Design Technology - 4.2 Materials

Contains info: Timber, metals and alloys, glass, textiles, composite.

Hardwoods

Hardwoods come from deciduous trees (broad-leafed trees) and generally have the following characteristics:

Slow growth (100+ years) & expensive (due to slow growth)

Stronger & more durable than softwoods

Wider planks available

More dense

Dark colour

Softwoods

Softwoods come from coniferous trees (cone bearing) and generally have the following characteristics:

Fast growth (20 years) & Low cost (due to the fast growth)

Long straight shape

Narrow planks

Less dense

Knotty

Grain

The lines/pattern running the length of the wood

These are growth rings of the tree

Wood is stronger parallel to the grain than perpendicular

Knots

Knots are branches that have grown from the trunk

Knots are very hard to cut and can fall out

Colour

Different types of timber have different colours

Some timbers (hardwoods) are selected because of their deep rich colour

Natural Characteristic - Smell

Some natural timbers have a unique/distinct smell

This can enhance the user experience/create an emotional response/evoke memories

Cedar is often used in saunas and it has a distinctive smell

Hickory and other aromatic woods are used for smoking foods and infusing flavour

Reason for seasoning

Timber is typically about 85% moisture

Once cut, the timber begins to lose moisture

Timber needs to have a moisture content below 20% for exterior applications and below 15% for interior applications

Seasoning

Once timber is felled and sawn it must be seasoned to prevent it from distorting →

Seasoning removes the moisture from the tree evenly

Correctly seasoned timber improves the strength, stability, resistance to decay of the wood and makes it easier to apply finishes or use adhesives/fasteners

Air-Dried Seasoning

Air-dried seasoning is the least expensive method

Air-dried timber planks are stored under cover and left to dry naturally

Air dried timber can only be used for outdoor applications as the moisture content of the wood is the same as the air outside

Kiln-dried seasoning

Kiln-dried seasoning is the most expensive method

Kiln-drying uses steam to artificially dry the timber and speed up the drying process

Produces the straightest timber that can be used indoors as it has a lower moisture content

Sustainable Timber production

Timber is considered to be a sustainable product as new trees can be grown to replace felled trees

In many parts of the world, timber is harvested faster than the rate it is being replanted

This causes many environmental problems such as desertification, deforestation and global warming

Sustainable Timber Production - sustainability

This means the supplier should be able to prove the timber has been sustainably harvested

FSC (Forest Stewardship Council)

Man-made Timber

Man-made timber is made in a factory by combining timber with adhesive

They can be made from waste wood, low-grade or recycled timber

Developed as an alternative to natural timbers

Are so popular now that companies are making all their products from manufactured boards

Man-made Timber - Plywood

Layers of veneer are glued together. The grain of each layer is perpendicular to each other

Very strong and stable and does not warp

Layers are visible on edges

Man-made Timber - MDF (medium density fibreboard)

Small wood fibres are pressed together with adhesive

Smooth surface, no wood grain

Not water resistant. The fine wood dust can cause health problems when sanding

Man-made Timber - Particle Board

Large wood chips are pressed together with adhesive

No wood grain

Not water resistant. Poor quality surface and edges. Usually covered with veneer

Advantages of man-made timber

Available in much larger sheets than solid timber

Can make large pieces of furniture without joining wood together

Consistent thickness & properties throughout the board

No knots or uneven parts in the wood

Advantages of man-made timber

They do not warp or twist as much as natural timbers

No need for seasoning

Smooth surface finish which requires little preparation

Available in many different finishes, veneers, and laminates

Lower cost compared to similar sized natural timber

Disadvantages of man-made timber

Toxic glues like Urea Formaldehyde used in the production which makes recycling difficult and cutting/sanding hazardous

Fall apart when wet (MDF and Particle Board)

Only available in thin sheets (up to 20mm)

Cannot support heavy loads over large spans (MDF and Particle Board)

Unattractive edges/surfaces that need to be covered with a finish

Do not take fasteners well (screws, nails)

Finishes

Timber needs to be finished for two reasons:

Enhance the aesthetics of the timber

Protect the timber against damage from the elements/wear or insects