Timber is a part of a tree means it is the best piece of log used for different purposes of designing in Civil Engineering. Timber has it another name called Lumber. So, that friends today we will talk about the trees, timber, parts of timber and the conversion to timber.
Trees are of three types:
- Trees possess distinct annual rings but indistinct medullary rays.
- The wood obtained from these trees is soft, weak, resigns, light in weight and light in colour hence are called softwood trees.
e.g. chir, deodar, pine, spiace
- These trees are also termed as broad-leaved trees.
- They shut their leaves in autumn which again grow back in springs.
- Wood obtained from these trees is hard, strong, heavy, non-resinous and dark in colour, hence called hardwood.
- These trees possess indistinct annual rings but distinct medullary rays.
- The wood used for engineering activities is mostly derived from these trees.
e.g. sal, teak, babool, oak.
- These are the trees which grow in bulk in an inward direction and consist of fibrous mass throughout the longitudinal section.
- Wood obtained from these trees has limited engineering applications.
e.g. Bamboo, cane, Palm.
Structure of tree
Tree basically consists of three distinct parts root, trunk, crown and timber cames out from the trunk. Timber has its inner structure like spider web consists of six parts.
- Cambium layer
- Medullary rays
- The innermost central portion of the tree is called pith or medulla.
- It entirely consists of cellulose which is used for nourishment of plant at its young age. As the plant grows into the tree it decays and does not take any active part in the growth of the tree.
- The movement of sap that takes place from wood surrounding pith.
- It is the darkest portion along the horizontal section of a tree trunk.
- The inner annual rings surrounding pith constitutes the heartwood. Its colour is also dark that represents the dead portion of tree i.e. this portion of the tree also does not take any part in actively growing tree but imparts strength and rigidity to it.
- The wood used for engineering purposes is mostly heartwood.
- The outer annular rings in between cambium layer and heartwood constitute sapwood.
- Its colour is comparatively light that represents, its active role in the growth of the tree.
- Cambium layer constitutes sap which is not yet being converted into sapwood i.e future growth of the tree is dependent upon the presence of these cambium layers only.
- If due to any purpose bark of the tree is removed, exposing the cambium layer, it leads to scissor of cells of wood in the cambium layer that finally leads to the death of the tree.
- The radial fibres extending from pith to the cambium layer holding the annual rings of sapwood and heartwood together is termed as medullary rays.
- The strength of the timber section in a transverse direction dependent on those medullary rays.
- It is protective covering provided over the cambium layer in order to safeguard the future growth of the tree.
Also read:-What is Cement. Types of cement
Processing of timber
Processing of timber is carried out in 3 distinct operation
- Felling of trees
- Seasoning in timber
- Conversion to timber
1.Felling of trees
- Felling of trees should be done at suitable age as if tree are cut when they are overmatured, decayed wood is obtained while cutting under mature trees gives softwood. In neither of cases, it is useful in engineering activities. Hence trees should be cut when it is sufficiently matured (50-100) years of age.
- Trees should be cut in such a way that maximum wood obtained from it. Hence for this purpose sawing is done just above the section over the ground.
- Felling of trees should be carried out in season when the abutment of sap is minimum.
- Hence, felling should be avoided in autumn and spring when sap moves vigorously through the section of the tree.
- In hilly areas cutting should be done in mid-summer and in winter rainfall occurs and in plain areas cutting in summer be done in winters as excessive loss of moisture may have a place in summers (shrinkage and cracking of timber).
2.Seasoning in timber
- Newly felled trees consist of approximately 50% of water by weight hence they are to be dried before using it in any engineering activities.
- This process of drying of timber to make it fit for engineering use is termed as a seasoning.
- Water in timber is generally present in between voids or in between cell walls. The former water is termed as free water and later is termed as bound water.
- During seasoning, free water is removed from the tree and the point at which it is completely removed is termed as fibre saturated point.
- Seasoning of timber can be carried out either naturally or artificially.
- It is the process in which logs of timber are boiled in water in temperature at which is placed up to a boiling point and is maintained for several hours after which it is dried naturally.
- Due to the increase in temperature of timber section rate of evaporation increases and the duration of seasoning reduces drastically.
- It is one of the quickest methods of seasoning but it is comparatively costly.
- In this method, the timber section is subjected to alternate cutting as wood is a bad conductor of electricity. It resists the flow of current thereby heating which.
- In this method logs of timber are placed in airtight and air which is fully saturated is forced in it at a temperature of 35-40 degree Celsius. The temperature in the kiln is increased gradually that leads to the heating of the timber section but does not result in evaporation. the relative humidity of air is now reduced gradually that leads to uniform drying of timber section.
- It is the process in which logs of suitable sections are immersed in water and are subjected to a stream of flowing water stream that larger portion of the section is placed in the upstream direction of flow that carries out removal of sap from the wood and water that replaces the sap can be removed comparatively in shorter duration.
- In this method of seasoning section of wood is immersed in a solution of suitable salts that increase the rate of evaporation and helps in bringing down the duration of seasoning.
3.Conversion to timber
- The process of sawing of timber into a section of suitable shape and size is termed as the conversion of timber.
- Conversion of timber can be carried out by any of the following methods:
- It is the most general, economical and easiest method of sawing available in which the cuts are made tangential to the annual rings.
- The wastage of timber in this method of sawing is very less. Hence it is found to be the most economical method but the sections obtained by this method are liable to shrink and warp.
- It is the method of sawing in which cuts are made at right angles to each other.
- This method of sawing is generally adopted when the annual rings are indistinct.
- The sections obtained by this method are liable to bend in a transverse direction.
- It is the method of sawing in which cuts are made tangential to the annual rings that meet each other at a right angle.
- The strength of the section obtained in this method of sawing is minimum as medullary rays are also cut that is used for holding the annual rings in position.
- It is a method of sawing in which cuts are made parallel to medullary rays in the radial direction that gives decorative effect in it.
- The section obtained in this method of sawing is strong but wastage, in this case, is comparatively more.