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DT - Technical Principles > 13. Enhancement of materials > Flashcards

13. Enhancement of materials Flashcards

(polymer, wood, metal)

1
Q

What is material enhancement?

A

a way of improving a material’s properties to better suit the requirements of the final product

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2
Q

What are the polymer additives?

A
  • lubricants
  • thermal antioxidants
  • pigments
  • antistatics
  • flame retardants
  • plasticisers
  • fillers
  • biodegradable plasticisers
  • bio-batch additives
  • antioxidants
  • UV light stabilisers
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3
Q

What is the reason for adding lubricants to polymers?

A
  • adding wax or calcium stearate reduces viscosity of molten polymer
    • less sticky, allowing more intricate shapes to be formed
  • allow moulding temp to be lowered
    • saves energy
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4
Q

What is the reason for adding thermal antioxidants to polymers?

A
  • prevent polymer oxidising or discolouring due to excessive heat during processing
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5
Q

What is the reason for adding pigments to polymers?

A
  • tiny particles mixed into molten polymer
  • give colour to final processed product
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6
Q

What is the reason for adding antistatics to polymers?

A
  • reduce likelihood of polymer building up static charge
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7
Q

What is the reason for adding flame retardants to polymers?

A
  • reduce likelihood of combustion or spread of fire (car engine components) or potential electrical fires ( e.g plug sockets)
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8
Q

What is the reason for adding plasticisers to polymers?

A
  • allow plastics to become less hard and brittle at normal temperature use
  • allow polymers to be easily formed at higher temperatures
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9
Q

What is an example of plasticisers being used?

A
  • in LDPE food wrap, so it can be stretched over the fod
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10
Q

What is the reason for adding fillers to polymers?

A
  • sawdust and wood flour provide bulk to the product
    • less polymer required
  • mineral fillers (chalk, clay, calcium carbonate) help increase thermal conductivity of polymer
    • heat up and cool down more quickly = shorter mould cycle times
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11
Q

What is the reason for adding biodegradable plasticisers to polymers?

A
  • make polymer more flexible, softer and easier to break down
    • faster degradation time
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12
Q

What is the reason for adding bio-batch additives to polymers?

A
  • oxy-degradable, photodegradable and hydro-degradable additives help reduce degradation time from 100s of years to a few years or months
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13
Q

What is the reason for adding antioxidants to polymers?

A
  • help reduce environmental deterioration of polymer from exposure to oxygen
  • help prevent increased brittleness and surface cracks
  • help prevent pigment discolouration
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14
Q

When are antioxidants often used?

A

polymer garden furniture

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15
Q

What is the reason for adding UV light stabilisers to polymers?

A
  • prevent polymer chains being broken down by sunlight
    • UV attack causes colour loss and brittleness
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16
Q

What are UV light stabilisers used in?

A
  • outdoor toys and play equipment
  • garden furniture
  • sports stadium seats
  • synthetic grass playing surfaces
17
Q

What are the wood enhancement methods?

A
  • resins and laminations
  • resins with fire retardant
  • laminations
  • preservatives
  • pigments
  • fire retardant preservatives
  • modified natural polysaccharide
  • structural composite lumber (SCL) and laminated veneer lumber (LVL)
18
Q

When are resins and lamination used?

How is chipboard made and its properties?

A
  • in engineered wood
    • to enhance the properties of the useable parts of the tree such as sawdust, wood chips and fibres
  • chipboard made from compressing wood chips with resin
  • chipboard is very stable, and not really affected by temperature and humidity
  • chipboard has a uniform strength across the board, with no grain problems like solid wood
19
Q

What are resins with fire retardants?

A
  • resin is impregnated with fire retardant cladding (e.g. for indoor flooring)
20
Q

When are laminations used?

A
  • veneers such as natural wood are laminated on to the board surface to enhance aesthetics
21
Q

What are preservatives?

A
  • protect wood from fungal and insect attack
  • wood can be pre-treated with copper-based preservative
    • penetrates the wood to protect the whole plank
  • copper has excellent fungicidal properties
22
Q

Why are pigments added?

A
  • added to preservative to give different coloured shades to enhance the aesthetics
    • e.g. outdoor decking
  • can also be used on cheaper softwoods to make them look like hardwoods
23
Q

Why are fire retardant preservatives used?

A
  • used to pressure treat wood for roof joists, cladding etc and exhibition stands
  • wood can also be treated to make it harder and more resistant in high wear situations such as flooring
24
Q

How is modified natural polysaccharide used?

A
  • wood is impregnated to cure within the wood cell structure
  • results in increased hardness, toughness and stability
  • often added to hardwood floor panels
25
Q

How is structural composite lumber (SCL) and laminated veneer lumber (LVL) made, and what are their properties?

A
  • made by layering strands (SCL) or veneers (LVL) of wood with resisns such as urea formaldehyde, pressing and heat curing them to produce a stable wood billet
  • SCL and LVL are less prone to defects such as warping, splitting or shrinking, and have greater load-bearing properties
26
Q

When is SCL and LVL used?

A
  • used in structural appliactions including beams, joints and rafters
27
Q

What is metal enhancement?

A

-metal properties can be enhanced through the controlled application of heating and cooling, known as heat treatment

28
Q

What are the different metal enhancement methods?

A
  • work hardening
  • annealing
  • case hardening
  • hardening
  • tempering
29
Q

What is work hardening?

A
  • when the metal is ‘cold worked’ by bending, rolling or hammering
30
Q

What happens to the metal during work hardening?

A
  • crystals within the metal are distorted and changed
    • leading to improved tensile strength and hardness in the worked area
  • when the metal crystals are distorted, they cannot move freely within the metal structure
    • can result in less ductility, cracking or damage in the worked area
31
Q

How can the affects of work hardening be removed?

A
  • by annealing the metal
32
Q

What is annealing?

A
  • used to make the work-hardened metal easier to work by making it less brittle and more ductile
  • the metal is heated and then cooled very slowly, allowing the metal crystals to grow and slowly move into place
33
Q

What is case hardening?

A
  • used for hardening the surface of steels with less than 0.4% carbon content
  • produces an outer casing of greater hardness, improved wear resistance to surface indentation
    • the inner core of the metal retains the original ‘softer’ properties
34
Q

What is the two stage process of case hardening?

A
  • carburising
  • quenching
35
Q

What is the carburising process?

A
  • changes chemical composition of the surface of low carbon steel so that it can absorb more carbon to increase surface hardness
  • steel placed in ceramic box packed with carbon
  • the box is heated to 930 - 950 degrees
  • the carbon atoms diffuse into the material’s structure to build up the surface carbon content
  • depth of carbon layer determined by length of time the material is exposed to carbon
  • longer time = thicker carbon layer
  • product then heated to 760 degrees and then quenched
36
Q

What is the quenching process?

A
  • the hot metal is quenches in water to fast cool it and seal the hard surface case while not affecting the properties of the inner core
37
Q

What is hardening?

A
  • medium and high carbon steel are heated to alter their crystalline structure
  • holding them at this temperature for a given time
  • then quenching them in water, oil or salt water baths
  • increases hardness but also brittleness
38
Q

What is tempering?

A
  • a heat treatment that reduces some of the excess hardness and brittleness of a hardened metal
  • increases toughness and ductility
39
Q

What is the tempering process?

A
  • metal heated to below the critical point for a given time then slowly air cooled
  • the exact temperature will determine the amount of hardness removed
  • tempering colour on the metal indicates the temperature at which the brittleness is removed

DT - Technical Principles (29 decks)

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