The process that corresponds to solid-liquid separation is called drying and is of fundamental importance in the treatment of wood. Why is that? Simple: when this material is found in nature, it contains large amounts of water, which undermines its strength and durability requirements for use in various human activities.
It is true that tree trunks release part of their water content when they are felled, but this is not enough, because it is only the free water, the water that occupies the empty spaces in the woody structure (called vacuoles): the largest quantities inside are the saturation water, which impregnates the cell walls of the wood and is released over a much longer period of time. Therefore, it is advisable to facilitate this de-humidification process by proceeding with drying, so that the moisture inside the timber is reduced to thresholds that allow it to be used within a reasonable time.
Phases and duration of the wood drying process
Time, as the introduction suggests, is a decisive discriminator in the woodworking process, in which drying (or curing) plays a decisive role. What you need to know, however, is that this process can be carried out in two different ways, either naturally or artificially, which involve different stages and durations:
– Natural drying. It is a process that takes place outdoors: the timber, cut into pieces calibrated according to the end use to which it will be put, is stacked neatly in planks, under sheds or roofs open at the sides, so that protection from rainwater and sunlight, but also the passage of wind, is guaranteed. Then, between each row, spacers are placed to allow adequate air circulation, and thus the curing process, which consists of water release and drying, begins. The overall duration of the process varies depending on environmental/climatic factors (which are variable and can cause delays), the type of wood in question and its end use, and is therefore rather unpredictable. The only certainty, however, is its excessive length, which is not in line with the time required by today’s market: natural drying does not usually take less than a year;
– Artificial drying. Unlike natural drying, artificial drying takes place indoors, more specifically in specific kilns that act on the humidity of the wood by regulating temperature and airflow. These possibilities of managing the decisive factors of drying result in much shorter timescales (ranging from a few hours to a few days, depending on the wood to be dried) and depend on the various machines capable of implementing this process, to which different types of artificial drying correspond:
- Conventional drying: the wood is placed in insulated chambers where air and humidity can be controlled, accelerating the process as required;
- Condensation drying: ideal for the most delicate types of wood, it takes place at low temperatures and constantly monitors the wood so that it is not damaged;
- High temperature drying: this is the fastest method and consists of passing very high-frequency electric fields through the wooden boards;
- Vacuum drying: this is carried out in airtight metal chambers in which the atmospheric pressure is considerably lowered. Low pressure accelerates the drying process to temperatures below 80° C. However, this process involves the use of large amounts of energy, which is why, with vacuum, the final production cost increases considerably.
Natural and artificial drying of wood
Let us now analyse the most relevant aspects arising from the comparison of the two processes. There is no doubt that the clearest and most obvious advantage in favour of artificial drying lies in its short duration, and this certainly needs no explanation. But other factors also contribute to make it the most profitable and efficient curing process.
In fact, in addition to the timeframe, there are further limitations to natural drying. First of all, the absolute contingency to which it is subjected: not only the type of wood to be dried, but also the seasonality hangs over it. As it takes place in the open air, it has to be calibrated according to the period of the year, as climatic factors can affect or even compromise it. Moreover, it is not able to lower the moisture content below 12%, making it unsuitable for those woods intended for specific processes, such as parquet, which require a lower water content in the wood structure.
Artificial drying, on the other hand, can take place at any time and can produce cured wood that can be used in any context. The only criticism levelled at this process is that it could lead to an overly aggressive action against the timber, compromising its structure. But, in reality, the problem does not arise: it is sufficient to use the appropriate machinery for curing to be carried out. For this, Incomac offers a wide range of options.
The advantages of drying systems: our solutions
Incomac drying systems, capable of performing any type of curing and opening up specific advantages by virtue of their peculiarities, are suitable for the treatment of any wood species. On the conventional drying side, we field three solutions (Icd, Tag and Idv), which act on the wood through the air exchange principle and can be supplied with any thermal fluid or energy source. Then, in the field of condensation drying, we propose the Mac and Mac_Hybrid systems, which utilise internal recirculation and air de-humidification for their purposes, distinguished by the refrigeration circuit located inside them: this, via a heat pump, reduces the required heat consumption by approximately one third.
Accelerated drying, due to the structural and colour modification of the wood and its stabilisation, is what our high-temperature machinery implements with great efficiency: the Vap steaming chambers and the Iht heat treatment systems work at operating temperatures above 90°C, guaranteeing top-quality results. We close with our special offers, which cannot only be applied to specific areas of the wood industry (such as Pal drying chambers, which thermally treat pallets, making them suitable for the ISPM 15 standard ), but also approach the sphere of pre-drying (Pre systems allow the storage of sawn timber at low temperature in large areas and in an insulated environment) or even into other industries (Ind drying systems).