DE102009047137A1 - Process for the thermal modification or tempering of wood and wood products - Google Patents

Abstract

The invention relates to a method for the thermal modification or tempering of wood and wood products (4) in thermal chambers, wherein the wood or wood product (4) to be modified in layers between gas-tight, temperature and corrosion resistant and good heat conducting cover plates (3) or hollow chamber profile plates (7 ) is placed from corrosion resistant sheet metal and the resulting sandwich layers (2) of wood or wood product to be treated (4) and cover plates (3) or hollow chamber profile plates (7) are assembled into stacked chambers (1).
In particular, the method is applicable to lumber, board sections, board slats, veneers or wood-based panels in thermal chambers both at atmospheric pressure and under modified pressure.

Description

The invention relates to a method for the thermal modification or tempering of wood and wood products. In particular, the method is applicable to sawn timber, board sections, board slats, veneers or wood-based panels in thermal chambers both at atmospheric pressure and under elevated pressure.

Efforts to heat up native and less or non-durable wood species by heat and make them more durable and dimensionally stable date back to the mid-twentieth century. Extensive investigations on the thermal modification are from the documents Strain AJ et al. (1937) Industrial and Engineering Chemistry, 29 (7), 831-833 , and Strain, AJ et al. (1946) Industrial and Engineering Chemistry, 38 (6), 630-634 , such as Stamm, AJ (1959) Tappi, 42 (1), 39-44 , known. It was treated wood in various gases or a bath of molten metal. The Humidity-Heat-Pressure (FWD) process, in which wood has been treated under autoclave-like conditions under the action of heat, is described in US Pat Burmester, A. (1973): Influence of heat-pressure treatment of semi-dry wood on its dimensional stability. Wood as raw material 31: 237-243 described and was according to Giebeler, E. (1983): Dimensional stabilization of wood by a moisture / heat / pressure treatment. Wood Raw Material 41: 87-94 further developed. The modification of wood by heat was for the first time in Finland in the late 1990s practicable with the Thermowood method according to the EP 0 695 408 B1 and the EP 0 759 137 B1 and the Stellac method according to the EP 0 922 918 B1 developed. The continuing shortage of enduring tropical woods or sinking qualities, as well as the increasingly critical attitude of consumers towards chemically protected wood, have brought wood modification as a possible alternative a significant advance.

The heat treatment of wood is used inter alia in the EP 0 018 446 , of the EP 0 612 595 , of the EP 0 623 433 , of the EP 0 622 163 , of the EP 0 759 137 and the US 5,678,324 described.

The chemical modification of wood pursues in principle similar goals as the thermal one. The production of chemically modified wood (CMT) is carried out by introducing a liquid reagent, usually by pressure impregnation, and their reaction / curing by the action of heat.

While CMT with the acetylation, furfurylation and Belmadur processes are currently in the market introduction phase, thermal wood modification can be considered as established, although the quantities produced for Europe in 2007 remain at about 131,000 m ³ comparatively low level ( Scheiding, W .; Rapp, AO; Krause, A. (2007): Thermally Modified Timber (TMT) Facing European Standards. 3rd European Conference on Wood Modification, Cardiff 15./16.10.2007 edited by Hill, CAS; Jones, D .; Militz, H .; Ormondroyd, GA [ed.] ).

A definition of thermally modified wood is given by CEN / TS 15679: 2007. Main criterion of according to Wienhaus, O. (1999): Modification of wood through mild pyrolysis - derived from the general principles of thermolysis of wood. Wiss. Z. TU Dresden, raw material wood Dresden 48 (1999) 2. - P. 17 to 22 The term "mild pyrolysis" is the action of heat alone in the range of about 160 ° C to 230 ° C with reduced oxygen content. Main effects of the thermal modification are the increase of the durability against wood-destroying fungi, the improvement of the dimensional stability or the reduction of swelling and shrinkage. The negative effect of any thermal modification is the sometimes considerable reduction in strength, especially flexural strength and fracture impact work. Therefore, the goal of any process development is to achieve the desired effects while minimizing the strength reduction. The now industrially established methods differ mainly by the way in which a reduction of the oxygen content is achieved. The Thermowood method and the Stellac method are based on the addition of water vapor during the heating phase, wherein the chamber atmosphere is additionally formed from the evaporated water from the wood and the wood gases. Starting material is usually technically dried wood with wood moisture between 8 and 12 percent.

The basic principle of the FWD process is described in the WO 03/106123 A2 describes the wood in the autoclave with additional introduction of carbon dioxide (CO ₂ ) is modified as an inert gas. A combination of autoclave and heat treatment is the so-called PLATO process. In the PLATO process, the wood is treated in four treatment steps - thermohydrolysis under elevated pressure, drying, thermal treatment and conditioning.

A procedure based on the same basic principle was further developed by the Danish company WTT A / S and realized for the first time in a system at Prodeo / Switzerland. According to the operator, increasing the pressure makes it possible to lower the treatment temperature with the same modification effect.

Between the Finnish procedure and the WTT procedure the BikoS procedure could be arranged. In the BikoS process, the thermal modification takes place at slightly elevated pressure with the addition of steam in a boiler.

The EP 1 118 828 A1 describes a process for the thermal treatment of wood in which no water vapor is added and the resulting wood gases are withdrawn from the chamber and burned or condensed. This procedure is implemented in two companies in Austria.

It is also possible to provide inert conditions for thermal wood modification with a nitrogen atmosphere. Such a method is known in France as Rétification or NOW method, which is in the publications FR 2 604 942 . FR 2 751 579 and FR 2 751 580 is described. The method of Balz Holz AG, Emmenthal / Switzerland is based on the same basic principle. The nitrogen is provided in a specially developed plant.

Opel Therm GmbH, Unterensingen, has developed a process and a device based on vacuum wood drying. Both apparatus and methods are described in various patents entitled "Vacuum Dryer for Timber and Method of Drying Timber", inter alia in U.S. Patent Nos. 4,646,655 and 4,605,842 DE 44 28 001 C2 . EP 0 760 930 B1 and WO 95/33170 , After that, wood is stacked between hot plates and the stack is placed in a vacuum dryer. The heating takes place via thermal oil, which is led via flexible hoses into corresponding channels in the heating plates. This principle is known, for example, from multi-layer chipboard presses. On the stack, a pressing pressure is exerted by a pneumatic device. The vacuum dryer provides for the stacking of wood between heating elements, the pressure-tight execution of the chamber and the arrangement of the printing device within it. The method comprises the pressure-tight introduction of the stack into the chamber and its evacuation during the supply of heat energy through the heating elements. In one described embodiment of the method, the increase in pressure above atmospheric pressure is provided. In a further embodiment, the heating elements are designed as plate-shaped aluminum hollow body through which a medium-settable temperature can flow.

The company Opel Therm GmbH uses the above mentioned method and the corresponding plant also for the thermal modification of wood. The vacuum dissipates water vapor and wood gases during the process. The method used for the solid wood coating is intended to produce low-emission, thermally modified wood (TMT) at lower treatment temperatures and the same modification effect and in a shorter treatment time. A first plant for thermal wood modification according to this method is operated by the company ETH Röthlisberger (Switzerland); Another plant is under construction in Rottleberode (timura company). The Opel wood modification process has been technologically derived from vacuum lumber drying, similar to other TMT processes, such as the Thermowood process, from which high-temperature wood drying was derived. Due to the hotplates and the vacuum design, this process requires more technical effort compared to the conventional basic thermal chamber processes such as the VTT, Stellac, Mühlböck, Mahild, Celloc, Bikos and Perdure processes. The described methods are mostly used for the treatment of sawn timber, more rarely of roundwood. It is possible by these methods but also the treatment of slats or veneers, from which are formed packages having a thickness corresponding to the otherwise usually modified lumber, to which the program is tuned. The veneer packages are usually strapped before treatment in the thermal chamber with temperature-resistant tape, the last of the industrial processes is the OHT process (oil-heat treatment), which in the DE 198 52 827 A1 , of the EP 1 002 630 and the US 6,217,939 B1 is described. The heat transfer and the oxygen termination are taken over here by heated vegetable oil.

Recently, the demand for thermally tempered, glued-on windows or door friezes has increased. These scantlings are usually made of low-quality lumber. In the process, branches and other wood defects are first cut off. The resulting, sometimes very short board sections (up to 25 centimeters) are then finger-jointed, glued to longer board lamellae of up to 16 meters and glued to bars. The thermal modification must now take place before the bonding; for reasons of material efficiency, it takes place on the short board sections. The stacking of these short pieces for treatment in the thermal chamber is compared to the usual stacking of lumber (boards) extremely complex and difficult.

In preliminary preliminary tests by the applicant, whole wood-based panels were thermally treated. Disadvantages were discoloration and condensate deposits on the surface of the plates, which required subsequent sanding, as well as deformation of the plates which occurred in the zone between the lasts.

The systems for thermal modification are either so-called thermal chambers similar to normal drying chambers, but designed for temperatures up to 250 ° C and possibly for steam supply, or boiler similar to those for the boiler pressure impregnation, but thermally insulated and corrosion protection reasons in stainless steel. The design as a boiler is more complex in terms of apparatus than the thermal chambers. In any case, process control takes place via computers and special programs.

Another variant was developed by O. W. I molded parts made of wood and plastic GmbH, Lohr, for the thermal modification of veneers. The veneers are individually thermally modified in a single pass with a belt dryer and then further processed into shaped parts.

It is known that the reduction of the oxygen content of the atmosphere surrounding the wood is a crucial parameter of all thermal modification processes and that the technical solution for this is often very expensive. Special or more detailed information on how to bring the wood into the thermal chamber, can be found in any of the above publications. In practice, the general principles of stacking for drying chambers are followed, partly with special solutions, for example the type of stacking strips (wood, aluminum, venturi strip or similar).

The object of the invention is to provide a method for the thermal modification of lumber, board sections, board lamellae, veneers or wood-based panels in thermal chambers are avoided in the damage caused by the pyrolysis, contamination and discoloration and a better heat distribution is achieved. Furthermore, the costs should also be reduced in comparison to the above-mentioned methods.

The solution of the object of the invention consists in a method for thermal modification or compensation of wood and wood products in thermal chambers in which the wood or wood product to be modified is placed in layers between gas-tight, temperature and corrosion resistant and good heat conducting cover plates and the resulting so-called sandwich layers be composed of wood or wood product to be treated and cover plates to stacks of stacks. The material used for the cover plates according to the invention is corrosion-resistant sheet, which is characterized by a high thermal conductivity.

A sufficiently dense packing of the layers can be ensured with the usual measures in the wood drying and in the thermal modification of wood, for example by applying temperature-resistant mass pieces, by strapping or by applying a pneumatically or hydraulically generated compressive force.

With this arrangement, various positive effects are achieved, in particular an oxygen termination in the surface, which reduces the damage to the wood to be modified by pyrolysis. Other benefits include shape stabilization and protection of the surfaces against unwanted discoloration and fouling during the process. In addition, a better heat distribution over the surface of the individual layers is achieved by equalizing the heat transfer in the area. This results in additional advantages, since the cover acts as a thermal buffer. A good heat transfer to the wood is - despite the coverage on the broadsides - guaranteed.

The preferred range for the thickness of the cover plates is between 1 and 10 millimeters. The material used for the gas-tight, temperature-resistant and good heat-conducting cover plates is especially aluminum. The advantage of aluminum is above all in its high thermal conductivity, which ensures good heat transfer to the material to be modified. In one embodiment, spacers are placed between the gas-tight, temperature-resistant and good heat-conducting cover plates in order to produce the necessary for the flow through with the gas mixture in the chamber. These spacers may be, for example, staple bars.

In an alternative solution variant, instead of individual cover plates and stacking strips, hollow-section profile plates made of corrosion-resistant sheet metal, in particular in the form of extruded aluminum hollow-section profile plates, can be used. The webs of the hollow chamber profile plates take over the function of stacking strips. In this alternative solution variant, the mutual stacking of wood layers and hollow chamber profile plates is provided, wherein the chambers are arranged in the flow direction. Although the hollow-section profile plates are more expensive to purchase, the manipulation is simplified compared to individual cover plates and staples essential or stacking effort is - especially for kleinteiligem material - significantly reduced. The stacking can be done manually or with a stacking device.

As the material to be treated are preferably lumber, board sections, board lamellae, cutting, peeling and sliced veneer or flat wood products, especially wood-based panels, in one or more layers to choose from.

The narrow sides of the wood layers are preferably either open or they can also be covered by enclosed gas-permeable material, in particular wooden strips. The advantage of such an embodiment is that it achieves a certain degree of oxygen also at the narrow surfaces and at the same time a pressure equalization is made possible. The resulting gases, water vapor and pyrolysis or wood gases can escape without problems on the narrow sides, so that damage, for example, tear as a result of internal vapor pressure can be avoided.

A further advantage of the invention is that in hygrothermal wood modification processes can be dispensed with the steam preparation, which is otherwise with the aim to prevent excessive drying during the process. The drying out of the material when using the method features according to the invention is - compared to other methods - but greatly reduced, since the wood dries less given the influence of temperature by the covering. The elimination of the steam preparation reduces the costs considerably, since the steam preparation is one of the most significant cost factors in hygrothermal wood modification processes.

In particular, the method according to the invention is suitable for the thermal modification or tempering of wood and wood products which are no longer planed or sanded after the treatment, but are to be further processed immediately, since in this case the protection of the surface comes into effect during the process.

In the thermal modification of veneers arise from the process of the invention over the treatment described above in the package particular advantages, since not only the access of oxygen is minimized, but the veneers are additionally smoothed (leveled), with a deformation by waves or the like largely to completely is prevented. In addition, the previously usual strapping the veneer packages with temperature-resistant bands, for example, with metal strips eliminated. Each sandwich layer is made up of several veneer sheets, the number of veneers per package being the veneer thickness and the maximum package thickness. In a particularly advantageous embodiment of the invention, a plurality of veneer packages with package thicknesses up to 50 millimeters, preferably between 10 to 30 millimeters, simultaneously thermally modified, without the veneer packages must be strapped. Also, by eliminating the strapping costs are reduced. The number of veneers per package is calculated from the veneer thickness and the waviness. Preliminary tests by the applicant confirmed that the method according to the invention is more gentle than, for example, the method practiced by OWI, since the strength reduction of the veneers as a result of the thermal treatment is lower than there.

The advantages of the solution according to the invention come into play especially when the material in the sandwich layer is of the same thickness and even. However, special advantages are obtained when using the method in the remuneration of short board sections for the production of finger-jointed window scantlings or the like, since the very short board sections (up to about 25 centimeters) can be placed with little effort without targeted distances and close together on a sheet What can be done manually or mechanically. The stacking effort compared to a classic stacking only with stacking strips can thereby be substantially reduced.

The inventive method is also very well suited for the thermal modification of board slats for solid wood panels. Here too, in principle, the special advantages described for the veneers come into play.

The process according to the invention can be used immediately without any special measures for all systems for thermal modification (thermal chambers) operated at atmospheric pressure. Alternatively, the thermal modification can also take place in a pressure-tight thermal chamber under modified, preferably elevated pressure. The method can be carried out in longitudinally and transversely flowed through chambers with cubic, polyhedral or cylindrical geometry of the interior. Likewise, a treatment in continuous systems is possible, as it is operated for example by the company Lunawood Oy, Finland.

• – keine Heizplatten, flexible Schläuche öder Ähnliches,
• – keine Vorrichtungen zur Erzeugung von Über- beziehungsweise Unterdruck,
• – kein Thermoöl als wärmeübertragendes Medium,
• – keine spezielle, das heißt druckfeste Ausführung der Kammer, und
• – keine besonderen Ausführungen der Kammer

erforderlich.Compared with the Opel-Therm process for thermal modification of solid wood, the following advantages can be mentioned:
There are

• - no heating plates, flexible hoses or the like,
• - no devices for generating positive or negative pressure,
• - no thermal oil as a heat transfer medium,
• - No special, that is pressure-resistant design of the chamber, and
• - no special comments by the board

required.

• – die gleichzeitige und damit homogene Vergütung einer Vielzahl von Furnieren ist möglich,
• – es ist keine spezielle Vorrichtung wie zum Beispiel ein Bandtrockner erforderlich.

Compared to the OWI process for the thermal modification of veneers are to be mentioned as advantages:

• - The simultaneous and thus homogeneous remuneration of a variety of veneers is possible
• No special device such as a belt dryer is required.

Further details, features and advantages of the invention will become apparent from the figures and the following description of exemplary embodiments.

Show it:

1 : two chamber stacks, with it

1a a stack of cover plates, wood or wood product to be modified, and of staple boards, and

1b : a stack of stacks of wood or wood product to be modified and of hollow profile sheets;

2 : two sandwich layers, with you

2a : a sandwich layer of wood / wood product and cover plates with cover on the narrow sides of the wood product and

2 B : a sandwich layer of wood / wood product and hollow profile plates with cover on the narrow sides of the wood product.

The 1a shows a chamber stack 1 that made sandwich layers 2 is formed. The sandwich layers 2 consist of gas-tight, temperature-resistant and good heat-conducting cover plates 3 and the wood or wood product to be modified 4 , depending on the product optionally in layers or side by side between the cover plates 3 is placed. According to 1a a flow-through cross-sectional area is formed by spacers 5 in the form of stacking strips 5 between the cover plates 3 are placed to prepare the necessary for the flow with a gas mixture distance. The chamber stack 1 is with a surcharge 6 complained.

The 1b shows a corresponding chamber stack 1 , but with spacers in the form of webs 8th in hollow chamber profile plates 7 , where the vertical bars 8th the same function as the stacking strips 5 according to 1a take.

2a shows how 1a a sandwich layer 2 made of wood or wood product 4 and cover plates 3 , 2 B shows like that 1b a sandwich layer 2 made of wood or wood product 4 and hollow profile plates 7 with bars 8th as spacers. Both in the execution according to 2a as well as in the execution according to 2 B but are the narrow sides of the wood layer 4 each through a gas-permeable material 9 covered.

LIST OF REFERENCE NUMBERS

1

chamber stack

2

sandwich documents

3

cover

4

Wood or wood products, material to be treated, wood layers

5

Spacers, stacking strips

6

ballasted

7

Hollow chamber profile plates

8th

(vertical) webs

9

gas permeable material

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0695408 B1 [0002]
• EP 0759137 B1 [0002]
• EP 0922918 B1 [0002]
• EP 0018446 [0003]
• EP 0612595 [0003]
• EP 0623433 [0003]
• EP 0622163 [0003]
• EP 0759137 [0003]
• US 5678324 [0003]
• WO 03/106123 A2 [0007]
• EP 1118828 A1 [0010]
• FR 2604942 [0011]
• FR 2751579 [0011]
• FR 2751580 [0011]
• DE 4428001 C2 [0012]
• EP 0760930 B1 [0012]
• WO 95/33170 [0012]
• DE 19852827 A1 [0013]
• EP 1002630 [0013]
• US 6217939 B1 [0013]

Cited non-patent literature

• Strain AJ et al. (1937) Industrial and Engineering Chemistry, 29 (7), 831-833 [0002]
• Strain, AJ et al. (1946) Industrial and Engineering Chemistry, 38 (6), 630-634 [0002]
• Stamm, AJ (1959) Tappi, 42 (1), 39-44 [0002]
• Burmester, A. (1973): Influence of heat-pressure treatment of semi-dry wood on its dimensional stability. Wood as raw material 31: 237-243 [0002]
• Giebeler, E. (1983): Dimensional stabilization of wood by a moisture / heat / pressure treatment. Wood Raw Material 41: 87-94 [0002]
• Scheiding, W .; Rapp, AO; Krause, A. (2007): Thermally Modified Timber (TMT) Facing European Standards. 3rd European Conference on Wood Modification, Cardiff 15./16.10.2007 edited by Hill, CAS; Jones, D .; Militz, H .; Ormondroyd, GA [ed.] [0005]
• Wienhaus, O. (1999): Modification of wood through mild pyrolysis - derived from the general principles of thermolysis of wood. Wiss. Z. TU Dresden, raw material wood Dresden 48 (1999) 2. - P. 17 to 22 [0006]

Claims (10)

Process for thermal modification or tempering of wood and wood products ( 4 ) in thermal chambers where the wood or wood product to be modified ( 4 ) in layers between gas-tight, temperature and corrosion resistant and good heat conducting cover plates ( 3 ) and the resulting sandwich layers ( 2 ) to be treated wood or wood product ( 4 ) and cover plates ( 3 ) to chamber stacks ( 1 ). Method according to claim 1, characterized in that the cover plates ( 3 ) consist of aluminum sheet whose thickness is in the range between 1 and 10 millimeters. Method according to claim 1 or 2, characterized in that between the cover plates ( 3 ) Spacers ( 5 ) are placed to prepare the necessary for the flow with the gas mixture in the chamber necessary distance. Process for thermal modification or tempering of wood and wood products ( 4 ) in thermal chambers where the wood or wood product to be modified ( 4 ) in layers between hollow profile sheets ( 7 ) is made of corrosion-resistant sheet metal and the resulting sandwich layers ( 2 ) to be treated wood or wood product ( 4 ) and hollow profile plates ( 7 ) to chamber stacks ( 1 ), wherein the hollow profile plates ( 7 ) vertical bars ( 8th ), wherein the webs ( 8th ) in the hollow chamber profile plates ( 7 ) the function of spacers ( 5 ) take. Method according to one of claims 1 to 4, characterized in that the material to be treated ( 4 ) consists of lumber, board sections, board lamellae, cutting, peeling and sliced veneer or flat wood products, in particular wood-based panels, in one or more layers. Method according to one of claims 1 to 5, characterized in that the cover plates ( 3 ) or the hollow profile sheets ( 7 ) consist of aluminum. Method according to one of claims 1 to 6, characterized in that the narrow sides of the wood layers ( 4 ) are covered by enclosed gas-permeable material, in particular wooden strips. Method according to one of claims 1 to 7, characterized in that a plurality of packages of veneers or board slats with package thicknesses up to 50 millimeters are thermally modified simultaneously. A method according to claim 8, characterized in that the package thicknesses of the packages of veneers or board slats are in the range between 10 to 30 millimeters. Method according to one of claims 1 to 9, characterized in that the thermal modification takes place in a pressure-tight thermal chamber under modified pressure.

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