EMV dryers: To dry quickly and without defects.
The modern technology applied in the wood workshops has resulted in the optimisation of the use and machining times of the raw materials.
However to try and save 0.5 mm on the thickness of a plank or 1 m. a second in the speed of a machine tool without paying the same attention to the “non quality” of the drying operation, can cause losses in yield of between 5 to 10% on the aforementioned machines.
The drier must therefore be considered as a machine which is part of production, guaranteeing a real saving on the raw material and on the quality of the finished product.
Dryers with continuous/discontinuous vacuum for boards:
the reduced sizes of dryers compared with the productivity.
The ISVE EM dryers are particularly suitable for drying boards using various types of wood.
They are called “dry kilns with continuous/discontinuous vacuum” because the vacuum phase can be interrupted by hot and humid air cycles allowing quick heating of the wood. In order to achieve optimal results the wood must be heated gradually and homogeneously.
In our EM, the pile is made of listeled boards which are placed on the carriage of the autoclave. The drying cycle starts when you close the machine and set all parameters on the computer.
Why choose a dryer EM?
The reduced sizes compared with the productivity of these units produce noticeable saving in terms of space and in terms of easy housing on the company premises without the need for any special brickwork or connections.
The quality materials used in the construction of the autoclave, such as stainless steel and aluminium, guarantee a long resistance against corrosion, whereas the choice of components from leading Italian and foreign companies means they are able to attain a high level of reliability.
These characteristics, common to all ISVE dryers, result in very high quality drying, short working times with reduced operating costs.
|Stack sizes m3||2||75|
|Internal lenght m.||5||18|
Heat diffusion system of ISVE EM dryer series
- Control frame
- Heating resistors
- Wood pile loading space
- Alternate flux fans
- Probes for temperature, wood humidity and ambient humidity
- Motorized loading cart
EM systems: how they work
In a first phase, hot air with a high content of humidity circulates in the autoclave.
At the beginning of the cycle, it is very important to gradually increase the wood temperature avoiding the beginning of drying of the board upper part. The humidity high value which is electronically controlled by probes, hinders some dangerous strains along the wood from taking place.
Once the temperature value of the pile has reached the required level, the vacuum pump eject air from the autoclave. When the fixed vacuum value is reached, the accumulated heating causes the evaporation of the water from the boards causing its drying.
These phases often take place during the process, mixing hot and humid air with vacuum which is an essential factor for a quick and good drying.
Loading carriage with pile of boards ready to be charged in the autoclave
How to choose which EM is the most suitable for one’s requirements
How to choose a vacuum dryer, but above all how to calculate its size according to one’s requirements?
The main parameters to be taken into consideration are as the follows:
- cu.m of wood to be dried per unit of time;
- type of wood (pine, fir-wood, oak, etc.);
- thickness of semi-finished product in mm;
- initial humidity level
From the graphic below, some indications of the drying times on the basis of initial humidity level and thickness of wood can be had.
By centring the initial humidity level of the boards with the vertical line of the thickness and then by moving down to where the whitish-grey lines of the different types of wood are crossed, the duration of the drying process, expressed in days, can be set.
From this result it is easy to see how the reduction in drying times means smaller capacity driers can be used compared with the volume of wood to be dried.
The advantages are clearly several:
They range from saving space to easier insertion in the company drying process logistics.
Last but not least, the monolithic characteristics of ISVE dryers permits an easy re-positioning in case is required a change in the company production line.
The drying and design’s quality are two important features of ISVE EMV dryers, making them simple to use and easy to insert in the company production cycle.
The Vacuum System: the secret of ISVE drying quality
The vacuum technology to drying wood
Drying of wood by exposing it to the open air or when using traditional dryers always have 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 dryer 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 linked to the need to use rather long process times in order not to create differences in humidity within the same area to be dried.
This process is however valid for lowering the water content in green wood.
ISVE vacuum drying
Drying by a vacuum process makes it possible to apply two natural physical principles:
- a reduction in pressure (to create a vacuum) transform the water present in the wood into steam at low temperatures (45°C at –700 mm Hg);
- 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 in thermal energy requirements, as the operation is carried out at low temperatures.
The second principle allows to control and regulate the amount of humidity removed from the wood, second by second, by regulating the temperature of the condensers.
The synergy of the two processes enables the humidity in the wood to be lowered uniformly and without 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, vacuum drying also guarantees the complete evaporation of vegetable solvents, thus causing an irreversible crystallization of the resin itself.