Wood and its derivatives¶
Wood is a raw material obtained from the trunk and branches of trees.
Index of contents:
Wood properties¶
Wood from different trees have different properties, but there are some properties common to all of them.
- Hardness of wood
Hardness varies greatly between different woods. Balsa wood is very soft and can be scratched very easily. At the other extreme, oak wood is a very hard wood.
The hardness of most everyday woods is relatively soft compared to other materials such as stones, metals or even plastics.
- Mechanical resistance of wood
The mechanical resistance varies greatly depending on the orientation of the wood. In the sense of fibers, wood is much more resistant and supports around 1 or 2 kg per square millimeter.
In the direction perpendicular to the grains, the wood resists little and separates relatively easily. For this reason, laminated boards are made with the fibers of one layer perpendicular to the fibers of the next layer, so that the board is resistant in all directions.
Although its resistance is less than that of steel or concrete, with wood you can make houses, boats, furniture, floors, etc. As a curious fact, all the buildings in Venice are supported by wooden beams under water.
- Flexibility of wood
- Wood is a fairly flexible material. This makes it very suitable for making ship masts, bows, curved pieces, etc.
- Wood density
Wood has a density similar to water (1kg per liter). Most woods have a lower density and float on water, but some harder, higher-density woods sink in water.
The density of wood is light, similar to that of plastics. In comparison, the density of metals or stones is much higher.
- Wood conductivity
- Wood is a poor conductor of heat and electricity. This makes it warm to the touch and a good insulator.
- Hygroscopicity of wood
It is the capacity of wood to absorb water. When absorbing water the wood swells occupying more volume. This can lead to problems. For example, when a parquet floor gets wet, the wooden boards swell and bend, peeling off.
- Oxidation of wood
- Although wood is highly resistant to oxidation, in humid conditions it can be attacked by fungi that degrade it in the same way that oxidation degrades metals. To avoid this, surface treatments are usually given with oils, varnishes or resins.
- Ecological properties of wood
Wood and its derivatives are recyclable, biodegradable and non-toxic.
However, paper manufacturing is a very polluting process due to the chemical processes necessary to separate the cellulose fibers and bleach them.
- Other properties of wood
- Wood cannot be melted, nor is it malleable or ductile. Therefore, most of the manufacturing processes are based on processes to remove material: cutting, sawing, drilling or milling the wood.
Parts of the tree trunk¶
- Cortex
- It is the outer part of the trunk. Its function is to protect the inner layers.
- Sapwood
- It is the outermost wood of the trunk. It is younger, softer and lighter in color.
- Heartwood
- It is the innermost wood of the trunk. It is harder and darker in color.
Yew trunk in which the heartwood can be distinguished from the sapwood.¶
Obtaining the wood¶
- Tala
It is the process of cutting the trunk of the tree. Once cut, the smallest branches are removed.
Video: John Deere 1470G harvester
- Transport
- The cut logs are transported from the forest by truck or by river to the sawmill.
- Sawmill
In the sawmill the bark is removed from the trunk and sawn into boards, planks or slats.
The logs can also be laminated with a knife to obtain veneers.
Video: Laminator Lathe
- Replanted
For wood to be a renewable resource, it is necessary to replant the same number of trees that have been cut down.
In the countries with more ecological awareness, it is sought that the timber plantations are of several species to increase the resistance of the forests against pests and droughts as a consequence of climate change.
Types of natural woods¶
- Softwoods
They come mainly from conifers.
Pine, fir, cedar, poplar, balsa wood.
- Hardwoods
They have greater density and hardness, which is why they are more difficult to work.
Oak, beech, chestnut, walnut, eucalyptus, mahogany.
Wood derivatives¶
- Wood veneer
Wood can be laminated by cutting it with a blade like a pencil sharpener does.
These sheets of wood can be used to cover other derivatives of wood such as chipboard and give the surface impression of natural wood.
- Plywood
- It is a wooden board made of thin sheets of wood glued together like a sandwich. The fibers of each sheet of wood are placed perpendicular to the previous sheet to improve its mechanical resistance and prevent it from sagging with moisture.
- Agglomerate
It is made up of wood shavings (sawdust) glued together.
The chipboard surface is usually covered with natural wood sheets or colored plastic resin sheets to give an appearance of natural wood, granite, uniform color, etc.
- MDF or MDF
It is made up of pressed wood fibers, similar to those used to make cardboard, joined together by a resin glue.
The most used example in houses are the back sheets of cabinets.
- Cork
It is a material that is obtained from the bark of a tree, the cork oak.
It can be used to make panels that have a very good response to sound for soundproofing rooms. It is also used in bottle caps, panels to hang papers, etc.
- Paper
- It is made up of very fine wood fibers, bleached with oxygen or chlorine and pressed into thin sheets.
- Cardboard
Its manufacturing process is similar to that of paper, but the fibers are not bleached. It usually contains recycled paper.
Corrugated cardboard consists of several sheets of paper glued together, with the central sheet corrugated.
Vídeo: El cartón corrugado.
Commercial forms¶
- Solid wood
They are obtained directly by cutting the trunk of the tree.
Slats: Long pieces with a small rectangular or circular section.
Profiles and mouldings: long pieces with an L section or various small shapes.
Tablones: piezas de gran superficie y de grosor entre 3mm y 25mm.
Veneers: sheets of wood with a thickness of less than 3 millimeters, which are used to cover lower quality wood, the back of cabinets and the bottom of drawers.
- Derivatives of wood
They are obtained by pressing blocks, sheets, shavings or glued wood fibers.
Boards have large dimensions (120cm x 240cm) and are not very thick. They can be cut into smaller sizes based on customer drawings. They can be made of plywood, chipboard or fiberboard (MDF).
Paper and cardboard reels: are made up of paper or cardboard rolled into a long reel.