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
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2
Q

METALS

annealing

A
  • metal is heated then cooled slowly
  • allows metal crystals to grow & move into place
  • metal loses its elasticity
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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
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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
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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

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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
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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
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8
Q

METALS
case hardening
(workshop technique)

A
  • metal is heated to red
  • dipped in carbon powder
  • heated again
  • quenched
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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
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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)
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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
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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
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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
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14
Q

TIMBERS
lamin board
(description)

A
  • thin strips of softwood sandwiched between veneer panels

- strips usually between 5-7mm in thickness

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15
Q

TIMBERS
lamin board
(advantages) (6)

A
  • light, cheap, strong
  • bend resistant (stiff)
  • easy to work with
  • higher quality than blockboard
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16
Q

TIMBERS
lamin board
(disadvantages) (1)
(uses) (1)

A
  • more expensive than chipboard

- USES: shelves

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17
Q

TIMBERS
blockboard
(description)

A
  • strips of softwood glued together & sandwiched between veneer panels (softwood, hardwood, MDF, particle board)
  • strips are up to 25mm in thickness
18
Q

TIMBERS
blockboard
(advantages) (4)

A
  • lightweight
  • corrosion resistant
  • strong
  • environmentally friendly
19
Q

TIMBERS
blockboard
(disadvantages) (3)
(uses) (5)

A
  • gap between strips of wood makes it difficult to work with
  • cheap & low quality blackboard may be vulnerable to insect attack
  • shrinking & swelling may occur
  • USES: doors, table, shelves, partition walls, paneling
20
Q

TIMBERS
plywood
(description)

A
  • thin sheets of wood are glued together with the grains at 90° to the previous layer
21
Q

TIMBERS
plywood
(advantages) (5)

A
  • lightweight
  • cheap
  • veneer can be added to enhance aesthetics
  • strong in all directions
  • can be made to any size
22
Q

TIMBERS
plywood
(disadvantages) (3)
(uses) (3)

A
  • glue used (urea formaldehyde) is carcinogenic
  • susceptible to water damage
  • edges need to be finished as layers visible
  • USES: furniture, structural work, cladding
23
Q

TIMBERS
structural composite lumber (SCL)
(description)

A
  • strands of wood layered with resins (eg urea formaldehyde)

- pressed & heat cured to produce a stable billet

24
Q

TIMBERS
structural composite lumber (SCL)
(advantages) (4)

A
  • remains stable
  • less prone to warping/shrinking/splitting
  • can carry larger loads than traditional lumber
  • environmentally friendly as uses recycled chips
25
TIMBERS structural composite lumber (SCL) (disadvantages) (1) (uses) (3)
- urea formaldehyde is carcinogenic | - USES: beams, joists, rafters
26
TIMBERS laminated veneer lumber (LVL) (description)
- veneers are layered with resins (eg urea formaldehyde) | - pressed & heat cured to produce a stable billet
27
TIMBERS laminated veneer lumber (LVL) (advantages) (6)
- cheap, strong - can be made to any length - few defects - less prone to warping/splitting/shrinking - can carry larger loads than conventional lumber
28
TIMBERS laminated veneer lumber (LVL) (disadvantages) (1) (uses) (3)
- urea formaldehyde is carcinogenic | - USES: beams, joists, rafters
29
TIMBERS | resins with fire retardants
- resin is impregnated with fire retardant cladding (eg for indoor flooring)
30
POLYMERS additives- process aids LUBRICANTS
- wax/calcium stearate reduces viscosity of molten polymer - make polymer less 'sticky' - allows more intricate shapes to be formed - allows moulding temperature to be lowered- saves energy
31
POLYMERS additives- process aids THERMAL ANTIOXIDANTS
- help prevent oxidising/discolouring due to excessive heat in processing
32
POLYMERS additives- enhance aesthetics PIGMENTS
- time particles mixed in at molten state to give colour to final product
33
POLYMERS additives- improve product function ANTISTATICS
- polymers are insulators so build up static charge which attracts dirt & dust - antistatic improve surface conductivity by attracting moisture from surroundings - this reduces static charge - eg plugs & sockets, electric wire covers
34
POLYMERS additives- improve product function FLAME RETARDANTS
- bromine, chlorine, phosphorous or metal when added to polymers reduce change of combustion/spread of fire - important in product exposed to heat (eg car engine parts) or potential electrical fires (eg plug sockets)
35
POLYMERS additives- improve product function PLASTICISERS
- allows plastics (eg PVC) to become less hard & brittle at normal temperature use - also help in processes to allows polymers to be easily formed at higher temps - eg added to LDPE for food wrap allowing it to be stretched over product
36
POLYMERS additives- improve product function FILLERS
- provide but to product (less product required) - improve polymer properties - common fillers: > provide bulk: sawdust, wood, flour > increase thermal conductivity: chalk, clay, calcium carbonate > polymers heat up & cool down more quickly = shorter mould cycle times
37
POLYMERS additives- prolong life (prevent degradation) ANTIOXIDANTS
- held reduce environmental deterioration of polymer from exposure to oxygen - polymer degradation can lead to increased brittleness, surface cracks & pigment discolouration
38
POLYMERS additives- prolong life (prevent degradation) UV LIGHT STABILISERS
- prevent polymer chains from being broken down by sunlight - UV attack causes polymers to lose colour & become more brittle - white pigment becomes yellow, dark pigment (eg green, blue) take on a 'milky' effect - eg PVC hosepipes- become brittle & cracks appear - other uses include sports stadium seats & synthetic grass
39
POLYMERS additives- encourage degradation BIODEGRADABLE PLASTICISERS
- similar to regular plasticisers | - make polymer more flexible, softer, easier to break down = faster degradation
40
POLYMERS additives- encourage degradation BIO-BATCH ADDITIVES
- oxy-degradable = degrade in presence of oxygen > often used for high volume single use items (eg carrier bags, food packaging) - photodegradable = degrade when exposed to UV light - hydro-degradable = degrade in presence of water