DEFECTS DUE TO NATURAL FORCES--- TIMBER

presentation by KIRTHIGA.E

THE MAIN NATURAL FORCES CAUSING DEFECTS IN TIMBER ARE : Burls Callus Chemical stain Coarse grain Dead wood Druxiness Foxiness Knots Rind galls Shakes Twisted fibres Upsets Water strain Wind cracks

BURLS : They are particularly formed when a tree recieves shock or injury in its young age.

Due to its injury,the growth of tree is completely upset and irregular projections appear on the body of timber

These are also known as excrescences.

CALLUS : It indicates soft tissue or skin which covers the wound of a tree

CHEMICAL STAIN : The wood is sometimes Discoloured by the chemical action caused withit by some external agency.

COARSE GRAIN : If the tree grows rapidly, the annual rings are widened. It is known as the coarsed grain timber

such timber possesses less strength 

DEAD WOOD: The timber which is Obtained from dead standing trees contains deadwood.

It is indicated by light weight and reddish colour.

DRUXINESS: This defect is indicated by white decayed spots which are concealed by healthy wood they are probably formed by access of fungi.

FOXINESS: This defect is indicated by

red or yellow tinge in wood

or reddish brown stains or

spots round the pith of tree

discolouring the timber

it is caused either due

to poor ventilation during

storage or by timber .

KNOTS :These are the bases of branches or limbs which

are broken or cut off from the tree.

The portion from which the branch is removed

recieves nourishment from the stem fora pretty

long time .

And it ultimately results in formation of

dark hard rings which are known as knots.

As continuity of wood fibres are broken by

knots,they form a source of weakness

CLASSIFICATION OF KNOTS BASED ON SIZES :

PIN KNOT:-diametre upto 6.50mm SMALL KNOT:-diametre upto 6.5 and

20mm MEDIUM KNOT:-diameter between 20

and 40mm LARGE KNOT:-diameter greater than

40mm

Classification of knots on basis of form and quality

DEAD KNOT:-knot which is seperated from body of wood.it is notsafe to use wood with such a knot for engineering purposes.

DECAYED KNOT:-popularly known as unsound knot and form by action of fungi on wood.

LIVE KNOT:-it is thoroughly fixed in wood and cannot seperated outfrom body of wood.it is free from cracks and decay.wood containing this knot can be used for engineering purposes.

LOOSE KNOT:-it is preliminary stage of dead knot. ROUND KNOT:-the cross-section of this type of knot

is either roundor oval TIGHT KNOT:-it is preliminary stage of live knot.the

fibres of knot arefirmly held in sorrounding wood.

RIND GALLS : the rind means bark and gall indicates abnormal growth. hence peculiar curved swelling foundon the body of tree are known as rindgall. they develop at points from where branches are improperly cut off or removed. they are rarely found in a tree and the

timber in this part is very weak and not durable.

SHAKES : Cup shakes Ring shakes heart shakes Star shakes Radial shakes

TWISTED FIBRES: these are known as wandering hearts and caused by twisting of young trees byfast blowing wind. the timbers with twisted fibres is unsuitable for sawing

UPSETS:- these indicate wood fibres which are injured by crushing or compression. the upsets are mainly due to improper felling of tree and exposure of tree in its young age to fast blowing wind 

WATER STAIN : The wood is sometimes dis--coloured when it comes into contact with water . This defect is usually found in converted timber

Wind cracks : if wind is exposed to atmospheric agencies, its exterior surface shrinks. Such shrinkage result into cracks.