EP1696193B1 - Woodworking method - Google Patents

Abstract

The invention relates to the woodworking industry and can be used for heat-moisture processing of wood, timber-based materials and various timber products. The inventive method consists in preheating wood by heating air in a chamber and, afterwards in repeatedly exposing said wood to a water steam action. Said processing method is carried out in such a way that the wood is alternately exposed to heat and water steam effects at predetermined temperature conditions. Said invention makes it possible to process a wood material whose thickness is greater than 200 mm, extend the range of the species of trees whose wood is heat-treatable, reduce equilibrium moisture, increase a wood texture homogeneity and the uniformity of the density thereof and to reduce the woodworking energy consumption.

Description

Field of the invention

The invention is intended for the woodworking industry. It can be used in the hydrothermal treatment of wood and various products of wood: boards, squared timber, parquet, workpieces of different shape, etc. It is for drying and tinting of hardwood (oak, beech, ash, etc.), as well as of inferior Wood (aspen, spruce, etc.) is particularly effective.

State of the art

One of the known methods is the treatment of wood by accelerated aging, including storage at temperatures of 110 to 190 ° C within 10 to 48 hours with subsequent treatment with 10-15% hydroperoxide solution within 10 to 15 hours (SU 719870, B 27 K 5/06, 1980). This method can be successfully used for accelerated aging of workpieces for high quality musical instrument manufacture and for restoration purposes.

Another known method of wood treatment is to heat in the chamber to the initial temperature lower than the boiling temperature of the moisture contained in the wood at the initial pressure in the chamber, then reduce the pressure in the chamber and dissipate the released moisture (RU 2145693, F 26 B 3/00). 2000). The wood is kept at a temperature of 120 to 200 ° C until the pressure in the chamber min. 2 atm. When increasing the pressure, e.g. At 8 atm, the softwood acquires a brownish hue.

Also known is a wood refining method by means of heat treatment: The workpieces are heated in an air bath and exposed within 1.5 to 4 hours at a temperature of 190 to 230 ° C and then cooled under natural conditions (RU 2099180, B 27 K 5/00, 1997 ). This gives the wood a very pronounced texture pattern and is comparable in terms of decorative properties with precious wood.

The method most closely related to the present invention (concerning the technical process and the result) is the wood heating with hot air and subsequent treatment with steam (SU 1250460, B 27 K3 / 00, 1986). Here, the wood structure is heated to 100 ° C with hot air. Then the air bath is replaced by wet steam, whose temperature is raised to 220 to 240 ° C; the treatment with steam takes at least 2 hours.

However, all so-called heat treatment methods with color change are used to process inferior types of wood (aspen, linden, softwood, etc.). But if precious woods are processed by the known heat treatment methods, no desired shade can be obtained on the entire cross section of pieces of wood with a thickness from 20 to 35 mm; It also creates lateral cracks, especially in thick pieces. Furthermore, the average residual moisture in the wood after processing with known heat treatment methods is uneven and is 4 to 15%.

One of the known wood drying plants includes a drying chamber where pieces of wood are stacked, supply and exhaust ducts, air heaters, fans and humidifying equipment (RU 2023963 F 26 B 3/04, 1994). This plant is used to dry hardwood at a maximum temperature of the heat carrier (wet steam) of 85 ° C. Therefore, the wood temperature does not reach the focal point.

Another known drying plant consists of the chamber with built-in nozzles for hot air supply to the wood stack (SU 94719, F 27 K 5/04, 1960). To change the rate of vapor condensation in the chamber, one of the chamber walls is made of thermally conductive material and lined with hinged ceramic pads from the outside. This allows the drying speed to be regulated. However, this plant has uneven warming of the wood pile along its length. This is due to a non-uniform hot air flow rate on the stack length, because the air pressure in the tuyeres decreases with distance from the fan.

GB 477,742 describes a method for carrying out a preservation treatment of wood in which the wood is kept at a temperature of 115 to 170 ° C for 3 to 5 hours.

GB 703,722 describes a method for hardening wood in which the wood is first held at room temperature in an atmosphere having a relative humidity of 50% to 70% and then exposed to saturated steam over a period of 1 to 3 hours.

EP 1 291 143 A2 describes a method for producing modified wood in which the wood for carrying out the modification at 120 to 200 ° C for 1 to 60 minutes is exposed to high-pressure steam of 0.2 to 1.6 MPa.

The plant closest to the present invention (concerning the technical process and the result) is that with a drying chamber for wood stacks, Heating elements and a drive device for the circulation of the heat carrier in the chamber, including inlet and outlet (RU 2182293, F 26 B 9/06, 2002). In the chamber area for the wood stack is a container with shelves for pieces of wood or with deposits between the wood pieces. In the opposite walls of the container, for example in the bottom and roof are openings whose size depends on the area of the intake and exhaust for the circulating propellant. This ensures a uniform effect of the medium in the chamber on the length of the wood stack. However, the existing walls do not allow a completely uniform throughput of the chamber medium; they also increase the media resistance during the circulation inside the chamber.

Presentation of the invention

The object of the present invention is to develop a wood treatment method for forming a wood structure having improved properties.

The technical results of this task are: possibility of treatment of pieces of wood with a thickness of over 200 mm; a wider range of types of wood for heat treatment; reduced average residual moisture in the wood after treatment; higher uniformity of the wood structure and its density; lower energy consumption for wood treatment.

These technical results are secured according to the method of the invention as follows: With preheating of wood in the chamber by air heating and subsequent wood treatment with steam, the air heating at a rate of 30 to 45 degrees / h to a temperature of 130 to 165 ° C; then the wood is treated with water vapor within 0.5 to 1.75 hours; the vapor-gas mixture produced in the chamber is then warmed to 160 to 200 ° C at a rate of 4 to 8 degrees / h; then the wood is treated with water vapor within 0.5 to 1.75 hours; the vapor-gas mixture in the chamber is then warmed to 160 to 200 ° C at a rate of 4 to 8 degrees / h; the pieces of wood are exposed to this temperature for 2.5 to 6 hours; then the wood is treated with water vapor within 0.5 to 1.75 hours; the vapor-gas mixture formed in the chamber is then heated to 160 to 200 ° C at a rate warmed up from 4 to 8 degrees / h; then the heating of the vapor-gas mixture in the chamber is stopped; 1 to 3.5 hours thereafter, the wood is treated with water vapor within 0.5 to 1.75 hours, with water vapor of 120 to 160 ° C is fed into the chamber and the vapor-gas mixture is discharged from the chamber.

wobei:

• Vs - Volumen des Holzstapels, m³;
• Vp - Inhalt der Hohlräume, m³;
• K₁ = 0,437 - experimentell ermittelter Faktor, KPa;
• K₂ = 5,62 - experimentell ermittelter Faktor, KPa.

In order to achieve the above-mentioned technical results in the drying plant with a drying chamber for wood stacks, heating elements and a driving device for the circulation of the heat carrier in the chamber, including inlet and outlet, the chamber is divided at least with a partition into two cavities, wherein the heat transfer medium can flow from one cavity via the section with the wood stack into the other cavity; the inlet of the circulating fluid is connected with a cavity and the outlet - with the other hydraulically. The pressure "N" of the circulating fluid is determined according to the following formula: $$N=\left(K_1÷K_2\right)\frac{\mathit{vs}}{\mathit{vp}}.$$

in which:

• Vs - volume of wood pile, m ³ ;
• Vp - content of the cavities, m ³ ;
• K ₁ = 0.437 - experimentally determined factor, KPa;
• K ₂ = 5.62 - experimentally determined factor, KPa.

One of the peculiarities of the newly developed method is that the wood structure is preheated with hot air to 130 to 165 ° C at a rate of 30 to 45 degrees / h. As a result of the pressure increase, the bound moisture leaves the intermediate pore space as well as pores formed by the plant cells of the wood. When preheating the wood structure with hot air up to 130 ° C at a speed of less than 30 degrees / h, the escape of the free moisture from the wood structure is significantly reduced; There is no tearing of the wood cells. Should the temperature and the heating rate exceed 165 ° C and 45 ° C / h, respectively, spontaneous destruction of the cells (pores) of the wood structure due to a substantial pressure increase and rapid migration of moisture from the central wood areas to the surface may occur. The preheating of the wood structure with hot air with said parameters is a preparatory stage for further heat treatment. After the preparation phase, the wood structure with water vapor within 0.5 treated up to 1.75 hours. This results in the averaging of the moisture values and the moisture content in the scope of the wood structure, because the water vapor is added at a temperature of 120 to 160 ° C in the chamber. Thereafter, the vapor-gas mixture formed in the chamber is heated to 160 to 200 ° C at a rate of 4 to 8 degrees / h; this increases the degree of destruction of the wood cells. Thereafter, the wood structure is again treated with water vapor within 0.5 to 1.75 hours; This also leads to the averaging of the moisture content and the moisture content in the scope of the wood structure. The vapor-gas mixture in the chamber is then reheated to 160 to 200 ° C at a rate of 4 to 8 degrees / h; the pieces of wood are exposed to this temperature for 2.5 to 6 hours. This further destroys the wood cells. Thereafter, the wood is treated again with water vapor within 0.5 to 1.75 hours, whereby a uniform distribution of the moisture content and the moisture content in the wood structure can be achieved. Subsequently, the vapor-gas mixture in the chamber is last heated to 160 to 200 ° C at a rate of 4 to 8 degrees / h; then the heating of the vapor-gas mixture in the chamber is stopped. After 1 to 3.5 hours of warming up, the wood is treated with water vapor within 0.5 to 1.75 hours. This finally stabilizes the uniformity of the wood structure. In each treatment with steam, the water vapor of 120 to 160 ° C is fed into the chamber and the vapor-gas mixture is discharged from the chamber. The parameters of the wood treatment with water vapor and conditions (temperature, duration) of the heating of the vapor-gas mixture in the chamber were determined experimentally. The degree of tinting of the pieces of wood depends on the chosen treatment parameters. The harder the treatment conditions, the higher the degree of tinting (browning).

wobei:

• Vs - Volumen des Holzstapels, m³;
• Vp - Inhalt der Hohlräume, m³;
• K₁ = 0,437 - experimentell ermittelter Faktor, KPa;
• K₂ = 5,62 - experimentell ermittelter Faktor, KPa.

The peculiarity of the corresponding system is that the chamber is divided at least with a partition wall into two cavities, wherein the heat transfer medium can flow from one cavity via the zone for the wood stack in the other; the inlet of the circulating fluid is connected with a cavity and the outlet - with the other hydraulically. The pressure "N" of the circulating fluid is determined according to the following formula: $$N=\left(K_1÷K_2\right)\frac{\mathit{vs}}{\mathit{vp}}.$$

in which:

• Vs - volume of wood pile, m ³ ;
• Vp - content of the cavities, m ³ ;
• K ₁ = 0.437 - experimentally determined factor, KPa;
• K ₂ = 5.62 - experimentally determined factor, KPa.

It has been proven experimentally that, when selecting the pressure of the circulating fluid in the specified range, a uniform throughput of the heat carrier is ensured over the length of the wood stack. This is due to the fact that the heat transfer medium in the cavity connected to the outlet of the circulatory propellant is compressed here by the overpressure created by the circulation propellant.

The wooden workpieces are to be arranged in the chamber in stacks with a certain distance between the wood layers of 5 to 20 mm.

In the chamber, the circulation of the vapor-gas mixture is to be effected, wherein the vapor-gas mixture flows through the woodpile.

In order to achieve a low degree of tinting, the air heating takes place at a rate of 30 degrees / h to a temperature of 130 ° C; then the wood is treated with water vapor within 0.5 hours; the vapor-gas mixture produced in the chamber is then warmed to 160 ° C at a rate of 4 degrees / h; then the wood is treated with water vapor within 0.5 hours; the vapor-gas mixture in the chamber is then warmed to 160 ° C at a rate of 4 degrees / h; the pieces of wood are exposed to this temperature for 2.5 hours; then the wood is treated with water vapor within 0.5 hours; the vapor-gas mixture produced in the chamber is then warmed to 160 ° C at a rate of 4 degrees / h; then the heating of the vapor-gas mixture in the chamber is stopped; One hour after the warm-up is stopped, the wood is treated with water vapor within 0.5 hours, with steam of 120 ° C being fed into the chamber and the vapor-gas mixture being discharged from the chamber.

To achieve a higher degree of tinting, the air heating is carried out at a rate of 46 degrees / h to a temperature of 165 ° C; then the wood is treated with water vapor within 1.75 hours; the vapor-gas mixture produced in the chamber is then warmed to 200 ° C at a rate of 8 degrees / h; then the wood is treated with water vapor within 1.75 hours; the vapor-gas mixture in the chamber is then warmed to 200 ° C at a rate of 8 degrees / h; the pieces of wood are exposed to this temperature for 6 hours; then the wood is treated with water vapor within 1.75 hours; the vapor-gas mixture produced in the chamber is then warmed to 200 ° C at a rate of 8 degrees / h; then the heating of the vapor-gas mixture in the chamber is stopped; 3.5 hours after the warm-up is stopped, the wood is treated with steam for 1.75 hours, with steam of 160 ° C being fed into the chamber and the vapor-gas mixture being discharged from the chamber.

The pressure in the chamber during the wood treatment must not exceed 0.2 MPa.

The present method can handle various construction elements and wooden workpieces.

The system should be equipped with a source of steam, the outlet of which is connected to the cavity of the chamber and condensate drainage.

The chamber should be provided with removable heat-insulating mats for at least part of the outer surface of the chamber.

The circulation driver can be mounted inside or outside the chamber.

The inlet and outlet of Umwälztreibers is hydraulically connected to the corresponding cavities by means of a two-point distributor, with the possibility of alternately connecting the inlet and outlet to the cavities of the chamber are provided.

The system may include at least one additional circulator installed inside or outside the chamber.

Brief description of the figures

FIG. 1

schematically shows the overall view of the wood treatment plant.

FIG. 2

shows a diagram of the layout in plan.

FIG. 3

shows a floor plan of another system variant.

FIG. 4

shows a system diagram from the door opening.

FIG. 5

shows a system diagram from the door opening for the second system variant.

FIG. 6

shows a system diagram from the door opening for another system variant.

Preferred embodiment of the invention

wobei:

• Vs - Volumen des Holzstapels, m³;
• Vp - Inhalt der Hohlräume, m³;
• K₁ = 0,437 - experimentell ermittelter Faktor, KPa;
• K₂ = 5,62 - experimentell ermittelter Faktor, KPa.

The wood treatment plant 1 with which the method according to the invention is carried out comprises an airtight chamber 2 with at least one door opening, which is closed with the door 3 and makes the chamber 2 airtight. Within the chamber, a section for the wood stack 4 is provided. In the chamber 2 are heating elements 5, which can be arranged in any known manner in the chamber 2. As heating elements, any known devices, such as thermocouples serve. The system 1 also includes a driver 6 for the circulation of the heat carrier in the chamber. The circulation driver 6 has an inlet 7 and an outlet 8 for suction or extraction of the heat carrier. The chamber is divided at least with a partition wall 9 into two cavities 10, wherein the heat carrier can flow from a cavity 10 via the section 4 for the wood stack in the other cavity 10. The inlet 7 of the circulator is hydraulically connected to one cavity 10 and the outlet 8 is connected to the other cavity 10. The pressure "N" of the circulating fluid is determined by the following formula: $$N=\left(K_1÷K_2\right)\frac{\mathit{vs}}{\mathit{vp}}.$$

in which:

• Vs - volume of wood pile, m ³ ;
• Vp - content of the cavities, m ³ ;
• K ₁ = 0.437 - experimentally determined factor, KPa;
• K ₂ = 5.62 - experimentally determined factor, KPa.

The plant 1 is provided with the steam source 11, whose outlet is connected via the valve 12 with the cavity of the chamber 2. For the discharge of condensate, the system 1 is provided with the device 13 for condensate drainage. This device 13 works in virtually all treatment phases and is most heavily used in the treatment with water vapor. The chamber 2 may be provided with removable thermal insulation mats 14 on a portion of the chamber surface. The circulation driver 6 is installed inside the chamber 2 and outside the chamber 2. For reversible flow over the heat carrier from a cavity 10 in the other cavity 10, the inlet 7 and the outlet 8 of the circulating 6 are hydraulically connected by means of a two-point distributor 15 with the respective cavities 10, with the possibility of alternately connecting the inlet and outlet ducts 7 and 8 are provided to the cavities 10 of the chamber 2. The system may include at least one additional circulating driver 16 installed inside or outside the chamber 2. The flap 17 is used to divert the vapor-gas mixture from the chamber 2. The stack is on a cart 18, the u.a. on rails 19 drives, be placed.

When using the method gem. In the present invention, the plant functions as follows. On the cart 18 or directly in the chamber 2 (see Fig. 5 and 6 ), the pieces of wood are put together in a stack. The wood layers are placed on each other at a distance of 5 to 20 mm by means of spacers or inserts. Then the cart 18 is retracted with the finished stack in the chamber 2 on rails 19. The chamber 2 is closed with the door 3. On the outer surface of the chamber 2 heat insulation mats 14 are hung, which reduce the heat losses. (The chamber walls can be made of heat-insulating material, thereby eliminating the heat insulation mats.) The heating elements 5 are turned on, thus the wood preheating begins in the chamber 2 by the warming of the air in the chamber at 130 to 165 ° C at a speed of 30 to 45 degrees / h. When warming up the pieces of wood, the moisture contained in the wood evaporates. For efficient air heating in the chamber, the heat transfer medium (vapor-gas mixture) in the chamber 2 is circulated by means of the driver 6.

After reaching the temperature of 130 to 160 ° C, steam from the water vapor source 11 is input to the chamber 2 within 0.5 to 1.75 hours. The vapor-gas mixture produced in the chamber is then warmed to 160 to 200 ° C at a rate of 4 to 8 degrees / h; then the wood is treated again with steam within 0.5 to 1.75 hours. The vapor-gas mixture in the chamber is then reheated to 160 to 200 ° C at a rate of 4 to 8 degrees / h; the pieces of wood are exposed to this temperature for 2.5 to 6 hours. Thereafter, the wood is again treated with water vapor within 0.5 to 1.75 hours; the vapor-gas mixture is then brought back to 160 to 200 ° C at a rate of 4 to 8 degrees / h; then the heating elements 5 are turned off and the heating of the vapor-gas mixture in the chamber is stopped. The wood is treated with steam for 0.5 to 1.75 hours 1 to 3.5 hours after warming up.

After completion of the heat treatment, the heat insulating mats 14 are removed from the outer surface of the chamber 2. The cooling of the wood stack is accelerated due to a higher heat output from the chamber 2 into the outside air. After cooling of wood in the chamber below 60 ° C, the door 3 is opened. The stack 4 is pulled out of the chamber 2 to the outside, where the wood is finally cooled.

All heat treatment processes can be automated by means of appropriate encoders and control devices. Any known devices can be used for this purpose.

All heat treatment phases are carried out by circulation of the vapor-gas mixture in the chamber by means of circulation. If only one circulation driver is used, the movement reversal of the heat carrier can be effected by means of a two-point distributor 15. The additional circulation driver 16 also enables the wood treatment in the reversible circulation of the heat carrier. For this purpose, the inlet of the main driver 6 is connected to one of the cavities 10, the inlet of the additional circulating driver 16 is connected to the other cavity 10. Accordingly, the outlets of the circulation drivers 6 and 16 are connected (see Fig. 6 ).

The investigations showed that the residual moisture in the wood does not exceed 6.2% at all treatment intervals.

After such heat treatment, the workpieces are given a beautiful appearance and unique characteristics and can be used in various fields, i.a. for the interior fittings of steam baths and sauna rooms, for exterior cladding of different buildings, for the production of floors, musical instruments etc.

As a result of the heat treatment, the wood cell structure changes in the mass, as if the wood had dried for several centuries. The water vapor acts as a protective medium in this case and prevents the ignition of wood at elevated temperatures, because the oxygen is displaced. During the heat treatment, it also decomposes sugar, thereby the microorganisms are brought to the nutrient medium. They are also killed by the heat treatment.

Economic applicability

The method acc. The present invention is economically applicable to the hydrothermal treatment of wood, wood products and various wooden products such as boards, squared timber, parquet, workpieces of different shapes. The method acc. The present invention requires no development of special equipment and equipment.

Claims (9)

1. A wood treatment method, characterized by the preheating of wood in the chamber by air heating and subsequent treatment of the wood with steam, wherein the air heating takes place at a rate of from 30 to 45 °/h to a temperature of from 130 to 165°C; after that, the wood is treated with steam within 0.5 to 1.75 hours; the steam / gas mixture formed in the chamber is then heated to 160 to 200°C at a rate of from 4 to 8 °/h; after that, the wood is treated with steam within 0.5 to 1.75 hours; the steam / gas mixture in the chamber is then heated to 160 to 200°C at a rate of from 4 to 8 °/h; the pieces of wood are subjected to this temperature for 2.5 to 6 hours; after that, the wood is treated with steam within 0.5 to 1.75 hours; the steam / gas mixture formed in the chamber is then heated to 160 to 200°C at a rate of from 4 to 8 °/h; then the heating of the steam / gas mixture in the chamber is stopped; from 1 to 3.5 hours after that, the wood is treated with steam within 0.5 to 1.75 hours, wherein steam at from 120 to 160°C is fed into the chamber and the steam / gas mixture is removed from the chamber.
2. A method according to claim 1, characterized by the arrangement of workpieces of wood in a stack.
3. A method according to claim 2, characterized in that the layers of wood are arranged at a distance in the stack.
4. A method according to claim 3, characterized in that the distance between the layers of wood amounts to from 5 mm to 20 mm.
5. A method according to any one of claims 1 to 4, characterized in that circulation of the steam / gas mixture takes place in the chamber.
6. A method according to claim 5, characterized in that the circulated steam / gas mixture flows through the stack.
7. A method according to any one of claims 1 to 6, characterized in that the heating of the air in the chamber to 130°C takes place at a rate of 30 °/h; after that, the wood is treated with steam within 0.5 hours; the steam / gas mixture formed in the chamber is then heated to 160°C at a rate of 4 °/h; after that, the wood is treated with steam within 0.5 hours; the steam / gas mixture in the chamber is then heated to 160°C at a rate of from 4 °/h; the pieces of wood are subjected to this temperature for 2.5 hours; after that, the wood is treated with steam within 0.5 hours; the steam / gas mixture formed in the chamber is then heated to 160°C at a rate of from 4 °/h; then the heating of the steam / gas mixture in the chamber is stopped; 1 hour after setting the heating, the wood is treated with steam within 0.5 hours, wherein steam at 120°C is fed into the chamber and the steam / gas mixture is removed from the chamber.
8. A method according to any one of claims 1 to 6, characterized in that the heating of the air in the chamber to 165°C takes place at a rate of 45 °/h; after that, the wood is treated with steam within 1.75 hours; the steam / gas mixture formed in the chamber is then heated to 200°C at a rate of 8 °/h; after that, the wood is treated with steam within 1.75 hours; the steam / gas mixture in the chamber is then heated to 200°C at a rate of from 8 °/h; the pieces of wood are subjected to this temperature for 6 hours; after that, the wood is treated with steam within 1.75 hours; the steam / gas mixture formed in the chamber is then heated to 200°C at a rate of from 8 °/h; then the heating of the steam / gas mixture in the chamber is stopped; 3.5 hours after setting the heating, the wood is treated with steam within 1.75 hours, wherein steam at 160°C is fed into the chamber and the steam / gas mixture is removed from the chamber.
9. A method according to any one of claims 1 to 8, characterized in that during the heat treatment a maximum overpressure of 0.2 MPa is created in the chamber.

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