IGCSE Wood PDF

Wood Hardwood Hardwoods are produced from deciduous (shed their leaves annually) and evergreen broad-leaved trees. The growth of hardwood trees is generally slow, taking around 100 years. This makes hardwood expensive. Hardwoods generally have more attractive grain...

Wood Hardwood Hardwoods are produced from deciduous (shed their leaves annually) and evergreen broad-leaved trees. The growth of hardwood trees is generally slow, taking around 100 years. This makes hardwood expensive. Hardwoods generally have more attractive grain structures, textures and colours, and greater durability than softwoods. Softwood Softwoods are mostly produced from evergreen conifers with thin needle-like leaves. The growth of softwood trees is much quicker than that of hardwoods and most become mature enough for felling in under 30 years. Softwoods are relatively cheap and are also easier to sustain by replanting. Man-made boards are wood-based materials manufactured by bonding together wood strips, veneers (thin layers), pulp or particles. They represent a very important manufacturing material, particularly in the furniture industry. There is a limit to the number of wide boards that can be cut from a tree and this makes it natural timber expensive. Manufactured board is available in sizes up to 1525 mm wide whereas hardwood is typically 300mm and softwood is 200mm maximum. Manufactured board is stable and of uniform thickness and consistent quality. Processing Once a tree has been cut down, branches and bark have been removed it must be processed into useable pieces. Sawing is used to cut the timber log along its length. Through and through sawn Quarter Sawn Seasoning The process by which the moisture in the wood is reduced to a required level. By reducing the moisture content, strength, elasticity, and durability properties are developed. A well-seasoned wood contains 15% moisture content. Air Seasoning Kiln Seasoning Air seasoning is done in the shed and relies on natural air flow. Care is Wood is put into a kiln. Steam is first forced in to regulate moisture taken to see that there is proper air circulation around each piece of and kill fungi and insects, then regulated heat, controlled humidity wood, they are separated by smaller pieces called sticks. and dry air are circulated. Seasoning is completed in 4 - 5 days. Advantages Disadvantages Advantages Disadvantages Cheaper Takes longer Faster More costly May not produce as uniform Simpler results. Controlled conditions - consistency More involved process Processing Forms of Supply When a tree is converted it is cut up into a variety of standard sizes. Keeping a set of standards is important because it enables designers to know the size of material that will be available for products. Timber can be purchased in three main states: Rough Sawn PAR PBS Rough Sawn This is straight This means Planned All This means Planned Both from the saw mill and has a Round. The wood has been Sides. The wood has been rough surface from the saw put through a planning planned on both faces to teeth. machine. It is smooth on all make it smooth and parallel sides and is accurate to a but the edges are left rough certain size. sawn. FORMS Strip Board Square PAR Dowel Half Round Quadrant Veneer Veneer is wood that has been cut very thinly so it is like a piece of paper. Instead of sawing a log into boards it is put into a machine like a giant pencil sharpener. Very thin sheets of wood called veneers are peeled off the log. This is a very economical way to use wood particularly rarer more expensive woods because the thin veneer can be stuck onto a cheaper material. Veneer allows many interesting techniques because it is very flexible. It can be bent into complex shapes that are not possible with solid boards. Timber defects Manufactured Boards