DE202013012197U1 - Press for the production of a wood material molding - Google Patents

Abstract

Press (1, 10) for the production of a wood-based molded part (3) using a wood-based material and a thermosetting binder, wherein for curing of the binder, a heat transfer into the wood material molding in the form of a steam blast, wherein the Einetagenpresse (1) a Press room (5), the continuous press (1) a pressing area (5) and a device (6, 7) for generating an overpressure such that before the heat transfer in the form of a burst of steam prevailing in the baling chamber (5) process air pressure opposite the outside of the baling chamber (5) prevailing atmospheric pressure can be increased, characterized in that by means of a pressure relief device (8, 19) during the pressing of the process air pressure is selectively lowered.

Description

The invention relates to the production of a wood-based molded part using a wood-based material and a thermosetting binder by pressing, wherein for curing of the binder, a heat transfer takes place in the wood material molding in the form of a steam blast.

The duration of the pressing time is primarily influenced by how fast the binder hardens. The example of a three-layer wood-based panel, which consists of a middle layer, an upper and a lower cover layer, the solutions known from the prior art are described below.

To produce the plate, a three-layer constructed wood material mat (fleece), consisting of the wood material base material and a thermosetting binder, fed to a press. Subsequently, a Heißpreßvorgang takes place. The curing of the binder (glue) in the outer cover layers by direct heat through heated press plates or bands. Due to the heat energy introduced into the plate on the one hand and the moisture in the plate on the other hand, a water vapor pressure gradient is formed in the plate.

The heat energy required to cure the middle layer is introduced into the plate via the so-called steam jet. For this purpose, the outer press plates are heated, for example, to 0 ° Celsius. When pressing the water (glue water) is then heated in the outer layers and transferred when the boiling point (100 ° C), suddenly in the vapor phase. This steam shoots vertically from both sides of the plate towards the center of the plate due to the water vapor pressure drop. This process is called steam shock.

Due to the temperature gradient between the outer sides of the outer layers and the middle of the middle layer (the temperature difference is for example 75 ° C), the vapor condenses in the still cool middle layer. It releases heat of condensation, which raises the temperature in the middle layer. The chemical curing reactions in the middle layer are faster and it takes less time for the binder to harden, resulting in a shorter press time. This steam jet principle is used in the production of numerous wood-based molded parts, for example in the production of chipboard, MDF, OSB, etc.

From the prior art, it is known to optimize the steam pulse principle in that the water vapor is previously heated and injected as superheated steam under pressure in the wood material molding. This is also referred to as steam injection technology. As a result, a shortening of the pressing time is possible to a limited extent.

However, it is disadvantageous that in the steam injection technique more water also gets into the interior of the wood-based molded part. Because of the basic principle of pressure and counterpressure, the internal pressure in the wood-based molded part is greatly increased in the steam injection technique. When the press opens, the binder must already be cured inside the molding so far that the internal vapor pressure does not lead to damage (spalling of parts) or destruction of the molding (delamination). It is attempted to counter this disadvantage with expensive cooling devices for cooling the moldings after hot pressing. Nevertheless, the press must remain closed comparatively long in the steam injection technique, so that the time advantage of the rapid curing of the binder is partially canceled.

In DE 1 2008 026 258 It was proposed to let the burst of steam under elevated pressure take place. The method described therein is characterized in that prior to the heat transfer in the form of a steam surge prevailing in the compression chamber process air pressure is increased relative to the prevailing outside the baling chamber atmospheric air pressure, but without the wood material molding moisture, especially in the form of water vapor to feed. A provided for the production of such a wood-based molded part press is characterized by a compression chamber and a device for generating an overpressure such that are increased before the heat transfer in the form of a burst of steam prevailing in the press room process air pressure relative to the prevailing outside of the baling chamber atmospheric air pressure can, but without, however, the wood material molding moisture, especially in the form of water vapor, supply.

By applying and maintaining an external overpressure during the pressing process is at DE 10 2008 026 258 ensures that the boiling point of the water is increased beyond 10 ° C. This has the consequence that with a shot of steam at z. B. 1 ° C significantly more heat energy can be introduced into the middle layer of the wood-based molding. This increased amount of heat that is released in the condensation of the water vapor in the still cold middle layer leads to a much higher temperature in the middle layer compared to the conventional steam injection technique, with the result that the curing reactions of the glue run much faster. Summarized with the in DE 10 2008 026 258 described technique of the shot of steam at a higher temperature, which leads to a shortening of the pressing time.

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

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

The core of the present invention is that during the pressing a targeted reduction of the process air pressure to initiate the steam pulse takes place. For this purpose, a press according to the invention is provided with a pressure relief device, so that during the pressing of the process air pressure targeted, even alternately lowered. By a targeted pressure relief during the pressing a sudden heating of the material, whereby timing and flow of the heating can be influenced.

The present invention is based on the in DE 1 2008 026 258 described basic knowledge, as described below:
Thereafter, leading to a technological dead end steam injection technique in which hot steam is pressed under pressure into the molding, no longer pursued. Instead, there is a return to the original steam shock technique, in which the steam pulse is automatically on reaching the boiling point. This steam shock technique will be in DE 1 2008 026 258 characterized in that during the pressing process, at least in the baling chamber of the press, the air pressure is greater than the atmospheric pressure of the environment. The pressing process takes place in other words under pressure, z. B. at 1.5 bar. At such an overpressure, the water evaporates at higher temperatures, for example at 11 ° C. The shot of steam is still automatic, but this time at a higher temperature. In comparison with a running under atmospheric pressure process, the shot of steam may take place at a somewhat later date, but with a correspondingly higher energy content corresponding to the higher boiling temperature.

In the DE 1 2008 026 258 described invention makes use of the dependence of boiling temperature and boiling pressure of each other to advantage. By increasing the pressure, for example, 0.5 bar = 500 hPa, an increase in the boiling point of the water from 10 ° C to about 11 ° C is reached. This increases the energy content of the water vapor compared to a process occurring at atmospheric pressure. When using the same amount of water, more heat can be transferred to the interior of the wood-based molding using the steam blast. This increases the achievable temperature in the middle class. According to the van't-Hoff rule (RGT rule), according to which the reaction rate is approximately doubled when the temperature is increased by 1 ° C, thus resulting in a significantly increased reaction rate for the chemical curing reactions of the binder. As a result, the pressing time can be significantly shortened, 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 shock technique, in which the heat energy introduced into the wood-based molded part is substantially increased by the amount of water vapor used is increased, founded in DE 1 2008 026 258 described invention on the idea to increase the reaction rate of the curing reactions of the binder in that with an equal amount of water vapor we transfer more heat energy. As a result, without the disadvantages of increased internal pressure, a high process temperature can be achieved.

The resulting water vapor is that portion of the moisture in the air that is already present in the air anyway, provided that no dry peel is used as the process atmosphere, as well as the water vapor that has its origin in the glue water of the cover layers.

The following presentation should again the difference between the known steam injection technique and in DE 1 2008 026 258 illustrate the invention described:
In the conventional steam injection technique, the partial pressure ratios result from a combination of (moist) air on the one hand and additionally superheated steam introduced into the system on the other hand: P (total) = p (air) + p (water)

When the boiling point of 10 ° C is reached, the steam pulse results from the water vapor contained in the moist air and from the water vapor, which has its origin in the glue water of the outer layers, as well as from the additionally introduced superheated steam.

At the in DE 1 2008 026 258 described invention is dispensed with the introduction of superheated steam. In the pressure chamber is only the usual process atmosphere, in the Usually air in usual composition (78% nitrogen, 21% oxygen, ...). It follows: Ptotal = P (air)

The burst of steam that results when reaching the (elevated) boiling point, for example, 11 ° C, 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 overpressure, a pressure chamber is provided in which the desired overpressure prevails. Under the atmospheric air pressure is then the pressure prevailing outside the pressure chamber in the atmosphere, caused by the weight of the air pressure to understand Under process air pressure, however, is the air pressure of the environment in which the pressing takes place. Since the pressing always takes place in a compression space, for example in the press nip arranged between press plates or belts, the process air pressure is in other words the (at least) prevailing in the compression chamber air pressure to which the wood-based molded part to be produced is exposed. In one embodiment of the in DE 1 2008 026 258 described invention, the baling chamber, in particular in the form of the press nip, designed to achieve the desired overpressure as a substantially closed pressure chamber. In another embodiment of the in DE 1 2008 026 258 described invention, a pressure chamber is provided which encloses next to the actual pressing chamber further parts of the press. In a further embodiment of the in DE 1 2008 026 258 described invention, the press on a completely surrounding pressure chamber; the entire press is then inside the pressure chamber.

In the DE 1 2008 026 258 For this purpose, the press described has suitable technical devices which are familiar to the person skilled in the art and therefore need not be listed in detail here. For example, if the press nip formed as a pressure chamber, so devices for sealing the press nip are provided, for. B. laterally mounted sealing rings, pressure devices, etc. In discontinuous presses, such as discontinuous single or multi-day presses, it is possible to provide lateral sealing surfaces that seal all four sides when closing the press. In addition to the structural elements and seals for delimiting the pressure chamber, a device for generating an overpressure is to be provided. It may be an overpressure container that provides an overpressure of, for example, 0.5 to 1 bar. For this an overpressure can be fed into the pressure chamber via pressure lines. Thus, the boiling point of the water on z. B. 11 ° C to 0 ° C can be adjusted.

In addition to the above findings, as in DE 1 2008 026 258 The present invention is based on the following considerations:
While in the original steam shock process, the steam was always spontaneous and also in the DE 1 2008 026 25 8 described technique, a spontaneous shot of steam is caused, the present invention proposes to maintain the principle of the steam blast under increased pressure, but to influence the timing of the steam blast. In other words, there is no spontaneous burst of steam anymore. Instead, the timing of the steam blast is controlled specifically. The steam burst is in other words initiated. The following is therefore also spoken of a "forced steam blast". In other words, a skilful control of the pressure curves during the pressing operation forces a steam movement (shot of steam) inside the mat.

A basic idea of the present invention thus lies in an additional relief step, namely a deliberate lowering of the previously established process air pressure during the pressing. In other words, there is a pressure relief before the end of the pressing time, this pressure relief takes place, depending on the application, either partially or completely. In other words, even after the pressure relief, an increased process air pressure may be present or else the process air pressure corresponds again to the atmospheric air pressure prevailing outside the compression space.

This targeted pressure reduction extremely rapid temperature increases are achieved in the fleece. The internal temperature not only rises very fast, but also to levels that are usually not reached. This is a significantly increased energy content. In other words, more energy can be introduced into the middle layer of the mat, there is a sudden heating of the material, combined with a high energy input, resulting in a significant reduction in the pressing times.

This principle will be explained in more detail below. According to the invention, the water located on the surface of the mat is prevented from boiling by the increased pressure. As a result, temperatures of well over 10 ° C can be achieved at this point. By deliberately lowering the process air pressure, there is an abrupt increase in the internal temperature of the mat, which is caused by the sudden formation of steam due to the pressure relief. As is known with the steam jet principle, here too the water vapor can only move towards the middle Spread the mat, which leads to very high temperature rises. In this case, compared with all other steam injection techniques known from the prior art, much larger temperature increases can be measured in an extremely short time. Thus, for example, in the case of a nonwoven in which a pressure relief was carried out after about 3 minutes press time, an increase in the internal temperature of 70 ° C by 47 ° K to 117 ° C within 1 second after the pressure relief.

A significant advantage of the present invention is that by the targeted forcing the steam blast the time of the steam blast, d. 11. The time at which the energy is sent to the middle layer of the mat can be optimally selected. As a result, this leads to a further shortening of the pressing time.

An optimal choice of the point in time of the steam blast means that the time of pressure release is chosen so that the remaining time left by the web in the press, just enough to cure the wood material molding, d. H. to stabilize the chemical bonds at least so far that the wood-base molding does not burst (delaminate) when the press is opened.

At the same time, forcing the steam pulse through an influenceable pressure relief means that the strength of the steam pulse can be influenced in a targeted manner. In other words, the manner in which the depressurization is carried out can influence the speed with which the jet of steam flows in the direction of the middle layer. This can be regulated by a defined lowering of the process pressure. If, for example, the process air pressure is spontaneously reduced to 1 bar, the steam pulse will be vehement. If the pressure is reduced within a period of, for example, a few seconds, this is more gentle for the structure of the molding. Too rapid pressure relief, which could possibly lead to damage to the structure of the wood matrix, is thus avoided. With other places, a delayed lowering of the process air pressure can protect the structure of the wood-based material Fomteils to be produced. Therefore, it is advantageous if a pressure control is provided by means of which the sealing device can be influenced so that the pressure in the press room can be selectively changed.

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

In the previously known methods had to be expected with more or less long process times that were difficult to influence. A control or regulation of the process was not or only partially possible. With the present invention, extended process control and control is possible. While in the known from the prior art method as the only parameter of the process air pressure was variable in the present invention in addition to this process air pressure in addition, the time of pressure reduction (pressure relief) and the speed of pressure reduction can be influenced. As a result, it is possible in an advantageous manner to influence the material structure of the wood-base molded parts produced and thus, above all, their strength properties.

As well as the in DE 1 2008 026 258 described method St it is not provided in the present invention, the wood-based molding during the pressing moisture, especially in the form of water vapor, supply. The moisture required for the steam pulse is already contained in the wood-based mat. However, an amount of moisture may be added to the molded article prior to the pressing operation, preferably by spraying or otherwise spreading onto the nonwoven fabric. The amount of sprayed water, depending on the material, for example, 1 to 2 g per side and millimeter plate thickness. By introducing this additional moisture, the subsequent burst of steam is enhanced.

Like that in DE 1 2008 026 258 described method is also the present method in the production of numerous wood-based molded parts can be used, for example, in the production of particleboard, MDF, HDF, OSB, etc. It may be in the wood-based molded parts to individual parts or a continuous through the press to be running continuous part. The method can be used both on discontinuous, as well as on continuously operating presses, for example on single or multi-day presses, double belt presses, etc.

Depending on which type of wood-based material molded parts is to be produced, the wood-base material is chips, fibers, stalls, etc. Thermosetting binders are, for example, 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 are used.

Embodiments of the invention are explained below with reference to the drawings. Show here

1 a representation of the present invention with reference to a discontinuous Einetagenpresse,

2 a representation of the present invention with reference to a continuously operating press.

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

In the production of a chipboard 3 In a first process step, wood, wood residues, wood moldings etc. are first machined, ie the desired optimum chip shape is produced by suitable comminution methods using knife ring chippers, long wood chippers, etc. In a second process step, the chips thus produced are dried until final humidities in the range of 0.5-2% are reached. Subsequently, the chips are fractionated, ie divided into sieve fractions. Thereafter, the separate gluing of the so-called. Cover and middle layer chips with thermosetting resins, especially urea, melamine or phenolic resins or mixtures thereof or with polymeric diisocyanates (PMDI) or with natural binders such as tannin and / or lignin. After machining, drying and gluing, the fourth step of the process is the scattering of the glued chips by means of wind or throw scattering, through which a so-called "chip mat" 4 or a "chipboard" is generated. Viewed over the fleece height, the smaller and finer cover shavings are primarily arranged at the top and bottom, while the coarser middle shavings are located predominantly in the middle of the chip mat 4 find. In this arrangement, the glued chip mat 4 now a press 1 fed, in which by simultaneous action of heat and pressure compression of the chip mat 4 to the final desired chipboard thickness takes place with simultaneous curing of the thermosetting binder. In 1 is an example of a discontinuous Einetagenpresse 1 represented, the press plates 2 having.

The chemical reactivities of the binders used in the top and middle layer (UF, MF, PF, MUF, PMDI, etc.) must be matched to the requirements of the compression reactions. Conversely, the moisture balance of the chipboard just emerging must be sized so that an optimal curing reaction in the top and middle layers can be done and the chipboard 3 not at the moment when they press 1 leaves and the external pressing pressure thus eliminated, delaminated by excessive internal vapor pressure, ie burst. The duration of the pressing time is primarily influenced by how fast the binder hardens.

The chip mat 4 gets the press 1 supplied, whose press nip 5 is designed as a pressure chamber. The press gap 5 is over pressure lines 6 with an overpressure container 7 connected, with the help of which after the introduction of the chip mat 4 and closing the press nip 5 by suitable seals (not shown), an overpressure of 0.5 bar in the press nip 5 is produced. Moisture, especially in the form of water vapor is the press nip 50 or the chip mat 4 not supplied. By increasing the process air pressure, there is an increase in the boiling temperature within the press nip 5 , The resulting at 11 ° C water vapor carries a much higher energy content, with the result that with the steam shot also significantly more condensation heat in the middle layer of the chip mat 4 arrives. This in turn means that the curing reactions of the binder in the middle layer proceed much faster. Thus, will. in the middle layer significantly faster sufficient strength achieved.

Thus, the pressing time can be significantly shortened or the feed rate of the press 1 be increased significantly without the risk that the chipboard 3 when extending from the press 1 delaminated. The burst of steam is not spontaneous, but is initiated by that a pressure relief valve 8th is opened before the end of the pressing time.

Another embodiment will be with reference to 2 described. The press is a continuous (floor) press 1 with a circulating press belt 12 , comprising a top and a bottom band. The press width is for example 2.20 m.

If the bulky fleece in the form of a first example, 0 to 120 mm thick chip mat 4 the press 10 is fed, takes place during the so-called "pre-pressing" first a compression. The mat 4 is compressed by the press mouth to its final thickness of, for example, 22 mm. The Preßbackentemperatur during the "pre-pressing" is for example 250 ° C. After a preheating of, for example, 80 seconds, the temperature of the water in the outer layers of the mat 4 following the "pre-pressing" z. B. 70 to 80 ° C. Subsequently, the Press 10 sealed. In this case, the press nip is used 5 again as a pressure chamber.

For sealing the press 10 only has the press mouth and the press nip 5 be sealed. A seal of the entire press 10 not necessary. The press gap 5 can be sealed using a simple pressure seal or pressure seal. This is done for a lateral sealing of the press nip 5 through to both sides of the press 10 Side-mounted sealing devices. The design effort is thereby reduced if each side of the press 10 a separate sealing device is assigned.

Such a sealing device is, for example, a circumferential, segmented pressure chain 19 or a circulating pressure band, which is one side of the press 10 seals. Such a pressure chain 19 consists of strung together limbs. The pressure chain 19 or the pressure belt sets in both the upper band, as well as on the lower band and presses between the bands against the lateral narrow surfaces of the mat 4 , The pressure chain 19 or the pressure band consists for example of a temperature-stable hard rubber material.

In a particular embodiment of the invention, the compression of the mat already effected by the "pre-pressing" is achieved 4 used. It may then even be necessary to vent air from the compression chamber during "prepressing" or subsequent thereto and before applying a sealing device to prevent excessive pressure rise.

The sealing of the press nip 5 However, usually takes place only after the "pre-pressing", ie after the mat 4 has reached its final thickness, or immediately thereafter. Only at this corresponding position of the press 10 If the sealing device comes into operation, so for example, the pressure chains 19 to the pages of the press 10 created. This position is usually relatively far forward, ie the pressure chain 19 start as possible with the press mouth. The seal towards the press mouth is preferably carried out without any further design effort, solely on account of the existence of the already existing, already pressed, or just fed, mat 4 ,

The sealing devices 19 extend to both sides of the press 10 in the direction of the press exit. They do not last until the end of the press 10 but ends before. This determines the time of the pressure release.

During the pressing time, in which the pressure chain 19 the press gap 5 seals, there is a further increase of temperature and pressure up to the desired target values, or these values have already been reached and are only kept constant. Before the expiration of the pressing time then takes place a discharge of the pressure built up. To do this, open the side surfaces of the mat 4 by removing the pressure chain 19 Will get removed. This is advantageously targeted, gradually and accomplished with the aid of a corresponding pressure control. Then takes place more or less suddenly the desired steam burst. More precisely, at a process air pressure of, for example, 3 bar, a temperature of for example 115 ° C. to 123 ° C. results in the cover layer of the mat 4 , Then according to the invention takes place a discharge (relaxation), because the pressure chain 19 no longer on the pages of the press 10 is present, then air can escape from the porous middle layer to the outside. With the pressure relief, the water evaporates from the cover layers of the mat 4 , It suddenly produces a lot of hydrogen, which moves into the middle class ("forced steam blast"). Once in the middle class, the steam condenses again. As a result, so much heat is introduced into the middle layer, that there the temperature (internal plate temperature) increases very quickly. It comes to a sudden warming of the mat 4 , This leads to a much faster curing compared to the prior art. Chemical reactions are faster. This shortens the pressing times. Depending on the version, the speed of the press can be increased by 15% or more.

It can be provided the press 10 initially operate normally, until the desired feed rate is reached, z. B. 4 seconds per millimeter plate thickness. If this is the case, using the appropriate pressure control, the seal according to the invention, for example in the form of pressure chains 19 , "Connected". The exact positions where the pressure chains 19 can be applied or removed depending on the press system and operating conditions. Preferably, the press 10 designed such that a variable positioning of the sealing device is possible. If the sealing device is on, the feed rate can be increased, for example to 3 seconds per millimeter plate thickness. In order to achieve the described functionality, it is preferably provided that the pressure chain 19 segmented form. This segmentation of the pressure chain 19 is therefore advantageously not only designed so that it allows a deflection of the print chain and thus a comparatively simple handling. Rather, allows a corresponding design of the print chain 19 also a locally variable application and lifting of the chain. In other words, the sealing device is preferably designed such that both the point on the side of the press 10 at the the Sealing is applied, a seal thus begins, as well as that point at which the sealing device is removed again, the sealing is thus canceled, variable, in particular, is freely selectable.

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

LIST OF REFERENCE NUMBERS

1

Press

2

press plate

3

chipboard

4

chip mat

5

nip

6

pressure line

7

Pressure vessels

8th

Pressure relief valve

10

Press

12

press belt

19

pressure chain

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• DE 12008026258 [0008, 0013, 0013, 0014, 0015, 0017, 0019, 0021, 0021, 0021, 0022, 0023, 0023, 0032, 0033]
• DE 102008026258 [0009, 0009]

Claims (4)

Press ( 1 . 10 ) for the production of a wood-based molded part ( 3 ) using a wood material base material and a thermosetting binder, wherein for the curing of the binder, a heat transfer into the wood material molding in the form of a steam shock, wherein the Einetagenpresse ( 1 ) a press room ( 5 ), the continuous press ( 1 ) a pressing area ( 5 ) and a device ( 6 . 7 ) for generating an overpressure such that before the heat transfer in the form of a burst of steam in the baling chamber ( 5 ) prevailing process air pressure compared to the outside of the press room ( 5 ) prevailing atmospheric pressure can be increased, characterized in that by means of a pressure relief device ( 8th . 19 ) is selectively lowered during pressing the process air pressure. Press ( 1 . 10 ) according to claim 1, characterized in that the baling chamber ( 5 ), in particular in the form of a press nip, is designed as a substantially closed pressure chamber. Press ( 1 . 10 ) according to claim 1 or 2, characterized in that at least one sealing device ( 19 ) the press nip ( 5 ) on both sides over a partial length of the press ( 10 ) seals. Press ( 1 . 10 ) according to one of claims 1 to 3, characterized by a with the sealing device ( 19 ) and the function of the sealing device ( 19 ) influenceable pressure control.

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