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A Level DT > 1.5 The Use of Finishes > Flashcards

1.5 The Use of Finishes Flashcards

1
Q

METALS

cellulose & acrylic paints

A
  • colour (& textured) finish
  • barrier against corrosion
  • used on low-cost metals (eg steel)
  • surface must be cleaned & degreased before application
  • primer coat used
  • applied w/ brush/spray
  • specialist paints add texture or special graphic effects (eg pearlescence)
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2
Q

METALS

electroplating

A
  • uses electrolysis to coat base metal in another metal (usually more expensive)
  • protective layer & greater aesthetic appeal
  • current passed through solution with the 2 metals)
  • anode & electrolyte made up of plating metal (anode replenishes metal in solution)
  • +ly charted ions attracted to cathode (-ly charged) & deposit on cathode forming plating
  • because +ly charged ions gain electrons at cathode
  • atoms in the anode lose electrons & dissolve into solution (oxidation)
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3
Q

METALS

polymer dip coating

A
  • metal product heated then dipped into tank of fine polymer powder
  • tank has air blowing through it (fluidisation bath) to help get an even coating
  • heat from product allows powder to melt over product
    USES: wire hangers, dish drainers, dishwasher racks, outdoor play equipment
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4
Q

METALS

metal dip coating

A
  • product is dipped into tank of molten donor metal
  • used for cheap metals (eg low carbon steel)
  • protects against corrosion
  • usually 2 types:
    > tin plating (eg food cans)
    > zinc plating (galvanising) (eg car bodies, gates, animal pens)
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5
Q

METALS

powder coating

A
  • product is statically (-ly) charged
  • sprayed with (+ly) charged thermoset polyester resin through airgun
  • charge causes strong attraction between powder & product
  • product baked in oven- heat melts powder over product & gives even coat
    USES: domestic white goods (fridge, dishwasher, etc), coloured finish to metal gates, fences etc
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6
Q

METALS

varnishing

A
  • clear finish
  • used on expensive metals (protects but allows colour to show)
  • eg brass, copper
  • applied with spray/fine brush
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7
Q

METALS

sealants

A
  • tough polymer-based
  • protect polished surfaces from decay & tarnishing
  • silicon-based cheap sealants used on cars to protect bodywork from weathering, insect attack, road salts, etc
  • applied using cloth/machine pad
  • produces film that is left to cure before buffed
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8
Q

METALS

preservatives

A
  • can be temporary in-process or medium to long-term protection
  • used on moulds/dies to prevent fingerprints, minor atmospheric corrosion or condensation build up
  • applied by wiping on with cloth/spray/immersion
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9
Q

METALS

anodising

A
  • commonly used on aluminium
  • enhances natural oxide layer> increased hardness & toughness
  • can also provide colour
  • similar to electroplating
    > electric current passes through sulphuric acid electrolyte solution from anode (part to be treated) to cathode
    > aluminium oxide builds up on treated part producing finish
    > can be finished with clear lacquer/varnish to seal and prevent scratches
    USES: outer casings of phones, hard drive covers etc
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10
Q

METALS
cathodic protection
(basic info)

A
  • all metals have a natural voltage
  • when 2 different metals are joined together there is an electric current
  • if water is present at the join an electrochemical cell is formed & one of the metals will corrode
  • current flows through the water from the anode (more actively corroding metal) to the cathode (less actively corroding metal)
  • eg aluminium sheets held together with brass screws in presence of rainwater- aluminium will corrode around joint
  • cathodic protection used to control the rate of corrosion
  • the anode is a sacrificial metal which protects the cathode
  • main use: protect steel structures buried in soil/underwater (eg pipelines, ship hulls, offshore platforms)
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11
Q

METALS
cathodic protection
(impressed current)

A
  • component to be protected is connected to electrical power supply
  • impressed direct current flows from an inert electrode through any liquid to the component to be protected
  • EG burned pipeline recipes direct current from electrode buried in the ground. pipe = anode, electrode = cathode, cathode corrodes over time and is monitored
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12
Q

METALS
cathodic protection
(sacrificial anodes)

A
  • uses a sacrificial metal to protect the metal product of more value
  • more electrochemically active metal is wrapped around/joined to the less active metal to provide corrosion resistance
  • on large structures the sacrificial metal is monitored for signs of corrosion and replaced when needed
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13
Q

POLYMERS

advantages of polymer finishing (4)

A
  • polymers are self-finishing
  • surface textures are produced from the mould
  • addition of pigments during manufacture adds colour making polymer self colouring
  • polymers are considered finished and ready to use when manufacture is complete
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14
Q

POLYMERS
overmoulding
(summary)

A
  • moulding a second polymer over specific parts of a product
  • TPE often used
  • primarily used to provide different areas of grip/texture or highlight different colours for different component parts
  • eg toothbrush handle
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15
Q

POLYMERS
overmoulding
(using two injection moulding moulds)

A
  • one mould is made for the product & one for the grip areas
  • product body is injection moulded then placed into second mould
  • overmoulding is injection moulded onto the body
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16
Q

POLYMERS
overmoulding
(twin shot injection moulding)

A
  • mould has two separate component cavities
  • can rotate 180° to line up with twin injection points
  • main body is made first
  • then mould opens up slightly and rotates to secondary position
  • mould closes again & second injection applies overmould
  • twin shot injection moulding is a continuous process- a new part made while another being overmoulded
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17
Q

POLYMERS

acrylic spray paint

A
  • fast-drying, water-soluble paint, becomes water resistant when dry
  • enhances aesthetics, protects against UV & weathering
  • allows for mass customisation (eg cars)
  • polymers can be pigmented during manufacture instead but not cost effective to keep changing granules in machine
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18
Q

POLYMERS

pigments

A
  • added during manufacture process
  • pigment particles can be added to hopper during injection moulding but more commonly bought as pre-pigmented stock forms
  • smart pigments (eg thermochromic etc) can be added in the same way
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19
Q

POLYMERS

gel coat & lay up process

A
  • pigment can be added during lay up process for GRP
  • polyester resin bought pre-pigmented then applied to mould before GRP matting
  • eliminates need to add individual pigments to resin
  • no need for additional finishing
  • eg boat hulls
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20
Q

WOOD

general purpose of wood finishing (4)

A
  • protect against absorbing water
  • protect against decay
  • protect against insect attack
  • enhance appearance
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21
Q

WOOD
wet rot
(summary)

A
  • occurs when moisture content of wood is very high (above 50%)
  • black fungus may grow on timber
  • wood fibres break down & fungus grows
  • timber feels soft & spongy
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22
Q

WOOD
wet rot
(treatment)

A
  • cause of moisture identified & stopped
  • wet rot treated with fungicide
  • sometimes affected area has to be removed & replaced
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23
Q

WOOD
dry rot
(summary)

A
  • caused by fast-spreading fungus
  • leaves cracks deep in the grain
  • white sheets of fungus (mycelium growth) can sometimes be seen
  • timber can become dry, soft and powdery
  • can spread throughout timber and cause significant structural damage
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24
Q

WOOD
dry rot
(treatment)

A
  • dry rot treatment used to eradicate moisture

- infected timber is replaced

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25
Q

WOOD
insect attack
(summary)

A
  • often known as wood worm
  • insects (eg furniture beetles) lay eggs in cracks in the wood
  • hatched larvae eat through wood forming tunnels
  • leaves tiny holes visible on surface of wood
26
Q

WOOD
insect attack
(treatment)

A
  • permethrin-based wood treatment applied to affected area with brush/spray
  • alternatively, it can be injected into the wood
27
Q

WOOD

preparing surface for finishing

A
  • surfaces made smooth by planing/sanding (progressively finer glass paper)
  • sanding should be done in direction of wood grain (avoid scratching)
  • cloth used to wipe away remaining dust
  • finish applied
28
Q

WOOD

polyurethane/acrylic varnish

A
  • 3 types: gloss, shear, matt
  • clear or coloured
  • APPLICATION: thin coat applied with brush, several coats applied in between glass paper to smooth surface
  • SURFACE FINSH/DECAY PREVENTION
    > hard, tough, heat proof, waterproof
    > clear finish allows wood grain to be seen
29
Q

WOOD

water-based paints

A
  • different finishes: gloss, matt, metallic, satin
  • mostly used for softwoods
  • knots must be treated before to prevent resin seeping out
    APPLICATION: primed & undercoated, paint applied with brush/roller
    SURFACE FINISH/DECAY PREVENTION:
    > provides protection & colour
    > can be used inside & outside
    > surfaces more aesthetically pleasing
    > harder, tougher, water resistant
30
Q

WOOD

stains

A
  • many different colours & types (eg mahogany, antique)
  • water/spirit based
  • surfaces need to be grease free before application
    APPLICATION: applied with brush/roller/spray
    SURFACE FINISH/DECAY PREVENTION:
    > helps colour, enhances grain
    > can be used to make cheap woods look more expensive
    > adds colour but allows grain to show
    > no protective properties
31
Q

WOOD

colour wash

A
  • many different colours
    APPLICATION: using wet sponge
    SURFACE FINISH/DECAY PREVENTION:
    > adds colour but grain still shows through
    > can be used to make wood more aesthetically pleasing/give vintage style while grain still shows
32
Q

WOOD

wax

A
  • clear & coloured
  • for indoor use
    APPLICATION: with brush/stockinet cloth, once dry buffed with lint-free cloth
    SURFACE FINISH/DECAY PREVENTION:
    > can be buffed for high gloss finish
    > increases surface hardness & toughness
    > clear- shows wood grain
33
Q

WOOD

pressure treating

A

APPLICATION:
- wood placed in a pressure vessel containing solution of copper sulphate & other preservatives
- vacuum & pressure control to force solution into wood
- wood is steam dried
DECAY PREVENTION:
> protects for up to 50 years from rot, insect & fungal attack & weathering
USES: decking, cladding, bridges, overhead cable poles

34
Q

WOOD

yacht varnish

A
  • high gloss or satin
    APPLICATION: with brush/spray
    SURFACE FINISH/DECAY PREVENTION:
    > increases hardness, toughness & weather resistance
  • for woods outside year round (eg doors, window frames, boat parts)
35
Q

WOOD

danish oil

A
  • clear or coloured tints
    APPLICATION:
  • with lint-free cloth, oil is rubbed into wood, in direction of grain
  • left for 5 mins to soak in, then excess wiped off
  • lightly sanded/rubbed with wire wool between coats to open up grain
    SURFACE FINISH/DECAY PREVENTION:
    > maintains natural appearance of timber
    > enhances grain
    > not very hardwearing finish but regular application builds up matte, water resistant finish
36
Q

WOOD

teak oil

A
  • clear tint
    APPLICATION:
  • with lint-free cloth, oil is rubbed into wood, in direction of grain
  • left for 5 mins to soak in, then excess wiped off
  • lightly sanded/rubbed with wire wool between coats to open up grain
    SURFACE FINISH/DECAY PREVENTiON:
    > mostly for outdoor use to improve weather resistance & resistance to insect & fungal attack
    > enhances grain
37
Q

PAPER & BOARD

laminating (encapsulation)

A
  • sheet of paper encapsulated in polymer pouch/film roll
  • paper is fed through desktop laminator & heat sealed leaving polymer sheet cover on both sides & border
  • polymer pouch is usually PET and EVA mix
38
Q

PAPER & BOARD

lamination (surface coating)

A 
- liquid or film lamination
LIQUID:
- applied with roller/spray
- protects from moisture, dirt, UV light
- eg for signage
FILM:
- usually PP with adhesive
- can be done with hot or cold processes
- laminate is fed from roller & pressure applied as paper fed through
- eg for menu cards, business cards
39
Q

PAPER & BOARD

embossing

A
  • creates a raised design on the surface of the paper
  • visual & tactile effect
  • uses 2 dies- male & female
  • dies can be cold or heated
  • substrate placed between the two dies & held under pressure until embossed design formed
  • embossed area can have ink/foil applied or left as is (blind emboss)
  • decorative technique- eg for cards, business cards, packaging
40
Q

PAPER & BOARD

debossing

A
  • same as embossing but produces imprinted depression
41
Q

PAPER & BOARD

foil blocking

A
  • application of heat & pressure to apply metallic foil to create areas of depth & texture
  • adds aesthetic impact
  • uses machine with heated die, design is stamped onto material through foil which is transferred as it sticks to paper
  • requires accuracy & consistency- too hot/pressure held for too long foil will bubble & peel, too cool/not enough pressure foil will not adhere
  • eg business cards, letterheads
42
Q

PAPER & BOARD

varnishing

A
  • clear, non-pigmented ink used on pre-coated paper/board to enhance colour & protect against dirt, fingerprints, water
  • gloss, matte, satin, tinted
  • applied as flood coat
  • only suitable for pre-coated papers because they won’t soak up ink and swell/bleed colour
43
Q

PAPER & BOARD

uv varnishing

A
  • very smooth finish
  • ink must be completely dry before application
  • specific machinery used that instantly cures UV varnish to provide high quality finish
  • usually gloss or matte
  • chemical & abrasion resistant
  • applied via set of rollers then passed under UV light to cure
44
Q

PAPER & BOARD

spot varnishing

A
  • varnish applied in specific areas of paper rather than whole surface
  • plate/set of plates presses onto surface & applies varnish
  • can be both varnish & UV varnish
45
Q

PAPER & BOARD
offset lithographic printing
(summary)

A
  • extremely versatile
  • one colour (single roller), 5 colours (CMYK + metallic), 10-feature (CMYK + metallic + varnishing + sports varnishing + duplex [both sides printed])
  • medium to long print runs (eg magazines, books, packaging)
  • uses principle that oil & water do NOT mix
46
Q

PAPER & BOARD
offset lithographic printing
(how/why it works)

A
  • oil & water do not mix
  • lithographic plates chemically treated to make image area oleophilic (easily absorbs oils) so receptive to oil-based ink
  • non-image area hydrophilic (absorbs water)
  • dampening solution applied to roller- mostly water based so attracted to non-image areas
  • ink applied and attracted to image area
  • ink and water don’t mix so solution prevents ink entering non-image area
47
Q

PAPER & BOARD
offset lithographic printing
(printing process)

A
  • printing substrate fed into printing machinery
  • printing plates produced by computer to plate (CTP) process using a laser to etch image onto plate
  • plates attached to machine & dampened
  • ink applied to printing plate, plate cylinder rotates onto blanket roller which is coated in ink
  • as substrate fed through image on blanket roller is transferred to substrate
48
Q

PAPER & BOARD
flexographic printing
(summary)

A
  • uses CMYK- inks are printed on top of each other in various quantities to produce print colour
  • colours must be precisely aligned to create accurate, non-blurry image- registration marks used
  • least expensive printing process- simple, fast-drying inks
  • rolls of substrate used rather than sheets to allow for continuous printing
  • eg newspapers, carrier bags, wallpaper, gift wrap
49
Q 
PAPER & BOARD
flexographic printing
(printing process)
A
  • flexible printing plate wrapped around rotating cylinders on web press
  • water-based/UV curable ink fed from 1st roller to anilox roller
  • anilox roller makes ink a uniform thickness and transfers ink to printing plate cylinder
  • substrate moves between plate cylinder & impression cylinder
  • impression cylinder applies pressure to plate cylinder to transfer image to substrate
  • web (now printed) fed into overhead dryer so ink is dry before it goes to next print unit
50
Q

PAPER & BOARD
screen printing
(summary)

A
  • used for small print runs (eg posters, t-shirts, display boards)
  • can be carried out in a workshop
  • minimal set up costs- basic screens & printing inks
51
Q 
PAPER & BOARD
screen printing
(printing process)
A
  • substrate sits on machine base & is secured
  • image is created on screen/stencil. this is a mesh held by the frame
  • screen has ‘open’ areas for ink to pass through
  • different screen required for each colour (can make process time consuming & increase production cost)
  • screen placed over substrate
  • pigmented printing ink placed on mesh
  • squeegee used to force ink through mesh & onto substrate
  • once each colour complete ink dries/cures
52
Q

PAPER & BOARD

digital printing

A
  • becoming more popular & widely used because of speed & versatility
  • full colour, highly detailed print runs
  • option of different designs on each page, both front and reverse sides
  • similar to laser printers- ink sits on top of substrate and allowed to dry/be laminated
  • both low & high volume print runs
  • ideal for mass customisation- use of fast drying inks
  • uses: flyers, business cards etc
53
Q

what does CMYK stand for?

A

Cyan
Magenta
Yellow
Key (black)

54
Q

advantages of offset lithography (7)

A
  • most common printing method
  • consistent high quality
  • fast
  • prints onto paper well
  • suitable for high print runs (1000+)
  • quick & easy to produce printing plates
  • long life of printing plates as they only come into contact with blanket roller which is less abrasive than substrate
55
Q

disadvantages of offset lithography (3)

A
  • expensive set up cost
  • only suitable for porous substrate materials
  • very expensive for small print runs
56
Q

advantages of flexography (5)

A
  • very fast
  • suited to long print runs
  • prints on wide variety of substrate (porous & non-porous)
  • low cost of equipment & consumables
  • low maintenance
57
Q

disadvantages of flexography (5)

A
  • expensive set up cost
  • cost of printing plates very high (but last for millions of print runs)
  • large amount of substrate needed to set up job
  • excess material may be wasted
  • time consuming to change for any alterations to print content
58
Q

advantages of screen printing (2)

A
  • good for short print runs

- can print on absorbent surfaces (eg fabric)

59
Q

disadvantages of screen printing (2)

A
  • slow

- not as high print quality as other methods

60
Q

advantages of digital printing (3)

A
  • allows for mass customisation
  • fast
  • highly detailed prints
61
Q

disadvantages of digital printing (2)

A
  • more expensive for longer print runs (usually fixed price per print)
  • can’t print lighter colours (eg white) on dark substrate

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