SB.6 Metals Flashcards
Metal extraction from ore: Electrolysis
Aluminium is extracted from bauxite. Bauxite is purified to produce aluminium oxide. This is converted to aluminium by electrolysis: passing electrical current through melted aluminium oxide, pure molten aluminium is separated
Metal extraction from ore: Liquation
Used w metals w a low mp (tin & lead). The impure metal is heated inside sloped container. Once melted, the liquid metal runs off leaving behind any impurities
Metal extraction from ore: Distillation
Mercury & zinc have low bp & can be distilled to remove impurities. Heated to vaporise, vapour collected & condensed producing pure metal
Metal extraction from ore: Blast furnace
Metals separated by heatinf in blast furnace. Iron extracted from iron ore by heating until becomes liquid. Liquid descends through furnace & separates from ore
Modifying metal properties: Annealing
Process of heating & slowly cooling metal to alter its properties, reducing hardness & increasing ductility. Improves malleability & reduces risk of fracture
Moifying metal properties: Hardening
Can be applied to steel to improve mechanical properties. Metal is heated at high temps until some of carbon content dissolves. Metal is then rapidly cooled, hardening & increasing strength & res, but increases brittleness
Nuts & bolts
Join 2 or more parts tg. A bolted joint can be disassembled & reassembled. Bolt heads usually hexagonal fir tightening w a spanner
Washer
Thin disc of metal to distribute the load in a nut & bolt fastening. Prevents damage to surface being fixed
Stock forms of metals
Tube
Sheet
Angle
Bar
Strip
Rod
I shaped grider
U shaped channel
Machine screws vs wood screws
Machine screws have finer threat & parallel shank w no point on the end
Rivets
Used to join 2 or more sheets of metal tg to create strong/permanent fixing. Riveting is suited to situations where workers cannot access the back of a product sa walls. Used in aircrafts where neatness & strength important but also lighweight.
See images for diff types of rivet shapes
How can metals be joined together
Brazing
Soldering
Welding
Brazing
Uses a molten filler (sa brass spelter) to join 2 surfaces of metals tg. High temp process, but a lower temp than welding. The work piece does not melt, only the molten filler, which cools & solidifies.
Soldering
Metals joined w metal filler known as solder. Solder has lower mp than adjoining metals. Soft soldering used in electrical circuits w copper components. Flux is used to help solder flow & keep join clean. Hard soldering used for joining precious metals
Welding
Fuses tg metals at very high temp. High temp melts the base materials. A metal filler (welding rod of the same/similar base metal) is melted to fill in joint. As they cool, the parts fuse tg, creating strong joint.
Spot welding - quick process for joining thin sheets of metal, the weld is only suitable for some metals as is small, less strong
Shaping metals: Milling
Milling machine removes metal in thin layers w cutter. The cutting head can be set to specific speed & cutting depth. Used in machining parts to precise tolerance or making surface completely flat.
Shaping metal: Bending
A sheet metal former will bend or fold metal sheets or bars to required shape.
Shaping metals: Casting
Process of heating metal into liquid & pouring into a mould w specific design/pattern. Sand-casting process offers most flexibility & enables complex shapes (ie. Engine parts).
Shaping metals: Pressing
Placing flat sheet of metal into stamping press. Hydraulic force pushes into a die to form a shape.
What is corrosion
Occurs when metal reacts w its env causing an electrochemcal reaction
Importance of surface finishing metals
Provides impermeable coating to prevent oxidation. If metal is exposed to oxygen & moisture, its susceptible to corrosion
Preparations before adding surface treatment
Metal must be clean, free of any grease
Sand blasting to smooth surface & remove debris
Primer applied to some before paint
Surfaces prepared w abrasive paper - a rough surface known as a ‘key’ needs ti be created using abrasive paper, ensures treatment properly adheres to the surface
Surface finish: Galvanising
Protective coating of zinc added to steel or iron to prevent rusting. Zinc is a more reactive metal than iron so if item is scratched, rinc reacts first.
Hot dipped galvanising submerges the metal in bath of molten zinc. Used on gates, pipes
Surface finishes: Powder coating
Protective layer to prevent corrosion & aesthetic reasons. Applied w spray gun, giving particles an electrostatic charge. The metal is grounded, which attracts the charged particles. Once coated, metal is cured in an oven to form tough bond
Surface finishes: Plastic dip coating
Protective & aesthetic plastic coating onto metal parts sa handles, giving soft, insulative grip. Heated metal is plunged into a fluidised bath of plastic powder. The metal is returned to oven to allow plastic to fuse onto it
