metal finishes

Question 1

metal finishes

Answer 1

• to protect from corrosion and decay
• most metals have oxide layer to protect against environment
• steels (except stainless) have a porous oxide layer which allows moisture to penetrate the metal = rust

Question 2

cellulose and acrylic paints

Answer 2

• surface cleaned and degreased
• primer applied
• coloured undercoat applied
• final paint colour applied
• can be applied using brush or spray
• special effect and texture paints can be added
• used on low cost metals

Question 3

electroplating

Answer 3

• metal product and donor metal are placed in container with electrolyte solution
• direct current applied
• product attracts donor metal
• donors include gold, zinc, copper and silver
• protective layer and more hardwearing finish

Question 4

polymer dip coating

Answer 4

• metal product heated to 230 degrees
• dipped into tank of fine polymer powder
• tank has air blowing through to provide even coating
• the heat melts the polymer onto the product
• then left to cool
• used on wire coat hangers, dishwasher racks etc

Question 5

metal dip coating

Answer 5

• metal products dipped into tank of molten plating metal (donor)
• metals must be clean and degreased
• tin plating
• zinc plating (galvanising)
• barrier against corrosion

Question 6

powder coating

Answer 6

• metal product is negatively statically charged
• thermoset polymer resin (positively charged) is sprayed using an air gun
• the charging results in a strong attraction and the heat melts the polymer to the metal
• washing machine bodies

Question 7

metal varnishing

Answer 7

• metal is polished and varnish applied with a fine brush or spray
• allows colour of base metal to show
• used on aluminium, brass and copper

Question 8

sealants

Answer 8

• sealant applied with cloth or machine pad to produce a film which is allowed to cure
• then buffed with a cloth to a shine
• protect from decay and tarnishing
• used in automotive industry against effects of weathering, rad salts and insect attack

Question 9

preservatives

Answer 9

• applied with a cloth, spray or immersion
• silicon sealants also classed as preservatives
• used on moulds and dies for preventing surface imperfections

Question 10

anodising

Answer 10

• electric current passes through sulphuric acid electrolyte solution
• current flows from part to be treated (positive anode) to the negative cathode
• aluminium oxide layer builds up on the treated part to produce an anodised finish
• increases hardness and toughness
• outer casings of torches

Question 11

cathodic protection

Answer 11

• helps prevent natural voltage of metals from corroding parts when exposed to water
• the anode is a sacrificial metal which corrodes whilst the base metal is protected
• used to protect steels structures buried in soil or immersed in water

Question 12

impressed current method of cathodic protection

Answer 12

• protects components by flowing a current through any liquid to the component
• cathode corrodes over time so needs to be monitored

Question 13

sacrificial anodes

Answer 13

• uses sacrificial metal to protect the metal of value
  -a more electrochemically active metal is joined to a less active metal
• provides more resistance to corrosion