SB.6 Metals

Question 1

Metal extraction from ore: Electrolysis

Answer 1

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

Question 2

Metal extraction from ore: Liquation

Answer 2

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

Question 3

Metal extraction from ore: Distillation

Answer 3

Mercury & zinc have low bp & can be distilled to remove impurities. Heated to vaporise, vapour collected & condensed producing pure metal

Question 4

Metal extraction from ore: Blast furnace

Answer 4

Metals separated by heatinf in blast furnace. Iron extracted from iron ore by heating until becomes liquid. Liquid descends through furnace & separates from ore

Question 5

Modifying metal properties: Annealing

Answer 5

Process of heating & slowly cooling metal to alter its properties, reducing hardness & increasing ductility. Improves malleability & reduces risk of fracture

Question 6

Moifying metal properties: Hardening

Answer 6

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

Question 7

Nuts & bolts

Answer 7

Join 2 or more parts tg. A bolted joint can be disassembled & reassembled. Bolt heads usually hexagonal fir tightening w a spanner

Question 8

Washer

Answer 8

Thin disc of metal to distribute the load in a nut & bolt fastening. Prevents damage to surface being fixed

Question 9

Stock forms of metals

Answer 9

Tube
Sheet
Angle
Bar
Strip
Rod
I shaped grider
U shaped channel

Question 10

Machine screws vs wood screws

Answer 10

Machine screws have finer threat & parallel shank w no point on the end

Question 11

Rivets

Answer 11

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

Question 12

How can metals be joined together

Answer 12

Brazing
Soldering
Welding

Question 13

Brazing

Answer 13

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.

Question 14

Soldering

Answer 14

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

Question 15

Welding

Answer 15

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

Question 16

Shaping metals: Milling

Answer 16

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.

Question 17

Shaping metal: Bending

Answer 17

A sheet metal former will bend or fold metal sheets or bars to required shape.

Question 18

Shaping metals: Casting

Answer 18

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).

Question 19

Shaping metals: Pressing

Answer 19

Placing flat sheet of metal into stamping press. Hydraulic force pushes into a die to form a shape.

Question 20

What is corrosion

Answer 20

Occurs when metal reacts w its env causing an electrochemcal reaction

Question 21

Importance of surface finishing metals

Answer 21

Provides impermeable coating to prevent oxidation. If metal is exposed to oxygen & moisture, its susceptible to corrosion

Question 22

Preparations before adding surface treatment

Answer 22

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

Question 23

Surface finish: Galvanising

Answer 23

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

Question 24

Surface finishes: Powder coating

Answer 24

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

Question 25

Surface finishes: Plastic dip coating

Answer 25

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