Metal Finishes Flashcards
Metal finishing
Which metals have an oxide layer and what does it do
What do steels have and why is it bad
Most metals except steels have oxide layer, provides some resistance against environmental effects
Eg Cu has red colour. Over time greenish protective oxide layer forms
Steels have oxide layer which is porous and leads to rusting
Porous oxide layer allows moisture to penetrate leading to layers of crumbling rust
Cellulose and acrylic paints
What does it provide - 3 things
What do specialist paints provide
What metals is it used on
Application:
What is done to metal b4 applying and why- 2 things
What primer is used and what is used after the primer
Provides colour and textured finish
Barrier against corrosion
Specialist paints provide texture or special effect eg pearlescence
Mainly used on low cost metals eg steel
Surface of metal is cleaned and degreased, ensures primer coat has good surface to grip to
Red oxide primer used, followed by an undercoat in a similar colour to final coat
Brush or spray used
Electroplating
What 3 things does it provide
What metals does it do, 7
Process? Like electrolysis
Provides protective layer, more hard-wearing finish and enhanced aesthetics
Metals included silver, good, zinc, copper, tin
Product and donor material placed in container with electrolyte solution. DC applied, p. attracts donor metal and p. Is electroplated
Polymer dip coating
What is it used on, what’s similar about those products
Process:
What is done to the metal before dipping
What does the tank have boating through it to ensure even coat
After what is done to ensure even coat more
Used on wire coat hangers, kitchen dish drainers, dishwasher racks, outdoor play equipment frames (so very thin tubular products)
Metal product heated to 230. Hot product dipped into tank of fine polymer powder,
has air blowing through it to provide even coating
The heated product then melts the polymer powder over the product, then air cooled = set evenly
Metaldip coating
What does it mainly provide
What does tin playing usually applied to and what does it give
Where is zinc plating used
What is the first protective layer on cars
Process:
What is it dipped into
Provide barrier against corrosion
Tin plating provides non corrosive coating to food cans
Zinc plating, used in industrial and agricultural p. Eg beams, gates, animal pens.
First protective layer on car bodies is low carbon steel
Dipped into tank of molten metal (of donor metal)
Metal must be cleaned and degreased
Zinc plating = galvanising
Powder coating
What does it provide protection from and what other stuff does it give
Why is it better than Paint
Where is it used
What is charged positively and negatively and why
What is it sprayed through
What happens after spraying and why
Protect from corrosion + aesthetic appeal, more hard-wearing than paint
Washing machine, dishwashers, grudges, metal gates, fencing - remember this
The p. to be coated is statically charged (-). Thermoset polymer is + charged. Then sprayed through air gun
Use of charge = strong attraction
P. Then baked in oxen, heat melts powder= even coating
Metal vanishing
What 2 things does it do
What metals is it used on
What 2 things happens b4 applying
Protects metal, allows colour to show through
Used on Al, brass, copper
Metal is polished to a shine, any surface grease removed
Varnish applied by spray or brush
Sealants OA (only a level)
Name 1 property of it
What does it protect a polished surface from, 2
What industry is it used in, and what does it protect the products from
How is it applied
How long is it left to cure for
Tough polymer based sealant
Protect polished surface from decay and tarnishing
Used in automotive industry against effect of weathering, road salts and insect attack
Applied with cloth to produce a film, cured for 15 minutes. Then buffed with a cloth to shine.
Preservatives AO
Is it temporary or permanent
How long does it last
What is it used on and why (what does it stop showing up on the surface)
How is it applied, 3 ways
If used on machine beds, what ADV does it provide
Provides TEMPORARY in process or final post process, MED to LONG term protection for metal surfaces
Used on moulds and dies to prevent fingerprints, condensation of minor atmospheric corrosion
Applied by wiping with cloth, spray or immersion
Silicon sealants can be classed as preservatives
Can be used on machine beds to provide smooth, snag free surface, allowed material to be pushed across bed more easily
Anodising AO - hard one
What 1 metal is it used on
What does it enhance on the metal
Where is it used
What is the positive anode and the negative cathode in this process
As the current flows, what happens that results in an anodised finish
After, what can be applied to seal it + what else does it do
Used on AL, enhance natural oxide layer = increased hardened & toughness
Can provide colour
Used in outer casing of torch, external hard drive covers, phone casing.
Current pdf through SO4 acid electrolyte from part to be anodised to negative cathode. As current flows, the AL oxide layer builds up
Then can be finished with clear lacquer or varnish to seal it + provide protection against scratches
Cathodic protection
What is a natural voltage and what is an electrochemical cell
Give an example of an electrochemical cell
What does cathodic protection control
What is the sacrificial metal
What is the main use
Metals have a natural voltage. When 2 metals joined in water, there is an electrochemical cell which means one of the metals will corrode.
Current flows from anode (more corroding material) to cathode (less corroding)
Eg 2 Al sheets held with brass screws in rain = electrochemical cell
N
Cathodic protection controls this rate of corrosion
The anode is a sacrificial metal, more easily corroded, then cathode is the metal u want to keep. So sacrificial metal corrodes while base metal is protected
Mainly used to protect steel structures burried in soil or water, eg pipelines, hulls, jetties and offshore platforms
2 methods of cathodic protection
Impressed current:
What is the component to be protected connected to
Where does DC flow from and to
Give eg of how a pipeline is protected
Sacrificial anodes:
Is a more or less electrochemically active is used?
How is it used
Impressed current:
Component to be protected is connected to power supply
The impressed DC flows from inert electrode through water to component
Eg pipelines recieved recieved DC from electrode buried in ground. Pipe = anode, electrode = cathode. Cathode corrodes over time and this is monitored so pipeline remains in tact
Sacrificial anodes:
More basic, it’s sacrificial metal to protect other metal. More electrochemically active metal wrapped around our joined to is active metal = resistance against corrosion.
On large structures, sacrificial metal monitored for corrosion and replaced.
