Download - To be able to identify and select a variety of different finishes

- To be able to identify and select a variety of different finishes techniques for wood, metal and
plastic
Why are they needed?
- To stop the decay, corrosion or degrade of a material
- Wood will decay through wet/dry rot or insect attack
- Metals will corrode through rust or electrochemical or chemical attack
- Electrochemical occurs when two joined metals react with each other to
create a natural voltage. This voltage in the presence of water can cause
corrosion
- Plastic will degrade over time and expose to a number of elements such
as UV and oxygen
- To be able to identify and select a variety of different finishes techniques for wood, metal and
plastic
Finishes
As well as changing the aesthetics of a product finishes are used to:
- Protect the material against corrosion
- Make the product water repellent
- Improve its resistance to wear and fatigue
- Improve its ability to reflect or absorb heat
- Improve its ability to insulate against heat or electricity
- To be able to identify and select a variety of different finishes techniques for wood, metal and
plastic
Wood paint
- Before paints are applied the wood will need to be prepared be by sanding it down, cleaning it and
treating any knots so that the finish is attach to it
- The use of a primer is used to prevent other layers absorbing into the wood
- As undercoat will help additional layers and a top coat attached better as well as give a better aesthetic
finish
- Sanding down between layers will also help give a quality finish
- Oil-based paints are hardwearing and non porous and so is used inside and outside for coating windows
and door frames
- Polyurethane paints are good for coating products such as toys. They are extremely hardwearing, tough
and stretch-resistant. Polyurethane vanishes are also used if the wood grain is required
- Yacht varnish is more appropriately for outdoor products as it is not affected by sunlight (whereas
polyurethane varnish is)
- Two-stage stain and varnish will both colour and protect wood. They can be used internally and externally.
The first layer will contain a colour and will stain the wood. The second will be a varnish which brings out a
wood grain under the coloured wood
- To be able to identify and select a variety of different finishes techniques for wood, metal and
plastic
Wood preservatives
- There are 4 many types which can all be applied by brush, dipping, spraying or pressure
treatment
- Creosote, Water-soluble, organic solvents and tantalising
Creosote
- Creosote is a tar-oil based preservation
- It is a traditional method but is very damaging to the environment
- It has now been banned and water-based alternatives are used
- These need to be more regularly applied in comparison
Tantalising
- This is when a solution of copper sulphate and other salts are impregnated into a timber
usually a pressure vessel.
- The wood is first dried to remove moisture
- Once in the vessel the pressure forces the minerals into the structure of the wood
- The wood is then steam dried before being used
- Timber treated like this can last up to 50 years
- To be able to identify and select a variety of different finishes techniques for wood, metal and
plastic
Metal finishes
- Natural barriers
- Ferrous metals will rust if moisture is present
-A number of metals will oxidise if damaged or stretched – this protects the metal from further damage
-Stainless steel has a natural barrier which prevents oxidisation or rust
- Other ferrous metals can go though blueing. This is heating them to 300C plus and then quenching them in
oil
- This creates a fine oxide layer
Electroplating
- This is a method of plating one metal with another
- It uses an electrochemical process that allows ions from a coating material to form on a base material to
create a coated protective layer
- This include chrome plating and silver plating
Anodising
- Aluminium can be anodised to give it s more durable and scratch resistant finish
- This is done in a similar way to electroplating but a lead is the coating layer
- The aluminium is finally sealed afterwards with a lacquer
- To be able to identify and select a variety of different finishes techniques for wood, metal and
plastic
- Dipping and Spraying
- Metals can be dipping or sprayed with a material coating when heated
- Galvanising (zinc plating) is done in this way by dipping steel into molten zinc (450-600C)
- Tin plating is also done in this way with steel (315-320C)
- Enamelling
- This is a process of coating metal in a fine glass powder
- This is then heating in a kiln so that the glass liquefies and forms a very hard glossy coating on the metal
- This is also heat and scratch resistance
- Titanium coating
- Due to titanium being so hardwearing it is used to coat tool and kitchen equipment
- This is done via two methods
- Plasma spray
- This uses a super heated inert gas (formed by an electrical arc) to melt fine titanium powder onto a
material
- Physical vapour deposition
- This uses a vacuum chamber which has the product placed in it. The coating material is evaporated by
intense heat. The atoms of the coating materials are then placed into the chamber and deposit onto the
surface of the product.
- To be able to identify and select a variety of different finishes techniques for wood, metal and
plastic
Metal finishes
- Painting
- As with woods metals have to be prepared before paint is applied
- Paraffin-based liquids are use to degrease the metal before it is primed.
- Layers of primer, undercoat and topcoat as applied similar to wood
- The paint can be brush, rolled or sprayed on
- Steel products like car bodies are forgot galvanising before paint to stop corrosion.
- Some specialist paints or lacquer can be used directing onto metal without any preparation
- Electrostatic coating
- This is a system which creates an electrostatic charge between the paint and the product
-This means that the paint is attracted to the surface of the metal product so make a secure bond and quality finish
-Powder coating
- This is a method with statically charge powder particles and then sprays them via an airgun onto the metal product
-This give an even coat like electrostatic coating
- The product is then placed into an oven or kiln which will bake the powder into the product and create a hard, tough finish
-Plastic coating
- Plastic dip coating works in the opposite way to powder coating
- The metal product is heated up in a oven or kiln (before any finish it applied)
- It is then dipped into a fluidised bath of plastic powder
- A coat of powder will attach and melt to the surface of the heated product and will cure are the product cools to give a hard and smooth finish
- To be able to identify and select a variety of different finishes techniques for wood, metal and
plastic
Plastic finishes
Self-finished
-Plastics are known as self-finishing
- This means that when they are processed into product the moulding and machine used is so high quality they would give a quality surface finish
-Self-coloured
- Plastic can be pigmented to have different colours
- This would be done during the manufacture of the plastic product
Texture
- Due to the design of some moulds texture can also be added to plastics
- The use of TPE will also have a natural texture to them which is why they are so good for grips and handles
Polymer coating
- In a similar way to titanium polymer can use physical vapour deposition to coat product with plastic. This is done with PMMA for glass lenses to
make them harder
Overmoulding
-This is a process which allows second polymers to be injected over the top of another (plastic component)
- This is used add a rubber grip to toothbrushes. The make body is formed first and then the rubber grip is injected in afterwards (and partly
embedded in to the body)
-https://www.youtube.com/watch?v=qGSiyPUI0fU
Twinshot injection moulding
- This is similar to overmoulding but two injectors are used at the same time to inject two different polymers into a single mould
-This is used in some phone cases and Ipod cases.
-https://www.youtube.com/watch?v=a3rLTHoHRFw