The Vacuum System: the secret of ISVE drying quality

Vacuum drying

The vacuum technology to drying wood

Drying of wood by exposing it to the open air or when using traditional driers always the following processes:

  • removal of water from the surfaces of the planks by exposing them to hot air (PHASE 1);
  • migration of the humidity from the centre of the more humid planks towards the drier surfaces (PHASE 2).

If the two processes are not carried out in perfect harmony abnormal tensions may be created (PHASE 3) causing warping and cracking of the wood.
The reliability of a traditional drying system is therefore tied to the need to use quite long process times so as not to create differences in humidity levels within the same area to be dried.
This process is however valid for lowering the water content in green wood.

ISVE vacuum drying

Drying, using a vacuum process, enables two natural physical principles to come into play:

  1. a reduction in pressure (to create a vacuum)) causes the water present in the wood to transform into steam at low temperatures (45°C at –700 mm Hg);
  2. the water vapour always moves from the hot areas to the cold ones.

The first principle guarantees rapid removal of the water vapour starting from the centre of the wood mass and a drastic reduction of the needs for thermal energy, in that the operation is carried out a low temperatures.
The second principle enables the quantity of humidity removed from the wood to be controlled and regulated, second by second, by adjusting the temperature of the condensers.
The synergy of the two processes enables the humidity in the wood to be lowered uniformly and without causing stress.

Considering the high technology applied to these machines and the possibility of being able to adjust each process phase very precisely, drying in a vacuum is very suitable for establishing a definite percentage level of humidity in the wood.
This result is of the utmost importance, especially and above all during the later finishing and assembly phases of the semi-finished product.

In the case of wood which has cavities of resin, drying in a vacuum guarantees also the complete evaporation of vegetable solvents, thus causing irreversible crystallisation of the resin itself.