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TIMBER

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TIMBER:The wood which is suitable or fit for engineering construction or engineering purpose is called timber.

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WOOD:

The organic matter obtained from trees is called wood.

LUMBER: The sawed wood meant for construction in the form of boards is called lumber.

Structure of a Tree

TYPES OF TREES:Trees are classified into two groups depending upon growth pattern.(1) Endogenous trees:The trees which grow inwards in longitudinal fibrous mass are called endogenous trees.

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(2) Exogenous tress :

The trees which grow in out wards across horizontal section of stem are called exogenous trees.

These trees are only fit for engineering construction.

Exogenous trees are again subdivided in to two types.

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Conifers or Evergreen:They give soft wood.

They have pointed leaves.

Examples:Deodar

Pine

Chir

Kail,etc

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Deciduous:

These have hard wood.

These have broad leaves.

Examples:

Teak

Sal

Shisham, etc.

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Hardwood Trees

Developed by:Nadeem Asghar 11

Softwood Trees

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SEASONING OF TIMBER:As fresh timber which is obtained from trees contains about 30 to 40 % sap or moisture. This sap is very harmful for the life of a timber. Therefore, it is necessary to remove that sap by applying some special methods. All those methods which are used for removing the sap from timber are collectively termed as seasoning of timber.

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Advantages of seasoned timber:

It has reduced weight,

It is strong and durable,

It has resistance to decay or rot,

It takes high polish,

It is easier to work,

Its life is more.

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Types of Timber Seasoning:

The main types of timber seasoning are as under.

(1)Natural Seasoning,

(2)Artificial Seasoning,

(a) Kiln Seasoning,

(b) Chemical Seasoning,

(c) Electric Seasoning,

(3) Water Seasoning,

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(1) Natural Seasoning:

In the air seasoning or natural seasoning or natural drying, seasoning of timber, timber is dried by direct action of air, wind and sun. In this method, the timber logs are arranged one over the other, keeping some space or distance between them for air circulation of fresh air.

Generally this type of seasoning requires few months to over a year, this is very slow process.

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(2) ARTIFICIAL SEASONING

(a) Kiln Seasoning,

(b) Chemical Seasoning,

(c) Electric Seasoning,

Developed by:G.S.Solangi 17

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(a) Kiln Seasoning:

In kiln seasoning timber is placed in a chamber with some special heating arrangement.

In this process one thing should be kept in mind that heating system should be under control, other wise timber will be crack or wrap. The time required for this seasoning is 3 to 12 days. This is quick process.

Kiln Seasoning

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(b) Chemical Seasoning:

In chemical seasoning carbon dioxide, ammonium carbonate or urea are used as agents for seasoning, those are applied in dry state, the inter surface of timber dries first than outer side.

This ensures uniform seasoning. The time required for this seasoning is 30 to 40 days.

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(c) Electric Seasoning:

In this method electric current is passed through the timber logs. The time required for this seasoning is 05 to 08 hours.

Electric Seasoning

Developed by:G.S.Solangi 22

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(3) Water Seasoning:

In water seasoning, timber logs are kept immersed whole in the flowing water. The sap present in timber is washed away. After that logs are taken out from water and are kept in open air, so water present in timber would be dried by air. The time required for this type of seasoning is 2 to 4 weeks.

Prepared by:G.S.Solangi

USES OF TIMEBR:Timber is used in:1.Building construction,2.Construction of house posts,3.Construction of beams,4.Construction of rafters,5.Construction of bridges,6.Construction of piles, poles and

railway sleepers,Continued--------

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7. For furniture making,

8. For light packing cases,

9. For high packing cases (for machinery and similar stores),

10.For manufacturing of agricultural implements,

11.For making toys, etc,

12.For manufacturing of veneers and ply woods.

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VENEER:Thin sheet of uniform thickness of wood is called veneer.

PLYWOOD: Veneers used for making plywood are known as plies and ply wood is made by gluing together plies in odd numbers. Gluing is done under pressure.

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DEFECTS IN TIMBER:

Most common defects in timber are:

1. Heart Shakes

2. Star Shakes

3. Cup Shakes

4. Radial Shakes

5. Rind Galls

6. Wind Cracks

7. Knots

8. Dead Wood

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(1) Heart Shakes:

These are splits occurring in the centre of the tree and running from the pith (inner most part) to wards the sap wood from the medullary (vascular tissues) rays.

In some timbers, these splits are hardly visible and in some timbers these are quite permanent.

Heart shakes are caused due to shrinkage of interior parts due to age. A heart shake straight across the trunk is not a serious defect.

Heart Shakes

Medullary Rays:

These are thin horizontal veins radiating from the pith to wards the bark. These carry sap from outer side to inner side.

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(2) Star Shakes:

These are splits which radiate from the centre of the timber or from the bark (outer side), running in the planes of medullary rays.

These occur due to severe frost or scorching heat of the sun.

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(3) Cup Shakes:

These are curved splits which separate the whole or part of one annual ring from an other. These are caused due to the unequal growth of the timber.

Cup Shakes

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(4) Radial Shakes:

These are similar to the star shakes and occur in felled timber when exposed to the sun during seasoning.

Radial shakes are generally irregular, fine and numerous.

In this many splits are appeared.

Radial Shakes

Radial Shakes

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(5) Rind Galls:

These are typical enlarged swellings and occur due to branches cut-off.

Rind Galls

Rind Galls

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(6) Wind Cracks:

These are shakes or splits on the sides of a bark of timber due to shrinkage of exterior surface exposed to atmospheric influence.

Wind Cracks

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(7) Knots:

These are the roots of the small branches of the tree. These are not harmful.

Knots

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(8) Dead Wood:

It is the deficient in strength and weight and is the result of trees being felled after maturity.

Dead Wood

DETERIORATION OF TIMBER(OR)

DECAY OF TIMBER:

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DETERIORATION OF TIMBER

(OR)

DECAY OF TIMBER:

There are so many agencies which may cause decay of timber. But there are three main harmful agencies which cause timber decay.

(1) Decay or Rot:

Decay or rot of timber is the result of the activity of various bacterias and fungi, which utilize various portions of timber as food; they require both oxygen and excess moisture. Hence timber having moisture content below 25 % will not rot easily.

(2) Insects:

There are so many insects which attack the wood, out of them termites (white ants) are the main insects which are very dangerous for timber. Termites of one class live under ground and eat wood and forms tubes or 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

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TIMBER PRESERVATIVES:

There are three main classes of timber preservatives.

(1) Oily substances insoluble in water

(2) Water soluble salts

(1)Oily substances insoluble

in water:

Coal tar oil is the best known and widely used preservative material of this class. It is obtained during the destructive distillation of bituminous coal. It is available in many grades and types. It has high degree of penetration. It has highly toxic effect to wood destroying fungi.

(2) Water soluble salts:

Zinc chloride is the most extensively used preservative of this type. It is clean and odourless.

SPECIAL PAINTS TO SAVE TIMBER

FROM FIRE:

Following paints are used to save

timber from fire.

Diammonium phosphate,

Mono ammonium phosphate,

Mono magnesium phosphate,

Phosphoric acid.

METHODS OF APPLYING PRESERVATIVES:

Before applying preservatives, the timber should be completely seasoned.

There are some important methods of applying timber preservatives which are given below.

1.Painting and dipping method

2.Pressure process or full cell process

3.Empty cell process

(1) Painting and dipping method:

This is the most common method in which the preservative material is applied by means of a brush several times. The timber is also immersed in a tank full of liquid (preservative material). In both types the penetration hardly exceeds 1/16’’. The duration of immersion and temperature of solution is increased the penetration rate.

(2) Pressure process or full cell process:

In this process, the timber is placed in an air tight chamber, from which air is with drawn by creating a vacuum. The cells are full emptied to receive preservative material. After that preservative material is pumped under pressure of 100 to 200 psi and at a temperature of 120degreeF. As the timber contains required quantity of preservative a low vacuum is maintained to remove excess preservative. Such a timber is generally used in case of piles in salt water and railway sleepers.

(3) Empty cell process:

This method is similar to the full cell process but initial vacuum is not to be maintained and no attempt is to be made to remove the air from cells. The preservative material is applied under pressure of 200 psi.

Developed by:Nadeem Asghar 61

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