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© Boardworks Ltd 20051 of 22 Resistant Materials Woods These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page. This icon indicates that the slide contains activities created in Flash. These activities are not editable. For more detailed instructions, see the Getting Started presentation. © Boardworks Ltd 2005 1 of 22
© Boardworks Ltd 20052 of 22 Learning objectives © Boardworks Ltd 20052 of 22 Learning objectives To understand the origins and structures of woods. To be able to describe the properties different woods have, and select appropriate woods for different uses. To be familiar with the different market forms of timbers. To realize the advantages and disadvantages of natural timber. To understand how manufactured boards are made and used.
© Boardworks Ltd 20053 of 22 The bark retains moisture in the body of the tree. It also protects the tree from the weather and prevents insect infestation. Under the bark, the tree grows. Sapwood cells are young, living cells. As these age, heartwood is formed. The heartwood is the wood we use to make products in design and technology. bark sapwood heartwood Inside a tree
© Boardworks Ltd 20054 of 22 There are two main groups of timbers: natural and manufactured. Natural timbers are produced from trees. There are two main groups of natural timbers: hardwoods and softwoods. Manufactured boards are produced using wood and glue. Timbers Hardwoods are obtained from short, fat trees which grow slowly in rainy climates. Softwoods are produced from tall, thin trees which grow quickly in cold, dry climates.
© Boardworks Ltd 20055 of 22 Where does wood come from?
© Boardworks Ltd 20056 of 22 Categories of timber
© Boardworks Ltd 20057 of 22 usually grow in colder climates and are mainly grown in Scandinavia and Northern Europe grow thin, needle-like leaves grow relatively quickly (30 years) are easier to sustain than hardwood trees are easy to cut and shape are usually cheaper than hardwoods. Softwoods Softwoods are usually obtained from coniferous trees, which keep their leaves in winter. Softwoods:
© Boardworks Ltd 20058 of 22 Hardwoods Hardwoods are usually obtained from deciduous trees, which lose their leaves in autumn. Hardwoods: usually grow in warmer more humid climates, mainly in South America and Asia grow slowly (80+ years) are more difficult to sustain than softwoods are more expensive than softwoods are strong and hardwearing.
© Boardworks Ltd 20059 of 22 Tropical hardwoods grow in the tropical rainforests of Central and South America, Asia and Africa. They grow very slowly, taking about one hundred years to mature. There are ecological issues regarding the harvesting of tropical hardwoods, as this can cause soil erosion, river pollution and problems with the atmosphere. If they are not sustained by replanting, they will be lost forever. Tropical hardwoods Tropical hardwoods include mahogany and teak. These woods have a strong colour and are hard to shape.
© Boardworks Ltd 200510 of 22 Timbers and their properties
© Boardworks Ltd 200511 of 22 Pine is a plentiful, native, sustainable softwood. It has a natural beauty which designers and users like. It is easy to work, which manufacturers find useful. Its availability and low cost has made it popular for the construction of domestic furniture over the years. Use of softwoods
© Boardworks Ltd 200512 of 22 Hardwoods like teak can be used for outdoor furniture. Alternatives to teak are being exploited. These alternatives are carefully harvested. They do not cause environmental damage or loss of natural resources in tropical rainforests. Uses of hardwoods
© Boardworks Ltd 200513 of 22 British hardwoods like oak are native, sustainable timbers. They have been used to produce attractive, high quality, durable furniture for hundreds of years in this country. Uses of hardwoods
© Boardworks Ltd 200514 of 22 Stock forms of timber
© Boardworks Ltd 200515 of 22 Wood is a natural material. Natural timber is widely used because it: is readily available is easy to cut and shape is relatively inexpensive looks good – it is aesthetic feels good – it is tactile. The advantages of natural timbers Knots can be a problem when you are working with natural timbers. However, it is possible to make a real feature of the interesting effects of knots.
© Boardworks Ltd 200516 of 22 Using wood outdoors The good weatherproof qualities of some timbers make them ideal for use in garden fence panels.
© Boardworks Ltd 200517 of 22 As a natural material, timber has some problems: it has irregular properties its grain varies it is stronger in some places than others knots can be a real problem because the wood is so hard wood is hygroscopic – it absorbs and releases water (this makes it shrink, swell and warp) woodworm may be a problem (not a problem for metals and plastics!). The disadvantages of natural timbers
© Boardworks Ltd 200518 of 22 Manufactured boards are made from the waste sections of felled trees. The wood is reduced to pulp, particles or thin strips and bonded together using special adhesives or resins. Manufactured boards come in sheet form (usually 1.2 x 2.4m) are extremely stable and of uniform thickness are less expensive than laminating planks of timber can be covered with veneers are available in a variety of thicknesses (3, 6, 9, 12, 15, 18, 22mm etc). Manufactured boards These flat-pack drawers are made from MDF covered with a veneer.
© Boardworks Ltd 200519 of 22 Manufactured timbers do not warp like natural timbers, and can be produced as large flat sheets. A simple example of this is blockboard. Blocks of wood are cut and glued together with the grain running in different directions. The blocks are then covered with a large, flat sheet of veneer. Blockboard natural timber blockboard
© Boardworks Ltd 200520 of 22 Plywood is a manufactured timber that has been used since the 19 th century for large, flat panels. A sharp blade cuts very thin layers (veneers) of wood as the timber is rotated. One layer of ply is called a veneer, and can be glued onto less expensive timber to produce a more attractive finish. 3 (or 5 or 7) layers or plies are glued together to make plywood. Plywood
© Boardworks Ltd 200521 of 22 A closer look at manufactured boards
© Boardworks Ltd 200522 of 22 Key points © Boardworks Ltd 200522 of 22 Key points Timbers can be broken down into three categories: hardwoods, softwoods and manufactured boards. Hardwoods include oak and beech. Hardwoods are usually tougher and more expensive than softwoods, such as pine and spruce. Timbers come in a variety of forms, for different uses. Natural timbers are readily available and aesthetically pleasing. However, they can suffer from warping, knots and woodworm. Manufactured boards, such as plywood and MDF, come in large sheets. They are less expensive than planks of timber and can be covered with a veneer to improve their appearance.
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