1.3 Enhancement of Materials Flashcards
1
Q
METALS
work hardening
A
- when the metal is cold worked eg by bending, rolling or hammering
- improves tensile strength
> crystals are distorted and changed & so cannot move freely within the structure of the metal
> reduced ductility
> cracking/damage in worked area - effects can be removed using annealing
2
Q
METALS
annealing
A
- metal is heated then cooled slowly
- allows metal crystals to grow & move into place
- metal loses its elasticity
3
Q
METALS
case hardening
(summary)
A
- used for hardening surface of steels with less than 0.4% carbon content
- produces an outer casing of great hardness, improved wear resistance & resistance to surface indentation
- inner core retains softness
4
Q
METALS
case hardening
(process)
A
CARBURISING:
- steel is placed in ceramic box & then packed with carbon
- box is heated to 930-950°C- carbon atoms diffuse into material’s structure to build up surface carbon content
- depth of carbon layer determined by length of time exposed to carbon
- longer time = thicker carbon layer
- metal then heated to 760°C & quenched
5
Q
METALS
quenching
A
- hot metal is cooled very quickly (in water)
- this seals hard surface case but doesn’t affect properties of inner core
6
Q
METALS
hardening
A
- medium & high carbon steels heated to alter crystalline structure
- held at temperature for a given time then quenched in water/oil/salt-water
- increases hardness but also increases brittleness
7
Q
METALS
tempering
A
- reduces some excess hardness & brittleness of a hardened metal
- increases toughness & ductility
- metal is heated below the critical point for a given time the slowly air cooled
- exact temperature determines amount of hardness removed
- tempering colour on metal indicates temperature at which brittleness is removed
8
Q
METALS
case hardening
(workshop technique)
A
- metal is heated to red
- dipped in carbon powder
- heated again
- quenched
9
Q
METALS yield point (definition)
A
- the point on the stress-strain graph that indicates the end of elastic behaviour and the beginning of plastic behaviour
10
Q
TIMBERS
disadvantages of timber that mean wood enhancement is necessary? (4)
A
- strength properties decrease when wood is wet
- highly combustible
- susceptible to fungal & insect attack & rot
- anisotropic (wood has different properties in different directions- eg easier to split along grain than against)
11
Q
TIMBERS
preservatives
A
- protect wood from fungal & insect attack
- wood can be pre-treated with copper-based preservative which penetrates the wood in order to protect the whole plank
- copper has excellent fungicidal properties
12
Q
TIMBERS
how is wood treated to make it harder?
A
- wood is impregnated with polysaccharide
- these cure within the cell structure of the wood
- produce wood with increased hardness, toughness & stability
13
Q
TIMBERS
how are softwoods treated to make them appeal to customers and how is this more environmentally friendly?
A
- pigments can be added to make them look more expensive & luxurious like hardwoods, but are more affordable
- softwoods are faster growing than hardwoods so can easily be replanted & regrown
14
Q
TIMBERS
lamin board
(description)
A
- thin strips of softwood sandwiched between veneer panels
- strips usually between 5-7mm in thickness
15
Q
TIMBERS
lamin board
(advantages) (6)
A
- light, cheap, strong
- bend resistant (stiff)
- easy to work with
- higher quality than blockboard
16
Q
TIMBERS
lamin board
(disadvantages) (1)
(uses) (1)
A
- more expensive than chipboard
- USES: shelves
