Metal finishing

Video explainers:

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Notes & Diagrams:

Cellulose Paint:

Advantages	Disadvantages
Quick drying time Provides a smooth finish Widely available	Not durable outdoors Can be affected by weather conditions

Uses: Vehicles, machinery, and industrial applications.

Acrylic Paint:

Advantages	Disadvantages
Flexible Good adhesion Quick-drying	Prone to scratching Less durable than other coatings

Uses: Wood, metal, and plastic surfaces.

Electro-plating:

How it works:

1. A cheap metal is coated onto a metal to protect it
2. An electric current is passed through an acidic electrolyte
3. The metal being protected (anode) then builds a layer of metal oxide

Advantages	Disadvantages
Corrosion resistant Easy to do Improves mechanical properties Improves aesthetics appeal Cost effective Durable finish	Time consuming Toxic fumes released Non-uniform finish

Uses: Spoons, taps, shower heads

Dip Coating:

How it works:

1. The product is dipped into a molten polymer or coating substance
2. Excess material is removed after dipping
3. The coating is then cured by heating

Advantages	Disadvantages
Provides a uniform coating Durable and corrosion-resistant finish	Not suitable for intricate parts

Uses: Automotive parts, tools, and fasteners.

Powder Coating:

How it works:

1. The metal is first cleaned and prepared to ensure proper adhesion
2. The metal is electrostatically charged
3. Powdered polymer is sprayed onto the metal surface
4. The coated metal is then heated in an oven (around 180–200°C) to melt and fuse the powder
5. The coating is allowed to cool and harden, forming a durable finish

Advantages	Disadvantages
Range of colour finishes Non-toxic Evenly coated finish More protective than paint Better for environment than paint	Harder to do than paint Uses energy/needs energy for heating powder (unlike paint)

Uses: Cars, wheel arches

Galvanising:

How it works:

1. The metal (usually steel) is dipped into molten zinc
2. The zinc reacts with the metal to form a protective coating

Advantages	Disadvantages
Corrosion resistant Low maintenance Long-lasting protection	Can be difficult to weld Appearance can be uneven

Uses: Steel beams, pipes, electrical transmission towers.

Sealants:

Advantages	Disadvantages
Waterproof finish Thermal/acoustical insulation Electrical insulation Used for simple smoothing/filling	Does not have great strength

Uses: Pipe threads, aquariums, roofs, hydraulic systems

Preservatives:

Advantages	Disadvantages
Extends the lifespan of metal Protects against rust and corrosion Can enhance appearance with coatings	Some contain harmful chemicals Requires proper application (e.g., priming, sealing)

Uses: Metal structures exposed to moisture, chemicals, or outdoor conditions

Anodising:

How it works:

1. Used to add a coating to aluminium
2. An electric current is passed through an acidic electrolyte
3. The metal being protected (anode) then builds a layer of aluminium oxide

Advantages	Disadvantages
Can be done in a range of colours Very durable finish Hard finish/scratch resistant Thin finish - doesn't block holes in product Heat resistant finish	Joining/machining can't be done after anodising Expensive

Uses: Window frames, bike frames

Plating:

Advantages	Disadvantages
Improves corrosion resistance Improves wear resistance Improves aesthetics	Not always durable Can be costly

Uses: Electronics, jewellery, automotive parts

Coating:

Advantages	Disadvantages
Durable finish Corrosion resistant Improves appearance	Can be affected by environmental conditions Costly in some cases

Uses: Aircraft, automotive parts

Cathodic protection (Impressed current and sacrifical anode):

How it works (Impressed current):

1. Metal is connected to electric power supply which is connected to a cathode
2. The cathode rusts over time whilst the anode (metal being protected) remains intact

How it works (Sacrifical anode):

1. A metal which is more reactive is connected to the metal being protected
2. The more reactive metal (sacrifical anode) rusts over time whilst the metal being protected remains intact

Advantages	Disadvantages
Proetcts structures that are buried in dirt/water Greatly increases lifespan of metal being protected Cost efficent to run	Hard to install Complex to upkeep Uses energy/needs connection for impressed current Expensive to install

Uses: Pipelines, ships, cars

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