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DT > 1.3 Enhancement of materials > Flashcards

1.3 Enhancement of materials Flashcards

1
Q

What is material enhancement?

A

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

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2
Q

What are the 5 ways a polymer can be enhanced through the use of additives?

A

1 make polymers easier and less expensive to process
2 enhance aesthetics
3 improve product function
4 prolong life (prevent degradation)
5 encourage degradation

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3
Q

What are the 2 additives that help to make the polymer flow more easily into the mould?

A
  1. Lubricants
  2. Thermal antioxidants
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4
Q

What is the additive used to enhance aesthetics?

A

pigments

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5
Q

What are the 4 additives used to improve produce function?

A
  1. antistatics
  2. flame retardants
  3. plasticisers
  4. fillers
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6
Q

What are the 2 additives used to prolong life (prevent degradation)?

A
  1. antioxidants
  2. UV light stabilisers
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7
Q

What are the 2 additives used to encourage degradation?

A
  1. biodegradable plasticisers
  2. bio-batch additives
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8
Q

What do lubricants do?

A

The addition of wax or calcium stearate reduces the viscosity of the molten polymer, making it less sticky, allowing more intricate shapes to be formed.
They can also allow the moulding temperature to be lowered, saving energy during the manufacturing process.

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9
Q

What do thermal antioxidants do?

A

these help to prevent the polymer oxidising or discolouring due to excessive heat during processing.

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10
Q

What do pigments do?

A

these are tiny particles that are mixed into the polymer in its molten state to give colour to the final processed product.

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11
Q

what do antistatics do?

A

Due to their poor electrical conductivity, plastics are used for insulating products. This insulating property can lead up to a build-up of static electrical charge, which attracts dirt and dust. The addition of antistatics improves the surface conductivity by attracting moisture from the room surroundings, therefore reducing static charge.

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12
Q

What do flame retardants do?

A

Bromine, chlorine, phosphorus or metal, when added to polymers reduce the likelihood of combustion or the spread of fire. This is particularly important in products exposed to heat, such as car engine components or potential electrical fires such as plug sockets.

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13
Q

What do plasticisers do?

A

These are added to allow plastics to become less hard and brittle at room temperature use.
They are added to LDPE in the manufacture of food wrap, allowing the wrap to be stretched over the food product.
They also help in processing because they allow polymers to be easily formed at higher temperatures.

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14
Q

What do fillers do?

A

To provide bulk for the product (meaning less polymer is required) and to improve the polymer properties.
Commonly used fillers are sawdust and wood flour as well as mineral fillers such as chalk, clay and calcium carbonate. Sawdust and flour provide bulk, therefore reducing the amount of polymer required for the product. Mineral fillers can help to increase the thermal conductivity of the polymer, meaning they will heat up and cool down more quickly, giving shorter mould cycle times.

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15
Q

What do antioxidants do?

A

They help to reduce the environmental deterioration of the polymer from exposure to oxygen in the air.
Polymer degradation can lead to increased brittleness, surface cracks and pigment discolouration.

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16
Q

What do UV light stabilisers do?

A

They prevent the polymer chains from being broken down by sunlight. UV attack causes the polymer to lose colour and become more brittle.

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17
Q

What do biodegradable plasticisers do?

A

Similar to plasticisers used to enhance processing, these make the polymer more flexible, softer and easier to break down, which means a faster degradation time.

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18
Q

What do bio-batch additives do?

A

Oxy-degradable (degrade in the presence of oxygen), photodegradable (degrade when exposed to UV light) and hydro-degradable (degrade in the presence of water) additives can be added to polymers to help recue the degradation time from hundreds of years to a few years or even months.

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19
Q

What are the 4 disadvantages of using natural wood as a manufacturing material?

A

1 the strength properties decrease when the wood is wet
2 natural wood is highly combustible
3 natural wood is susceptible to fungal attack, insect attack and rot
4 natural wood is anisotropic, which means it has different properties in different direction, for example wood is easier to split along its grain than against the grain

20
Q

How is wood protected from fungal and insect attack?

A

It can be pre-treated with preservatives which penetrate the wood to give the enhanced properties throughout the wood section. These preservatives often use a copper based preservative because copper is a naturally occurring mineral which has excellent fungicidal properties.

21
Q

What products are wooden preservatives often used on?

A

outdoor timbers as they need to be able to prevent rot and degradation

22
Q

What products are wooden preservatives with pigments used on?

A

outdoor decking in garden projects

23
Q

What products are wooden preservatives with fire retardants used on?

A

roof systems, cladding, joists and exhibition stands

24
Q

When would wood be treated to make it harder and more resistant in high wear situations?

A

flooring

25
Q

How is wood treated to make it harder and more resistant?

A

The wood is impregnated with a modified natural polysaccharide, similar to cellulose in timber. The polysaccharides effectively cure within the wood cell structure to produce wood that has increased hardness, toughness and stability.

26
Q

What can be added to softwoods to give them similar aesthetics and properties to hardwoods? Why do manufacturers do this?

A

Polysaccharides to increase hardness and toughness and then pigments to give the same colours. This enables manufacturers to provide more affordable and environmentally friendly products to consumers, because softwoods grow much faster and have a faster replanting time than hardwoods.

27
Q

How does chipboard have very enhanced properties?

A

Chipboard is made from compressing woof chips with resin such as urea formaldehyde. This produces a board which is very stable and is not affected by temperature and humidity as much as solid wood. Chipboard also has uniform strength across the board with none of the grain problems as seen in solid wood. The resins used for manufactured boards can also be impregnated with fire retardant additives, giving boards many more used such as internal cladding, structural components and flooring.

28
Q

How are SCL (structural composite lumber) and LVL (laminated veneer lumber) made? Why are their properties advantageous?

A

They are engineered woods made by layering either veneers or strands of wood with resins such as urea formaldehyde, pressing and heat curing them to produce a stable wood billet. Both these timbers offer advantages over the original material such as being less prone to defects such as warping, splitting or shrinking along with greater load bearing properties.

29
Q

What products are made from SCL AND LVL?

A

Structural applications such as beams, joists, rafters and lintels

30
Q

What are the 4 ways that metals can be enhanced?

A

1 work hardening
2 annealing
3 case hardening
4 hardening and tempering

31
Q

What are work hardening?

A

When a metal is ‘cold worked’ such as bending, rolling or hammering, the 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 are prevented from moving freely within the metal structure, which can result in less ductility, in cracking or damage in the worked area.

32
Q

How can the effects of work hardening be removed?

A

Annealing the metal

33
Q

What is annealing?

A

Annealing is used to make the work hardened metal easier to work by making it less brittle and more ductile. The metal is heated and then very slowly cooled, allowing the metals crystals to grow and slowly move into place.

34
Q

In industry, how is annealing completed?

A

by using a specific temperature-controlled furnace

35
Q

In schools/college workshops, how is annealing completed?

A

using a brazing hearth

36
Q

What is the purpose of case hardening?

A

It produces a steel with an outer casing of greater hardness and resistance to surface indentation, while the inner core of the metal retained the original ‘softer’ properties. Case hardening provides the metal with improved wear resistance.

37
Q

What type of products is case hardening used on?

A

vehicle cam shafts, gears, bearings and valves

38
Q

What are the names of the two stages of case hardening?

A

1 carburising
2 quenching

39
Q

What is carburising in case hardening?

A

This changes the chemical composition of the surface if low carbon steel so that it can absorb more carbon to increase surface hardness. In industry, the steel is placed in a ceramic box which is packed with carbon. The box is then heated to about 930-950 degrees Celsius for a predetermined length of time. At this temperature, the carbon atoms can diffuse into the material’s structure to build up the surface carbon content. The depth of carbon layer is determined by the length of time the material is exposed to carbon. The longer the time, the thicker the carbon layer.

40
Q

What is quenching in case hardening?

A

The hot metal is quenched in water. This is a fast cooling process, which seals the hard surface case while not affecting the properties of the inner core.

41
Q

How can case hardening be completed in a workshop?

A

The steel is heated to red-hot, dipped in carbon powder, heated again and then quickly quenched in cold water.

42
Q

What is the process of hardening?

A

The process of heating medium and high carbon steels to alter the crystalline structure, holding them at this temperature for a given time and then quenching them in water, oil or salt water baths.

43
Q

What is the purpose of the hardening process?

A

The hardening and subsequent quenching greatly increases the hardness property but it also increases the brittleness of the material.

44
Q

What is tempering?

A

It is a heat treatment process for medium and high carbon steels that is carried out after hardening, to reduce some of the excess hardness and increase the toughness. The reduction in hardness leads to an increase in ductility and decreases the brittleness of the metal.

45
Q

How do you temper a metal?

A

The metal is heated to below the critical point for a given time and then slowly air cooled. The exact temperature will determine the amount of hardness removed.

46
Q

What does it mean by the critical point when tempering a metal?

A

The temperature at which the atoms of carbon and steel mix freely before bonding together to become a solid.

47
Q

The rise of tempering temperature of metal results in what? (2)

A

1 a reduction of hardness
2 an increase in toughness

DT (29 decks)

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