EP1236552B1 - 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 process for the production of wood-based panels, in particular of fibreboards in semi-dry process according to the preamble of claim 1 and a system for carrying out the method of claim 28. Such a method or such a system is known from WO 98/41372 known.

Fibrous boards, 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 adhesive. In contrast, the adhesive content of fiberboards by the dry process - for example of MDF boards - over 10% based on the wood substance (urea formaldehyde resin). However, an adhesive content of, for example, 12% causes up to 30% of the cost of producing an MDF board, and as the cost of petroleum increases, the cost of the adhesive continues to rise, making the fiberboard very expensive.

Fibrous plates from the semi-dry and wet process are so far pressed only on discontinuous multi-floor systems. During the production of fibreboards in the wet process, a large amount of polluted sewage is produced, on the one hand during the formation of nonwoven fabric via a wire and, on the other hand, during the hot pressing. This process was further developed in the 40 and 50 years to the semi-dry process to reduce wastewater pollution. There are a number of protective 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 squeezed out of the mat during the semi-dry process at the beginning of the hot pressing. For example, the pressing time for a 3 mm fibreboard is about 4 minutes, which in the dry process is just under 1 minute. Due to the long pressing time, the multi-floor press must have a large number of floors (up to 35 units) to ensure that the capacity of the system is sufficient for operation. Due to the high number of floors, the presses are expensive. The operating costs of such a system are due to the multi-day press also very high.

In the semi-dry process, the fibers must be dried to a moisture content of less than 35% so that they can be formed into a fiber mat without the use of a wire. At higher humidities, the fibers are matted, so that a pneumatic or mechanical scattering is not possible is. After scattering the fiber mat is pre-pressed continuously and divided into individual fiber mat sections according to the floor size by means of a saw. These mat sections are transported on screens or metal wire mesh, which are often still mounted on sheets, in the loading basket, where they vary in length depending on the floor.

Frequently, the fiber mat sections are dried to a moisture content of about 18% and, after the pre-press, water is sprayed onto the top of the fiber mat. Due to the water, the fiber mat moisture in front of the press rises to about 32%. Since at the beginning of the pressing the water is only on the upper side and therefore heats up the top faster than the bottom, the fiber mat top is plasticized at the beginning of the pressing more than the bottom. The sieves and sheets are transported back to the form strand after pressing around the press or under the press, which takes a few minutes. In addition, the screens must be cleaned in some plants with water. During transport and cleaning, the screens and sheets cool. They must then be heated to the heating plate temperature of 190 ° C at the beginning of the pressing, which takes 20 - 60 seconds.

In order to remove some of the water from the fiber mat, without having to evaporate it, is at the beginning of the pressing a high specific Pressure of 5.5 to 6 N / mm ² applied to the fiber mat. At this stage, a small portion 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. In this phase, the density of the outer fibreboard layers is also defined. Due to the uneven plasticization, the density is higher on the outside of the panel facing away from the panel than on the panel side facing the panel. The density profile of the fiber board thus produced is thus usually asymmetric, which leads to disadvantages in some applications by a plate distortion. When the fiberboard picks up or releases moisture, it swells or shrinks more due to its asymmetric density profile and therefore warps.

After the high pressure phase, the specific pressure is reduced and the fiber mat is dried in 2 - 4 minutes to about 8% moisture, with the water vapor is discharged through the sieve. The specific pressure is usually adjusted so that it is slightly larger than the vapor pressure in the fiber mat. This prevents the fiber mat from bursting in the press.
Subsequently, in a third phase, the fiber mat is compacted at a specific pressure of about 3 N / mm ² to the final thickness and dried to about 2% moisture. A path control of the individual floors can not be performed, the fiberboard therefore have high thickness tolerances.

The invention is based on the object to provide a method and to provide a system with which a fiberboard with little or no adhesive can be produced and with which the pressing time can be drastically shortened, and the properties of the plate and the thickness tolerances of the plate can be improved ,

1. a) die ohne Klebstoff aufbereiteten oder nur mit niedrigem Klebstoffgehalt beleimten Fasern werden auf eine Feuchte von 16% - 25% getrocknet und aus einer Streustation auf ein Transportband zur Fasermatte gestreut,
2. 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,
3. 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 Pressspalt einer kontinuierlich arbeitenden Presse eingeführt,
4. 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,
5. 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
6. 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 of this task consists according to claim 1 in the realization of the following method steps:

1. a) the fibers prepared without adhesive or glued only with low adhesive content are dried to a moisture content of 16% -25% and scattered from a scattering station onto a conveyor belt to the fiber mat,
2. b) the moisture of the fiber mat is increased in a continuous pre-press by introducing saturated steam or superheated steam or steam / air mixtures so that a humidity of at least 25% to a maximum of 35% is reached immediately before entering the press, which at the same time there is a substantial heating of the fiber mat,
3. c) immediately thereafter, the fiber mat is placed on an endless stainless steel belt surrounding the lower steel belt handed over to press working continuously and inserted into the press gap of a continuously working press,
4. 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 maximum 5.5 N / mm ² while water is pressed out,
5. e) in a subsequent drying phase within the continuously operating press, the evaporation and removal of the vapor and the water in particular from the middle layer with reduced specific pressure of 1 N / mm ² and is maintained until a moisture in the fiber mat of 5 to 8% is reached and
6. f) in a final curing phase in the continuous press the fiber mat is compacted under a maximum pressure of 3.5 N / mm ² to final gauge and dried until an approximate humidity of 2% is reached in the middle layer.

For the first time, even fibreboards up to a thickness of 50 mm can be produced with these process steps, since shorter pressing times are possible with the proposed preheating of the fiber mat.

• Dabei wird die Feuchte der Fasermatte 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.

Even with the following adapted process steps of claim 1 as claimed are fiberboard to manufacture:

• The moisture of the fiber mat in a continuously operating pre-press by introducing saturated steam or superheated steam or air / air mixtures by a humidity of 2% to 7% and by hot water spray before and after the pre-press by a humidity of 2% to 8% so increases that a humidity of at least 25% to a maximum of 35% is reached immediately before entering the press, whereby at the same time there is a significant heating of the fiber mat.

• im Verfahrensschritt d) wird innerhalb von etwa 20% der Pressenlänge der kontinuierlich arbeitenden Presse die Fasermatte in einer Verdichtungsphase mit hohem spezifischen Druck von maximal 5,0 N/mm² komprimiert und dabei Wasser ausgepresst, und
• im Verfahrensschritt f) wird in einer abschließenden Aushärtephase in der kontinuierlich arbeitenden Presse 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 further embodiment according to claim 3, the preferred production for a fibreboard ≤ 4 mm is characterized by the following adaptation of the method steps:

• in process step d) is compressed within about 20% of the press length of the continuously operating press the fiber mat in a compression phase with a high specific pressure of not more than 5.0 N / mm ² and thereby squeezed out water, and
• In process step f), the fiber mat is compacted to the final dimension under a maximum pressure of 4 N / mm ² in a final curing phase in the continuously operating press and dried until an approximate moisture content of 2% is reached in the middle layer.

The system for carrying out the method according to claim 28 is that there is a continuously operating press with the pressing pressure transmitting and the fiber mat passing through the press nip endless steel belts as press, the steel belts are guided circumferentially about drive frame and idler pulleys around the frame top and the frame base , Which are supported with adjustable press nip on revolving, guided with their axes transverse to the strip running direction rolling bars relative to the Rahmenober- and frame base, wherein the rolling rods are guided at both ends in guide chains, that before and between the scattering station and the continuously operating press several on the Hot water spraying devices and devices for applying release agents are arranged on the conveyor belt and directed towards the surfaces of the fiber mat, from the continuously operating press a pre-press with steam preheating device and upper and lower wire belt v is seen, the continuously operating press as a storage for the fiber mat and water and steam removal from the fiber mat an existing stainless material, with the lower steel belt circumferentially guided, endless metal fabric belt, which led before entering the press nip on a hot plate and the lower steel strip for discharging the squeezed out water is made larger in width than the upper steel strip.

By the method according to the invention and the plant according to the invention, the pressing time can be significantly reduced compared to the known cyclic half-drying processes. For example, the pressing time for a 4 mm thick fiberboard is reduced from 4 minutes to about 1 minute (see Table 1). A significant advantage is that the heating of the fiber mat is drastically reduced by the steam preheating of the fiber mat to at least 100 ° C. At this temperature, the viscosity of the water decreases, whereby the flow resistance is reduced and the water can be squeezed faster from the mat. The steam preheating of the fiber mat to 100 ° C is particularly advantageous in the production of fibreboard with a thickness greater than 4 mm, as this, the press time reduction is particularly high.
The table shows selected process parameters during hot pressing in a continuous press according to the method of the invention for a 4 mm thick fiberboard. phase Time [seconds] Sp. Pressure [N / mm ² ] Start - End Damp DS [%] Start - End Humidity MS [%] Start - End Temperature MS [° C] Start - End 1. compaction DS 5 - 15 0 - 5 35 - 2 35 - 6 100-105 2. Dry 20 - 35 1 - 1 2 - 0.5 36 - 6 105 - 110 3. Curing (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, in the continuous press the fiber mat can also be pressed with a hotplate temperature higher than 190 ° C, because the pressing time is shorter and at the end of the pressing the fiberboard can be cooled. As a result, the pressing time is significantly reduced. - In the multi-daylight press, increasing the pressure plate temperature is not possible due to the risk of steam bursting, especially the upper surface layer. - If the fiberboard is cooled to around 110 ° C at the end of the continuous pressing process, the risk of topcoat bursting is significantly reduced.

With the continuous process according to the invention, a predetermined path-pressure program can be regulated very accurately in the continuous press, wherein the continuous press is preferably designed so that very large deformations per meter of press length are possible in the transport direction. As a result, the press nip can be optimally adapted to the individual phases. Thus, during drying, the press nip can be enlarged so far that just surface blemishes are avoided. This reduces the flow resistance perpendicular to the surface in the fiber mat and the fiberboard can be dried faster. Likewise, the fiber board can be relieved after an optimized program at the end of the pressing. In connection with the cooling of the fiber mat surface, the moisture content of the fiberboard must not be below 2%. be reduced, which on the one hand shortens the curing phase and in the subsequent air conditioning of the plate is beneficial. Immediately after the continuous press, the fiberboard has a more even distribution of moisture over the slab cross-section.

Due to the precise adjustment of the press nip over the entire press width in the continuous press, it is possible to produce fiberboard with very small thickness tolerances. As a result, the raw plate thickness and thus the grinding allowance can be reduced. This in turn contributes to a press time reduction, since for the same finished plate thickness, a smaller plate thickness can be driven in the hot press.

The continuous compression according to the invention also leads to significantly reduced electrical and thermal energy costs. For the discontinuous pressing, the loading and unloading about 70% more electrical energy per m ^{3 of} produced fiberboard is required compared to the continuous process according to the invention, since a much higher connected load must be installed. Since the multi-day press including the required sieves has higher radiation losses, more thermal energy is required to operate the press. In addition, in a multi-day press on average with higher press plate temperatures pressed. Since the temperature in the continuous press is lowered significantly towards the end of the pressing, less water is needed and evaporated from the fiber mat and thus less energy is brought into the fiber board. Furthermore, in the steam preheating steam with a low vapor pressure below 3 bar can be used, which is available as a very favorable steam from the fiber processing available. This also reduces the cost of the heating energy at the beginning 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 of the wood constituents cellulose and hemicellulose, and on the other hand through the softened lignin. For both bond types, it is important that the individual fibers have very close contact with each other over a longer distance. The following advantage can now be achieved by steam preheating: the fibers are already plasticized at the beginning of the pressing and are therefore very flexible, as a result of which more contact surfaces between the fibers can form during the first compression. They are crushed less during compaction. They nestle close together and are easier to press into cavities. The transverse tensile strength of the fiberboard is thereby slightly better with the same adhesive content than without steam preheating and the irreversible springback in the thickness swelling is reduced.

The wood chips are prebaked in the preheating at a temperature higher than 180 ° C, preferably 190 to 220 ° C, in the preheating in order to achieve that substances are formed in the wood by conversion processes, which lead to a better bonding during the hot pressing. In particular, the formation of furfural is promoted by the formation of acids in the preheater. The formation of acids is supported by the high temperature in the preheating. Furfural promotes condensation reactions between the wood components. Eventually, during preheating or refining, acid - such as sulfuric acid - may be added, which also promotes the formation of furfural. Hardwoods usually produce more sticky substances than softwoods. Therefore, deciduous trees are particularly suitable for this process. Furthermore, it is advantageous to add aluminum sulfate about 0.5% of free substance for precipitation of the artificial condensation adhesives and the natural resin acids during preheating or in the refiner or in the blow-line. It is also advantageous for the precipitation of the resins that the pH of the fibers is lowered to less than 4.5 by the addition of acid.

At the beginning of the hot pressing to about 20% of the pressing length, some water is squeezed out of the fiber mat, which is transported through the metal fabric belt as water or as steam to the edge of the lower steel belt. There the water is collected and the steam is sucked off. Of the extracted steam is condensed and mixed with the collected water. This water must be passed through a filter to clean it from coarse insoluble parts. The treated water contains dissolved or suspended wood substances, which are particularly suitable for bonding. Therefore, it is used again as a spray water. In addition, the water cycle is closed by the reuse of the water, so that compared to the dry process no major pollution of drinking water occurs.

The fiber mat can be scattered by means of a single scattering machine or the fibers are divided after production in the refiner into coarse and fine fibers or already prepared separately by means of two refiners. The coarse fibers are then preferably scattered into the center of the fiber mat as the middle layer and the fine fibers as the cover layer. For fiberboards which are to be directly painted, it is favorable to scatter very fine fibers (fine fibers) or dust on the surface in an amount of 20-50 g / m ² . Due to the very fine fibers, a very closed surface can be achieved on the fiberboard, whereby, for example, the paint consumption can be reduced.

To carry out the process according to the invention, the fibers must not be dried below a moisture content of 16% or the fibers must not a humidity of 16% fall below, otherwise they verborn. Horny fibers only form an insufficient hydrogen bond. This means that care must also be taken during the transport of the fibers that the moisture content is not undershot. Since during transport of the fiber in the air stream with air of a relative humidity lower than the equilibrium moisture content of the fiber, the fibers quickly release moisture, either the transport air must be air-conditioned by, for example, steam injection or the fibers should have a slightly higher humidity after the dryer as having on the forming belt.

The moisture of the fiber mat is increased by the steam preheating depending on the preheating by the condensation of water vapor. If the entire fiber mat is warmed through, the mat moisture increases by about 7%. When about 50% of the mat is heated, the humidity increase is about 4%. The method must be controlled in any case so that the fiber mat moisture at the beginning of the hot pressing is not less than 25% and not more than 35%, because if the humidity is below 25%, only insufficient wood-specific adhesive joints can be formed. Then the consumption of glue increases very strongly. If the humidity is over 35%, on the other hand, the pressing time is greatly increased due to the longer drying period.

In order to obtain a closed fibreboard surface with a high density and to protect the steel strips from soiling, it is favorable to spray water onto the fiber mat surface in a total amount of 20-700 g / m ² , depending on the consistency of the fibers and the fiberboard thickness. The water can also be sprayed onto the conveyor belt or onto the sieve belt during steam preheating. It is also favorable to spray release agent onto the fiber mat surface and / or the conveyor belt so that the fibers do not stick to the metal fabric belt during the preheating, the conveyor belt, the steel belts and the metal belt in the continuously operating press. The amount of water that is sprayed on before the steaming, however, should not be so large that there is free water on the fiber mat surface, as it then comes to problems in the vaporization by an uneven condensation of steam and uncontrollable conditions.

Therefore, a larger amount of water than 60 g / m ² can be sprayed onto the fiber mat only after the 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 the spraying to the fiber mat contact with the steel strip in the continuous press is very short, this water is almost not absorbed by the fibers and thus affects the density profile only insignificantly. From Another advantage is that the water is only sprayed from above onto the fiber mat. The water is then evaporated immediately on contact with the steel strip and can only flow vertically into the fiber mat. If the water is applied to the lower fiber mat half, so the sieve-facing Fasermatteseite, the vapor formed does not penetrate into the fiber mat. After evaporation, the steam flows over the metal fabric belt from the press against the transport direction towards the inlet and transverse to the transport direction to the edge of the press. 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 on the fiber mat side, which faces the metal fabric tape, since the moisture of the fiber mat would then not increased and the pressing time would not be shortened.

For the process according to the invention, the fibers must be dried to a moisture content which, in addition to the moisture due to the vapor deposition, the water spraying and the water from the release agent application, is within the abovementioned range. In order to precisely control the moisture input into the individual fiber mat layers, the amount of sprayed-on water and the added amount of steam must be measured separately for the upper and lower fiber mat sides. The amount of steam required to heat the water sprayed on and taken up by the wood can be calculated from the water temperature and the sprayed water Calculate amount of water. Similarly, the amount of steam needed to heat the fibers can be calculated from the initial temperature and humidity of the fibers. That is, the penetration depth of the steam is determined separately for the upper and lower bobbins due to the measured and controlled amount of steam. Thus, the moisture distribution over the fiber mat cross section is directly determinable. By appropriate measuring devices - such as microwave measuring devices - the moisture distribution over the fiber mat cross section can also be measured. The knowledge of the moisture and the moisture distribution over the fiber mat cross-section immediately before the continuously operating press is important both for the formation of a sufficient bond and a minimum pressing time as well as for the formation of the density profile of importance. For a low pressing time is favorable to steam the fiber mat over the entire cross-section and spray as much hot water on the fiber mat.

To control the depth of vapor deposition, the amount of water sprayed on and to control the metal belt temperature and the top and bottom heating plate temperature in the continuous press, the density profile of the finished fiberboard should be measured immediately after the continuous press. Fibrous plates from the semi-dry process often have no significant density reduction in the Fiberboard center on. Fiberboards produced in the dry process show a density minimum in the middle of the fibreboard, which leads to higher bending strengths with the same material input. It has now been found that fibreboards with similar density profiles as are produced by the dry process can be produced by the process according to the invention. For this purpose, not the entire fiber mat cross section should be preheated and softened with steam, but only the outer layers. In addition to the change in the press nip at the beginning of the hot pressing and during the drying phase, the evaporation depth must be reduced by reducing the amount of steam introduced and possibly the amount of water sprayed on be increased. Also important is an increased heating of the metal fabric strip temperature in the inlet to the continuously operating press, which should be at least 40 ° C higher than the temperature of the steel strips in the inlet to the continuously operating press. A separate control of the top and bottom heating circuit of the press plates has proved to be advantageous.

Since in the continuous process according to the invention at the beginning of the pressing a higher platen temperature can be driven, the temperature of the fiber mat in the outer layers is also slightly higher than in the cycle. It has been found that this higher temperature promotes the formation of condensation reactions - especially of lignin - so that In the method according to the invention a firmer fiber to fiber bond can be achieved. Slightly better bending properties can therefore be achieved with the same adhesive content.

The transverse tensile strength of the fiber boards produced in the laboratory process according to the invention are slightly lower at the edge of the fiber board than in the center of the fiber board. This is caused by the fact that the curing temperature at the edge is slightly lower. The curing temperature is lower in the fiber mat because the steel belts, the press plates and the rolling bars are cooler at the edge than in the center of the press. They cool by the escaping water and the circulating air. In general, the press plates are 50 mm wider on each press side 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 to ≥ 100 mm, the curing temperature at the edge is higher and the transverse tensile strength of the fiberboard at the edge is significantly improved. In addition, the fiber mat can be scattered at the edge even with a higher basis weight, which can also achieve an increase in the transverse tensile strength.

The continuous fiberboard strand produced in accordance with the invention is subjected to after-treatment after a size-spreading, as in the conventional semi-dry process, to improve the properties.

In particular, the fiberboard are passed through a heat channel or stacked warm in a heated hall. The heat treatment of the fiber boards at temperatures between 110 ° and 200 ° C after the continuous press increases the bonding of the individual fibers, which improves the bending properties and the swelling values. To carry out the heat treatment, the fiberboard can be warmly stacked or pulled as a package through a heat channel.

The metal fabric belt in the continuous press has the function to allow drainage and Entdampfung the fiber mat. The metal fabric belt must therefore have a structure which allows a removal of the water and the water vapor within the structure perpendicular to the transport direction without large flow resistance. This means that a larger free cross-section is present within the metal fabric belt transversely to the transport direction. By using the metal fabric tape, the continuous press can be performed in a width of more than 4 m, since the fiber plate is drained and evaporated only on the metal fabric belt. In this case, the metal fabric tape to the fiber mat side may have a smooth or coarse structure. Mostly a smooth structure is desired if the fiberboard is to be coated later. For individual applications, a coarse structure with a screen print on the plate surface is favorable.

Since cast steel or unalloyed steel is too rusty, only a non-rusting material such as phosphor bronze or stainless steel for the semi-dry plant is possible as the material for the metal fabric belt.

In tests, it has now been found that the steel strips are much cooler at the edge of the press, as in the middle of the press, making bowls to the fiber mat. Therefore, the plant is designed so that the lower steel strip is wider than the upper steel strip and covers the guide chain for guiding the rolling bars. In some places, the lower steel band can then be pressed down with hold-down rollers. At these points, the water is collected and removed. These hold-down rollers are provided from the beginning of the press to about 20% of the press length.
The specific pressure is important because of the avoidance of relative movements between metal fabric belt and steel strip due to thermal expansion and thus avoidance of scratches on the steel strip. Since this process mainly produces thin fiberboard, the metal fabric tape must not have any thickness tolerances greater than ± 0.075 mm. The thickness tolerance would also show up in the product and lead to a larger cut.

Further advantageous measures and embodiments of the subject matter of the invention will become apparent from the dependent claims and the following description with reference to 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:

FIG. 1

the plant according to the invention in side view,

FIG. 2

in a section AA and cutting out FIG. 1 a part of the right longitudinal center with guidance of the roll bars on the press edge and

FIG. 3

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

The drawing shows the system as the fiber mat 10 made according to the pressing program from left to right, treated and how it is pressed in the continuous press 5 to the fiber board 30 and cured. First, the fiber mat 10 is compressed in the continuous press 5 at high pressure, pressed out some water and then relieved and dried. Towards the end of the pressing, the fiber mat 10 is compacted to the final thickness and cured, the curing phase is started when the moisture content of the fiber mat 10 is 5% - 8%.

From the FIG. 1 is the system shown in a schematic representation, with which the fiber mat 10 is sprinkled from fibers on a conveyor belt 20 from the scattering station 1. The conveyor belt 20 serves to further guide the fiber mat 10 if necessary by a pre-press 2, hot water spraying and / or Trennmittelsprühvorrichtungen 21 to the pre-press with Dampfvorwärmeinrichtung 4. The endless conveyor belt 20 is guided over pulleys 24. The fiber mat 10 is continued with the conveyor belt 20 down to the lower endless belt 23 of the pre-press with Dampfvorwärmeinrichtung 4, wherein at the reversal, the guide roller 24 is arranged recoverable to guide the fiber mat 10 in a discharge chute 22 in case of disturbances. To control the fiber mat moisture between the scattering station 1 and the pre-press with Dampfvorwärmeinrichtung 4 a mat moisture sensor 3 is arranged. From scattering station 1, a single or multi-layer fiber mat 10 can be scattered as needed. For this purpose, five or more different scattering bins are provided, for example, with superfine 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 for the middle layer. The pre-press with Dampfvorwärmeinrichtung 4 consists of two endless, around the steam feed 29 and pulleys 27 rotating sieve belts 23, wherein the lower wire 23 leads the possibly preheated fiber mat 10 close to the inlet region of the continuously operating press 5 or to the Metal fabric tape 25 hands. As a continuously operating press 5 a so-called double belt press is provided, which consists in its main parts of a movable frame upper part 9 and a stationary frame lower part 8, which form the adjustable press nip 11. Frame upper part 9 and frame lower part 8 are circulated via drive drums 16 and deflection drums 17 of steel belts 18 and 19. At the press nip 11 facing sides of the frame top 9 and frame lower part 8 are heated and coolable press plates 12 and 13 are mounted, which support the steel belts 18/19 by means of likewise circulating guided with guide chains 39 and 40 rolling rods 37 and 38. The finished wood-based material or fiber board extending from the continuously operating press 5 is designated 30. According to the invention, the lower steel belt 18, a guided over pulleys 27 associated with circulating metal mesh belt 25, which consists of a stainless material of high thermal conductivity such as stainless steel or phosphor bronze, the upper and lower steel belt 18 and 19 and the metal belt fabric 25 in the return common are passed through an insulated tunnel 26 to prevent heat dissipation and to save energy, and the metal fabric belt 25 is heated by a hot plate 28 to a much higher temperature before entering the press nip 11, as the associated steel strip 18 in the inlet to the press nip 11 owns.

The press length is expediently divided into a heating zone 6 and a cooling zone 7. For a separate control of these zones, both the heating zone 6 and the cooling zone 7 with the cooling plates 14 and 15 via a separate Rollteppichabstützung equipped with guide chains circulating guided rolling rods. At the outlet of the continuously operating press 5, the density profile of the finished fiberboard 30 is checked by means of a raw density sensor 31 and regulated with the determined value, the temperature and humidity of the fiber mat prior to entry into the continuously operating press 5. In a section AA off FIG. 1 is in FIG. 2 On the longitudinal members 41 and 42 of the two longitudinal sides of the continuously operating press 5, the guide chains 39/40 are guided with the rolling rods 37 and 38 on guide rails 47 and 50. To hold down the lower, executed with greater width steel strip 18 a plurality of hold-down rollers 43 are mounted on the lower side rail 41. A trained on the lower side rail 41 channel 44 serves to derive the emerging from the fiber mat 10 via transverse grooves 45 of the metal fabric belt 25 water and condensing vapor. A purpose designed metal fabric tape 25 is in FIG. 3 in side view according to the FIG. 1 shown. The longitudinal wires shown as a chain 46 thereby form a sufficiently flat support surface for the fiber mat 10 and are held together by the transverse wires designated as shot 48.

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 above

14th

Cooling plate below

15th

Cooling plate above

16th

driving drum

17th

Umlenktrommel

18th

Steel band below

19th

Steel band above

20th

conveyor belt

21st

Hot water spray device or release agent spray device

22nd

chute

23rd

Sieve belt in pre-press with steam preheater 4

24th

Pulleys for 20

25th

Metal mesh tape in continuous press 5

26th

Isoliertunnel

27th

Pulleys for screen 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 down

38th

Roll bars above

39th

Guide chain below

40th

Leadership 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

49. 50.

Guide rail for guide chain 40

Claims (37)

1. A method for producing wood-based boards such as chipboards and fiberboards, especially fiberboards made of wood or other ligno-cellulose materials, in which a fiber mat (10) which is provided with a low or no percentage of adhesive is formed from a dispersing station (1) on a continuously moving conveyor belt (20), which mat, after having been placed on a metal fabric belt (25), is introduced between the pressing plates (12, 13) of a press (5) and is pressed and hardened into a fiberboard (30) under application of pressure and heat, characterized by the following method steps:

   1.1 the fibers which are treated without adhesive or are glued with only a low percentage of adhesive are dried to a humidity of 16% to 25% and dispersed from a dispersing station (1) onto a conveyor belt (20) into a fiber mat (10);

   1.2 the humidity of the fiber mat (10) is increased in a continuously working prepress (4) by introduction of saturated steam or superheated steam or mixtures of steam and air in such a way that a humidity of a minimum of 25% up to a maximum of 35% is reached directly prior to entrance into the press, thus simultaneously providing a substantial heating of the fiber mat (10);

   1.3 directly thereafter the fiber mat (10) is transferred to an endless stainless metal fabric belt (25) of a continuously working press (5), which belt revolves with the bottom steel band (18), and is introduced into the press nip (11) of a continuously working press (5);

   1.4 within approximately 20% of the press length of the continuously working press (5) the fiber mat (10) is compressed in a compression phase under high specific pressure of a maximum of 5.5 N/mm2 and water is pressed out thereby;

   1.5 in a subsequent drying phase within the continuously working press (5) the evaporation and discharge of the steam and the water occurs, especially from the middle layer (34) with reduced specific pressure of a maximum of 1 N/mm2 and is maintained for such a time until a humidity of 5 to 8% is reached in the fiber mat (10), and

   1.6 in a final hardening phase in the continuously working press (5) the fiber mat (10) is compressed to the final dimension under a maximum pressure of 3.5 N/mm2 and dried until an approximate humidity of 2% is reached in the middle layer (34).
2. A method according to claim 1, characterized in that the humidity in the fiber mat (10) is increased in a continuously working prepress (4) by introduction of saturated steam or superheated steam or mixtures of steam and air by a humidity of 2% to 7% and by means of spraying with hot water before and after the press (4) by a humidity of 2% to 8% in such a way that a humidity of a minimum of 25% to a maximum of 35% is reached directly before the entrance into the press (5), through which simultaneously there is a relevant heating of the fiber mat (10).
3. A method according to one of the preceding claims 1 or 2 for producing a thin fiberboard (30) ≤4 mm, characterized in that in the method step 1.4 within approximately 20% of the press length of the continuously working press (5) the fiber mat (10) is compressed in a compression phase with high specific pressure of a maximum of 5.0 N/mm2 and water is pressed out thereby, and that in method step 1.6, in a final hardening phase in the continuously working press (5), the fiber mat (10) is compressed to the end dimension under a maximum pressure of 4 N/mm2 and is dried until an approximate humidity of 2% is reached in the middle layer (34).
4. A method according to claim 1, characterized in that in the compression phase the fiber mat (10) is compressed during a time of 5 to 15 seconds and at a heat in the middle layer (34) of 105° Celsius to 110° Celsius until a humidity of approx. 2% is reached in the cover layers and a humidity of approx. 35% is reached in the middle layer (34).
5. A method according to claim 1, characterized in that in the drying phase the fiber mat (10) is dried during a time of 20 to 35 seconds and at a heat in the middle layer (34) of 105° Celsius to 110° Celsius under evaporation and discharge of the water until a humidity of approx. 2% to 2.5% is reached in the cover layers and a humidity of approx. 6% is reached in the middle layer (34).
6. A method according to one or several of the preceding claims 1 to 5, characterized in that during the production of thin fiberboards of ≤4 mm, the fiber board (10) is compressed and hardened in the hardening phase during a time of 25 to 50 seconds and at a heat in the middle layer of 110° Celsius to 135° Celsius until a humidity of approx. 0.5% to 0.2% is reached in the cover layers and a humidity of approx. 6% to 2% is reached in the middle layer (34).
7. A method according to one or several of the preceding claims 1 to 6, characterized in that only the cover layers of the fiber mat (10) are humidified with saturated steam or superheated steam or a mixture of steam and air.
8. A method according to claim 1, characterized in that the fiber mat (10) is heated to a minimum temperature of 80° Celsius by introduction of saturated steam or superheated steam or a mixture of steam and air under a vapor pressure of 0.07 to 3 bar.
9. A method according to one or several of the preceding claims 1 to 8, characterized in that more than 60 g/m2 of water is only sprayed onto the fiber mat surfaces prior to the entrance in the continuously working press (5) which are not in contact with the metal fabric belt (25) in the continuously working press (5).
10. A method according to one or several of the preceding claims 1 to 9, characterized in that a cooling phase follows the hardening phase.
11. A method according to one or several of the preceding claims 1 to 10, characterized in that at the end of the pressing the fiber mat surface is cooled within the continuously working press (5) to a minimum of 115° Celsius, preferably 100° Celsius.
12. A method according to one or several of the preceding claims 1 to 11, characterized in that the water pressed out and collected from the fiber mat (10) is cleaned and is used as spray water.
13. A method according to one or several of the preceding claims 1 to 12, characterized in that the middle layer (34) is dispersed from rough fibers, the intermediate layers (33, 35) from fine fibers, and the cover layers from ultra-fine fibers (32, 36) and/or wood dust.
14. A method according to claim 13, characterized in that ultra-fine fibers (32, 36) or wood dust are only dispersed on the surface of the fiber mat (10) which is disposed opposite of the metal fabric belt (25).
15. A method according to one or several of the preceding claims 1 to 14, characterized in that the fibers are conditioned by steam injection or by introducing conditioned air to a humidity of ≥16% during the transport from the dryer to the hopper of the dispersing station (1).
16. A method according to one or several of the preceding claims 1 to 15, characterized in that a water quantity of 20 to 700 g/m2 is applied to one or both surfaces of the fiber mat (10).
17. A method according to one or several of the preceding claims 1 to 16, characterized in that the hot water and/or the separating agent are sprayed onto the conveyor belt (20) and/or the surface of the fiber mat (10) and/or the screen belts (23) of the prepress with preheating device (4).
18. A method according to one or several of the preceding claims 1 to 17, characterized in that the water quantities to be applied to the surfaces of the fiber mats are calculated and controlled on the basis of the actually sprayed water quantity and the initial humidity of the fiber mat.
19. A method according to one or several of the preceding claims 1 to 18, characterized in that the steam quantity to be introduced into the fiber mat (10) for heating the fibers is calculated and controlled from the initial temperature and the humidity of the fibers.
20. A method according to one or several of the preceding claims 1 to 19, characterized in that the steam quantity to be introduced for heating the fibers is detected and controlled separately for the upper and bottom halves of the fiber mat.
21. A method according to one or several of the preceding claims 1 to 20, characterized in that prior to the entrance in the press region the metal fabric belt (25) is heated to a temperature which is at least 40° Celsius higher than the associated bottom steel band (18) at the inlet.
22. A method according to one or several of the preceding claims 1 to 21, characterized in that controlling and adjusting the evaporation depth, the water quantity to be sprayed, the temperature of the upper and bottom pressing plates 12, 123) or the upper and bottom heating circuits of the pressing plates (12, 13) occurs depending on the raw density profile in the finished fiberboard (30) as measured directly after the continuously working press (5).
23. A method according to one or several of the preceding claims 1 to 22, characterized in that the finished, already divided fiberboards (30) are guided for conditioning through a heat conduit and/or are stacked in there in a hot way.
24. A method according to one or several of the preceding claims 1 to 23, characterized in that the wood chips are pre-steamed at a temperature of 190° Celsius to 220° Celsius and/or acid is placed in the digester.
25. A method according to one or several of the preceding claims 1 to 24, characterized in that the steam extraction occurs up to the end of the drying phase at the edges of the pressing plates (12, 13).
26. A method according to one or several of the preceding claims 1 to 25, characterized in that the fiber mat (10) is dispersed in a width on the conveyor belt (20) which leaves exposed a space of ≤100 mm per longitudinal side at the longitudinal edge of the pressing plate (12, 13) in the continuously working press (5).
27. A method according to one or several of the preceding claims 1 to 26, characterized in that the specific pressing pressure on the fiber mat (10) is exerted not under 0.3 N/mm2 during the first 80% to 90% of the pressing time in the continually working press (5).
28. An installation for producing chipboards and fiberboards, especially fiberboards (30) made of wood or other ligno-cellulose materials, comprising a dispersing station (1), a conveyor belt (20) moved continuously beneath the dispersing station (1), and a press (5), with a single- or multi-layer fiber mat (10) being dispersable from the dispersing station (1), the press (5) consisting of a movable upper frame part and a stationary bottom frame part and heatable and coolable pressing plates (12, 13, 14, 15) which are attached thereto, for performing the method according to claims 1 to 27, characterized in that a continuously working press (5) is provided as a press which comprises endless steel bands (18, 19) which transmit the pressing pressure and draw the fiber mat (10) through the press nip (11), the steel bands (18, 19) being guided in a revolving manner via drive and deflection drums (16, 17) about the upper frame part (9) and the bottom frame part (8), which drums rest with adjustable press nip (11) against the upper frame part (9) and the bottom frame part (8) via entrained rolling bars (37, 38) guided with their axes transversally to the direction of the band run, with the rolling bars (37, 38) being guided at both ends in guide chains (39, 40), several hot water spraying devices and devices for applying separating agents (21) which are directed against the conveyor belt (2) and the surfaces of the fiber mat (10) are arranged before and between the dispersing station (1) and the continuously working press (5), a prepress with a steam preheating device (4) and upper and bottom screen belt (23) being provided before the continuously working press (5), the continuously working press (5) comprises an endless metal fabric belt (25) as a deposit for the fiber mat (10), which belt consists of a stainless material and is guided in a revolving manner with the bottom steel band (18) and is guided before the inlet into the press nip (11) via a heating plate (28) and the bottom steel band (18) is arranged with a larger width (b) for discharging the pressed water than the upper steel band (19).
29. An installation according to claim 28, characterized in that the bottom longitudinal beam (41) for the guide chain support is provided on both longitudinal sides with a holding-down roller (43) for the bottom steel band (18).
30. An installation according to claims 28 and 29, characterized in that the bottom longitudinal beams (41) are each provided with a conduit (44) for discharging the pressed-out water.
31. An installation according to claims 28 to 30, characterized in that the metal fabric belt (25) comprises free transversal grooves (45) for discharging the pressed-out water.
32. An installation according to claims 28 to 31, characterized in that the press length is divided into a heating zone (6) and a cooling zone (7).
33. An installation according to claims 28 to 32, characterized in that the metal fabric band (25) consists of special steel or phosphor bronze.
34. An installation according to claims 28 to 33, characterized in that especially the inlet region of the continuously working press (5) with deflection drums (17), steel bands (18, 19) and optionally the compression angles which can be changed with inlet heating plates can be heated to high temperature and thus to high thermal input.
35. An installation according to claims 28 to 34, characterized in that the metal fabric belt (25) has a thickness tolerance of less than ± 0.075 mm.
36. An installation according to claims 28 to 35, characterized in that an endless metal fabric belt (25) which rests on the fiber mat (10) is provided to be revolving also with the upper steel band (19).
37. An installation according to claims 28 to 36, characterized in that for high thermal input the pressing plates (12, 13) of the continuously working press (5) have heating bores in large numbers close to the fiber mat (10) and are designed and arranged for high flow speeds of the heating medium, mainly water.

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