reapplied regularly
-several coats needed
what’s oil finish used for?
to replace natural oils lost overtime to revive natural beauty
cons of oils
oils deep into wood which gives little scratch protection
pros of oils
non toxic
food safe
used on kids toys as it’s safe
pros of danish oil
-water resistant
-durable
-satin finish
-can be used as primer before paint
-food safe once aired
what preservative does pressure treated timber use
antimicrobial copper based preservatives
what’s pressure treatment used for
high level protection where timbers are exposed to constant weathering and fungal attack
-used for construction, landscaping, fencing and play grounds
name 8 stock forms of wood
-rough sawn
-planed square edge
-planed all around
-sheets
-board
-moulding
-dowel
-plank
rough sawn timber
-cheapest
-rough surfaces from industrial saws
-used in construction
planed timber
-prepared using a planer and thicknesser
-90* edge
PSE and PSR
-planing makes timber smaller and smoother
-3mm from each surface
-PSE has one square edge
-PAR square on all sides
-PSE and PAR you pay more for less material
what are mouldings and what are they used for
- machined profiles made for functional and aesthetic purposes
- used for decorative features in interiors
-skirting boards
what are softwoods and examples
-fast growth, low cost, long straight shape from coniferous trees
-pine
-spruce
-cedar
-larch
-douglas fir
what’s pine
-softwood
-most commonly used in furniture and wood flooring
-lightweight
-straight grain
-has knots
what’s cedar
-has a high oil content so resistance to decay, moisture, weathering and insect attack
-lightweight, easy to work with, knot free
-used for bit building
-softwood
what’s larch
-hard timber with an attractive reddish brown colour- fades to grey in sunlight
-high resin content- clogs up cutting blades
-used for veneers
what are hardwoods and examples
-slow growing and need more land which means it’s expensive
-deciduous
-favoured for aesthetics
-strong and durable
-oak
-mahogany
-teak
-birch
-beech
-ash
oak
-tough
-durable
-hardwearing
-resistant to rot
-contains tannic acid which erodes steel
-hardwood
ash
-springy hardwood
-large open pores which gives elastic quality
-shock resistant
-used for tool handles
-hardwood
mahogany
-aesthetic
-working properties make is expensive
-excellent stability, workability and grain
-long timber as tree is tall
-hardwood
teak
-naturally high in oils so ideal for outdoor products
-decay resistant
-high resistance to acid and alkalis
-hardwood
birch
-hardwood
-fine grain=uniform, even texture so used for veneers
-less resilient to rot and insect attacks
plywood
-manufactured board
-strong, can’t split across grain
-uses lower grade hardwood and softwood veneers
-hard, smooth, uniform surface
-some knots
flexible plywood
-manufactured board
-aero ply and flexi ply can be curved into shape
what’s aeroply made from
-several birch veneers
what’s flexi ply made of
-thin central veneer, 2 softer outers
chipboard
-larger chips
-less predictable
MDF
-fine wood dust particles bonded with resin under pressure
-perfectly smooth finish and uniform density
-ideal for CNC milling
polymer laminated
-melamine formaldehyde laminates are used to give a protective and attractive surface finish to low cost timbers
-make materials hard and durable
wood veneers
-veneers r stuck to surface and edges of manufactured boards to add to aesthetics
-add aesthetics without cost of using hardwoods
what can woods be tested for
-tensile strength
-toughness
-hardness
-corrosion
-malleability
how do you test tensile strength
-tested by applying weight to test piece and monitoring how much the material bends and deflects
-ruler or vernier callipers can measure the deflection
how do you test hardness
hit a centre punch into material and measure dent size
how do you test for toughness
-hold test piece in vice and hit with equal pressure
-most brittle materials will snap
-toughest will absorb impact like beech and birch
how to test for corrosion
-test pieces of same size and shape can be left outside for same amount of time to asses damage
what’s industrial testing
-highly accurate tests that require specialist equipment
what does a tensile testing machine do
-clamps test piece at each end and pulls the material apart until it breaks
what does the worm drive test do
-pulls clamps apart at a constant rate and the load and distance travelled is plottet
what’s the janka hardness test
-measures the ability of wood to resist scratches or dents
-measures average force needed to plunge a 0.44” or 11.28mm steel ball halfway into a piece of wood
what are charpy and izod tests
tests toughness as materials are set to size with 2mm deep notch in the centre
-pendulum is dropped to strike the test piece
-the distance pendulum travels after contact with test piece shows how tough the material is
how do izod and charpy tests differ
-charpy= material is horizontal, notch faces away from hammer
-izod= material is verticals, notch faces hammer
what are non destructive tests
-tests for tensile strength, toughness and hardness without breaking the material
what’s the ultrasound test
-sound waves are pulsed into material and intensity or reflected sound waves are recorded which deferents internal deflects
-highly accurate and can be used in any material, it’s quick and portable
whats the x-ray beams test
-x-rays are passed through the material and project an image onto a film on a screen and can measure density and weight
how can wood be enhanced?
-combining wood with resin to create a composite material
-adding a preservative or finish to increase resistance
-adding a laminate to improve surface properties
what do preservatives do?
-guard against insect and fungal attack, moisture, fire damage and rot aswell as enhancing aesthetics
- they often contain copper which has antimicrobial properties which reduces chances of fungal attack
what’s glulam
-combines natural wood planks with glued to create large laminated curved beams for structural architecture
-sustainable
-finger joints connect small planks to larger lengths
-joints are staggered to avoid weakness
traits one off production
-time consuming
-requires a high level of skill
-expensive to produce
traits of batch production
-10-100000 products
-use of jugs, templates and patterns
-more highly mechanised
—eg moulded furniture and toys
what are patterns
-positive forms used in resin casting to produce negative moulds
-enables us to produce identical copies
-can be made from many materials
-sprayed with release agent before casted
what are moulds
-may be made from a range of materials depending on how many times it will be used
what’s mass production
-uses production line to produce high numbers of identical products quickly
-highly automated
-requires less skill labour
-eg plastic bags and cups
-materials purchased in bulk
continuous production
-no down time in manufacture
-uses production line
what’s calendering
-production process which uses a serious of rollers to produce a thin polymer sheet
-polymer pellets are heated and softened
-softened polymer feedstock is extruded through a series of heated rollers
-flattens and stretches the polymer
-final rollers cool the sheet and it’s rolled and cut to length
what’s extrusion
-production method used to create a continuous flow of plastic that’s pushed through a die to create a specific profile
-used for cables and pipes
what forms do polymers come in to start with
powder or granule and are processed to produce usable stock forms for manufacture
where’s vacuum forming used
school workshop and industrial businesses
what’s vacuum forming used to make
plastic yogurt pots and bath tubs
