Home Products Machines Process Management About Us Location Contact Us Hot Line: +95-9-50-20-797, +95-9-97-41-47-797

About Wood, Science of Wood

Hardwood and Softwood
Trees are divided into two classes: hardwoods and softwoods. The hardwoods such as Teak, birch, maple have broad leaves. The terms “hardwoods” and
“softwoods” are not directly associated with the hardness or softness of the wood although in most cases hardwoods are actually harder and tougher than
softwoods. In general softwoods originate from cone-bearing trees and hardwoods from trees that have their seeds contained in a seed-case.

Sapwood
Sapwood plays and important part in a tree’s living process. In general only the last few outside layers of sapwood are alive. The rest of the sapwood carries
moisture from the roots to the leaves and store food for the tree. It usually have a higher moisture content than the heartwood.

Heartwood
During the life of the tree, sapwood gradually changes into heartwood. As it does so, it becomes less permeable. Since moisture movement is retarded
considerably, heartwood dries more slowly than sapwood. Heartwood usually surface checks and honeycombs more readily than sapwood, hence requires
milder drying conditions. It is usually darker in color and also more resistant to decay than sapwood.

log_section

 

 

A : Cambium layer inside of inner bark
B : Inner bark
C : Outer bark
D : Sapwood
E : Heartwood
F : Pitch
G : Wood rays

 

Wood and Moisture

All wood in growing trees contains considerable quantities of water. It is present in two forms, i.e. (a) Free-water in the cell cavities and (b) Bound-water
bounded to the cell walls. Most of this water should be removed in order to obtain the satisfactory service from the wood in use. The removal of free-water is
much easer than that of bound-water from the wood and there is no change in dimension or in strength properties by removing free-water.

The wood is said to be in a state of Fiber Saturation Point (FSP) when no free-water is present and the cell wall is saturated with bound-water. In this state,
moisture content in wood is between 25% and 30% and removal of water below fiber saturation point (FSP) results dimensional change (shrinkage) and
increase in many of the strength properties.

Because of its hygroscopic nature wood is always seeking to equilibrate its vapour pressure with that of the environment. That is wood always try to maintain its
Equilibrium Moisture Content (EMC) which correspond to the environment. It is the unique characteristic of wood that expends when it absorb moisture if its
EMC is higher than its existing moisture content, whereas contracts or shrinks when it loses moisture if its EMC is lower than its existing moisture content.

Anisotropy of Wood
As wood possesses a complex fiber-composite structure, it varies in its most properties with the directions, called anisotropy. Moreover its difference in structure
occurs not only between different species but also between trees of the same species grown in different environments or different parts of a single tree. This
results undesirable variation in its properties as a material.

The figure below shows three principal axes of wood with respect to grain direction and growth rings.
axes
The three principal axes of wood with respect to grain direction and growth rings.