Product Design (Finishes)
Overview of Finishes
- Created by: Luke Bisset
- Created on: 09-04-12 22:08
Finishes
This means applying a finish to the surfaces of materials to -
- To protect the material from corrosion
- Make the product water repellent
- Improve resistance to wear & fatigue
- Improve ability to absorb or reflect heat
- Improve ability to insulate against heat or electricity
It also means applying a finish to -
- To enhance the appearance of the surfaces (eg) applying teak oil to a patio chair to bring out the grain
Self Finishing Materials
Self-finishing/coloured materials (No finishing needed) –
- Some materials, mainly polymers do not need the application of a finish
- A polypropylene chair seat is textured from the pattern on the inside of the injection moulding mould
- Polythene washing up bowl is the same colour all through the material because that is the colour of the polythene
Cutting Processes
- Saws & other machines produce rough edges (burrs) which have to be removed.
- Modern methods of cutting materials – laser & plasma cutting do not produce rough edges (burrs)
Finishes on metals – Natural Barriers
- Oxides exist on most metals to form a protective layer
- Iron oxide is porous so steel carries on rusting when it becomes wet
- Stainless steel does not rust
- Steel can be ‘blued’ by heating up to 300°C and then quenching in oil
- This gives a fine oxide layer which protects the steel
Finishes on metals – Applied Barriers
Steels in particular need protecting from corrosion
Finishes can be applied by:-
- Brushing
- Rolling
- Spraying
- Dipping
- Electroplating
Electroplating
- Ions from the coating material form on the base material
- E.g. Chromium is used to enhance & protect car parts, bathroom fittings, and kitchen equipment
- Gold – Silver – Tin – Zinc & Copper can all be used as coatings
Anodising on aluminium
- Anodising makes aluminium more durable and resistant to scratches
- An electric current passing through the electrolyte builds up a tough oxide layer
- Can be coloured with dyes then lacquered
Dipping and Spraying & Zinc Plating - Galvanising
Dipping and Spraying -
- Metals can be coated with other metals
- Base metal must be clean - washed in detergent, then pickled, then rinsed
Zinc Plating - Galvanising -
- Steel is dipped in molten zinc 450-460°C
- Usually the first protective layer for car bodies
Enamelling & Tin plating
Enamelling -
- Finely ground glass is sprayed onto a metal product – gas cooker, steel bath.
- This is fired in a kiln
- This gives a scratch & heat proof surface but it can chip
- Glass enamels can be fused onto jewellery to give an attractive & colourful finish
Tin Plating -
- Steel sheets are passed through baths of molten tin at 315-320°C
- Used in manufacture of food cans
Painting
- Surfaces must be clean & free of rust & oil
- Car bodies are first galvanised
- Primer coat keys into the metal surface
- Then an undercoat to give a good colour & smooth base for the top coat
- Then a top coat is applied
- Car bodies also have a hard coat of lacquer
- Spraying gives a better quality finish than brushing
Powder coating
- Positively charged powder is sprayed onto a negatively charged product
- This gives a very strong bond
- Product is then baked in an oven giving a harder & tougher finish than conventional paints
- Used on ‘white goods’, gates & fences
- No solvents or propellants so environmentally sound
Plastic dip coating
- The product is heated to 230°C
- It is then dipped into a fine dust of fluidized polythene
- Heat from the product melts the polythene into an even plastic coat over the product
Injection moulding –
- A thicker layer of plastic coating can be applied by injection moulding
- This is used on the handles of tools
- Gives a better grip & electrical insulation
Finishes on woods
- Unprotected wood expands & contracts when it absorbs water then dries
- This causes cracks & splits
- Also resins that hold the cells together break down weakening the wood
- Bacteria & fungi also cause the wood to rot & decay
- Hardwoods are generally more resistant to the environment than softwoods
- Teak contains oil helping to repel rain
Finishes on woods – Applied barriers
Paints
- As for metals
- Primer – Undercoat – Top coat
- Rub down with glass paper between coats
- Oil based paints are hard wearing, non - porous and available in a range of colours
- Polyurethane paints are used on toys, because they are harder wearing, tougher & scratch resistant
Finishes on woods – Applied barriers Continued...
Where natural grain of the wood are to be visible varnishes & polishes are used:-
- Polyurethane varnish brush applied, tough, hardwearing, gloss, matt, satin
- Sanding sealer – cloth wad applied light, clear polish
- Teak oil – cloth wad applied can be used on all wood, indoors & out
- Wax polish – applied on top of other polishes for a final polish
Wood Preservatives
Wood Preservatives
3 main groups
- Tar- oil derivatives – creosote
- Water soluble preservatives
- Organic solvent preservatives
All can be applied by:-
- Brushing
- Dipping
- Spraying
Water soluble preservatives & Tanalising
Water soluble preservatives –
- These solvents come in a wide variety of colours
- Need to maintained more regularly
Tanalising –
- Wood is pressure treated in large tanks
- Dry wood is impregnated with copper sulphate solution under pressure for deep penetration – not just on the surface
- Wood is then steam dried
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