Metals (incomplete) Flashcards
ferrous metals
metals containing iron, they are magnetic and degrade in the form of rust
non-ferrous metals
metals that do not contain iron
alloys
metals consisting of two or more different metals combined to improve their properties
sheet metal (stock form)
large flat sections of metal with thickness < 3 mm
Plate (stock form)
thick areas of metal generally > 3 mm
Bar (stock form)
solid prisms of metal with a range of cross sections (e.g. round bar, flat bar ect)
Tube (stock form)
hollow bar with a range of cross sections (e.g. square, hexagonal, round ect)
structural angular (stock form)
shapes such as H, L and I beams, T bar and channel
metal ore
impure metal locked inside other rocks and minerals that is purified and separated into pure metal
chalcopyrite
Copper ore
Bauxite
Aluminium ore
Cassiterite
Tin ore
Zinc blende
Zinc ore
Work Hardening
cold working a material (such as bending or rolling) compresses and distorts the crystal structure of a metal preventing the crystals from moving which improves hardness but increases brittleness and cracking
Case Hardening
used to harden steels with a less than 0.4 % carbon content
the metal is heated and carbon is allowed to impregnate the surface material making it harder high carbon steel on the surface but softer, less brittle low carbon steel in the core
Annealing
hard metal is heat and then slowly cooled
this relaxes and expands the crystal structure and softens the material
Quenching
hot metal is cooled very quickly in water, oil or salt water. This cools the metal without allowing the crystal structure to relax, keeping the outside of the material hard while maintaining a soft core
Carburising
steel is placed in a ceramic box with carbon and heated to 930-950 C
carbon atoms impregnate the metals structure
the longer it is held at this temperature the more carbon that enters the material and the harder it gets
the metal is removed and heated to 750 degrees and quenched to seal the surface
Hardening (general explanation)
the crystal structure of a metal is compressed and altered holding each crystal in place which prevents the material from bending easily or altering its shape and thus it is harder
Tempering
metal is heated below a critical temperature and air cooled
this relaxes some of the crystal structure and removes some of the hardness
Tempering colour
the colour a metal glows to indicate an amount of brittleness is removed
Forming processes
materials are deformed into a new shape but no material is added or removed
redistribution
melting and reforming a material into a new shape
wastage
material is cut away until the material is the correct shape
Press forming
Spinning
Cupping/deep drawing
Drop forging
Wrought iron forging
wrought iron bars (Carbon < 0.08%) are heated in a forge and forged using hammers or hydraulic presses in order to make complex shapes
suitable for batch or one off production
Bending
Stock form: sheet or plate
Process: a punch is presses a sheet material into a angled die causing it to bend into the desired shape, does not punch or trim the metal
Uses: seams on metal edges, casing/ housing units
Rolling
Sand casting
Gravity die casting
low melting point metals are poured into a open die where gravity causing the metal to fill the mould
less precise than pressure die casting but cheaper and easier to do
Hot chamber pressure die casting
Cold chamber pressure die casting
Investment casting
Low temperature Pewter casting
MIG welding
Metal Inert Gas welding
a large potential difference builds up on the electrode and the work piece
and arc of current jumps the gap melting both the electrode and the small area of the work piece joining them together
an inert gas such as CO2 shields the join from oxidation
the electrode is constantly used up
TIG welding
Oxy-acetylene welding
a mixture of oxygen and acetylene (ethyne) are pumped out of a torch and ignited in a high temperature controlled flame which melts a filler rod into a join in the base metal creating a join
Spot welding
sheet metal is held between two copper electrodes. an electrode discharges at a single point connecting the sheet together.
individual single points connect the sheet at many points along the length
Soldering
Brazing / Hard soldering
Riveting/ Pop riveting
Milling
Turning
Flame cutting
Plasma cutting
Laser cutting
A high power beam of light vaporises a single point on the material cutting through it. an inert gas such as CO2 clears away the cut material preventing it from reforming.