EP1236552A1 - Method and plant for the production of fiberboards - Google Patents

Abstract

In a process to manufacture chipboard, a continual fed of wood chips or fibre is scattered with a small quantity of a bonding agent (or no bonding agent) onto a non-corroding endless metal belt as this advances through a press. The wood fibre and bonding agent are pressed and heated into a fibreboard. Also claimed is a chipboard or fibreboard manufacturing press assembly with a particle scatter station over a conveyer belt feeding a press. The scatter station may feed one or more layers simultaneously. The press has a moving upper frame and a stationery lower frame with heating and cooling press plates. In the process the mixture of chips and bonding agent are dried to bring moisture content to the range 16 to 25 per cent and scattered onto the belt, where application of saturated steam and hot water spray raises the humidity to the range 25 to 35 per cent immediately prior to entering the press. The moistened chip matrix passes into the press where, during 20 per cent of the press travel, it is compressed to a maximum of 5.5 N/mm2. Water is expelled and the matrix dries under core pressure of no more than 1 N/mm2, until core moisture content falls to 5-8 per cent. In the final hardening phase the board is subjected to a maximum pressure of 3.5 N/mm2 and compressed to final dimensions and dried until the core moisture falls to 2 per cent.

Description

The invention relates to a method for producing wood-based panels, in particular of fiberboard in the semi-dry process according to the generic term of claim 1, 2 and 3 and a system for performing the The method of claim 28.

Fiberboard, which are produced in the semi-dry or wet process, have a very low adhesive content of about 0.5 - 1%, or some fiberboard are produced entirely without glue. On the other hand is the adhesive content for fiberboard after the dry process - for Example of MDF boards - over 10% based on the wood substance (Harnstofformaldehyharz). An adhesive content of, for example, 12% however, up to 30% of the cost of manufacturing an MDF board, with increasing Petroleum Cost The cost of the glue continues to rise and the fiberboard so it becomes very expensive.

Fiberboard from the semi-dry and wet process are so far only pressed on discontinuous multi-level systems. A large falls during the production of fiberboard using the wet process Amount of polluted waste water, on the one hand when fleece is formed over a Fourdrinier wire and secondly during hot pressing. This method was further developed to the semi-dry process in the 40 and 50 years, to reduce waste water pollution. There are a number of Intellectual Property Rights (U.S. Patent 2,757,115; U.S. Patent 2,757,148; U.S. Patent 2,757,149 and U.S. Patent 2,757,150). A small amount of water is also used in the Semi-dry process from the mat at the start of hot pressing squeezed. The pressing time is, for example, for a 3 mm fibreboard about 4 minutes, which is just under 1 minute in the dry process. So that the capacity of the system is sufficiently large for operation, the Multi-daylight press due to the long pressing time very many floors (up to 35 pieces). Due to the high number of floors, the presses expensive. The operating costs of such a system are due to the Multi-day press also very high.

With the semi-dry process, the fibers must be dried so that they become one without the use of a wire Fiber mat can be molded. At higher humidities the fibers are matted so that pneumatic or mechanical scattering is not possible is. After spreading, the fiber mat is continuously pre-pressed and in individual fiber mat sections according to the floor size using a Split saw. These mat cuts are on sieves or Metal wire mesh, which are often still mounted on metal sheets, in the Feeding basket transported where they lie for different lengths depending on the floor.

The fiber mat sections are often heated to a moisture of around 18% dried and after the pre-press, water is applied to the top of the fiber mat sprayed. The fiber mat moisture rises in front of the press through the water about 32%. Since at the beginning of the pressing the water is only on the Top is located and therefore the top warms up faster than the Underside, the fiber mat top becomes stronger at the beginning of the pressing plasticized as the bottom. The screens and sheets are made after pressing transported around the press or under the press back to the molding strand, which takes a few minutes. In addition, the screens in some plants be cleaned with water. During transportation and cleaning cool the screens and trays. You then have to press on at the beginning the heating plate temperature of 190 ° C, including 20 - 60 Seconds are needed.

In order to remove part of the water from the fiber mat without having to evaporate it, a high specific pressure of 5.5 to 6 N / mm ^{2 is} applied to the fiber mat at the beginning of the pressing. In this phase, a small part of the water is squeezed out of the fiber mat. The water is transported through the sieve to the fiber mat narrow surfaces and then runs down from the press plates. The density of the outer fibreboard layers is also defined in this phase. Due to the uneven plasticization, the density on the outside of the plate facing away from the screen is higher than on the outside of the plate facing towards the screen. The density profile of the fiberboard produced in this way is therefore usually asymmetrical, which in some applications leads to disadvantages due to a warping of the board. If the fiberboard absorbs or releases moisture, it swells or shrinks more on one side due to the asymmetrical density profile and warps as a result.

After the high pressure phase, the specific pressure is reduced and the fiber mat is dried to about 8% moisture in 2-4 minutes, the steam being removed via the sieve. The specific pressure is usually set so that it is slightly higher than the vapor pressure in the fiber mat. This prevents the fiber mat from bursting in the press. Then in a third phase the fiber mat is compressed to a final pressure with a specific pressure of approx. 3 N / mm ² and dried to approx. 2% moisture. It is not possible to regulate the travel of the individual levels, so the fibreboards have high thickness tolerances.

The invention is based on the object of specifying a method and a method To create plant with a fiberboard with little or no glue is producible and with which the pressing time can be drastically reduced, and improved the properties of the plate and the thickness tolerances of the plate become.

a) die ohne Klebstoff aufbereiteten oder nur mit niedriegem Klebstoffgehalt beleimten Fasern werden auf eine Feuchte von 16%- 25% getrocknet und aus einer Streutstation auf ein Transportband zur Fasermatte gestreut,

b) die Feuchte der Fasermatte wird in einer kontinuierlich arbeitende Vorpresse durch Einleiten von Sattdampf oder überhitztem Wasserdampf oder Dampf-/Luftgemischen um eine Feuchte von 2% bis 7% und mittels Warmwassersprühung vor und nach der Vorpresse um eine Feuchte von 2% bis 8% so erhöht, dass eine Feuchte von minimal 25% bis maximal 35% unmittelbar vor dem Eintritt in die Presse erreicht wird, womit gleichzeitig eine wesentliche Erwärmung der Fasermatte erfolgt,

c) unmittelbar daran wird die Fasermatte auf ein endloses mit den unteren Stahlband umlaufendes nicht rostendes Metallgewebeband einer kontinuierlich arbeitenden Presse übergeben und in den Pressspalt einer kontinuierlich arbeitenden Presse eingeführt,

d) innerhalb von etwa 20% der Pressenlänge der kontinuierlich arbeitenden Presse wird die Fasermatte in einer Verdichtungsphase mit hohem spezifischen Druck von maximal 5,5 N/mm² komprimiert und dabei Wasser ausgepresst,

e) in einer sich anschließenden Trocknungsphase innerhalb der kontinuierlich arbeitenden Presse erfolgt die Verdampfung und Abführung des Dampfes sowie des Wassers insbesondere aus der Mittelschicht mit reduziertem spezifischem Druck von maximal 1 N/mm² und wird solange aufrecht erhalten, bis eine Feuchte in der Fasermatte von 5 bis 8% erreicht ist und

f) in einer abschließendem Aushärtephase in der kontinuierlich arbeitenden Presse wird die Fasermatte unter einem maximalen Druck von 3,5 N/mm² auf das Endmaß verdichtet und getrocknet bis in der Mittelschicht eine ungefähre Feuchte von 2% erreicht ist.

The solution to this problem consists in the implementation of the following process steps:

a) the fibers prepared without adhesive or glued only with a low adhesive content are dried to a moisture content of 16% - 25% and scattered from a spreading station onto a conveyor belt to the fiber mat,

b) the moisture of the fiber mat is measured in a continuously operating pre-press by introducing saturated steam or superheated steam or steam / air mixtures by a moisture of 2% to 7% and by means of hot water spraying before and after the pre-press by a moisture of 2% to 8% increased in such a way that a moisture content of at least 25% to a maximum of 35% is reached immediately before entering the press, which at the same time results in a substantial heating of the fiber mat,

c) immediately thereafter, the fiber mat is transferred to an endless stainless steel fabric belt running around the lower steel belt in a continuously operating press and introduced into the press nip of a continuously operating press,

d) within about 20% of the press length of the continuously operating press, the fiber mat is compressed in a compression phase with a high specific pressure of a maximum of 5.5 N / mm ² and water is pressed out,

e) in a subsequent drying phase within the continuously operating press, the evaporation and removal of the steam and water, in particular from the middle layer, takes place with a reduced specific pressure of at most 1 N / mm ² and is maintained until a moisture content in the fiber mat of 5 to 8% is reached and

f) in a final curing phase in the continuously operating press, the fiber mat is compressed to a final size under a maximum pressure of 3.5 N / mm ² and dried until an approximate moisture of 2% is reached in the middle layer.

With these process steps, for the first time even fiberboard up to one Produce thickness of 50 mm, because with the proposed preheating Fiber mat shorter pressing times are possible.

a) die ohne Klebstoff aufbereiteten oder nur mit niedriegem Klebstoffgehalt beleimten Fasern werden auf eine Feuchte von 16%- 25% getrocknet und aus einer Streutstation auf ein Transportband zur Fasermatte gestreut,

b) die Feuchte der Fasermatte wird in einer kontinuierlich arbeitende Vorpresse durch Einleiten von Sattdampf oder überhitztem Wasserdampf oder Dampf-/Luftgemischen so erhöht, dass eine Feuchte von minimal 25% bis maximal 35% unmittelbar vor dem Eintritt in die Presse erreicht wird, womit gleichzeitig eine wesentliche Erwärmung der Fasermatte erfolgt,

c) unmittelbar daran wird die Fasermatte auf ein endloses mit den unteren Stahlband umlaufendes nicht rostendes Metallgewebeband einer kontinuierlich arbeitenden Presse übergeben und in den Pressspalt einer kontinuierlich arbeitenden Presse eingeführt,

d) innerhalb von etwa 20% der Pressenlänge der kontinuierlich arbeitenden Presse wird die Fasermatte in einer Verdichtungsphase mit hohem spezifischen Druck von maximal 5,5 N/mm² komprimiert und dabei Wasser ausgepresst,

e) in einer sich anschließenden Trocknungsphase innerhalb der kontinuierlich arbeitenden Presse erfolgt die Verdampfung und Abführung des Dampfes sowie des Wassers insbesondere aus der Mittelschicht mit reduziertem spezifischem Druck von maximal 1 N/mm² und wird solange aufrecht erhalten, bis eine Feuchte in der Fasermatte von 5 bis 8% erreicht ist und

f) in einer abschließendem Aushärtephase in der kontinuierlich arbeitenden Presse wird die Fasermatte unter einem maximalen Druck von 3,5 N/mm² auf das Endmaß verdichtet und getrocknet bis in der Mittelschicht eine ungefähre Feuchte von 2% erreicht ist.

Fiberboard with a thickness ≥ 4 mm can also be produced with the following method steps of claim 2:

a) the fibers prepared without adhesive or glued only with a low adhesive content are dried to a moisture content of 16% - 25% and scattered from a spreading station onto a conveyor belt to the fiber mat,

b) The moisture of the fiber mat is increased in a continuously operating pre-press by introducing saturated steam or superheated steam or steam / air mixtures so that a moisture of a minimum of 25% to a maximum of 35% is reached immediately before entering the press, which means at the same time there is substantial heating of the fiber mat,

c) immediately thereafter, the fiber mat is transferred to an endless stainless steel fabric belt running around the lower steel belt in a continuously operating press and introduced into the press nip of a continuously operating press,

d) within about 20% of the press length of the continuously operating press, the fiber mat is compressed in a compression phase with a high specific pressure of a maximum of 5.5 N / mm ² and water is pressed out,

e) in a subsequent drying phase within the continuously operating press, the evaporation and removal of the steam and water, in particular from the middle layer, takes place with a reduced specific pressure of at most 1 N / mm ² and is maintained until a moisture content in the fiber mat of 5 to 8% is reached and

f) in a final curing phase in the continuously operating press, the fiber mat is compressed to a final size under a maximum pressure of 3.5 N / mm ² and dried until an approximate moisture of 2% is reached in the middle layer.

a) die ohne Klebstoff aufbereiteten oder nur mit niedriegem Klebstoffgehalt beleimten Fasern werden auf eine Feuchte von 16% - 25% getrocknet und aus einer Streutstation auf ein Transportband zur Fasermatte gestreut,

b) die Feuchte der Fasermatte wird durch Aufsprühen von Warmwasser auf die Oberflächen der Fasermatte so erhöht, dass eine Feuchte von minimal 25% bis maximal 35% unmittelbar vor dem Eintritt in die Presse erreicht wird, womit gleichzeitig eine Erwärmung der Fasermatte erfolgt,

c) unmittelbar daran wird die Fasermatte auf ein endloses mit dem unteren Stahlband umlaufendes, nicht rostendes Metallgewebeband einer kontinuierlich arbeitenden Presse übergeben und in den Presspalt einer kontinuierlich arbeitenden Presse eingeführt,

d) innerhalb von etwa 20% der Pressenlänge der kontinuierlich arbeitenden Presse wird die Fasermatte in einer Verdichtungsphase mit hohem spezifischen Druck von maximal 5,0 N/mm² komprimiert und dabei Wasser ausgepresst,

e) in einer sich anschließenden Trocknungsphase erfolgt innerhalb der kontinuierlich arbeitenden Presse die Verdampfung und Abführung es Dampfes sowie des Wassers insbesondere aus der Mittelschicht mit reduziertem spezifischem Druck von maximal 1 N/mm² und wird solange aufrecht erhalten, bis eine Feuchte in der Fasermatte von 5 bis 8% erreicht ist und

f) in einer abschließenden Aushärtephase in der kontinuierlich arbeitenden Presse wird die Fasermatte unter einem maximalen Druck von 4 N/mm² auf das Endmaß verdichtet und getrocknet bis in der Mittelschicht eine ungefähre Feuchte von 2% erreicht ist.

And according to a third embodiment according to claim 3, the process for a fiberboard ≤ 4 mm is characterized by the following process steps:

a) the fibers prepared without adhesive or glued only with a low adhesive content are dried to a moisture content of 16% - 25% and scattered from a spreading station onto a conveyor belt to the fiber mat,

b) the moisture of the fiber mat is increased by spraying hot water onto the surfaces of the fiber mat in such a way that a moisture of at least 25% to a maximum of 35% is reached immediately before entering the press, which simultaneously heats the fiber mat,

c) immediately thereafter, the fiber mat is transferred to an endless, rustproof metal fabric belt running around the lower steel belt of a continuously operating press and introduced into the press nip of a continuously operating press,

d) within about 20% of the press length of the continuously operating press, the fiber mat is compressed in a compression phase with a high specific pressure of at most 5.0 N / mm ² and water is pressed out,

e) in a subsequent drying phase, the evaporation and removal of steam and water takes place within the continuously operating press, in particular from the middle layer, with a reduced specific pressure of at most 1 N / mm ² and is maintained until a moisture content in the fiber mat of 5 to 8% is reached and

f) in a final curing phase in the continuously operating press, the fiber mat is compressed to a final size under a maximum pressure of 4 N / mm ² and dried until an approximate moisture of 2% is reached in the middle layer.

With the method step according to claim 3 is by water spraying a simple and inexpensive preheating of the fiber mat for Fiberboard ≤ 4 mm can be produced.

The system for carrying out the method according to claim 28 consists in that as a press a continuously working press with the press pressure transmitting and the fiber mat through the press nip endless Steel belts exist, the steel belts over drive and deflection drums the upper frame part and the lower frame part are guided all the way around with adjustable press gap over moving, with their axes transverse to Belt running direction of the guide rods opposite the upper frame and Support the lower part of the frame, with the roller bars at both ends in Guide chains are guided that in front of and between the spreading station and the continuously working press several on the conveyor belt and to the Surfaces of the fiber mat directed hot water spray devices and Means for applying release agents are arranged from the continuously working press with a pre-press Steam preheating device and upper and lower screen belt is provided, the continuously working press as storage for the fiber mat and for Water and steam discharge from the fiber mat one made of rustproof Material existing, guided with the lower steel band, Endless metal tape that has before entering the press nip is guided over a heating plate and the lower steel strip for deriving the squeezed water is carried out with a greater width than the upper one Steel strip.

By means of the method according to the invention and the plant according to the invention, the pressing time can be significantly reduced compared to the known intermittent dry drying method. For example, the pressing time for a 4 mm thick fiberboard is reduced from 4 minutes to approx. 1 minute (see Table 1). A major advantage is that the preheating of the fiber mat to at least 100 ° C drastically reduces the heating time of the fiber mat. At this temperature, the viscosity of the water drops, which reduces the flow resistance and allows the water to be squeezed out of the mat more quickly. Steam preheating of the fiber mat to 100 ° Celsius is particularly advantageous in the production of fiberboard with a thickness greater than 4 mm, since the shortening of the pressing time is particularly high.
The table shows selected process parameters during hot pressing in a continuous press according to the inventive method for a 4 mm thick fiberboard. phase Time [seconds] Sp. Pressure [N / mm ² ] start-end Humidity DS [%] start-end Moist MS [%] start-end Temperature MS [° C] start-end 1. Compact DS 5 - 15 0 - 5 35 - 2 35-36 100-105 2. Drying 20-35 1 - 1 2 - 0.5 36 - 6 105-110 3. Hardening (and compacting MS) 25-50 4-2.5 0.5 - 0.2 6-2 110-135

In contrast to the production in multi-daylight presses, the continuous press the fiber mat even with a higher one Hot plate temperature than 190 ° C, since the pressing time is shorter and the fiberboard can be cooled at the end of the pressing. This will the pressing time is significantly reduced. - In the multi-daylight press is on the ground the danger of steam space, especially the upper surface layer, the raising of the Press plate temperature not possible. - If the fiberboard at the end of the Continuous pressing is cooled to around 110 ° C, the danger of Coverage burst significantly reduced.

With the continuous process according to the invention can in the continuous press a specified path-pressure program very precisely be corrected, the continuous press preferably carried out in this way is that very large deformations per meter of press length in the direction of transport possible are. This allows the press nip to optimally match the individual phases be adjusted. So the press nip can go so far during drying be enlarged so that surface bursts are just avoided. This reduces the flow resistance perpendicular to the surface in the fiber mat and the fiber board can be dried more quickly. As well the fiberboard can be pressed at the end of an optimized program be relieved. In connection with the cooling of the Fiber mat surface the moisture of the fiberboard must not be below 2% be reduced, which on the one hand shortens the hardening phase and in the later air conditioning of the plate is advantageous. The fiberboard has immediately after the continuous press a more even one Moisture distribution across the panel cross-section.

Through the exact setting of the press nip over the entire Press width in the continuously operating press it is possible To produce fiberboard with very small thickness tolerances. This can the raw plate thickness and thus the grinding allowance are reduced. This carries in turn contribute to a reduction in press time, as for the same Finished plate thickness drove a smaller plate thickness in the hot press can be.

The continuous pressing according to the invention also leads to significantly reduced electrical and thermal energy costs. For discontinuous pressing, loading and emptying, about 70% more electrical energy per m ^{3 of} fiberboard produced is required compared to the continuous process according to the invention, since a significantly higher connected load has to be installed. Since the multi-day press including the required screens has higher radiation losses, more thermal energy is also required to operate the press. In addition, on a multi-daylight press, pressing is carried out on average with higher press plate temperatures. Since the temperature of the continuous press is significantly reduced towards the end of the pressing, less water is required and evaporated from the fiber mat, thus bringing less energy into the fiber board. Furthermore, steam with a low steam pressure below 3 bar can be used for steam preheating, which is available as very cheap steam from fiber processing. This also reduces the cost of the heating energy at the start of the pressing.

In the semi-dry process, fiber-fiber bonding is achieved in two ways: on the one hand via a so-called hydrogen bond, especially the Wood components cellulose and hemicellulose and the other about the softened lignin. For both types of bindings it is important that the individual Fibers in very close contact with each other over a longer distance exhibit. The following advantage is now achieved by steam preheating are: the fibers are already plasticized at the beginning of the pressing and thus very flexible, which creates more contact areas between the fibers during of the first compression. They become less when compacting zerquescht. They nestle close together and are easier to get in Press cavities. The transverse tensile strength of the fiberboard is thereby same adhesive content slightly better than without steam preheating and also the irreversible springback in the thickness swelling is reduced.

The wood chips are preheated at a higher temperature than 180 ° C, preferably 190 to 220 ° C, pre-steamed in preheating to achieve that substances are formed in the wood through transformation processes that lead to better bonding during hot pressing. In particular, the formation of furfural is caused by the formation of acids in the Promoted preheater. The formation of acids is due to the high temperature assisted in preheating. Furfural promotes condensation reactions between the wooden components. Possibly can with the preheating or the refiner Acid - such as sulfuric acid - are added, which also the Promotes formation of furfural. With deciduous trees usually more sticky substances formed than in conifers. Therefore are suitable for this process hardwoods particularly well. It is also cheap Aluminum sulfate about 0.5% dry substance to precipitate from the artificial Condensation adhesives and the natural resin acids during the Preheat or add in the refiner or in the blow line. Also for Precipitation of the resins, it is advantageous that the pH of the fibers to less than 4.5 is lowered by the addition of acid.

At the beginning of the hot pressing up to about 20% of the pressing length, some water is added squeezed out of the fiber mat, which as a Water or as steam transported to the edge of the lower steel belt becomes. There the water is collected and the steam is extracted. The extracted steam is condensed and with the collected water mixed. This water has to be passed through a filter to get it from to clean rough insoluble parts. The treated water contains dissolved or suspended wood substances that are particularly suitable for gluing suitable. Therefore it is used again as water spray. In addition, by reusing the water the water cycle is closed, so that in comparison to the dry process there is no major contamination of Drinking water occurs.

The fiber mat can be scattered using a single scattering machine, or the fibers are divided into coarse and fine fibers after production in the refiner or are already produced separately using two refiners. The coarse fibers are then preferably scattered into the middle of the fiber mat as the middle layer and the fine fibers as the top layer. For fiberboard that are to be coated directly, it is favorable to sprinkle very fine fibers (very fine fibers) or dust on the surface in an amount of 20 - 50 g / m ² . Thanks to the very fine fibers, a very closed surface can be achieved on the fiberboard, which, for example, can reduce paint consumption.

The fibers must not be used to carry out the method according to the invention Dried under a humidity of 16% or the fibers must not below a humidity of 16%, otherwise they will horny. calloused Fibers only form an insufficient hydrogen bond. The means that care is also taken during the transport of the fibers must not fall below the humidity. Because during transportation the fiber in the air stream with air of a relative humidity that is lower than the equilibrium moisture content of the fiber, the fibers must release moisture quickly either the transport air is conditioned by, for example, steam injection or the fibers should be a little bigger after drying Have moisture than on the ribbon.

The moisture of the fiber mat is dependent on the steam preheating the preheating depth increased by the condensation of the water vapor. If the entire fiber mat is heated, the mat moisture increases about 7%. If about 50% of the mat is heated, it will be Humidity increase about 4%. The process must definitely be controlled in this way that the fiber mat moisture is not under at the beginning of the hot pressing 25% and not more than 35%, because if the humidity is below 25%, insufficient wood glued joints can be formed. Then the glue consumption increases very much. If the humidity is over 35% on the other hand, the pressing time is extended due to the longer Drying phase very strong.

In order to achieve a closed fiberboard surface with a high density and to protect the steel strips from contamination, it is advantageous to spray water in a quantity of 20-700 g / m ² onto the fibrous mat surface, depending on the consistency of the fibers and the fiberboard thickness. The water can also be sprayed onto the conveyor belt or onto the screen belt during steam preheating. It is also favorable to spray release agents onto the fiber mat surface and / or the conveyor belt so that the fibers do not stick to the metal fabric belt during preheating, the conveyor belt, the steel belts and the metal fabric belt in the continuously operating press. However, the amount of water that is sprayed on before steaming must not be so large that there is free water on the surface of the fiber mat, since there are problems with steaming due to uneven condensation of steam and uncontrollable conditions.

Therefore, a larger amount of water than 60 g / m ² can only be sprayed onto the fiber mat after steaming in the pre-press with steam preheating. The water should preferably be heated to temperatures of 60 - 95 ° C before spraying. Since the residence time of the water from spraying to contact with the fiber mat with the steel strip in the continuously operating press is very short, this water is almost not absorbed by the fibers and thus has only an insignificant influence on the density profile. It is also advantageous if the water is only sprayed onto the fiber mat from above. The water is then evaporated immediately upon contact with the steel strip and can only flow vertically into the fiber mat. If the water is applied to the lower half of the fiber mat, that is to say the side of the fiber mat facing the screen, the steam formed does not penetrate the fiber mat. After evaporation, the steam flows over the metal fabric belt from the press against the transport direction in the direction of the inlet and across the transport direction to the press edge. The moisture of the fiber mat is then not increased and the pressing time is not shortened. A larger amount of water must not be sprayed onto the side of the fiber mat that faces the metal fabric band, since the moisture of the fiber mat would then not be increased and the pressing time would not be shortened.

For the process according to the invention, the fibers have to be moist can be dried, plus the moisture due to the vaporization, the Water spraying and water from the release agent application inside of the above range. To the moisture input into the individual Controlling fiber mat layers precisely requires the amount of sprayed on Water and the amount of steam added for the top and bottom The fiber mat side can be measured separately. The amount of steam that is used Heating of the sprayed water and the water absorbed by the wood is required can be determined from the water temperature and the sprayed Calculate the amount of water. Likewise, the amount of steam needed for heating of the fibers is required from the initial temperature and the humidity of the Fibers are calculated. That is, the depth of penetration of the steam Because of the measured and regulated amount of steam for the upper and lower Half of the fiber mat is determined separately. This is also the moisture distribution Can be determined directly via the fiber mat cross-section. By appropriate measuring devices - such as microwave measuring devices - can Moisture distribution over the fiber mat cross section can also be measured. Knowledge of the moisture and the moisture distribution over the Cross section of fiber mat immediately in front of the continuously operating press is both for the formation of a sufficient bond and one minimum pressing time important as well as for the formation of the bulk density profile significant. For a short pressing time, the fiber mat is cheap vaporize the entire cross section and as much hot water as possible on the Spray fiber mat.

To control the depth of vaporization, the amount of water sprayed and Control of the metal mesh belt temperature or the upper and lower Hot plate temperature in the continuously operating press should do that Raw density profile of the finished fiberboard immediately after the continuous working press can be measured. Fiberboard from the Semi-dry processes often do not show a significant decrease in density in the Center of the fibreboard. Fiberboard produced in the dry process shows a Minimum density in the middle of the fiberboard, which leads to higher bending strengths leads with the same use of materials. It has now been found that after the method according to the invention fiberboard with similar density profiles, how they are produced in the dry process can be produced. For this, the entire cross section of the fiber mat should not be preheated with steam and are softened, just the top layers. In addition to changing the Press nip at the beginning of the hot pressing and during the drying phase the depth of vaporization must be reduced by reducing the Reduced steam quantity and possibly increased the sprayed water quantity become. It is also important to heat the Metal fabric belt temperature in the inlet to the continuously operating press, which are at least 40 ° Celsius higher than the temperature of the steel strips in the Inlet to the continuously working press should be. Has been an advantage also a separate control of the top and bottom heating circuit Press plates proved.

Since in the continuous process according to the invention at the beginning of the pressing a higher press plate temperature can be reached is the temperature the fiber mat in the outer layers is also somewhat higher than in Stroke process. It has been found that this higher temperature Formation of condensation reactions - especially of lignin - promotes that achieved a stronger fiber to fiber bond in the process according to the invention can be. Somewhat better bending properties are therefore the same Adhesive content achievable.

The transverse tensile strength of the method according to the invention produced in the laboratory Fiberboard is slightly lower on the fiberboard edge than in the Fibreboard middle. This is caused by the curing temperature is slightly lower at the edge. The curing temperature is in the fiber mat lower because of the steel straps, the press plates and the roller bars on the edge are cooler than in the middle of the press. They cool through the escaping water and the circulating air. Generally the press plates are 50 mm each Press side wider than the fiber mat. It has now been found that by increasing the distance from the edge of the press plate to the fiber mat ≥ 100 mm the curing temperature at the edge is higher and the transverse tensile strength the fiberboard at the edge can be improved significantly. In addition, the Fiber mat strewn on the edge with a higher basis weight be, which also achieve an increase in transverse tensile strength leaves.

The continuous strand of fiberboard produced according to the invention is after a format division - as with the conventional semi-dry process - after-treatment to improve the properties.

In particular, the fiberboard is passed through a heat channel or in warmly stacked in a heated hall. By heat treatment of the Fiberboard at temperatures between 110 ° and 200 ° C after the Continuous press is used to bond the individual fibers increases, which improves the bending properties and the swelling values. To carry out the heat treatment, the fiberboard can be warm be stacked or pulled as a package through a heat duct.

The metal fabric tape in the continuously operating press has the Function, a drainage and evaporation of the fiber mat too enable. The metal fabric tape must therefore have a structure that a removal of water and water vapor within the Structure perpendicular to the direction of transport without large flow resistances allows. That means that within the metal fabric band across Transport direction there is a larger free cross-section. Through the Use of the metal cloth tape can be the continuous one Press also run in a width of over 4 m because of the fiberboard is dewatered and evaporated exclusively via the metal mesh belt. The metal fabric tape can be a smooth or to the fiber mat side have a rough structure. Usually a smooth structure is desired if the Fiberboard should be coated later. For individual applications too a rough structure with a screen print on the plate surface favorable.

Since cast steel or unalloyed steel rusts too much, is the material for that Metal cloth tape just a rustproof material like phosphor bronze or Stainless steel possible for the semi-dry system.

Tests have now shown that the steel belts at the press edge are significantly cooler than in the middle of the press, which means that they fluff towards the fiber mat. The system is therefore designed so that the lower steel belt is wider than the upper steel belt and covers the guide chain for guiding the roller bars. At some points the lower steel band can then be pressed down with hold-down rollers. The water is also collected and discharged at these points. These hold-down rolls are provided from the start of the press up to approx. 20% of the press length.
The specific pressure is important because of the avoidance of relative movements between the metal fabric belt and the steel belt due to thermal expansion and thus the avoidance of scratches on the steel belt. Since this process mainly produces thin fiberboard, the metal fabric tape must not have thickness tolerances greater than ± 0.075 mm. The thickness tolerance would also show up in the product and would lead to a larger sanding.

Further advantageous measures and refinements of the subject of Invention emerge from the subclaims and the following description based on three embodiments with the drawing.

Figur 1

die Anlage gemäß der Erfindung in Seitenansicht,

Figur 2

in einem Schnitt A-A und Ausschnitt aus Figur 1 einen Teil der rechten Längsmitte mit Führung der Rollstangen am Pressenrand und

Figur 3

das Metallgewebeband in Längsrichtung zum Abführen des ausgepressten Wassers aus der Fasermatte.

Show it:

Figure 1

the system according to the invention in side view,

Figure 2

in a section AA and section from Figure 1, a part of the right longitudinal center with guidance of the roller bars on the press edge and

Figure 3

the metal fabric tape in the longitudinal direction for removing the squeezed water from the fiber mat.

The drawing shows the system as the fiber mat 10 according to the Press program manufactured from left to right, treated and how they are in the continuously working press 5 pressed to fiberboard 30 and is cured. First, the fiber mat 10 in the continuous working press 5 compressed with high pressure, pressed out some water and then relieved and dried. Towards the end of the pressing the Fiber mat 10 compressed to the final thickness and cured, the Curing phase is started when the moisture of the fiber mat 10 5% - 8% is.

The system shown in a schematic representation can be seen from FIG. 1, with which the fiber mat 10 made of fibers on a conveyor belt 20 from the Street station 1 is sprinkled. The conveyor belt 20 is used for Continuation of the fiber mat 10 if necessary through a pre-press 2, Hot water spray devices and / or release agent spray devices 21 to the pre-press with steam preheater 4. The endless conveyor belt 20 is guided over pulleys 24. The fiber mat 10 is with the Conveyor belt 20 continued to the lower endless belt 23 of the Prepress with steam preheater 4, the reverse at the Deflection roller 24 is arranged resettable to the fiber mat in the event of malfunctions 10 to lead into a chute 22. To control the Fiber mat moisture is between the spreading station 1 and the pre-press Steam preheating device 4 a mat moisture sensor 3 is arranged. Out Scattering station 1 can be a single or multi-layer fiber mat as required 10 are scattered. There are five or more different litter bunkers for this Example with fine fibers 32 and 36 (or also wood dust) for the Cover layers, with fibers 33 and 35 for the intermediate layers and with Coarse fibers 34 are provided for the middle layer. The pre-press with Steam preheater 4 consists of two endless to the Steam feed 29 and deflection rollers 27 rotating sieve belts 23, wherein the lower screen belt 23, the possibly preheated fiber mat 10 to close in leads to the inlet area of the continuously operating press 5 or to the Metal fabric tape 25 passes. As a continuously operating press 5 is one so-called double belt press provided, which in its main parts a movable upper frame part 9 and a stationary lower frame part 8, which form the adjustable press nip 11. Frame top 9 and Lower frame part 8 are via drive drums 16 and deflection drums 17th encircled by steel strips 18 and 19. At the press nip 11 facing sides of the upper frame part 9 and lower frame part 8 are heated and coolable press plates 12 and 13 attached to the steel strips 18/19 by means of guide chains 39 and 40 which also run around Support roller bars 37 and 38. The one from the continuously working Press 5 extending finished wood-based or fiberboard is at 30 designated. According to the invention, the lower steel strip 18 is an over Deflection rollers 27 associated with the rotating metal fabric band 25 assigned, that from a rustproof material with high thermal conductivity like stainless steel or phosphor bronze, the upper and lower steel strips 18 and 19 and the metal fabric tape 25 in the return jointly by one Isolation tunnel 26 are guided to prevent heat radiation and around To save energy, as well as the metal fabric tape 25 before entering the Press nip 11 to a much higher temperature via a heating plate 28 is to be heated as the associated steel strip 18 in the inlet to the press nip 11 has.

The press length is expediently in a heating zone 6 and Cooling zone 7 divided. For separate control of these zones, both Heating zone 6 and the cooling zone 7 with the cooling plates 14 and 15 via a own rolling carpet support with all-round guidance chains Equipped with roller bars. At the outlet of the continuously operating press 5 becomes the density profile of the finished fiberboard 30 by means of a bulk density sensor 31 checked and with the determined value the temperature and humidity of the Regulated fiber mat before entering the continuously operating press 5. In a section A-A of Figure 1, the formation of the Pressing area shown, especially for the heating zone 6. On side members 41 and 42 of the two long sides of the continuously operating press 5 the guide chains 39/40 with the roller bars 37 and 38 on guide rails 47 and 50 out. To hold down the lower one with a larger width executed steel belt 18 are several hold-down rollers 43 at the bottom Side member 41 attached. A trained on the lower side member 41 Channel 44 is used to discharge the fiber mat 10 via transverse channels 45 of the metal fabric band 25 emerging water and condensing Steam. A suitable metal mesh tape 25 is shown in Figure 3 shown in side view corresponding to Figure 1. The chain 46 The longitudinal wires shown form a sufficiently flat contact surface for the fiber mat 10 and are designated by the weft 48 Cross wires held together.

LIST OF REFERENCE NUMBERS

1.

spreading station

Second

pre-press

Third

Matt humidity sensor

4th

Prepress with steam preheater

5th

continuously working press

6th

heating zone

7th

cooling zone

8th.

Frame bottom

9th

Upper frame

10th

fiber mat

11th

press nip

12th

Press plate below

13th

Press plate on top

14th

Cooling plate below

15th

Cooling plate on top

16th

driving drum

17th

Umlenktrommel

18th

Steel band below

19th

Steel band at the top

20th

conveyor belt

21st

Hot water spray device or release agent spray device

22nd

chute

23rd

Screen belt in pre-press with steam preheater 4

24th

Pulleys for 20

25th

Metal fabric tape in a continuously operating press 5

26th

Isoliertunnel

27th

Deflection rollers for sieve belt

28th

heating plate

29th

steam injection

30th

fibreboard

31st

Rohdichtesensor

32nd

super-fine fiber

33rd

interlayer

34th

middle class

35th

interlayer

36th

super-fine fiber

37th

Roll bars below

38th

Roll bars above

39th

Guide chain below

40th

Guide chain above

41st

Side member below

42nd

Side member above

43rd

Hold-down rollers

44th

channel

45th

transverse grooves

46th

Chain

47th

Guide rail for guide chain 39

48th

shot

49th 50th

Guide rail for guide chain 40

Claims (37)

Process for the production of wood-based panels, such as chipboard and fiberboard, in particular fiberboard made of wood or other lignocellulosic materials, in which a fiber mat with a low or no adhesive content is formed from a scattering station on a continuously moving conveyor belt inserted between the press plates of a press and pressed and hardened into a fiberboard using pressure and heat,
characterized by the following process steps: 1.1 the fibers prepared without adhesive or glued only with a low adhesive content are dried to a moisture content of 16% -25% and scattered from a spreading station onto a conveyor belt to the fiber mat, 1.2 The moisture of the fiber mat is measured in a continuously operating pre-press by introducing saturated steam or superheated steam or steam / air mixtures by a moisture of 2% to 7% and by means of hot water spraying before and after the pre-press by a moisture of 2% to 8% increases that a moisture of at least 25% to a maximum of 35% is reached immediately before entering the press, which at the same time results in a substantial heating of the fiber mat, 1.3 immediately thereafter the fiber mat is transferred to an endless stainless steel fabric belt running around the lower steel belt in a continuously operating press and introduced into the press nip of a continuously operating press, 1.4 within approximately 20% of the press length of the continuously operating press, the fiber mat is compressed in a compression phase with a high specific pressure of a maximum of 5.5 N / mm ² and water is pressed out, 1.5 In a subsequent drying phase within the continuously operating press, the evaporation and removal of the steam and water, in particular from the middle layer, takes place with a reduced specific pressure of at most 1 N / mm ² and is maintained until a moisture content in the fiber mat of 5 up to 8% and 1.6 in a final curing phase in the continuously operating press, the fiber mat is compressed to a final size under a maximum pressure of 3.5 N / mm ² and dried until an approximate moisture of 2% is reached in the middle layer. Process for the production of wood-based panels, such as chipboard and fiberboard, in particular fiberboard made of wood or other lignocellulosic materials, in which a fiber mat with a low or no adhesive content is formed from a scattering station on a continuously moving conveyor belt inserted between the press plates of a press and pressed and hardened into a fiberboard using pressure and heat,
characterized by the following process steps: 2.1 the fibers prepared without adhesive or glued only with a low adhesive content are dried to a moisture content of 16% -25% and scattered from a spreading station onto a conveyor belt to the fiber mat, 2.2 The moisture of the fiber mat is increased in a continuously operating pre-press by introducing saturated steam or superheated steam or steam / air mixtures in such a way that a moisture of at least 25% to a maximum of 35% is reached immediately before entering the press, which means at the same time that there is substantial heating of the fiber mat, 2.3 immediately thereafter the fiber mat is transferred to an endless stainless steel fabric belt running around the lower steel belt of a continuously operating press and introduced into the press nip of a continuously working press, 2.4 within approximately 20% of the press length of the continuously operating press, the fiber mat is compressed in a compression phase with a high specific pressure of a maximum of 5.5 N / mm ² and water is pressed out, 2.5 In a subsequent drying phase within the continuously operating press, the evaporation and removal of the steam and water, in particular from the middle layer, takes place with a reduced specific pressure of at most 1 N / mm ² and is maintained until a moisture content in the fiber mat of 5 up to 8% and 2.6 In a final curing phase in the continuously operating press, the fiber mat is compressed to the final dimension under a maximum pressure of 3.5 N / mm ² and dried until an approximate moisture of 2% is reached in the middle layer. Process for the production of wood-based panels, such as chipboard and fiberboard, in particular fiberboard made of wood or other lignocellulosic materials, in which a fiber mat with a low or no adhesive content is formed from a scattering station on a continuously moving conveyor belt is inserted between the press plates of a press and is pressed and cured therein using pressure and heat to or a fiberboard, in particular according to claim 1, characterized by the following process steps for producing a thin fiberboard ≤ 4 mm: 3.1 the fibers prepared without adhesive or glued only with a low adhesive content are dried to a moisture content of 16% - 25% and scattered from a spreading station onto a conveyor belt to the fiber mat, 3.2 the moisture of the fiber mat is increased by spraying hot water onto the surfaces of the fiber mat in such a way that a moisture of at least 25% to a maximum of 35% is reached immediately before entering the press, which simultaneously heats the fiber mat, 3.3 immediately thereafter, the fiber mat is transferred to an endless, rustproof metal fabric belt running around the lower steel belt of a continuously operating press and introduced into the press nip of a continuously working press, 3.4 within approximately 20% of the press length of the continuously operating press, the fiber mat is compressed in a compression phase with a high specific pressure of at most 5.0 N / mm ² and water is pressed out, 3.5 In a subsequent drying phase, the evaporation and removal of steam and water, in particular from the middle layer, takes place within the continuously operating press with a reduced specific pressure of maximum 1 N / mm ² and is maintained until a moisture content in the fiber mat of 5 up to 8% and 3.6 in a final curing phase in the continuously operating press, the fiber mat is compressed to the final dimension under a maximum pressure of 4 N / mm ² and dried until an approximate moisture of 2% is reached in the middle layer. A method according to claim 1, characterized in that in the compression phase, the fiber mat is compressed for a period of 5 to 15 seconds and with a heat in the middle layer from 105 ° Celsius to 110 ° Celsius until a moisture of about 2% in the outer layers and a humidity of about 35% is reached in the middle class. A method according to claim 1, characterized in that in the drying phase the fiber mat is dried for a period of 20 to 35 seconds and with a heat in the middle layer from 105 ° Celsius to 110 ° Celsius with evaporation and removal of the water until in the outer layers Humidity of approximately 2% to 2.5% and a moisture level of approximately 6% in the middle layer. Method according to one or more of the preceding claims 1 to 5, characterized in that in the production of thin fiberboard ≤ 4 mm, in the curing phase the fiber mat for a period of 25 to 50 seconds and with a heat in the middle layer of 110 ° Celsius up to 135 ° Celsius is compressed and cured until a moisture of approx. 0.5% to 0.2% is reached in the outer layers and a moisture of approx. 6% to 2% is reached in the middle layer. Method according to one or more of the preceding claims 1 to 6, characterized in that only the outer layers of the fiber mat are moistened with saturated steam or superheated steam or a steam-air mixture. A method according to claim 1, characterized in that the fiber mat is heated to a minimum temperature of 80 ° Celsius by introducing saturated steam or superheated steam or a steam-air mixture under a steam pressure of 0.07 to 3 bar. Method according to one or more of the preceding claims 1 to 8, characterized in that more than 60 g / m ^{2 of} water is sprayed onto the fiber mat surfaces only before entering the continuously operating press, which is not in contact with the metal fabric tape in the continuously working press Contact is there. Method according to one or more of the preceding claims 1 to 9, characterized in that the curing phase is followed by a cooling phase. Method according to one or more of the preceding claims 1 to 10, characterized in that at the end of the pressing the fiber mat surface within the continuously operating press is cooled to a minimum of 115 ° Celsius, preferably 100 ° Celsius. Method according to one or more of the preceding claims 1 to 11, characterized in that the water squeezed out and collected from the fiber mat is cleaned and used as spray water. Method according to one or more of the preceding claims 1 to 12, characterized in that the middle layer of coarse fibers, the intermediate layers of fine fibers and the outer layers of fine fibers and / or wood dust are scattered. A method according to claim 13, characterized in that fine fibers or wood dust are scattered only on the surface of the fiber mat, which are located opposite the metal fabric tape. Method according to one or more of the preceding claims 1 to 14, characterized in that the fibers during the transport from the dryer into the bunker of the scattering station are conditioned by steam injection or by introducing conditioned air to a humidity ≥ 16%. Method according to one or more of the preceding claims 1 to 15, characterized in that a quantity of water of 20-700 g / m ^{2 is} applied to one or both surfaces of the fiber mat. Method according to one or more of the preceding claims 1 to 16 that the hot water and / or the release agent on the Conveyor belt and / or the surface of the fiber mat and / or on the pre-press screen belts sprayed with preheating equipment become. Method according to one or more of the preceding claims 1 to 17, characterized in that the amount of water to be applied to the fiberboard surfaces is calculated and controlled on the basis of the amount of water actually sprayed on and the initial fiber mat moisture. Method according to one or more of the preceding claims 1 to 18, characterized in that the amount of steam to be introduced into the fiber mat for heating the fibers is calculated and controlled from the initial temperature and the moisture of the fibers. Method according to one or more of the preceding claims 1 to 19, characterized in that the amount of steam to be introduced for heating the fibers is recorded and regulated separately for the upper and lower half of the fiber mat. Method according to one or more of the preceding claims 1 to 20, characterized in that the metal fabric strip is heated to a temperature which is at least 40 ° Celsius higher than the associated lower steel strip at the inlet before entering the press area. Method according to one or more of the preceding claims 1 to 21, characterized in that for the regulation and control of the vapor deposition depth, the amount of water to be sprayed on, the temperature of the upper and lower press plates or of the upper and lower heating circuits of the press plates in accordance with the directly after the continuously operating Press measured bulk density profile on the finished fiberboard. Method according to one or more of the preceding claims 1 to 22, characterized in that the finished, already divided fiberboard is passed through a heat channel for air conditioning and / or warm stacked. Method according to one or more of the preceding claims 1 to 23, characterized in that the chips are pre-steamed at a temperature of 190 ° Celsius to 220 ° Celsius and / or acid is added to the stove. Method according to one or more of the preceding claims 1 to 24, characterized in that the steam suction takes place at the edges of the press plates until the end of the drying phase. Method according to one or more of the preceding claims 1 to 25, characterized in that the fiber mat is sprinkled onto the conveyor belt in a width which leaves a distance of ≥ 100 mm on each longitudinal side in the continuously operating press at the longitudinal edge of the press plates. Method according to one or more of the preceding claims 1 to 26, characterized in that the specific pressing pressure on the fiber mat during the first 80% to 90% of the pressing time in the continuously operating press is not exerted below 0.3 N / mm ² . Plant for the production of particle board and fiberboard, in particular fiberboard made of wood or other lignocellulosic materials, comprising a spreading station, a conveyor belt moving continuously under the spreading station and a press, whereby a single or multi-layer fiber mat can be spread from the spreading station, the press from one movable upper frame part and a stationary lower frame part and attached heatable and coolable press plates, for performing the method according to claims 1 to 27,
characterized in that the press is a continuously operating press (5) with the endless steel belts (18, 19) transmitting the pressing pressure and pulling the fiber mat (10) through the press nip (11), the steel belts (18, 19) via drive and Deflection drums (16, 17) around the upper frame part (9) and the lower frame part (8) are guided, which with adjustable press nip (11) over moving, with their axes transversely to the tape running direction (37, 38) with respect to the upper frame (9) and lower frame part (8) are supported, the roller rods (37, 38) being guided at both ends in guide chains (39, 40), that before and between the spreading station (1) and the continuously operating press (5) several the conveyor belt (2) and hot water spraying devices and devices for applying release agents (21) directed to the surfaces of the fiber mat (10) are arranged, from the continuously operating press (5) a pre-press Provided with steam preheating device (4) and upper and lower sieve belt (23), the continuously operating press (5) as a deposit for the fiber mat (10) and for water and steam removal from the fiber mat (10), a stainless steel material, with the lower steel band (18) has a continuous, continuous metal fabric band (25), which is guided before the entry into the press nip (11) over a heating plate (28) and the lower steel band (18) for discharging the squeezed water with a larger one Width (b) is designed as the upper steel band (19). System according to claim 28, characterized in that the lower longitudinal members (41) for the guide chain support are provided on both longitudinal sides with hold-down rollers (43) for the lower steel band (18). System according to claims 28 and 29, characterized in that the lower longitudinal members (41) are each designed with a channel (44) for discharging the water pressed out. Installation according to claims 28 to 30, characterized in that the metal fabric band (25) has free transverse channels (45) for discharging the squeezed water. Plant according to claims 28 to 31, characterized in that the press length is divided into a heating zone (6) and a cooling zone (7). System according to claims 28 to 32, characterized in that the metal fabric band (25) consists of stainless steel or phosphor bronze. System according to claims 28 to 33, characterized in that in particular the inlet area of the continuously operating press (5), with deflection drums (17), steel belts (18, 19) and, if necessary, the compression angles that can be changed with inlet heating plates to high temperature and thus high heat input are recordable. Installation according to claims 28 to 34, characterized in that the metal fabric tape (25) has a thickness tolerance of less than ± 0.075 mm. Installation according to claims 28 to 35, characterized in that an endless metal fabric band (25) resting on the fiber mat (10) is also provided all around with the upper steel band (19). Installation according to claims 28 to 36, characterized in that the press plates (12, 13) of the continuously operating press (5) for a high heat input into the fiber mat (10), the heating holes with a large number near the fiber mat (10) and for high Flow rates of the heating medium, mainly hot water, are designed and arranged.

Images