DE102012001293B4 - Process and press for producing a wood-based molded part - Google Patents

Abstract

Method for producing a wood-based molded part (3) using a wood-based base material and a heat-curable binding agent by pressing in a continuously operating press (10) with a pressing chamber (5), the pressing chamber (5) being designed in the form of a press gap (5) as a substantially closed pressure chamber, wherein heat is transferred to the wood-based molded part in the form of a steam jet to harden the binding agent, wherein before the heat is transferred in the form of a steam jet, the process air pressure prevailing in the press gap (5) is increased compared to the atmospheric air pressure prevailing outside the press gap (5) by means of a device (6, 7) for generating an overpressure, wherein a targeted reduction in the process air pressure takes place during pressing, wherein the reduction in the process air pressure takes place with the aid of a sealing device (19) which seals the press gap (5) on both sides over a partial length of the press (10), and wherein a control the process air pressure is controlled via a pressure control connected to the sealing device (19) and which can influence the function of the sealing device (19).

Description

The invention relates to a method for producing a wood-based molded part using a wood-based base material and a heat-curable binding agent by pressing, whereby heat is transferred to the wood-based molded part in the form of a steam jet to cure the binding agent. The invention also relates to a continuous press for producing such a wood-based molded part.

Such methods are known from the state of the art. The length of the pressing time is primarily influenced by how quickly the binding agent hardens. The solution approaches known from the state of the art are described below using the example of a three-layer wood-based panel consisting of a middle layer, an upper and a lower cover layer.

To produce the board, a three-layer wood-based mat (fleece) consisting of the wood-based base material and a heat-curable binding agent is fed into a press. A hot pressing process then takes place. The binding agent (glue) in the outer cover layers hardens through the direct supply of heat via heatable pressing plates or belts.

Due to the thermal energy introduced into the plate on the one hand and the moisture contained in the plate on the other, a water vapor pressure gradient forms in the plate.

The heat energy required to harden the middle layer is introduced into the board via the so-called steam burst. For this, the outer pressing plates are heated to 200° Celsius, for example. During pressing, the water (glue water) in the outer layers is then heated and, when the boiling temperature (100°C) is reached, is suddenly transferred to the steam phase. Due to the water vapor pressure gradient, this steam shoots vertically from both sides of the board towards the middle of the board. This process is known as a steam burst.

Due to the temperature gradient between the outside of the cover layers and the middle of the middle layer (the temperature difference is 75°C, for example), the steam condenses in the still cool middle layer. Condensation heat is released, which increases the temperature in the middle layer. The chemical curing reactions in the middle layer take place more quickly and less time passes until the binding agent has hardened, which ultimately shortens the required pressing time. This steam burst principle is used in the production of numerous wood-based molded parts, for example in the production of chipboard, MDF, OSB, etc.

It is known from the state of the art that the steam jet principle can be optimized by heating the steam beforehand and blowing it into the wood-based molded part as hot steam under pressure. This is also referred to as steam injection technology. This also makes it possible to shorten the pressing time to a certain extent.

However, the disadvantage is that more water gets into the interior of the wood-based material molded part with the steam injection technique. Due to the basic principle of pressure and counterpressure, the internal pressure in the wood-based material molded part is greatly increased with the steam injection technique. When the press opens, the binding agent inside the molded part must already have hardened to such an extent that the internal steam pressure does not lead to damage (chipping off of parts) or destruction of the molded part (delamination). Attempts are made to counteract this disadvantage with complex cooling devices for cooling the molded parts after hot pressing. However, the press must remain closed for a comparatively long time with the steam injection technique, so that the time advantage of the rapid hardening of the binding agent is partially canceled out.

In DE 10 2008 026 258 A1 it was proposed that the steam blast take place under increased pressure. The method described therein is characterized in that, before the heat transfer in the form of a steam blast, the process air pressure prevailing in the press chamber is increased compared to the atmospheric air pressure prevailing outside the press chamber, but without additionally supplying moisture, particularly in the form of water vapor, to the wood-based material molded part. A press intended for the production of such a wood-based material molded part is characterized by a press chamber and a device for generating an overpressure in such a way that, before the heat transfer in the form of a steam blast, the process air pressure prevailing in the press chamber can be increased compared to the atmospheric air pressure prevailing outside the press chamber, but without additionally supplying moisture, particularly in the form of water vapor, to the wood-based material molded part.

By applying and maintaining an external overpressure during the pressing process, DE 10 2008 026 258 A1 achieved by increasing the boiling point of the water above 100°C. This means that with a burst of steam at 120°C, for example, significantly more heat energy is introduced into the middle layer of the wood-based molded part. This increased amount of heat, which is released during the condensation of the water vapor in the still cold middle layer, leads to a significantly higher temperature in the middle layer compared to the conventional steam jet technique, with the result that the curing reactions of the glue take place significantly faster. In summary, the DE 10 2008 026 258 A1 The steam jet described in the technique is at a higher temperature, which leads to a shortening of the pressing time.

The DE 32 33 241 A1 discloses a discontinuously operating press in which a pre-formed lignocellulose mat is inserted. The press has an upper heatable tool half and a lower tool half, which are connected to a press table. Between the tool halves, a pressing chamber is designed as an essentially closed pressure chamber, whereby a targeted reduction in the process air pressure can be achieved via a valve during pressing.

An object of the present invention is to provide a technique for producing a wood-based material molded part, with the aid of which the pressing time can be shortened even further.

This object is achieved by a method according to claim 1 or by a press according to claim 5. Advantageous embodiments of the invention are specified in the subclaims.

The advantages and embodiments explained below in connection with the method also apply mutatis mutandis to the devices according to the invention and vice versa.

Specifically, the present invention is directed to the method mentioned at the outset for producing a wood-based material molded part in a continuously operating press and to a corresponding continuous press for producing a wood-based material molded part.

The press according to the invention has a pressing chamber which is designed as a press gap as an essentially closed pressure chamber. Before the heat transfer in the form of a steam jet, the process air pressure prevailing in the press gap is increased compared to the atmospheric air pressure prevailing outside the press gap by means of a device for generating an overpressure.

The essence of the present invention is that during continuous pressing, a targeted reduction in the process air pressure takes place to initiate the steam jet. For this purpose, the continuous press according to the invention is provided with a sealing device with the aid of which the process air pressure can be specifically reduced during pressing. The sealing device seals the press gap of the continuous press on both sides over a partial length of the press, with a pressure control connected to the sealing device and the function of the sealing device being able to be influenced. Through targeted pressure relief during the pressing time, the material is suddenly heated through, with the time and sequence of the heating through being able to be influenced.

In the method according to the invention, the reduction of the process air pressure is thus carried out with the aid of the sealing device, which seals the press gap on both sides over a partial length of the press, wherein the process air pressure is controlled via the pressure control connected to the sealing device and which can influence the function of the sealing device.

• Danach wird die in eine technologische Sackgasse führende Dampfinjektionstechnik, bei der heißer Wasserdampf unter Druck in das Formteil eingepresst wird, nicht mehr weiterverfolgt. Stattdessen erfolgt eine Rückkehr zu der ursprünglichen Dampfstoß-Technik, bei welcher der Dampfstoß selbsttätig bei Erreichen der Siedetemperatur erfolgt. Diese Dampfstoß-Technik wird in DE 10 2008 026 258 dadurch verbessert, dass während des Pressvorgangs zumindest im Pressraum der Presse der Luftdruck größer ist als der Atmosphärendruck der Umgebung. Der Pressvorgang findet mit anderen Worten unter Überdruck statt, z. B. bei 1,5 bar. Bei einem solchen Überdruck verdampft das Wasser bei höheren Temperaturen, beispielsweise bei 110°C. Der Dampfstoß erfolgt immer noch selbsttätig, diesmal allerdings bei einer höheren Temperatur. Im Vergleich mit einem unter Atmosphärendruck ablaufenden Verfahren erfolgt der Dampfstoß unter Umständen zwar zu einem etwas späteren Zeitpunkt, jedoch mit einem entsprechend der höheren Siedetemperatur wesentlich höheren Energiegehalt.

The present invention is based on the DE 10 2008 026 258 described basic findings as described below:

• After that, the steam injection technique, which leads to a technological dead end and involves injecting hot steam under pressure into the molded part, is no longer pursued. Instead, there is a return to the original steam jet technique, in which the steam jet occurs automatically when the boiling temperature is reached. This steam jet technique is used in DE 10 2008 026 258 This is improved by the fact that during the pressing process, at least in the pressing chamber of the press, the air pressure is higher than the ambient atmospheric pressure. In other words, the pressing process takes place under excess pressure, e.g. at 1.5 bar. At such excess pressure, the water evaporates at higher temperatures, for example at 110°C. The steam burst still occurs automatically, but this time at a higher temperature. Compared to a process that takes place under atmospheric pressure, the steam burst may occur at a slightly later point in time, but with a much higher energy content due to the higher boiling temperature.

The in DE 10 2008 026 258 A1 The invention described makes use of the dependence of boiling temperature and boiling pressure on each other. By increasing the pressure, for example, by 0.5 bar = 500 hPa, the boiling temperature of the water increases from 100°C to approximately 110°C. This increases the energy content of the water vapor compared to a process that takes place at atmospheric pressure. When using the same amount of water, the steam can be used to More heat can be transferred to the interior of the wood-based molded part during the impact. This increases the temperature that can be achieved in the middle layer. According to the van't Hoff rule (RGT rule), according to which the reaction rate roughly doubles when the temperature is increased by 10°C, this results in a significantly increased reaction rate for the chemical curing reactions of the binder. As a result, the pressing time can be significantly shortened, and the risk of delamination is no longer present, since no additional water vapor is introduced into the molded part.

In contrast to the original steam jet technique, in which the heat energy introduced into the wood-based molded part is essentially increased by increasing the amount of steam used, the steam jet technique used in DE 10 2008 026 258 A1 The invention described is based on the idea of increasing the reaction speed of the curing reactions of the binder by transferring more heat energy with the same amount of water vapor. This makes it possible to achieve a high process temperature without the disadvantages of increased internal pressure.

The resulting water vapor consists of the moisture content of the air that is already contained in the air - assuming that no dry air is used as the process atmosphere - as well as the water vapor that has its origin in the glue water of the covering layers.

The following illustration will once again show the difference between the known steam injection technology and the DE 10 2008 026 258 described invention:
In conventional steam injection technology, the partial pressure ratios result from a combination of (moist) air on the one hand and superheated steam additionally introduced into the system on the other: $${\text{p}}_{\text{in total}}=\text{p}\left(\text{Air}\right)+\text{p}\left({\text{H}}_2\text{O}\right)$$

When the boiling temperature of 100°C is reached, the steam burst results from the water vapor contained in the moist air as well as from the water vapor that has its origin in the glue water of the covering layers, as well as from the additionally introduced superheated water vapor.

At the DE 10 2008 026 258 In the invention described, the introduction of superheated steam is dispensed with. The pressure chamber only contains the usual process atmosphere, usually air in the usual composition (78% nitrogen, 21% oxygen, ...). The following follows: $${\text{p}}_{\text{in total}}=\text{p}\left(\text{Air}\right)$$

The steam burst that occurs when the (increased) boiling temperature of, for example, 110°C is reached contains significantly less moisture and at the same time a higher heat energy, which leads to the advantages described above.

Since the pressing process takes place under excess pressure, a pressure chamber is provided in which the desired excess pressure prevails. The atmospheric air pressure is then the air pressure prevailing in the atmosphere outside the pressure chamber, caused by the weight of the air. The process air pressure, on the other hand, is the air pressure of the environment in which the pressing process takes place. Since the pressing process always takes place in a pressing chamber, for example in the press gap arranged between press plates or belts, the process air pressure is in other words the air pressure prevailing (at least) in the pressing chamber to which the wood-based molded part to be produced is exposed. In one embodiment of the DE 10 2008 026 258 In the invention described, the pressing chamber, in particular in the form of the pressing gap, is designed as a substantially closed pressure chamber to achieve the desired overpressure. In another embodiment of the invention described in DE 10 2008 026 258 In the invention described, a pressure chamber is provided which encloses other parts of the press in addition to the actual press chamber. In a further embodiment of the DE 10 2008 026 258 In the invention described, the press has a pressure chamber that completely surrounds it; the entire press is then located within the pressure chamber.

The in DE 10 2008 026 258 A1 The press described has suitable technical equipment for this purpose, which is familiar to the expert and therefore does not need to be listed in detail here. If, for example, the press gap is designed as a pressure chamber, devices are provided for sealing the press gap, e.g. sealing rings attached to the side, pressure devices, etc. In the case of discontinuously operating presses, for example discontinuously operating single- or multi-stage presses, it is possible to provide lateral sealing surfaces that seal all four sides when the press is closed. In addition to the structural elements and seals for delimiting the pressure chamber, a device for generating an overpressure must be provided. This can be an overpressure container that provides an overpressure of, for example, 0.5 to 10 bar. From this, pressure can be used to Overpressure is fed into the pressure chamber via pipes. This allows the boiling point of the water to be set to e.g. 110°C to 150°C.

• Während bei dem ursprünglichen Dampfstoß-Verfahren der Dampfstoß stets spontan erfolgte und auch bei der in DE 10 2008 026 258 A1 beschriebenen Technik ein spontaner Dampfstoß hervorgerufen wird, schlägt die vorliegende Erfindung vor, das Prinzip des Dampfstoßes unter erhöhtem Druck beizubehalten, jedoch den Zeitpunkt des Dampfstoßes zu beeinflussen. Mit anderen Worten findet kein spontaner Dampfstoß mehr statt. Stattdessen wird der Zeitpunkt des Dampfstoßes gezielt gesteuert. Der Dampfstoß wird mit anderen Worten initiiert. Im Folgenden wird daher auch von einem „forcierten Dampfstoß“ gesprochen. Anders ausgedrückt wird durch eine geschickte Steuerung der Druckverläufe während des Pressvorgangs eine Dampfbewegung (Dampfstoß) innerhalb der Matte forciert.

In addition to the above findings, as presented in DE 10 2008 026 258 A1 described, the present invention is based on the following considerations:

• While in the original steam jet process the steam jet always occurred spontaneously and also in the DE 10 2008 026 258 A1 While the technique described above causes a spontaneous steam burst, the present invention proposes to retain the principle of the steam burst under increased pressure, but to influence the timing of the steam burst. In other words, there is no longer a spontaneous steam burst. Instead, the timing of the steam burst is controlled in a targeted manner. In other words, the steam burst is initiated. In the following, we will therefore also refer to a "forced steam burst". In other words, a steam movement (steam burst) is forced within the mat by skillfully controlling the pressure curves during the pressing process.

A basic idea of the present invention therefore lies in an additional relief step, namely a targeted reduction of the previously built-up process air pressure during pressing. In other words, pressure is relieved before the end of the pressing time. This pressure relief takes place either partially or completely, depending on the application. In other words, an increased process air pressure can also be present after the pressure relief, or the process air pressure can again correspond to the atmospheric air pressure prevailing outside the pressing chamber.

This targeted reduction in pressure results in extremely rapid temperature increases in the fleece. The internal temperature not only rises particularly quickly, but also to values that are not usually reached. This means that there is a significantly increased energy content. In other words, more energy can be introduced into the middle layer of the mat. The material is heated through suddenly, combined with a high energy input, which results in a significant reduction in pressing times.

This principle is explained in more detail below. In the method according to the invention, the water on the surface of the mat is prevented from boiling by the increased pressure. This means that temperatures of well over 100°C can be reached at this point. By deliberately lowering the process air pressure, an abrupt increase in the internal temperature of the mat can be recorded, which is caused by the water vapor that is suddenly generated due to the pressure relief. As is known from the steam jet principle, the water vapor can only spread towards the middle of the mat, which leads to very strong temperature increases. In comparison to all other steam jet techniques known from the state of the art, much greater temperature increases can be measured in an extremely short time. For example, in a fleece in which the pressure was released after about 330 minutes of pressing, an increase in the internal temperature from 70°C by 47K to 117°C was measured within 10 seconds after the pressure was released.

A significant advantage of the present invention is that the targeted forcing of the steam jet allows the timing of the steam jet, i.e. the time at which the energy is sent to the middle layer of the mat, to be optimally selected. As a result, this leads to a further reduction in the pressing time.

An optimal choice of the timing of the steam burst means that the time of pressure release is chosen so that the remaining time that the fleece remains in the press is just enough to harden the wood-based material molded part, i.e. to stabilize the chemical bonds at least to such an extent that the wood-based material molded part does not burst (delaminate) when the press is opened.

At the same time, forcing the steam jet through an adjustable pressure relief means that the strength of the steam jet can be specifically influenced. In other words, the way in which the pressure relief is carried out can influence the speed at which the steam jet flows towards the middle layer. This can be regulated by a defined reduction in the process pressure. If, for example, the process air pressure is allowed to collapse spontaneously to 1 bar, the steam jet will be violent. If the pressure is reduced within a period of a few seconds, for example, this is gentler on the structure of the molded part. This avoids too rapid a pressure relief, which could potentially damage the structure of the wood matrix. In other words, a delayed reduction in the process air pressure can protect the structure of the wood-based molded part to be produced. It is therefore advantageous if a pressure control is provided with the aid of which the sealing device can be influenced in such a way that the pressure in the press chamber can be changed in a targeted manner.

But an accelerated reduction in the process air pressure by additionally applying a vacuum and thus increasing the pressure gradient is also possible and can be useful in certain applications. For example, to increase the pressure difference, it would be conceivable to apply an overpressure at the press mouth and a vacuum at the press outlet. By applying a negative pressure, the water vapor is then literally sucked out of the wood-based molded part.

With the previously known processes, more or less long process times had to be expected that were hardly controllable. Controlling or regulating the process was not possible at all or only partially possible. With the present invention, an extended process control and regulation is possible. While with the processes known from the prior art the only parameter that could be changed was the process air pressure, with the present invention, in addition to this process air pressure, the time of the pressure reduction ("pressure relief") and the speed of the pressure reduction can also be influenced. This makes it possible to influence the material structure of the wood-based molded parts produced in an advantageous manner and thus above all their strength properties.

Just like the one in DE 10 2008 026 258 In the present invention, as described in the method, moisture, particularly in the form of water vapor, is not added to the wood-based material molded part during pressing. The moisture required for the steam jet is already contained in the wood-based material mat. Nevertheless, a quantity of moisture can be added to the molded part before the pressing process, preferably by spraying or otherwise distributing it onto the fiber fleece. Depending on the material, the quantity of water sprayed on can be, for example, 1 to 2 g per side and millimeter of panel thickness. By introducing this additional moisture, the subsequent steam jet is further enhanced.

As in DE 10 2008 026 258 As with the method described above, the present method can also be used in the production of numerous wood-based material molded parts, for example in the production of chipboard, MDF, HDF, OSB, etc. The wood-based material molded parts can be individual parts or an endless part that runs continuously through the press. The method according to the invention is used on continuously operating presses, for example on single- or multi-stage presses, double-belt presses, etc.

Depending on the type of wood-based molded parts to be produced, the wood-based material base material is chips, fibers, stands, etc. Urea, melamine or phenolic resins or mixtures thereof or mixtures of these resins with polymeric diisocyanates (PMDI) or with natural binders such as tannin and/or lignin resins can be used as thermosetting binders.

An embodiment of the invention is explained in more detail below in the single figure using a continuously operating multi-stage press.

All figures show the invention only schematically and with its essential components. The same reference symbols correspond to elements with the same or comparable function.

When producing a chipboard 3, wood, wood residues, wooden moldings, etc. are first chipped in a first process step, i.e. the desired optimal chip shape is produced by suitable crushing processes using knife ring chippers, long wood chippers, etc. In a second process step, the chips produced in this way are dried until final moisture levels in the range of 0.5-2% are reached. The chips are then fractionated, i.e. divided into sieve fractions. The so-called "top and middle layer chips" are then separately glued with heat-curing resins, primarily urea, melamine or phenolic resins or mixtures thereof or with polymeric diisocyanates (PMDI) or also with natural binding agents such as tannin and/or lignin resins. After machining, drying and gluing, the fourth process step involves scattering the glued chips by means of wind or throwing, which produces a so-called "chip mat" 4 or a "chip fleece". Looking at the fleece height, the smaller or finer top layer chips are primarily arranged at the top and bottom, while the coarser middle layer chips are primarily found in the middle of the chip mat 4. In this arrangement, the glued chip mat 4 is then fed to a press 10, in which the chip mat 4 is compressed to the final desired chipboard thickness by the simultaneous action of heat and pressure, while the thermosetting binder hardens at the same time.

The chemical reactivities of the binding agents used in the top and middle layers (UF, MF, PF, MUF, PMDI etc.) must be tailored to the requirements of the compaction reactions. Conversely, the moisture content of the chipboard being produced must be precisely measured to ensure optimum curing. reaction can take place in the top and middle layers and the chipboard 3 does not delaminate, ie burst, due to excessive internal steam pressure at the moment it leaves the press 10 and the external pressing pressure is thus removed. The length of the pressing time is primarily influenced by how quickly the binding agent hardens.

The press is a continuous multi-stage press 10 with a rotating press belt 12, having an upper and a lower belt. The press width is, for example, 2.20 m.

When the large-volume fleece is fed to the press 10 in the form of a chip mat 4 that is initially 100 to 120 mm thick, for example, compression initially takes place during the so-called "pre-pressing". The mat 4 is compressed by the press mouth to its final thickness of 22 mm, for example. The press jaw temperature during "pre-pressing" is 250°C, for example. After a pre-heating phase of 80 seconds, for example, the temperature of the water in the outer layers of the mat 4 following "pre-pressing" is 70 to 80°C, for example. The press 10 is then sealed. The press gap 5 again serves as a pressure chamber.

To seal the press 10, only the press mouth and the press gap 5 must be sealed. Sealing the entire press 10 is not necessary. The press gap 5 can be sealed using a simple pressure seal or contact seal. To do this, the press gap 5 is sealed laterally using sealing devices attached to both sides of the press 10. The design effort is reduced if each side of the press 10 is assigned a separate sealing device.

Such a sealing device is, for example, a rotating, segmented pressure chain 19 or a rotating pressure belt that seals one side of the press 10. Such a pressure chain 19 consists of links arranged in a row. The pressure chain 19 or the pressure belt is attached to both the upper belt and the lower belt and presses between the belts against the narrow side surfaces of the mat 4. The pressure chain 19 or the pressure belt consists, for example, of a temperature-stable hard rubber material.

In a particular embodiment of the invention, the compression of the mat 4 already achieved by the "pre-pressing" is used. It may then even be necessary to release air from the pressing chamber during the "pre-pressing" or after it and before applying a sealing device in order to prevent an excessive increase in pressure.

However, the sealing of the press gap 5 usually only takes place after "pre-pressing", i.e. after the mat 4 has reached its final thickness, or immediately after this. The sealing device only comes into operation at this corresponding position of the press 10, i.e. for example the pressure chains 19 are placed on the sides of the press 10. This position is usually relatively far forward, i.e. the pressure chain 19 starts as soon as possible with the press mouth. The sealing towards the press mouth preferably takes place without any further construction effort, simply due to the existence of the mat 4 located there, which has already been pressed or has just been fed in.

The sealing devices 19 extend on both sides of the press 10 in the direction of the press outlet. However, they do not extend to the end of the press 10, but end beforehand. This determines the point in time at which the pressure is released.

During the pressing time in which the pressure chain 19 seals the press gap 5, a further increase in temperature and pressure takes place in a controlled manner up to the desired target values, or these values have already been reached and are only kept constant. Before the end of the pressing time, the pressure that has built up is then relieved. To do this, the side surfaces of the mat 4 are opened by removing the pressure chain 19. This is advantageously carried out in a targeted, step-by-step manner and with the aid of an appropriate pressure control system. The desired burst of steam then takes place more or less suddenly. To be more precise, with a process air pressure of, for example, 3 bar, a temperature of, for example, 115°C to 123°C results in the top layer of the mat 4. If, according to the invention, relief (relaxation) then takes place because the pressure chain 19 is no longer in contact with the sides of the press 10, air can escape from the porous middle layer to the outside. When the pressure is released, the water evaporates from the outer layers of mat 4. A large amount of hydrogen is suddenly created, which moves into the middle layer (“forced steam burst”). Once in the middle layer, the water vapor condenses again. This introduces so much heat into the middle layer that the temperature (internal plate temperature) rises very quickly. Mat 4 is suddenly heated through. This leads to much faster curing compared to the previous technology. Chemical reactions take place more quickly. This shortens the pressing times. The speed of the Press can be increased by 15% or more depending on the version.

It can be provided that the press 10 is initially operated completely normally until the desired feed rate is reached, e.g. 4 seconds per millimeter of plate thickness. If this is the case, the seal according to the invention, for example in the form of the pressure chains 19, is "switched on" using the appropriate pressure control. The exact positions at which the pressure chains 19 are applied or removed again can vary depending on the press system and operating conditions. The press 10 is preferably designed in such a way that variable positioning of the sealing device is possible. If the sealing device is applied, the feed rate can be increased, for example to 3 seconds per millimeter of plate thickness.

In order to achieve the functionality described, it is preferably provided that the pressure chain 19 is designed in segments. This segmentation of the pressure chain 19 is therefore advantageously not only designed in such a way that it allows the pressure chain to be redirected and thus relatively easy to handle. Rather, a corresponding design of the pressure chain 19 also allows the chain to be applied and removed at different locations. In other words, the sealing device is preferably designed in such a way that both the point on the side of the press 10 at which the sealing device is applied, i.e. sealing begins, and the point at which the sealing device is removed again, i.e. sealing is canceled, are variable, in particular freely selectable.

All features presented in the description, the figure and the following claims can be essential to the invention both individually and in any combination with one another.

List of reference symbols

3

chipboard

4

chipboard mat

5

press nip

10

press

12

press belt

19

pressure chain

Claims (7)

Method for producing a wood-based molded part (3) using a wood-based base material and a heat-curable binding agent by pressing in a continuously operating press (10) with a pressing chamber (5), the pressing chamber (5) being designed in the form of a pressing gap (5) as a substantially closed pressure chamber, wherein, to harden the binding agent, heat is transferred to the wood-based molded part in the form of a steam blast, wherein, before the heat is transferred in the form of a steam blast, the process air pressure prevailing in the pressing gap (5) is increased compared to the atmospheric air pressure prevailing outside the pressing gap (5) by means of a device (6, 7) for generating an overpressure, wherein, during pressing, a targeted reduction in the process air pressure takes place, wherein the reduction in the process air pressure takes place with the aid of a sealing device (19) which seals the pressing gap (5) on both sides over a partial length of the press (10). and wherein the process air pressure is controlled via a pressure control connected to the sealing device (19) and which can influence the function of the sealing device (19). procedure according to Claim 1 , characterized in that a partial pressure relief takes place before the end of the pressing time. procedure according to Claim 1 , characterized in that complete pressure relief takes place before the end of the pressing time. Method according to one of the Claims 1 until 3 , characterized in that the process air pressure is at least 0.5 bar above the atmospheric air pressure. Continuous press (10) for the production of a wood-based molded part (3) using a wood-based base material and a heat-curable binding agent, wherein heat is transferred to the wood-based molded part in the form of a steam jet to cure the binding agent, wherein the press (10) has a rotating process belt (12) with an upper and lower belt and a pressing chamber (5) and a device (6, 7) for generating an overpressure such that, before the heat transfer in the form of a steam jet, the process air pressure prevailing in the pressing chamber (5) can be increased compared to the atmospheric air pressure prevailing outside the pressing chamber (5), wherein the pressing chamber (5) is designed in the form of a pressing gap (5) as an essentially closed pressure chamber, wherein the process air pressure can be reduced in a targeted manner during pressing with the aid of a sealing device (19), wherein the sealing device (19) seals the pressing gap (5) seals on both sides over a partial length of the press (10) and wherein a pressure control is provided which is connected to the sealing device (19) and which can influence the function of the sealing device (19). press after claim 5 , characterized in that the lateral sealing of the press gap (5) is carried out by sealing devices (19) attached laterally to both sides of the press (10), preferably with each side of the press (10) being assigned a separate sealing device (19). press after claim 5 or 6 , characterized in that the sealing device (19) is designed as a circumferential, segmented pressure chain or as a circumferential pressure band, wherein the pressure chain consists of links arranged in a row, wherein the pressure chain or the pressure band is attached to both the upper band and the lower band and presses between the bands against the lateral narrow surfaces of the wood-based material molded part (3).

Images