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DT - Technical Principles > 19. The use of finishes > Flashcards

19. The use of finishes Flashcards

1
Q

Why are finishes used?

A
  • prevent material from absorbing moisture
  • protect against decay or corrosion
  • protect against insect attack
  • enhance the appearance of the final product
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2
Q

What are the paper and board finishing processes?

A
  • lamination via encapsulation
  • lamination via surface coating
  • embossing
  • debossing
  • varnishing
    • UV varnishing
    • spot varnishing
  • foil blocking
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3
Q

Why are paper and board finishing processes used?

A
  • provide protection for the material
  • enhance appearance
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4
Q

What is lamination via encapsulation?

A
  • sheet of paper is encapsulated by a polymer pouch or film roll
  • desktop laminator
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5
Q

What is lamination via surface coating?

A
  • liquid lamination (for signage)
  • film lamination (for menu cards)
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6
Q

What is embossing?

A
  • creates a raised design on the surface of paper or card
  • gives a visual and tactile effect
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7
Q

What is debossing?

A

produces an imprinted depression that sits below the surface of paper or cars

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8
Q

What is varnishing?

A
  • clear, non-pigmented ink used on pre-coated papers and boards to enhance the colour
  • offers some protection against dirt, fingerprints and water
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9
Q

What is UV varnishing?

A
  • provides very smooth finish
  • usually high gloss or matt
  • abrasion and chemical resistant
  • applied to a sheet via a set of rollers, then passed under a UV light to cure
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10
Q

What is spot varnishing?

A
  • applied in specific areas or spots
    • rather than to the whole surface area
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11
Q

What is foil blocking?

A
  • heat and pressure applied to metallic paper (foil) to create areas of depth and texture
  • add aesthetic impact
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12
Q

Why are paper and board printing processes used?

A
  • colours, text and images can provide aesthetic appeal
  • information such as barcodes, safety warnings and product ingredients can be printed to communicate specific data to the consumer/retailer
  • printing processes often use the term ‘substrate’
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13
Q

What is the substrate?

A

the material on to which the print ink is applied

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14
Q

What are the paper and board printing processes?

A
  • screen printing
  • flexographic printing
  • offset lithographic printing
  • digital printing
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15
Q

What is screen printing?

A
  • can be carried out in a workshop with minimal set up costs due to use of basic screens and printing inks
  • screen has open areas for the ink to pass through
  • different screen required for each colour
  • quite a slow process with a reasonably high cost per product
  • used for small print runs of items such as posters, display boards and textile T-shirts
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16
Q

What is flexographic printing?

A
  • use a four colour process (cyan, magenta, yellow and key black (CMYK))
  • four colours are printed on top of one another in various quantities on to the substrate surface to create the print colour required
  • colours must line up exactly to ensure a non-blurry image
  • simple process
  • least expensive due to fast drying water based inks
  • used for newspapers, comics, catalogues, folding packaging cartons, labels, carrier bags and continuous patter products such as wallpaper and gift wrap
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17
Q

What are the advantages of flexographic printing?

A
  • high print speed
  • ideally suited to long runs
  • prints on a wide variety of substrate materials
  • low cost of equipment and consumables
  • low maintenance
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18
Q

What are the disadvantages of flexographic printing?

A
  • cot of the printing plates is relatively high, but last for millions of print runs
  • takes a large amount of substrate to set up the job, so excess material may be wasted
  • time consuming to change for any alterations to the print content
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19
Q

What is offset lithographic printing?

A
  • extremely versatile printing process
  • capable of producing one colour (single roller)
  • five colours (CMYK plus additional metallic colour on a five roller machine)
  • ten feature machine (CMYK, metallic, varnishing, spot varnishing and duplex (both sides printed) on a ten roller machine)
  • used for printing medium and long print runs of books, business forms and documentation, magazines, posters and packaging
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20
Q

What are the advantages of offset lithographic printing?

A
  • consistently high image quality
  • suited to higher quality print runs of 1,000 or more
  • quick and easy production of printing plates
  • long life of printing plates because they only come into contact with the printing blanket, which is softer and less abrasive than the substrate
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21
Q

What are the disadvantages of offset lithographic printing?

A

expensive set up and running costs for small quantities

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22
Q

What is digital printing?

A
  • widely utilised resource for printing products, due to its speed and efficiency
  • digital printers produce full colour, highly detailed print runs with option of different designs on each page, both front and reverse sides
  • can be used for both low and high volume print runs
  • very popular for printing promotional materials such as business flyers and business cards
  • ideal for mass customisation, due to fast drying inks
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23
Q

What is polymer finishing?

A

polymers are self-finishing materials as they require no additional finishing process once manufactured

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24
Q

What do polymer finishes do?

A
  • enhance aesthetics
  • improve product function
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25
Q

What are the polymer finishes?

A
  • overmouldings
  • acrylic spray paints
  • addition of pigments
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26
Q

What is overmoulding?

A
  • moulding a second polymer over specific parts of a product
  • TPE (thermoplastic elastomer) is often used
  • provide areas of grip or texture
  • can highlight different colours for different component parts on products
  • two methods
    • two injection moulding moulds
    • twin-shot injection moulding
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27
Q

What is two injection moulding moulds?

A
  • one mould for the product
  • one mould for the grip areas
  • product is injection moulded, then placed in second mould where overmoulding polymer is injection moulded onto the body
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28
Q

What is twin-shot injection moulding?

A
  • injection moulding machine has a mould designed to product the product in one cycle
  • mould has two sepaprate component cavities, and can be rotated 180 degrees so they line up with the twin injection points
  • main product part is created in first mould cavity
  • mould opens slightly and rotates 180 degrees to secondary position
  • mould closes and second injection applies the overmould
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29
Q

What are acrylic spray paints?

A
  • enhance aesthetics
  • fast drying
  • water soluble paint that becomes water resistant when dry
  • can provide additional protection against effects of UV light and weathering
  • often used for mass customisation
  • used in automotive industry
  • could be pigmented, but impractical and not cost effective for manufacturer
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30
Q

What is adding pigments?

A
  • provides colour
  • pigment particles can be added during manufacturing process or during manufacture of polymer stock form
  • smart pigments can be added the same way, producing ready finished smart polymer products
  • pigments can be added to gel coats when laying up GRP
  • can be used for kitchen chopping boards to identify different ones for different foods
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31
Q

What is metal finishing?

A
  • most metals have oxide layer (except steels), which provides barrier against environmental effects
  • steels (not stainless steel) have an oxide layer, which is porous, allowing moisture to penetrate the metal, leading to rust
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32
Q

What are the metal finishes?

A
  • cellulose and acrylic paints
  • electroplating
  • polymer dip coating
  • metal dip coating
  • powder coating
  • metal varnishing
  • sealants
  • preservatives
  • anodising
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33
Q

What are cellulose and acrylic paints?

A
  • paints primarily used on low cost metals such as steel
  • surface of metal is cleaned and degreased, which ensures the primer coat has a sound surface to ‘key’ / grip to
  • red oxide primer often used, followed by undercoat in a similar colour to the final top coats
  • paints can be applied by brush or spray
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34
Q

What is the purpose of cellulose and acrylic paints?

A
  • provide colour and textured finish
  • provide barrier against corrosion
  • specialist paints provide texture or special graphic effects such as pearlescence
35
Q

What is electroplating?

A
  • metals for electroplating include silver, gold, zinc, copper and tin
  • product and donor material are placed in a container with an electrolyte solution
  • as direct current is applied, the product attracts the donor metal and the product is electroplated
36
Q

What is the purpose of electroplating?

A
  • protective layer
  • more hardwearing finish
  • enhanced aesthetics
37
Q

What is polymer dip coating?

A
  • metal product is heated to approx. 230 degrees
  • then dipped into a tank of fine polymer powder, which has air blowing through it to provide an even coating on the product
  • the retained heat from the product melts the polymer powder over the product
  • then air cooled to allow the coating to set evenly
38
Q

What is the purpose of polymer dip coating?

A

used on products such as wire coat hangers, kitchen dish drainers, coat hooks, dishwasher racks and outdoor play equipment

39
Q

What is metal dip coating?

A
  • metals are coated by dipping the product into a tank of molten plating metal (donor metal)
  • metals must be clean and degreased
  • tin plating
    • pass sheets of steel through a tank of molten tin at approx. 320 degrees
  • zinc plating (galvanising)
    • dipping steel into molten zinc at approx. 460 degrees
40
Q

What is the purpose of metal dip coating?

A
  • provides barrier against corrosion
  • tin plating is often used to provide a non-corrosive coating to food cans
  • zinc plating is used for many industrial and agricultural applications
    • beams, gates and animal pens
  • zinc plating is also used as the first protective layer in car bodies made from low carbon steel
41
Q

What is powder coating?

A
  • product to be coated is statically charged (negatively)
  • thermoset polymer resin (positively charged) is then sprayed through an airgun
  • the use of charge results in a strong attraction between the powder and product
  • the product is then baked in an oven
  • the heat melts the powder over the product to give an even coating
42
Q

What is the purpose of powder coating?

A
  • protection from corrosion
  • aesthetic appeal
  • more hardwearing than paint
  • used on washing machine bodies and refrigerator bodies, metal gates, fencing and railings
43
Q

What is metal varnishing?

A
  • metal is polished to a shine and any surface grease removed
  • varnish then applied by either a spray or with a fine brush
44
Q

What is the purpose of metal varnishing?

A
  • protects metal
  • allows colour of base metal to show through
  • used on aluminium, brass and copper
45
Q

What are sealants?

A
  • sealant applied with a cloth or machine pad to produce a film
  • film then allowed to cure for up to 15 mins
  • then buffed with a cloth to a shine
46
Q

What is the purpose of sealants?

A
  • tough polymer-based sealant coatings to protect polished surfaces from decay and tarnishing
  • often used in automotive industry against effects of weathering, road salts and insect attack
47
Q

What are preservatives?

A
  • applied by wiping on with a cloth, spray or immersion of the product
  • silicon sealants can also be classed as preservatives
  • can be used on machine bed to provide a smooth, snag-free surface to allow materials to be pushed across the bed more easily and safely
48
Q

What is the purpose of preservatives?

A
  • can provide temporary in-process or final post-processing, medium to long-term protection for metal surfaces
  • often used on moulds and dies for preventing fingerprints showing on surfaces, minor atmospheric corrosion or condensation build up
49
Q

What is anodising?

A
  • electric current passes through the sulphuric acid electrolyte solution from the part to be treated to a negative cathode
  • as the current flows from the part to be treated (positive anode) to the negative cathode, the aluminium oxide layer builds up on the treated part, producing the anodised finish
  • anodised products can then be finished with a clear lacquer or varnish to seal the finish and provide further protection against surface scratches
50
Q

What is the purpose of anodising?

A
  • commonly used for aluminium products to enhance the natural oxide layer, resulting in increased hardness and toughness
  • can also provide colour
  • used in outer casings of torches, external hard drive covers, and casings for mobile phones or digital music players
51
Q

What do all metals have?

A

a natural voltage

52
Q

What happens when two different metals join, and if water is present?

A
  • there is an electrical current
  • if water present at the join, this results in an electrochemical cell and one of the metals will corrode
53
Q

What is the reaction?

A

current flow through the water from the anode (more actively corroding metal) to the cathode (less actively corroding metal)

54
Q

What is cathodic protection?

A
  • method used to control the rate of corrosion
  • makes the metal the cathode of an electrochemical cell
  • the anode is a sacrificial metal which is more easily corroded
  • the anode corrodes while the base metal is protected
55
Q

What is the main use of cathodic protection?

A
  • to protect steel structures buried in soil or immersed in water
    • e.g. pipelines, ship hulls, jetties and offshore platforms
56
Q

What are the two methods of cathodic protection?

A
  • impressed current
  • sacrificial anodes
57
Q

What is the impressed current method?

A
  • component to be protected is connected to an electrical power supply
  • the impressed direct current flows from an inert electrode through any liquid to the component to be protected
58
Q

Give an example of how impressed current works.

A
  • a buried pipeline receives direct current from an electrode buried in the ground
  • the pipe becomes the anode
  • the electrode is the cathode
  • the cathode corrodes over time and such corrosion is monitored so the pipeline stays intact
59
Q

What is the sacrificial anodes method?

A
  • more basic because it uses a sacrificial metal to protect the metal product of value
  • a more electrochemically active metal is wrapped around or joined to the less active metal to provide resistance to corrosion
  • on large structures, the sacrificial metal is monitored for signs of corrosion and replaced when the base metal is no longer protecteed
60
Q

What is the purpose of finishing wood?

A
  • prevent absorption of moisture
  • protect against decay
  • protect against inset attack
  • enhance appearance of final product
61
Q

How does natural wood degrade?

A
  • wet rot
  • dry rot
  • insect attack
62
Q

What is wet rot?

A
  • alternating wetness and dryness means moisture is absorbed
  • though the surface may dry out, moisture remains below the surface
  • leads to breaking down of the wood fibres
  • fungus spreads through
  • wood becomes soft, wet and crumbly
63
Q

What is dry rot?

A
  • different, fast spreading fungus causes dry rot
  • quickly turns wood into a dry, soft, powdery state
64
Q

What is insect attack?

A
  • furniture beetle (woodworm) attacks softwood and hardwood
  • deathwatch beetle attacks hardwood
  • both lay their eggs in cracks in the wood
  • the hatched larvae eat into the wood, creating tunnels
  • when the beetle forms, it eats its way out of the wood via a flight hole
65
Q

What should you ensure before applying a wood finish?

A
  • make the surfaces smooth
    • by planing and/or sanding with glass paper in the direction of the grain using progressively finer grades
  • remove all dust with a cloth before the finish is applied
66
Q

What are the methods of wood finishing?

A
  • polyurethane varnish / acrylic varnish
  • water based paints
  • stains
  • colour wash
  • wax
  • yacht varnish
  • danish oil
  • teak oil
  • pressure treating
67
Q

How is polyurethane varnish / acrylic varnish applied?

A
  • available in gloss, satin and matt, clear or colours
  • apply a thin coat with a brush in the direction of the grain
  • several thin coats can be applied, rubbing down between coats with fine grade glass paper
68
Q

How does polyurethane varnish / acrylic varnish enhance appearance or prevent decay?

A
  • provides a hard, tough, heatproof, waterproof finish
  • clear finish allows the grain of the wood to be seen through the finish
69
Q

How are water based paints applied?

A
  • available in gloss, satin, matt and metallic effects
  • applied with a brush, roller or spray
  • wood knots should be treated with knotting solution to prevent the resin oozing out and spoiling the finish
  • the surface should then be primed and an undercoat applied prior to the paint finish
70
Q

How do water based paints enhance appearance or prevent decay?

A
  • paint provides both protection and colour
  • can be applied for both indoor and outdoor use
  • predominantly used for softwoods
  • paint makes surfaces more aesthetically pleasing, tougher, harder and resistant to moisture
71
Q

How are stains applied?

A
  • available in many different colours and types
  • applied with a brush, roller or spray
  • surfaces should be grease free prior to application
72
Q

How do stains enhance appearance of prevent decay?

A
  • help colour and enhance the grain
  • can be used to colour an inexpensive wood to make it look more expensive, or to add colour
  • do not have any specific protective properties
73
Q

How is a colour wash applied?

A
  • available in many different colours
  • applied with a wet sponge
74
Q

How do colour washes enahnce appearance or prevent decay?

A
  • used to help colour the wood to make it more aesthetically pleasing, or to add a vintage style
  • allows the grain to show
75
Q

How is wax applied?

A
  • available in clear and coloured waxes for indoor use
  • applied with a brush or a stockinet cloth
  • then once dry, buffed with a clean lint free cloth
76
Q

How does wax enhance appearance or prevent decay?

A
  • can be buffed to provide a high gloss finish
  • increases surface hardness and toughness
  • clear finish allows grain to be seen
77
Q

How is yacht varnish applied?

A
  • available in high gloss and satin
  • applied with a brush or sprayed directly on to the wood
78
Q

How does yacht varnish enhance appearance or prevent decay?

A
  • suitable for woods that are outside all year round, such as doors, window frames or boat parts
  • increases toughness, hardness and weather resistance
79
Q

How is Danish oil applied?

A
  • available in clear or colour tints
  • apply with a lint free cloth
  • rub the oil into the surface of the wood in the direction of the grain
  • leave to absorb for 5 mins, then rub away excess with a clean cloth
  • lightly sand or rub with wire wool to open up the grain between coats
80
Q

How does Danish oil enhance appearance or prevent decay?

A
  • maintains natural appearance of timber
  • soaks into the wood and enhances the grain
  • not a hardwearing finish
  • regular application and subsequent coats build up a matt, water resistant finish
81
Q

How is teak oil applied?

A
  • available in clear tint
  • apply with a lint free cloth
  • rub the oil into the surface if the wood in the direction of the grain
  • leave to absorb for 5 mins, then rub away excess with a clean cloth
  • used for naturally oily woods
82
Q

How does teak oil enhance appearance or prevent decay?

A
  • mainly used for outdoor wood products to improve weather resistance and resistance to fungal and insect attack
  • aesthetically pleasing as grain is enhanced
83
Q

How is wood pressure treated?

A
  • wood placed in pressure vessel containing a solution consisting of copper sulphate and other preserving salts
  • vacuum and pressure are controlled to force the preservative deep into the fibres of the wood
  • the wood is then steam dried
84
Q

How does pressure treating enhance appearance or prevent decay?

A
  • helps protect wood for up to 50 years from rot, insect and fungal attack and weathering
  • suitable for products such as decking, overhead cable poles, harbour or bridge construction

DT - Technical Principles (29 decks)

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