TIMBERSubmitted By:AkshayIsha PreetiRAKSHIT

INTRODUCTIONTimber denotes wood the organic matter obtained from trees which is suitable for building or for carpentry and various engineering purposes

CLASSIFICATION OF TREES :

Trees Exogenous

Conifers

DeciduousEndogenou

s

TYPES OF TREES:ENDOGENOUS : THE TREES WHICH GROWS INWARDS IN LONGITUDINAL FIBROUS MASS ARE CALLED ENDOGENOUS TREES .FOR EXAMPLE : PALMS BAMBOO

EXOGENOUS TREES :

THE TREES WHICH GROWS OUTWARDS ACROSS HORIZONTAL SECTION OF STEM ARE CALLED EXOGENOUS TREES .THEY ARE FURTHER DIVIDED INTO TWO TYPES :1. CONIFERS or EVERGREEN: They gives soft wood They have pointed leaves for example : sall,devdar,shisam2. DECIDUOUS : They gives hardwood They have broad leaves for example :teak ,toona

TREE STRUCTURE :

SEASONING OF TIMBER : This is a process by which moisture content in a freshly cut tree is reduced to

a suitable level. By doing so the durability of timber is increased. The various methods of seasoning used may be classified into:(i) Natural seasoning(ii) Artificial seasoning.

1. NATURAL SEASONING :1. Air seasoning:  It may be air seasoning or water seasoning. Air seasoning

is carried out in a shed with a platform. Over a period, in a natural process moisture content reduces. A well seasoned timber contains only 15% moisture. This is a slow but a good process of seasoning.

2.Water seasoning : Water seasoning is carried out on the banks of rivers. The

thicker end of the timber is kept pointing upstream side. After a period of 2 to 4 weeks the timber is taken out. During this period sap contained in the timber is washed out to a great extent. Then timber is stalked in a shed with free air circulation.t 300 mm high platform timber balks are stacked

2. ARTIFICIAL SEASONING :  In this method timber is seasoned in a chamber with regulated heat,

controlled humidity and proper air circulation. Seasoning can be completed in 4 to 5 days only. Thedifferent methods of seasoning are:(a) Boiling(b) Kiln seasoning(c) Chemical seasoning(d) Electrical seasoning.

TYPES OF ARTIFICIAL SEASONING :1.BOILING SEASONING : In this method timber is immersed in water and then water is boiled for 3 to 4 hours . Then it is dried slowly. Instead of boiling water hot steam may be circulated on timber. The process ofseasoning is fast, but costly.2.Kiln Seasoning: Kiln is an airtight chamber. Timber to be seasoned is placed inside it. Then fully saturated air with a temperature 35°C to 38°C is forced in the kiln. The heat gradually reaches inside timber. Then relative humidity is gradually reduced and temperature is increased, and maintained till desired degree of moisture content is achieved.

3.Chemical Seasoning: In this method, the timber is immersed in a solution of suitable salt . Then the timber is dried in a kiln. The preliminary treatment by chemical seasoning ensures uniform seasoning of outer and inner parts of timber.

4.Electrical Seasoning: In this method high frequency alternate electric current is passed through timber. Resistance to electric current is low when moisture content in timber is high. As moisture content reduces the resistance reduces. Measure of resistance can be used to stop seasoning at appropriate level.

ADVANTAGES OF SEASONED TIMBER : It has reduced weight It is strong and durable It has resistant to decay or rot It takes high polish It is easier to work Its life is more

DISADVANTAGES OF TIMBER : Combustible Diminish due to rusting Destroyed and decayed due to attack of insects ,fungi ,termites etc. Timber swells and undergoes shrinkage with changing atmosphere

humidity Subjected to rot dry rot and wet rot if not seasoned

USES OF TIMBER : Air dispenser Artificial limbs Bakers equipment Balconies, decks and

terraces Boat and Ship construction Bee hives Cladding Carvings and sculptures Cooperage Cabinet making Fencing Flooring Railway sleepers Windows Furniture Glass manufacture Log

cabins Musical instruments Construction of houses

DEFECTS IN TIMBER : (i) Due to natural forces

(ii) Due to defective seasoning and conversions.(iii) Due to attack by fungi and insects.(iv) Defects due to Natural Forces: The following defects are caused by natural forces:

(a) Knots (b) Shakes (c) Wind cracks (d) Upsets

(A)Knots: When a tree grows, many of its branches fall and the stump of these branches in the trunk is covered. In the sawn pieces of timber the stump of fallen branches appear as knots. Knots are dark and hard pieces. Grains are distorted in this portion. If the knot is intact with surrounding wood, it is called live knot. If it is not held firmly it is dead knot.

(B) Shakes: The shakes are cracks in the timber which appear due to excessive heat, frost or twisting due to wind during the growth of a tree. Depending upon the shape and the positions shakes can be classified as star shake, cup shake, ring shakes and heart shakes

(c) Wind Cracks: These are the cracks on the outside of a log due to the shrinkage of the exterior surface. 

(d) Upsets: This type of defect is due to excessive compression in the tree when it was young. Upset is an injury by crushing. This is also known as rupture.

DETERIORATION OF TIMBER : There are so many reasons for deterioration of timber .but there are three

main harmful reasons for deterioration of timber 1.decay or rot 2.insects 3.fire

1.DECAY OR DRY ROT Decay or rot of timber is the result of the activity of various bacteria's and

fungi , which utilize as food ; they require both oxygen excess moisture . Hence timber having moisture content below 25% will not rot easily .

Dry rot is wood decay caused by certain species of fungi that digest parts of the wood which give the wood strength and stiffness. It was previously used to describe any decay of cured wood in ships and buildings by a fungus which resulted in a darkly colored deteriorated and cracked condition.

2.INSECTS :There are so many insects which attacked a wood ,out of termites (white ants ) are the main insects which are very dangerous for timber .termites of one class live under the ground and eat wood and forms tubes and tunnels inside it

3.FIRE Fire is also the damaging factor for timber .as timber has tendency to burn so fire can damage it easily

PRESERVATION OF TIMBER : Preservation of timber means protecting timber from fungi and insects attack so that its life is increased. Timber is to be seasoned well before application of preservatives. The following are the widely used preservatives:1. Tar2. Paints3. Chemical salt4. Creosote5. ASCO

1. TarHot coal tar is applied to timber with brush. The coating of tar protects the timber from the attack of fungi and insects. It is a cheapest way of protecting timber. Main disadvantage of thismethod of preservation is that appearance is not good after tar is applied it is not possible to apply other attractive paints. Hence tarring is made only for the unimportant structures like fence poles.

2. PaintsTwo to three coats of oil paints are applied on clean surface of wood. The paint protects the timber from moisture. The paint is to be applied from time to time. Paint improves theappearance of the timber. So lignum paint is a special paint which protects the timber from the attack of termites.

3. Chemical saltThese are the preservatives made by dissolving salts in water. The salts used are copper sulphate, masonry chloride, zinc chloride and sodium fluoride. After treating the timber withthese chemical salt paints and varnishes can be applied to get good appearance.

4. CreosoteCreosote oil is obtained by distillation of coal tar. The seasoned timber is kept in an air tight chamber and air is exhausted. Then creosote oil is pumped into the chamber at a pressure of0.8 to 1.0 N/mm2 at a temperature of 50°C. After 1 to 2 hours timber is taken out of the chamber.

5. ASCOThis preservative is developed by the Forest Research Institute, Dehradun. It consists of 1 part by weight of hydrated arsenic pentoxide (As2O5, 2 H2O), 3 parts by weight of copper sulphate(CuSO4⋅5 H2O) and 4 parts by weight of potassium dichromate (K2Cr2O7) or sodium dichromate (Na2Cr2O7⋅2 H2O). This preservative is available in powder form. By mixing six parts of this powder with 100 parts of water, the solution is prepared. The solution is then sprayed over the surface of timber.This treatment prevents attack from termites.

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