Defects in timber -- natural force
Transcript of Defects in timber -- natural force
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DEFECTS DUE TO NATURAL FORCES--- TIMBER
presentation by KIRTHIGA.E
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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
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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.
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CALLUS : It indicates soft tissue or skin which covers the wound of a tree
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CHEMICAL STAIN : The wood is sometimes Discoloured by the chemical action caused withit by some external agency.
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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
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DEAD WOOD: The timber which is Obtained from dead standing trees contains deadwood.
It is indicated by light weight and reddish colour.
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DRUXINESS: This defect is indicated by white decayed spots which are concealed by healthy wood they are probably formed by access of fungi.
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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 .
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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
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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
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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.
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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.
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SHAKES : Cup shakes Ring shakes heart shakes Star shakes Radial shakes
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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
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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.