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The drying of wood before its commercial utilisation is carried out for
the following reasons;
- The main reason is to reduce its shrinkage or swelling when in service.
If wood is dried to a moisture content (equilibrium moisture content) that
is in equilibrium with the environment in which it will be used then shrinkage
or swelling of the wood will be minimised. In Australia, EMC
is approximately 12% MC. The equilibrium moisture content of wood varies
between different locations and in different environments and consequently
wood intended for interior uses is dried to lower moisture contents than
woods used outdoors.
The equilibrium moisture content of timber in NSW (Pratt
1974)
| Moisture Equilibrium % |
Town |
Maximum |
Minimum |
Mean |
| Sydney |
13.8 |
10.0 |
12.3 |
| Albury |
15.8 |
9.6 |
12.3 |
| Armidale |
15.8 |
9.7 |
12.5 |
| Broken Hill |
13.7 |
5.5 |
9.9 |
| Forbes |
16.5 |
6.4 |
11.5 |
| Tumut |
17.5 |
8.4 |
13.1 |
Equilibrium moisture content of wood as a function of dry bulb temperature,
wet bulb depression and relative humidity (Compliments of CSIRO,
Forestry and Forest Products)
For enlarged picture
- Below a moisture content of 20% the possibility of wood being degraded
by fungi is minimised.
- Wood when dry is easier to paint, glue, nail, screw, and machine.
- Most wood strength properties are improved when wood is dried below
the fibre saturation point.
- Certain processes ie., timber preservation require the removal of free
water from wood.
- Wood is lighter after drying and therefore the costs of transporting
it are reduced.
- Wood burns better when dry.
- Wood is a better insulator and has a higher electrical resistance when
dry.
Factors
Affecting Drying
The processes involved in moisture movement in wood are as follows
(Pratt 1974);
For
more info from the web
Drying
Methods
There are three main methods of drying timber;
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URL: http://www.anu.edu.au/Forestry/wood/drying/intro.html |
