1.3 Enhancement of materials

A comprehensive set of 50 flashcards covering the performance characteristics, enhancement methods, and processing techniques for polymers, woods, and metals based on the lecture material.

What three factors besides product function must a designer consider for material selection?

Manufacturing method, material cost, and impact on the environment.

What is the original natural source of papers and boards?

Wood pulp.

At what stage does the largest amount of shrinkage occur in wood?

After the tree is cut down and is seasoned.

Approximately what percentage of the Earth's crust is made up of metal ores?

$$25\,\text{per cent}$$

What is the most common ore mined from the ground?

Bauxite.

How are polymers typically produced from crude oil?

Via the fractional distillation of crude oil.

What are some natural sources that can be used to make biodegradable polymers?

Cellulose, sugar, and starch.

What is the primary purpose of material enhancement?

Improving a material's properties to better suit the requirements of the final product.

How can the toughness of brittle metals be improved to prevent fracture during shaping?

The use of heat treatments to alter the crystalline structure.

What specific type of additive helps a polymer flow more easily into a mould?

Process aids (such as lubricants).

Which substances are commonly used as lubricants in polymer processing?

Wax or calcium stearate.

What is a manufacturing benefit of adding lubricants to polymers?

They allow more intricate shapes to be formed and can lower moulding temperatures to save energy.

What additives prevent a polymer from discolouring due to excessive heat during processing?

Thermal antioxidants.

What are pigments?

Tiny particles mixed into the polymer in its molten state to give colour to the final product.

Why are antistatics added to polymer products like electric wire covers?

To improve surface conductivity by attracting moisture, which reduces the build-up of static electrical charge that attracts dirt.

Which chemical elements or substances are added to polymers to act as flame retardants?

Bromine, chlorine, phosphorous, or metal.

What is the function of plasticisers in materials like PVC or LDPE?

They allow plastics to become less hard and brittle at normal use temperatures and help in processing.

What are the two main functions of fillers in polymer production?

To provide bulk to the product (reducing the amount of polymer needed) and to improve polymer properties.

Name three materials commonly used as mineral fillers.

Chalk, clay, and calcium carbonate.

How do mineral fillers affect the mould cycle times in polymer manufacturing?

They increase thermal conductivity, meaning the material heats up and cools down more quickly.

What are the visible effects of polymer degradation caused by exposure to oxygen?

Increased brittleness, surface cracks, and pigment discolouration.

What do UV light stabilisers prevent in polymer chains?

They prevent the chains from being broken down by sunlight.

What color change typically occurs in white pigmented polymers due to UV attack?

They will turn yellow.

What are the three types of bio-batch additives used to encourage degradation?

Oxy-degradable, photodegradable, and hydro-degradable.

In what type of products are oxy-degradable additives commonly used?

High volume single use items such as food packaging and carrier bags.

What does the term 'anisotropic' mean in relation to natural wood?

It has different properties in different directions, such as being easier to split along the grain than against it.

Why is copper often used in wood preservatives?

It is a naturally occurring mineral with excellent fungicidal properties.

How is wood treated to increase its hardness for high-wear situations like flooring?

It is impregnated with a modified natural polysaccharide that cures within the wood cell structure.

Why are softwoods considered more environmentally friendly than hardwoods for manufacturing?

They grow much faster and have a faster replanting time.

What are the standard dimensions for long, wide sheet materials in the wood industry?

$$1,220\,\text{mm} \times 2,440\,\text{mm}$$

Which resin is used to compress wood chips to create chipboard?

Urea formaldehyde.

What is a key aesthetic enhancement applied to most manufactured boards?

Veneers laminated onto the surface.

What do the abbreviations SCL and LVL stand for in the context of engineered wood?

Structural composite lumber (SCL) and Laminated veneer lumber (LVL).

What are the advantages of SCL and LVL over original natural wood?

They are less prone to defects like warping, splitting, or shrinking, and have greater load bearing properties.

Metal properties are influenced by the structure of what tiny components?

Metal grains.

What is work hardening?

The improvement of tensile strength and hardness in a localised area when a metal is cold worked.

What process is used to remove the effects of work hardening and make metal more ductile?

Annealing.

Describe the industrial cooling process for annealing metal.

The metal is heated and then very slowly cooled.

What is the maximum carbon content allowed in steels for case hardening?

Less than $0.4\,\text{per cent}$ carbon.

Which process changes the chemical composition of low carbon steel's surface to increase hardness?

Carburising.

In industrial carburising, to what temperature range is the steel heated in a ceramic box?

$$930\text{--}950\,^\circ\text{C}$$

What determines the depth of the carbon layer during the carburising process?

The length of time the material is exposed to carbon at high temperature.

At what temperature is a product heated before quenching during the case hardening process?

$$760\,^\circ\text{C}$$

What is quenching?

The rapid cooling of a heat-treated metal, often in water, oil, or salt water baths.

What is the primary purpose of quenching in the case hardening process?

It seals the hard surface case while not affecting the properties of the inner core.

What happens to a medium or high carbon steel's properties immediately after the hardening process?

Hardness increases greatly, but so does the material's brittleness.

What heat treatment is performed after hardening to reduce excess hardness and increase toughness?

Tempering.

To what temperature level is metal heated during the tempering process?

Below the critical point.

What does 'tempering colour' indicate on a metal?

The temperature at which brittleness is removed.

Which term describes the temperature at which atoms of carbon and steel mix freely before bonding?

Critical point.