FI110891B - Method and apparatus for drying and / or heat treating wood materials - Google Patents

Description

110891

Method and apparatus for drying and / or heat treating wood material

The invention relates to a method for drying and / or heat treating wood material, wherein the batch of wood material to be treated is placed in a defined drying space, The invention further relates to an apparatus for drying and / or heat treating wood material.

In the woodworking industry, drying wood to a suitable production and manufacturing moisture, as well as heat treatment, has been an essential process in the long term. In many cases, drying of the timber has taken up to weeks, so the drying process has led to attempts to handle even very large quantities of timber at a time. Handling large quantities of timber at one time results in large stocks of timber which, in turn, are capital intensive, and in addition, not all affordable options, such as otherwise suitable but smaller quantities of wood materials, are always available to procure timber. A further disadvantage of the prior art V is that, in the course of drying, also non-useful material is dried. With large amounts of wood material to be dried, the amount of such non-recoverable ··: 25 material to be dried is also substantial.

It is an object of the invention to provide a method and apparatus,. which eliminate the drawbacks of the prior art.

This has been achieved by the invention. The method according to the invention is characterized in that, after removing the negative pressure, the pressure in the drying space is raised to the overpressure side to reduce water evaporation and / or during heat treatment. The apparatus according to the invention, in turn, is characterized in that the apparatus comprises second means for generating overpressure in the drying space. The disadvantage of the current: vacuum drying technology is that at low pressures it is not possible to rapidly transfer the energy required for evaporation to the drying material; 35 I wake up, especially to the interior of the tree. This is not a disadvantage when using large hair technology.

2 110891

The main advantage of the invention is that the drying process is significantly accelerated compared to the prior art. To clarify this, the invention refers to hours at drying time, whereas prior art refers to 5 days and even weeks. The fast drying process, in turn, allows for a low-capital, fast-moving raw material cycle. In addition, a fast raw material cycle also enables you to obtain customer-oriented timber for the right purpose. Rapid drying of the wood in the form of ready-to-use blanks also saves costs, since only the wood used for recovery is dried. A prerequisite for drying in the form of preforms is error-free drying and has proved to be easy to achieve in the drying according to the invention. An advantage also arises from the fact that the invention enables the preparation of preforms of the products to be manufactured before drying. A further advantage of the invention is that the volume of the drying space is made substantially smaller than when using the conventional technique, whereby the cost is reduced compared to the prior art.

The invention will now be explained in more detail with the aid of the accompanying drawings, in which: Figure 1 is a side elevational view of the apparatus 20, Figure 2 is a schematic view of a preferred electrode arrangement of the invention; and a preferred embodiment and Figure 4 illustrates a preferred embodiment of the angle of the electrode of the apparatus according to the invention.

Figure 1 shows in principle the apparatus according to the invention. In the example of Figure 1, the surrounding drying space is denoted by the reference _; 1 and the batch of wood material under consideration are respectively 2.

'. . * 30 The batch of wood material to be processed 2 may be, for example, a board; · a batch or, for example, a batch of preforms or, ”· a prefabricated batch, so that each piece has sufficient margins: ·: for product components. The blanks or preforms can preferably be stacked, even in a batch, so that in one batch all blanks or preforms 35 are the same, or in one batch, all blanks or preforms needed to make the product are, e.g. The batch of wood material to be treated 2 can be inserted into the drying space through a suitable opening opening. The filling opening may be formed, for example, so that the other end of the drying space is formed as an opening. The filling opening is not shown in Figure 1.

The above-mentioned preforms or preforms may be sawn into shape, for example, curved chair rear foot preforms or the like. Blanks or components are made from fresh or pre-dried or dried wood below the saturation point of the wood grain. However, as stated above, the batch of wood material to be treated can also consist of, for example, 10 board articles, etc. The batch of wood material to be treated 2 is lost inside the drying space 1 without gaps or with small gaps compared to conventional drying load.

In accordance with the essential idea of the invention, a vacuum is formed in the drying space 1 and the energy used for drying is introduced into the drying space 15 as high frequency energy. After the moisture has dropped near the final humidity, the vacuum is removed from the drying space 1, whereby the final drying and / or heat treatment takes place by hot drying. Further, after depressurization, the pressure in the drying space 1 can be increased to the side of the overpressure to reduce water evaporation and / or during heat treatment of the batch of wood material.

The vacuum in the drying space 1 is formed by means of the vacuum pump 3.

Reference numeral 4 represents a control valve which can be controlled, for example, by automatic means. Reference numeral 5, in turn, denotes a condenser. The high-frequency energy is generated by the plate-shaped or suitably shaped electrodes j * 6, 7 and the high-frequency generator 8. The electrodes 6, 7 are arranged on opposite sides of the wood material batch being processed. Vacuum removal from the drying space: implemented by means of a loaded non-return valve 9. In addition, a non-return valve 9 may be provided with a control valve 10, which can be controlled in the same way as a valve 4. For generating a higher overpressure, the apparatus may be provided with an overpressure pump 11. / 30 which can be controlled as well as valves 4 and 9.

The apparatus of Figure 1 operates in principle as follows. •. '> · The batch of wood material to be treated is placed in a drying space 1, the drying space is closed and a vacuum is created therein by means of a vacuum pump 3. Drying of a batch of wood material. occurs by generating high-frequency energy with the high-frequency generator 8 and 35 by transferring it to the drying state by means of electrodes 6, 7. Since the drying state 1 has a ': negative pressure, the water leaving the batch of wood material boils at a temperature below the normal boiling point of water. The energy needed to evaporate the water is introduced by electrodes 6, 7 into the water-containing areas of the wood, whereupon the water is vaporized and ejected out of the wood material to be treated. The moisture exiting the wood material is discharged from the drying space in a suitable manner, for example, after condensation as water, through an outlet or the like arranged at the bottom of the drying space.

When drying is close to final moisture, the vacuum pump 3 is initially stopped and the condenser 5 is closed. After the pressure has increased in the drying state, the valve 4 is closed and the valve 10 is opened and switched to hot drying. 10 By adjusting the load on the non-return valve, it is also possible to use a pressure higher than normal atmospheric pressure in drying space 1, thereby slowing down the evaporation of water. If high overpressure is required then an overpressure pump is used. In this case, the structure of the equipment naturally has to take into account the particular structure. excess pressure. The hot-drying step can also be only an equilibration step in the process. 15 The equipment can also be used for heat treatment of timber combined with drying. Since the equipment is made to withstand high pressure as stated above, the equipment can be used after drying for heat treatment of the timber after drying which can be carried out under normal pressure or in an overpressure state.

20 Equalizing the final moisture can be achieved in different ways by a suitable drying scheme. For example, the following methods may be used as drying formulas. The drying is initially carried out by vacuum drying under a high frequency field at a pressure of 0.01-0.3 bar. When near target humidity is reached, increase the drying pressure to 0.6 - 1.0 bar and continue to finish. Towards the end butter- ··; The pressure of 25 d also raises to 1.0 bar in one or more steps.

Higher pressures and the higher temperatures therein improve the high frequency field uniformity and slow down the drying of the final phase, which factors offset the final humidity. In addition, the pressure can be raised in drying room 1: also to the overpressure, which accelerates the stabilization during the final drying.

L. '30 In the exemplary embodiment of Figure 1, electrodes 6, 7 of a size corresponding to the dimensions of the batch of wood material to be treated are used. However, the batch size electrodes do not always achieve a uniform * high frequency field. Thus, in certain circumstances, it is advantageous in the context of the invention to use electrodes that are larger in all directions than the size of 35 batches of material to be processed. Such a solution is shown in principle in Figure 2. The electrodes 6, 7 can in each direction be, for example, 50 to 200 5 110891 mm larger than the size of the batch of material to be treated. In addition, the electrodes may also be smaller than the size of the batch of material to be treated.

The electrodes 6, 7 may also be shaped in an appropriate manner to provide an advantageous result. The corners and / or edges of the electrodes can be bent outward, i.e. away from the batch of wood material to be treated, as shown in Figure 3. The corners of the electrodes may also be rounded as shown in Figure 4. Em. of course, the details can of course also be combined in the same construction.

The invention is also particularly well suited for drying round timber 10 so as to obtain an error-free drying result. The round timber elements, i.e. logs, jaws, logs or other round billets are then loaded between the electrodes 6, 7 perpendicular to the electrodes or parallel to the electrodes.

Because of the rapid drying, control, and especially the end of drying at 15 correct drying rates, has been difficult since no moisture measurement of the wood is possible in the high frequency field. The process of the invention can be controlled on the following grounds. The loss coefficient of the high frequency field of wood and thus power consumption depends on the species of wood, the moisture content of the wood, the direction of the wood grain and the amount of wood. During the drying run, the values of the anode and lattice currents of the high frequency generator are measured at a certain vacuum and temperature in each autumn direction and with the necessary electrode alternatives at certain amounts of wood and at certain humidity. When the amount of lumber, the direction of the causes, is known, and the anode and lattice currents are determined at a given vacuum and temperature; The system automation then calculates the amount of water to be removed: **: 25 based on the amount of water and drying end, and also controls '·': drying so that no overflow and breakthrough occurs.

». ; *. Interchangeable electrodes can also be used in connection with the invention, which are replaced according to the dimensions of the batch of wood to be treated. Electron. . the trodes can be further replaced during the drying process, for example, by interrupting the drying manually or automatically so that the drying process is not; · 'Interrupt. The interruption of the drying process during electrode change can be prevented, for example, by changing the pressure in the drying space 1. dried; ·: A drying chamber can also be used for final equalization of the moisture left in the material, which provides optimal conditions for humidity equalization. Em. 6 110891 can also be used for the final equalization of moisture, where a separate batch of wood material 2 is transferred at a particular stage of the process.

The foregoing embodiments are not intended to limit the invention in any way, but the invention may be modified freely within the scope of the claims. For example, the apparatus according to the invention or its details need not necessarily be exactly as shown in the figures, but other solutions are possible, etc.

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Claims (14)

A method for drying and / or heat treating wood, where the wood part (2) to be treated is placed in a drying space (1) defined from its surroundings, into which energy is conducted for drying the wood, and where a vacuum is formed in the drying space. (1) and the energy to be used for drying are fed into the drying space (1) as high-frequency energy by means of disc-shaped or shaped electrodes (6, 7), and when the moisture has dropped near the final humidity, the negative pressure is removed from the drying space 10 (1), final drying and / or heat treatment takes place as heat drying or hot air drying, characterized by decreasing after the vacuum has been removed, the pressure in the drying space (1) is raised to an overpressure to reduce water absorption and / or during the heat treatment. Process according to claim 1, characterized in that the vacuum is removed from the drying space (1) in a stepwise manner according to a drying scheme. 3. Process according to claim 2, characterized in that the drying is carried out at an initial pressure of 0.01-0.3 bar and after the moisture has almost reached the final humidity level, the pressure is raised to 0.6-1.0 bar. 20 Method according to claim 3, characterized in that the pressure is increased in one step to 1.0 bar. The method according to claim 3, characterized in that the pressure is increased in several steps to 1.0 bar. A method according to any of the preceding claims, in which the wood part to be treated consists of round wood, characterized in that the round wood elements are stacked between the electrodes (6, 7) perpendicular to the relative to the electrodes or parallel to the electrodes. Method according to claim 1, characterized in that at the beginning a certain amount of wood timber and certain humidity are measured anode and galvanic values of a high frequency generator (8) connected to the electrodes (6, 7). at a certain negative pressure and at a certain temperature in each of the wood: vein direction and with the required electrode alternatives, and the moisture is determined from the above information, and the amount of water to be removed and the drying time calculated, and the drying is controlled on the basis of; The above mentioned information said that no overflow and no impact occurs. 10 110891 8. Plant for drying and / or heat treatment of wood, where the wood part (2) to be treated is arranged to be placed in a drying space (1) bounded from its surroundings, to which energy is arranged to be led for drying the wood, plant comprises first means (3, 4) for forming a negative pressure in the drying space (1) and second means (9,10) for removing the negative pressure from the drying space (1) and disc-shaped or shaped electrodes (6, 7), to be arranged on opposing sides of the woodwork portion (2) to be treated and arranged to supply high frequency energy to the woodwork, characterized in that the plant comprises other means (11, 12) for generating an overpressure in the drying space (1). ). Installation according to claim 8, characterized in that the size of the electrodes (6, 7) is in each direction larger than the size of the wood part (2) to be treated. Installation according to claim 8, characterized in that the size of the electrodes (6, 7) is in each direction smaller than the size of the wood part (2) to be treated. Installation according to any of the preceding claims 8-10, characterized in that the corners and / or edges of the electrodes (6, 7) have been bent away from the wood material portion (2) to be treated. Installation according to any of the preceding claims 8-11, characterized in that the corners of the electrodes (6, 7) are rounded. Installation according to any of the preceding claims 8-12, characterized in that the electrodes (6, 7) are arranged as interchangeable; 1 element according to the dimensions of the wood part (2) to be treated. i 25 Installation according to claim 13, characterized in that: the electrodes (6, 7) are arranged to be replaced during the process. '1 · <I ·> I • 1 1 »· t I