1.5 Metal Finishing Flashcards
What is the simmilarity between copper and stainless steel when it comes to oxidising
A oxide layer over the copper and stainless steel forms and protects the copper and stainless steel from corrosion
What is the difference between rusting and passivation and give an example metal for both
Rusting:
Iron/Steel - A slow and continuous rate of oxidation with an oxide layer that continues to crumble and flake away.
Passivation:
Aluminium - An initially rapid oxidation produces an oxide layer which helps to prevent further oxidation.
What metal finishing does “Low cost but slow so only suitable for one-offs & small batches. Smooth or textured (hammered) effect” apply to
Brush painting
What metal finishing does “Basic equipment so suitable for one-off & batch production. Generally acrylic based nowadays. Matt, satin and gloss effects” apply to
Spray painting
Outline two ways that painting an iron railing will change its characteristics.
Providing a colour change and providing protection from corrosion
What are the 3 prep stages and 1 application stage for brush painting
Remove any loose rust, Stabilise rust with a chemical treatment, Clean & degrease
Apply the paint in 1-2 coats
Explain why a primer coat is required if a metal part is to be spray painted.
It creates a smooth even surface to stick to the top coat
Outline two ways that spraying a wheel will change its characteristics.
Change colour, Corrosion barrier
What are the 3 application steps of spray painting
Primer, Undercoat, Topcoat
What metal finishing does “Basic equipment so suitable for one-off & batch production. Limited control over the variables that affect output quality. Adhered layer up to 1mm thick.” apply to
Polymer powder dip coatiwng
What metal finishing does “Expensive and time consuming but suitable for batch production. Chemically bonded non-metallic layer. Hazardous chemicals” apply to
Electroplating
Outline two or more ways that chrome (chromium) plating a metal part will change its characteristics.
Provide water protection
To give a more shiny finish
Give examples of electroplated parts
Teapot, Kitchen taps, wall heater
Outline two ways that polymer dip coating a steel part will change its characteristics.
Provide a colour finish(Limited finish)
Provide a therm and electrically insulating layer
Provide a protective plastic layer
What are the 4 steps in polymer powder dip coating
Part is heated to 250oC in Thermoplastic powder e.g. PE is fluidised (air is forced through it)
The part is moved around to help ensure an even coverage is achieved
Heat from the part melts polymer onto its surface
A plastic layer forms over the metal, A smooth, continuous coating is achieved
Give examples of polymer dip coated parts:
Wire hangers, outdoor equipment frames
Outline one way that zinc plating a steel part will change its characteristics.
Provide a corrosion barrier
What metal finishing does “Cost effective for batch production. Chemically bonded layer. Highly functional finish.” apply to
Hot metal plating (Galvanising(With zinc))
Give examples of galvanised steel parts:
Hinges, clamps, railings
What metal finishing does “Upfront costs but suitable for batch production. Less wastage and more durable than a spray painted finish but less colour choices achievable” apply to
Polymer powder spray coating
Outline two ways that electrostatically powder spray coating a steel part will change its characteristics.
Provide a protective plastic layer
Provide a colour layer
Give examples of electrostatically powder spray coated parts
Dishwasher bodies, fridge bodies
What part (The nozzle or the product) is grounded to earth and with what charge in polymer powder spray coating
Product is grounded at -ve
What is the process of polymer powder spray coating
The electrode nozzle sprays the grounded product with a thermoset powder and the powder coated part is then placed into an oven to melt the plastic particles over the part and leave a even finish
What are the 3 metal clear finishes
Varnishes/lacquers, Sealants, Preservatives
What metal finishing process does “Low cost solutions suitable for one-offs. A degree of protection is achieved. Generally sprayed application but can be brushed or wiped on” apply to
Clear finishes
What clear metal finish provides A clear protective finish.
Varnishes/lacquers
What clear metal finish provides Chemical resistance, water-beading action (hydrophobic) and added shine.
Sealants
What clear metal finish Helps prevent fingerprints, corrosion and condensation on surfaces. Can also help reduce friction on moving parts/surfaces.
Preservatives
What metal finish does “Low cost solutions suitable for one-offs. A degree of protection is achieved. Generally sprayed application but can be brushed or wiped on” apply to
clear finishes
What metal finish does “Expensive and time consuming but suitable for batch production. Chemically bonded metallic layer. Hazardous chemical” apply to
Anodising
Outline two ways that anodising an aluminium part will change its characteristics.
Increasing hardness and toughness
Providing a colour to the part
What are the 4 steps for anodising
Treated part
Porous oxide layer
Added dye
Sealed with lacquer
Give examples of anodised parts:
Hard Drive cover, mobile phone cases
Explain how an electrochemical cell is created.
When 2 metals join a current flows through them,when there is water added between the 2 a cell is made
What corrodes in sacrificial annodes
The anode (more active metal) will be corroded and protect the cathode (less active metal).
What are the 2 types of cathodic protection
Sacrificial annodes, impressed current
Explain what happens when an electrochemical cell has been created.
The more reactive metal starts to corrode as current flows from the anode to the cathode via the water, then the cathode is more protected
What metals are used for sacrificial annodes
More reactive metals such as zinc and aluminium are used as sacrificial anodes.
Fill in the blank “The sacrificial anodes don’t have to _________ _____ the cathode to protect it, but will need to be _________ and ______ when they can no longer provide sufficient protection to the cathode.”
completely cover, monitored and replace
What is the idea of impressed current
An underwater/ground pipe or structure (Cathode) is protected by a positive current flow and if any corrosion does occur it is at the Anode
Why are steel food cans e.g. baked beans, now lined on the insides with more than just tin?
To prevent the food from corroding the can
Give two reasons why cellulose paint is now not widely used.
As it is very harmful to human health
Emits a lot of odor
How is pearlescent paint different to metallic paint?
The particles are ceramic rather than metallic
