Metal DON’T NEED Flashcards
What is silver made from?
Silver is made from nuggets and crystals of pure silver as both can exist in nature. It can also exist together with other metals such as gold, copper, lead and zinc ores.
What is the chemical symbol of silver
Ag
List some properties of silver
- Best conductor of heat and electricity of all known metals.
- Strong
- Malleable (easily mouldable).
- Can endure extreme temperatures
- Ductile ( able to be drawn out into a thin wire)
- Reflects light
What can silver be used for?
- Electronics: contacts in electrical switches for appliances such as kettles, toasters and food mixers.
- Found in light weight batteries that work at high temperatures.
- Used in soldering (joining together metals)
- Most common use is to make coins, mirrors and jewellery.
How much does silver cost per ounce
About £12 not too expensive
Is silver toxic to humans?
Not at all, it is very unreactive and non-toxic and can even be used in food decoration
How are metals usually produced?
By mining ore from the earth and extracting the metal out of rocks in a large industrial process
There are three main categories of metal. What are they?
Ferrous
Non-ferrous
Alloys
What are ferrous metals?
These are metals that consist mainly of iron and small quantities of other elements and metals.
What happens when ferrous metals are exposed to moisture?
Prone to rusting if exposed to moisture
Can ferrous metals be picked up with a magnet?
Yes they can
Give three examples of ferrous metals
Stainless steel
Iron
Mild steel
Metal is bought in sections. Give some examples of the types of section.
Flat bar Round tube Sheet Square tube Round bar
What are non ferrous metals?
These are metals that do not contain any iron at all.
Do non ferrous metals rust?
No, they do not rust in the same way when exposed to moisture
Are non ferrous metals attracted with a magnet?
No
Give some examples of non ferrous metals
Copper Nickel Titanium Gold Silver Lead Platinum Aluminium Zinc
What is an alloy?
These are substances that contain two or more metals and sometimes other elements. The metals are carefully chosen and mixed to achieve specific properties e.g. a low melting point.
Give some examples of alloy metals
Bronze
Brass
Pewter
Solder
What are steel alloys?
Steel alloys contain a % of carbon and usually one or more other metals.
What are steel alloys used for?
Tools
Car bodies
Cutlery
Saucepans
List the four principal ways of joining metals.
- Adhesives
- Mechanical joining
- Heat joining
- Flux
Discuss which adhesives are useful for joining metals
Epoxy resin (Araldite) is a two part polymer (plastic glue) that can be used to join metals
Discuss how mechanical joining can be used to join metals
These include nuts, bolts, rivers and screws. These come in a variety of lengths and diameters
List the 3 process used as a way of joining metals
Soldering
Brazing
Welding
What are the similarities and differences between soldering and brazing?
Soldering occurs below 450C while brazing occurs above 450C.
Both occur at a temperature below the melting point of the metal and use an alloy.
Which process stresses the metal the most when joining by heat?
Welding as soldering and brazing both occur at a temperature below the melting point of the metal and do not stress the metal as it does not melt.
What is welding as a method of heat joining of metal?
Welding joins two or more pieces of metal together by melting them.
It is a process common with metals but is also used in the plastics industry.
The two pieces of metal need to be identical as does the filler rod as they all need to melt at the same temperature.
What is flux as a method of joining metals?
Fluxes facilitate soldering, blazing and welding by removing oxidation from the metals to be joined. This helps them join more easily.
What is oxidation in terms of metals?
Most metals are prone to oxidation, this builds up as a layer on the surface which is often inert and prevents further oxidation and degradation of the metal.
Give a famous example of oxidation of a metal.
A green surface builds up on copper, hence the copper Statue of Liberty is green.
What is the green surface oxidation called?
Verdigris
What is oxidation of irons and steels called?
Rust
Why is rust such a problem on irons and steels?
It peels off and thus exposes fresh patent metal to be oxidised and so the object continues to CORRODE.
How can rust be prevented on a bike for example?
By applying a surface finish such as painting or galvanising or by cathodic protection.
Before applying a finish, the metal will need to be prepared. How is this done?
Wet and dry sandpaper and an emery cloth are used to remove oxides.
Name the 8 possible finishing s that can be applied to metal
- Aesthetics
- Protection
- Plating
- Galvanising
- Paint
- Lacquer
- Dip coating
- Anodising
What is aesthetics in terms of metal finishing?
A finish will improve the way a product looks
What is protection in terms of metal finishing?
Applying a surface will protect the product in use; with steels inhibiting the build-up of rust
What is plating in terms of metal finishing?
Coating a cheaper metal with a higher quality one ie. silver plated cutlery
What is galvanising in terms of metal finishing?
As with plating, but this term is generally applied to zinc being plated onto steels
What is paint in terms of metal finishing?
This adds colour to the metal. Paints are usually oil or solvent based
What is lacquer in terms of metal finishing?
Adds a clear shine to metal, allowing the colour and lustre to the metal to show through and the oxides not to build up
What is dip coating in terms of metal finishing?
A hot piece of metal is dipped into a bath of plastic dust then this adheres to the heated metal producing an impenetrable coat
What is anodising in terms of metal finishing?
This adds a vivid colour to aluminium. In addition to colour the process hardens the surface.
Metals have different properties. This means that some metals are better suited to than others for a specific purpose. Give an example of an inappropriate choice of metal for a sailing boat explaining why.
Mild steel with no finishing or coating would be no use for a sailing boat as it would quickly corrode, whereas stainless steel would be perfect.
List 8 typical properties that can be displayed by metals
Elasticity Ductility Malleability Hardness Brittleness Toughness Tensile strength Compressive strength
In terms of metal properties, explain what elasticity means
The ability to regain its original shape after it has been deformed
In terms of metal properties, explain what ductility means
The ability to be stretched without breaking
In terms of metal properties, explain what malleability means
The ability to be easily pressed, spread and hammered into shapes
In terms of metal properties, explain what hardness means
Resistance to scratching, cutting and wear
In terms of metal properties, explain what brittleness means
Easily breaks without bending
In terms of metal properties, explain what toughness means
Resistance to breaking bending or deforming
In terms of metal properties, explain what tensile strength means
Strength when stretched
In terms of metal properties, explain what compressive strength means
Strength when under compression
Discuss the stages of the enamelling process
- Prepare the metal with wet and dry sandpaper and an Emery cloth
- Add the powdered paint
- Kiln
- Cool
What can be some problems with the enamelling process?
The enamel can crack if it is cooled too quickly
At what temperature does the powdered glass melt in the kiln?
400C
What is enamelling?
A decorative process that involves powdered glass being fused to metal by high temperatures
What group of materials does enamel belong to?
Ceramics
What are the three best metals for enamelling?
Gold
Silver
Copper
What must you ensure before the enamelling process begins?
Need to ensure there is no oxidation on the metal which would prevent the bonding process
