Wood has played an important role in the history of civilization. Humans have used it for fuel, building materials, furniture, paper, tools, weapons, and more. Our relationship to this resource has remained relatively unchanged over time, and our methods of developing and managing woodlands continue to rely on tried and true techniques established by early civilizations.
what is wood?
Wood is a porous and fibrous structural tissue found in the stems and roots of trees, and other woody plants. It has been used for thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers (which are strong in tension) embedded in a matrix of lignin which resists compression. Wood is sometimes defined as only the secondary xylem in the stems of trees,or it is defined more broadly to include the same type of tissue elsewhere such as in the roots of trees or shrubs.
In a living tree it performs a support function, enabling woody plants to grow large or to stand up by themselves. It also conveys water and nutrients between the leaves, other growing tissues, and the roots. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, or wood chips or fiber.
Here is the anatomy of a Tree:
1. Pith: The inner most part of the tree. Varies in shape and size. The pith is the oldest part of exogenous tree and when the plant becomes old, the pith dies and becomes and dark and fibrous.
2. Heart Wood: The portion surrounding pith. Strong and dark in color. Heart wood is useful for several engineering purpose. The dead part of wood and consists of various annular rings.
3. Sap Wood: Next to heart wood is sap wood. Sap wood is instrumental in the growth of trees through permitting sap to move upward. Annual rings in sap wood are less sharply divided and light in color. Sap wood may also be referred to as “alburnum”.
4. Cambium Layer: Thin layer of fresh sap between the sap wood and the inner bark. The Cambium layer has sap which is not still converted into sap wood. If the bark is removed and Cambium layer exposed to atmosphere, the cells cease to be active and the tree dies.
5. Inner Bark: An inner skin of tree defending the cambium layer. It provides protection for the delicate and very important cambium layer.
6. Outer Bark: The outer skin of the tree made up of wood fibers. Sometimes it contains cracks and gaps.
7. Vascular (Medullary) Rays: Thin radial fibers extending from pith to cambium layer. They work together to hold the annular rings. In some of trees they are broken and some others are simply not prominent.
what are the various stages of woodworking ?
There are various stages of the production cycle of wood:
1 – initial stage: determined after killing the tree, which does not occur randomly but according to some well-informed choices, in defense of forests. Private of branches and bark, is cut so as to obtain strips, with different axes of round or square cutting pattern according to the necessity.
2 – phase bonding: in which the wood is joined together by gluing substances that, thanks to the porosity of the material allows it to penetrate deeply in them.
3 – phase grouting, polishing and planing: in order to close the pores of the wood, reducing its roughness and promote the painting.
4 – painting phase: the paint which is applied, forms a solid and elastic film on the wood, with the purpose of protection from physical and chemical agents as well as aesthetic.
5 – the stage of application of the primer: paint product that has the purpose of creating the basis for the finishing paint, between a hand and the other the material must be sanded to achieve a smooth and homogeneous surface.
6 – finishing phase: constitutes the last layer of paint applied to the manufactured article to confer the final appearance.
What are its characteristics?
Strength: Physically, wood is strong and stiff but, compared to a material like steel, it’s also light and flexible. It has another interesting property too. Metals, plastics, and ceramics tend to have a fairly uniform inner structure and that makes them isotropic: they behave exactly the same way in all directions. Wood is different due to its annual-ring-and-grain structure. Wood is anisotropic, which means a lump of wood has different properties in different directions. Traditional wooden buildings are supported by huge vertical poles that transmit forces down into the ground along their length, parallel to the grain. That’s a good way to use wood because it generally has high compressive strength (resistance to squeezing) when you load it in the same direction as the grain. Wooden poles are much weaker placed horizontally; they need plenty of support to stop them bending and snapping. That’s because they have lower tensile strength (resistance to bending or pulling forces across the grain). Not all woods are the same, however. Oak has much higher tensile strength than many other woods, which is why it was traditionally used to make the heavy, horizontal beams in old buildings.
Durability: One of the best things about wood is how long it lasts. The buried remains of some ancient wooden article—a wooden tool, perhaps, or a simple rowboat or the remnants of a huge building—that are hundreds or even thousands of years old. Like other natural materials, it’s subject to the natural forces of decay through a process known as rotting, in which organisms such as fungi and insects such as termites and beetles gradually nibble away the cellulose and lignin and reduce wood to dust.
Wood and Water: It’s hygroscopic, which means that, just like a sponge, it absorbs water and swells up in damp conditions, giving out the water again when the air dries and the temperature rises. The trunk of a tree is designed to carry water from the roots to the leaves. A freshly cut piece of “green” wood typically contains a huge amount of hidden water, making it very difficult to burn as firewood without a great deal of smoking and spitting. Some kinds of wood can soak up several times their own weight of water, which is absorbed inside the wood by the very same structures that transported water from the roots of the tree to the leaves when the tree was a growing plant.
Wood and energy: It’s a relatively good heat insulator (which comes in handy in building construction), but dry wood does burn quite easily and produces a great deal of heat energy if you heat it up beyond its ignition temperature (the point at which it catches fire, anywhere from around 200–400°C, 400–750°F). Although wood can absorb sound very effectively , wooden objects can also be designed to transmit and amplify sounds—that’s how musical instruments work. Wood is generally a poor conductor of electricity but, interestingly, it’s piezoelectric (an electric charge will build up on wood if you squeeze it the right way).
types of wood
Wood is divided into two distinct kinds called hardwood and softwood, though confusingly the names don’t always refer to its actual hardness or softness:
- Hardwoods are ones that come from broad-leaved (deciduous) trees (those that drop their leaves each fall, also known as angiosperms because their seeds are encased in fruits or pods). Examples include ash, beech, birch, mahogany, maple, oak, teak, and walnut.
- Softwoods come from evergeen (coniferous) trees (those that have needles and cones and retain them year-round, also called gymnosperms). Examples include cedar, cypress, fir, pine, spruce, and redwood.
It’s generally true that hardwoods are harder than softwoods, but not always. Balsa is the best-known example of a hardwood that is actually very soft. Hardwoods have lovely, attractive grains and are used for such things as making fine furniture and decorative woodwork, whereas softwoods often come from very tall, straight trees, and are better suited for construction work (in the form of planks, poles, and so on).
how wood was used THROUGHOUT history ?
The ancient Middle East
Today it is hard to believe that in antiquity vast forests were growing in the Middle East. However, during the early part of the third millennium BCE, the mountain slopes of this region were covered with massive cedar forests. These forests disappeared in the millennia before Christ’s birth about two thousand years ago. The destruction of the cedar forests of the Middle East is told in the oldest know, surviving written story in the world: The epic of Gilgamesh. The epic was written in Mesopotamia sometime during in the 3rd millennium BCE.
The forests of the ancient Near East were the resource for the construction of temples and palaces in the kingdoms and empires in the Fertile Crescent. The rulers of these kingdoms and empires undertook massive building programmes to display their power and wealth.
The Phoenicians, one of the oldest sea-trading nations in the world, needed timbers for their ships and used the cedars of Lebanon to construct them. Writers such as Homer, Pliny, and Plato, along with the Old Testament provide us with well-documented descriptions of the once richly forested mountains of Lebanon. The Bible also vividly describes the practice of rulers in the Ancient Middle East to fell cedar trees to build massive monuments.
The Hellenic period
In the millennium that followed the Greek world developed into one of the major power centres of the Mediterranean. Two conditions were important for the growing influence of this region: the first is the long coastline of Asia Minor and Greece and the many islands scattered along these coasts; secondly the availability of timber. The first condition made communication by sea easy and the availability of timber made this communication possible because it allowed the construction of ships. The availability of wood turned the different civilisations that developed in Greece and Asia Minor into formidable maritime and trading powers.
The Roman period
For the Romans, as for other civilisations before, wood played an important role in their economy. The importance of wood is reflected in Pliny’s Natural History.
In Pliny’s time Italy was almost completely stripped of its forest cover. For this reason the Romans had to import most of the timber form all parts of the Empire and metallurgic industries, which depended heavily on charcoal, moved out of Italy. The centres of mining and metal smelting became the most deforested areas of the Roman Empire. The Romans realised that these forests were an important resource for their industries. Faced wood shortages, Rome increasingly turned to northern Europe for their wood supplies. Unfortunately for them they never succeeded in conquering the areas east of the Rhine and they had to turn elsewhere for timber, in particular to the Mediterranean.
The rise of Britain
During late Middle Ages and early Modern Period, of large-scale shipping and industry around the North Sea basin, shortages of wood only appeared in the early Modern Period.
In England the first signs of timber shortages were noticed during the wars against France in the 1620’s. In order to obtain enough timber for its fleet, England started to import wood supplies, first from the Baltic region and Scandinavia, later from the Colonies in North America. In the middle of the 18th century Europe faced an acute shortage of wood, and as a consequence, an energy crisis. The response to the energy shortage was the increasing use of an inferior fuel: coal.The change from wood to coal as major energy source had far reaching consequences.
The shift to coal first happened in England, where the shortage of wood was most acute. Wood was not only used for the construction of ships but also for heating and cooking as well as industrial processes. In order to provide a sufficient supply of charcoal woodlands in England were managed with a coppice rotation system but over time these woodlands could not supply enough fuel for the growing demands of domestic users and industry, in particular the iron industry. The problem was that mineral coal was useless for iron smelting so the industry desperately needed wood. However, in regions where wood was scarce but coal abundant Iron masters had long been experimenting with coal as a fuel for smelting.
Finally the Darby family in the early 18th century, succeeded with transforming coal into coke. This processed type of coal was clean and therefore useful as a fuel to smelt iron. The knowledge how to make coke spread slowly but surely and soon the production of iron rose because of the abundant availability of the new fuel in many localities, especially Northern England and the Midlands. These developments ended the supremacy of wood as a construction material and fuel and it was replaced by steel as the chief construction material and coal as the major energy source.This process was also reinforced when the railways, also depending on coal, could transport the fuel to any part of the country making the production of iron independent of the location. The coal revolution in England made it the first country to leave the wood era, and enter the true iron age and the industrial period.
How is it used today?
- Plywood is made by taking layers of wood (or plies) and gluing them together with an outer coating of veneer. Typically each ply is placed at 90 degrees to the one underneath so the grains alternate. That means a piece of plywood is usually much stronger than a piece of the natural wood from which it’s made.
- Laminated wood is a weaker kind of plywood in which the grain of each layer runs in the same direction.
- Particle board (often called chipboard) is made by taking the waste chips, flakes, and sawdust from a mill and forcing it under high pressure, with glue, in a mold so it sticks together to make planks and panels. Low-cost and self-assembly furniture is often made this way.
- Fiber-board is similar, but made with wood-pulp fibers instead of wood chips and sawdust.
- Hardboard is a thin sheet of wood made from wood fibers in much the same way.
image source: https://en.wikipedia.org/wiki/Wood