The most common natural Defects in Timber are knots, shakes, cross-grain, crookedness, rind galls, burr, and curl.
(a) Burls ⟹ is a tree growth in which the grain has grown in a deformed manner. It is commonly found in the form of a rounded outgrowth on a tree trunk or branch that is filled with small knots. A burl results from a tree undergoing some form of stress. It may be caused by an injury, virus, or fungus.
(b) Callus⟹ it indicates soft tissues or skin which covers the wound of trees.
(c) Chemical stain ⟹ Discolored due to chemical action on trees.
(d) Coarse grain ⟹ Trees grow rapidly hence, annual rings are widened and hence timber possesses less strength.
(e) Deadwood ⟹ Timber obtained from dead standing trees.
(f) Druxiness ⟹ White decay spots of fungi.
(g) Foxiness ⟹ This defect in timber is indicated by red or yellow tinge in wood or reddish-brown stains or spots round the pith of tree discoloring the timber. it is caused either due to poor ventilation during storage or by timber.
(h) 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 receives nourishment from the stem for a pretty long time. And it ultimately results in the formation of dark hard rings which are known as knots. As continuity of wood fibers are broken by knots, they form a source of weakness.
CLASSIFICATION OF (Defects in Timber) KNOTS BASED ON SIZES :
- PIN KNOT:-diameter up to 6.50mm
- SMALL KNOT:-diameter up to 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 separated from the body of wood.it is not safe to use wood with such a knot for engineering purposes.
- DECAYED KNOT:-popularly known as unsound knot and form by the action of fungi on wood.
- LIVE KNOT:-it is thoroughly fixed in wood and cannot separate out from the body of wood.it is free from cracks and decay. Wood containing this knot can be used for engineering purposes.
- LOOSE KNOT:-it is the preliminary stage of the dead knot.
- ROUND KNOT:-the cross-section of this type of knot is either round or oval.
(i) Rind Galls ⟹ the rind means bark and gall indicates abnormal growth, hence peculiarly curved swelling found on the body of the tree is known as rind gall. 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.
(j) Shakes ⟹ These are cracks which partly or completely separate is often found in older trees that grow in wet areas. These are either radial or tangential shakes-
- Star shakes: – radial splits in timber originating from bark and narrowing towards pith are known as star shakes. These spilled tends to open more and more as the timber seasoned.
- Heart shakes: – generally occur in over mature trees. More frequent in hardwoods than in conifers. They are due to shrinkage of the interior part of the tree which is approaching maturity.
- Frost shakes: – begins on the outside where moisture from rain or other means has penetrated and freezes, causing damage to the wood on the inside.
- Cup shakes: – caused by the rupture of tissue in a circular direction.
- The ring shakes – results from the pulling apart of two or more growth rings.
(k) Twisted fibers or Wandering Hearts ⟹ they are caused by twisting of young trees by fast blowing wind in one direction.
(l) Upsets ⟹ Indicate wood fibers that are injured by crushing or compression.
(m) Excrescences ⟹ are formed when the tree has received certain shock or injury so that the growth of the tree completely upset and irregular projections appear on the body of timber.
Defect Due to Conversion (Defects occurs during converting timber to commercial form)
- Chip mark ⟹ or sign placed by a chip on the finished surface of the timer.
- Diagonal grain ⟹ Due to improper sawing of timer Torn Grain ⟹ Due to falling of tool, the impression is formed.
- Wane ⟹ Presence of original rounded surface on the manufactured piece of timber.
- When beam supporting brittle coverings like AC sheets, earthenware, slates, gypsum, etc. then maximum deflection should not be more than span/360. Otherwise, the deflection of span/ 240 is allowed.
- In the case of cantilever deflection should not exceed clear span/180.
Application of timber obtained from different trees:-
- BABUL: – used for bodies of bullock cart, tool handles agricultural instruments, etc.
- BENTEAK: – furniture construction works, building construction, and boat construction, etc.
- MULBERRY: – used for sports goods, baskets, hockey sticks tennis rackets, cricket bats, etc.
- BIJASAL: – ordinary building construction, cartwheel, furniture, etc.
- SHISHAM OR SISSOO:- since it is strong durable and tough and takes fine polish hence is used for high-class furniture, plywood’s, bridge poles, sports goods, railway carriages, etc.
- TEAK WOOD: – high quality and durable furniture, shipbuilding, railway carriage, well curbs, piles, house construction, etc.
- SANDALWOOD: – used for agricultural implements, wheels, mallets, boxes, fancy goods.
- DEODAR:- it provides softwood and is used for making cheap and rough furniture, railway sleepers, packing boxes, structural work, etc.