Method and apparatus for producing material sheets from a pressed mat

Abstract

Method for producing material sheets from a material spread to form a pressed mat, which is mixed with at least one binder that can be cured by heat and / or pressure, characterized by the fact that The pressing mat (1) is compacted in a double belt press (10) with steel belts (12) that are warmer than the pressing mat (1) and heated by heat conduction, whereby the surface layers (3) in contact with the steel belts (12) are heated to a temperature above the setting temperature of the binder and harden and The uncured parts of the pressed material mat (1) in the middle layer (3) are heated and cured in a subsequent double-belt continuous oven (20) by means of electromagnetic waves to a temperature above the setting temperature of the binder.

Description

[0001] The invention relates to methods for producing material sheets from a material scattered to form a pressed mat, according to the preamble of claim 1.

[0002] Furthermore, the invention relates to a device according to the preamble of claim 22 for the production of material plates.

[0003] The production of engineered wood panels by pressing free-flowing or granular materials in calender, indexing, or double-belt presses is a well-known state of the art. Mixtures of lignocellulosic materials, such as wood, woody plants, or annuals, are granulated with or without binders in one or more layers and cured under pressure and / or heat to form stable engineered wood panels. These panels can be pliable or flexible (thin MDF panels made from fibers) but still exhibit a certain inherent stiffness against pressure. Engineered wood panels are also available for furniture construction, mostly particleboard (usually multi-layered and laminated with foils) or oriented strand board (OSB) made from flat chips. Substitution with plastics, recycled wood, or other fillers is common. Such processes or systems are known, for example, under CA1270433A, DE19718771A1, or DE102019000767A1.

[0004] Binders, mostly methylene diphenyl isocyanate (MDI) or polymeric methylene diphenyl isocyanate (pMDI), but also other curable adhesives, are used in their production. The worldwide ban on formaldehyde, boric acid, and sodium borates, which can be used in such binders, has led to a change in thinking. For decades, the industry has been trying to meet increasingly stringent standards for formaldehyde emissions in indoor air and furniture manufacturing.

[0005] One approach is the use of chemical formaldehyde scavengers in a composite board, which either absorb or convert the formaldehyde during the curing of the binder. However, these generally have the disadvantage of significantly extending the curing time. In addition, numerous attempts have been made to activate the lignin inherent in lignified cells as a binder. Water-based and starch-based binders, as well as adhesives based on epoxidized vegetable oils, synthetic lignin-based polymers, and other alternative binders have also been the subject of research and development for the production of composite boards. However, it has been shown that the curing time and / or temperature is significantly longer or higher than with the conventional isocyanate-based binders.All these binders have in common that their setting behavior changes significantly during the production of the material sheets, particularly increasing considerably compared to standard commercial applications. It is also known that additives can be added to the binder to facilitate excitation and thus heating by electromagnetic radiation. These additives can also be mixed directly into the material itself that forms the pressed mat.

[0006] It is well known and technically standard practice that a pressed material mat undergoes deaeration by pre-compression in a pre-press before entering the main press. During or after this pre-press, the mat can be preheated using steam, hot air, or electromagnetic waves. The purpose of this preheating is not to harden the binder, but rather to introduce the pre-pressed material mat into the main press already warmed, so that the heat transfer (conduction) through the steel belts allows the binder to reach its setting point as quickly as possible. This results in either a shorter press length or a higher production speed.

[0007] Preheating with electromagnetic waves is very demanding in terms of process and plant engineering. Nevertheless, this technique has proven effective for heating the press mat. A disadvantage of preheating using electromagnetic waves is that, if the mat is openly rejected before the main press, unnecessarily heated material is cooled again. Furthermore, the start-up phase, until a balanced energy budget is established for the production of material sheets, is difficult to automate, and its reduction usually depends on experienced operators. These disadvantages are particularly pronounced with very dry or thick press mats.

[0008] In the production of engineered sheets, it is also known to utilize a so-called steam burst effect in the infeed area of ​​a continuous press. Upon contact with the hot steel belts of the press, moisture, sometimes applied to the material mat beforehand via spray nozzles, evaporates, and the steam flows into the center of the mat to heat it. Besides the disadvantage that this creates a temperature sink at the steel belts, which then needs to be equalized, a problem with this effect is that steam pressure builds up or remains within the material mat as it passes through the continuous press. If the steel belts lift away from the material mat at the press exit, and the degree of hardening and thus the strength of the material mat is not greater than the steam pressure, this can lead to surface cracking.Although large-scale cracks are now under control from a process technology perspective, macro and macro-cracks on the surface regularly downgrade material sheets to B-grade quality, as these can show through during subsequent finishing processes.

[0009] Pressed material mats can be single-layered or multi-layered. Particleboard is generally multi-layered and may also have a graded particle size distribution, so that the coarser material is located in the central layer between the surface layers, and finer material layers are applied to one or both surface layers. OSB boards are also multi-layered, but usually have differently oriented layers and can also vary in material size. Single-layer pressed material mats (usually MDF) can have fine material or dust added to the surface; these can then also be described as multi-layered.

[0010] Besides the commercially successful processes, presses, and systems described in the state of the art, there are also various special types of presses that attempt to achieve direct curing in the main pressing area using electromagnetic waves. These attempts have generally not been commercially successful, as the energy or technical costs were usually too high. The required press pressure of several N / mm² further complicates matters. 2 in conjunction with strong compression bands, the application of electromagnetic waves or correspondingly permeable compression bands is diametrically opposed.

[0011] The object of the present invention is to provide a method and a device that makes it possible to avoid the disadvantages mentioned above compared to the prior art. In particular, it should make it possible to build the existing double belt presses smaller and to shift the curing area into the electromagnetically operated continuous oven.

[0012] The invention essentially relates to a method for producing material sheets in which material scattered to form a pressable mat, which is mixed with at least one binder that can be hardened by heat and / or pressure, is hardened.

[0013] The object of the invention is achieved for the method by compressing the pressed material mat in a double belt press with steel belts that are warmer than the pressed material mat and heating it by heat conduction, whereby the surface layers in contact with the steel belts are heated to a temperature above the setting temperature of the binder and harden and The uncured parts of the pressed material mat in the middle layer are heated and cured in a subsequent double-belt continuous oven using electromagnetic waves to a temperature above the setting temperature of the binder.

[0014] The invention has surprisingly demonstrated that it is possible to significantly reduce the previously known effort required for continuously operating double-belt presses with a length of 25 meters or more by essentially using the double-belt press only for curing the surface layers, while the main part of the curing process can be carried out by electromagnetic radiation in the subsequent separate continuous oven. This eliminates the need for excessively long steel belts and the associated effort required for their guidance.

[0015] Preferably, a pressure of more than 3 N / mm can be applied in the double belt press. 2 , preferably more than 4 N / mm 2 , especially preferred to be more than 5 N / mm 2The coatings are applied to the pressing mat. The direct heat transfer from the heated steel belts hardens the coatings, which are preferably dimensioned in thickness to reduce the springback of the pressing mat after it exits the double belt press and to prevent breakage before reaching the double belt continuous oven.

[0016] Advantageously, pressure rollers or sliding shoes can be arranged in the transition between the double belt press and the double belt continuous furnace to moderate the springback.

[0017] Alternatively or cumulatively, the cured surface layers, after leaving the double-belt press, can have a thickness of more than 1 mm, preferably more than 2 mm, and most preferably more than 4 mm and up to 6 mm. This will generally also depend on the expected springback forces to prevent the surface layers from cracking at the transition.

[0018] Alternatively or cumulatively, the thickness of both cured surface layers can be 15%, particularly preferably 12%, and most preferably 6% to 10%, based on the thickness of the material sheet to be produced. This design rule is particularly useful in the production of thin sheets.

[0019] The following exemplary values ​​result for the desired curing thickness of the top layers depending on the final thickness of the material plates: An 80 mm thick material panel with a factor of 0.15 results in 2 x 6 mm top layers. An 18 mm thick material panel with a factor of 0.15 results in 2 x 1.35 mm top layers. A 3 mm thin sheet with a factor of 0.15 results in 2 x 0.2 - 0.3 mm top layers.

[0020] Preferably, electromagnetic waves in the high-frequency range, preferably at 13 or 27 MHz, or in the microwave range, preferably at 915 MHz or 2.45 GHz, can be used in the dual-band continuous oven. These are within the ISM range and are not normally subject to increased licensing requirements by regulatory authorities.

[0021] Alternatively or cumulatively, the pressed material mats can be processed in the double-belt continuous furnace at a pressure of less than 0.75 N / mm². 2 preferably less than 0.6 N / mm 2 and especially preferably with a pressure of less than 0.5 N / mm² 2 The process involves applying pressure to the surface layers. By creating the top layers, the necessary pressure in the double-belt continuous oven can be kept low, while the electromagnetic radiation ensures the hardening of the pressed material mat.

[0022] Alternatively or cumulatively, electromagnetically transparent belts, sliding beams, sliding surfaces, and / or pressure rollers can be used in the double-belt continuous furnace. These elements serve to adjust or support the necessary pressure and can preferably be designed to be adjustable.

[0023] Alternatively or cumulatively, the setting temperature of a first binder used can be above 130°C, preferably above 150°C, and most preferably above 160°C. This makes adhesive systems with a high setting temperature usable, particularly in the production of thick material sheets.

[0024] Alternatively or cumulatively, finer or dust-like material can be used in the top layers compared to the middle layer(s).

[0025] Alternatively or cumulatively, the surface layer material can be mixed with a second or different binder that has a lower setting temperature than the first binder and preferably cures below 120°C, and most preferably below 100°C. This allows the length of the double-belt press to be significantly reduced again, or the production speed to be increased due to the faster curing of the surface layers.

[0026] Alternatively or cumulatively, after the middle layer has hardened, the material plate can be pressed to the target dimension in a double-belt calibration press between two steel belts, preferably with a pressure of 2 to 3 N / mm². 2, are compressed and / or held in place. Even when one speaks of a fully cured material plate, meaning that the material plate is so thoroughly cured that it no longer springs back or chips on the surface, chemical reactions continue to take place within the still-hot material plate.

[0027] Therefore, to calibrate the specified final dimension, it may be necessary to place the material sheet back into a relatively short calibration press. Preferably, the surface layers of the material sheet are smoothed, embossed, and / or cooled during this process. For embossing, the calibration press may be equipped with an additional or even a single circulation loop for an embossing belt.

[0028] It is particularly preferred that the process be used to produce material plates with a target thickness of more than 10 mm, preferably more than 30 mm, and most preferably more than 60 mm. Especially with thick plates, heating the middle layers offers significant advantages, since, according to the prior art, heat conduction from the steel strips through the surface layers to the middle layers generally takes too long.

[0029] Alternatively or cumulatively, the moisture content of the top layers and middle layers in the pressed material mat can be essentially the same, but different moisture content levels are preferred.

[0030] Alternatively or cumulatively, by adapting existing manufacturing processes for material sheets, preferably adopting process parameters or layered press mats from processes in which the press mat is cured by means of heat conduction through-curing double belt presses, the moisture content can be increased by 10%, most preferably by 20%, in the top layers and / or the middle layers.

[0031] Alternatively or cumulatively, the material mat can be subjected to pre-compression for aeration before entering the double belt press. Aeration itself is a known process in the production of material sheets by means of pre-pressing and is preferably carried out with at least one air-permeable fabric belt while the thickness of the material mat is reduced.

[0032] Alternatively or cumulatively, the material slab exiting the double-belt continuous furnace can be subjected to a tensile force in the production direction, preferably by the double-belt calibration press or a calender roller arrangement. Applying this force somewhat reduces wear on the belts in the continuous furnace and / or reduces the stress on these belts during production.

[0033] Alternatively or cumulatively, in the double-belt continuous furnace, the belts can be supported or pressed by capacitor plates to introduce the high frequency. It can also be provided that friction-reducing agents such as coatings or air cushions are used between the capacitor plates and the belts.

[0034] Alternatively or cumulatively, the belts together with the pressing mat can be compressed in the transport direction in the double belt continuous furnace by a calender roller arrangement in front of the continuous furnace and / or subjected to a thrust force in the transport direction.

[0035] Alternatively or cumulatively, after the double-belt continuous oven, uncured pressed material mats can be disposed of in a disposal container and / or, in a double-belt calibration press, uncured pressed material mats can be transferred to a disposal container in a reversing operation opposite to the transport direction.

[0036] Starting up an electromagnetic continuous furnace is not straightforward. Depending on the control system, the magnetrons or microwave generators can only be switched on if the entire pressing mat is present in the chamber. This would result in uncured pieces of the pressing mat being discharged at the end of the furnace and not being properly conveyed further. Even during normal operation, a discharge hopper after the furnace is useful to collect material falling off the edges of the pressing mat that is not, or no longer, firmly bonded to the material sheet.

[0037] The problem for a device for producing material sheets from a material spread to form a pressable mat, which is mixed with at least one binder that can be cured by heat and / or pressure, is solved by the fact that In the direction of transport, a double belt press is arranged, which compacts and heats the pressed material mat and has two endlessly circulating steel belts for hardening the top layers by means of heat conduction through the steel belts, and that, for the curing of the uncured areas of the pressed material mat, a double-belt continuous oven with a generator for electromagnetic waves in the high-frequency or microwave range is subsequently arranged, which heats and cures the uncured parts of the pressed material mat in the middle layer by means of electromagnetic waves to a temperature above the setting temperature of the binder.

[0038] Advantageously, the individual features listed in the table below can be cumulatively combined, arbitrarily combined, or independently improved to enhance the solution of the device or the method: - The double belt press is particularly suitable for a pressure of more than 3 N / mm² 2 , preferably more than 4 N / mm 2 , especially preferred by more than 5 N / mm 2 to be applied to the pressing mat. For this purpose, appropriate adjusting devices would need to be provided to regulate the pressure accordingly, or a frame structure that can absorb the pressure. - Generators for electromagnetic waves in the high-frequency range, preferably at 13 or 27 MHz, or in the microwave range, preferably at 915 MHz or 2.45 GHz, are arranged in the double-band continuous oven. - The double belt continuous oven may be suitable for pressing the material mat with a pressure of less than 0.75 N / mm². 2 preferably less than 0.6 N / mm 2 and especially preferably with a pressure of less than 0.5 N / mm² 2 to impose. - Electromagnetically transparent belts and / or pressure rollers can be arranged in the double-belt continuous oven to assist in applying pressure during curing and are preferably adjustable. - The double-belt continuous oven, with its heat output, can be suitable for generating a temperature in the pressed material mat that is above the setting temperature of over 130°C of a first binder used, preferably above 150°C, and most preferably above 160°C. For this purpose, the corresponding power would have to be provided by generators or devices for generating the high frequency or microwaves and fed into the chamber of the continuous oven. - In the transport direction after the double-belt continuous oven for curing the middle layer of the material plate, a double-belt calibration press with two endlessly circulating steel belts can be arranged, which is preferably suitable for setting the target dimension, preferably with a pressure of 2 to 3 N / mm². 2 , to adjust or to hold. - In this context, it would be advantageous if the double-belt calibration press included means for smoothing, embossing and / or cooling the surface layers of the material plate. - In the transport direction of the press mat in front of the double belt press, a pre-press for venting and compaction, preferably with at least one air-permeable fabric belt, can be arranged. - To apply a tensile force in the production direction to the material plate exiting the double-belt continuous furnace, a double-belt calibration press or a calender roller arrangement can be arranged. - Capacitor plates can be arranged in the double-belt continuous furnace to support the endlessly circulating belts and to generate electromagnetic high-frequency. Friction-reducing agents such as coatings or air cushions can be arranged between the capacitor plates and the tapes. To compact the pressed material mat and / or to introduce a thrust force in the transport direction within the double-belt continuous furnace, upstream of the furnace or chamber, a calender roller assembly can be arranged on the continuously circulating belts that rest against the pressed material mat. This arrangement allows a thrust in the transport direction to be introduced onto the surface layers, which supports the drive power of the circulating belts and reduces their stress by "helping" to push the pressed material mat or the material sheet through the continuous furnace. - Preferably, the calender rollers can be coated with plastic. - To prevent the belts from becoming charged, a deionization strip for the belts can be arranged at the top and / or bottom of the double-belt continuous oven. - A compaction zone can be arranged in front of the calender roll or the continuous furnace (chamber) in the double belt continuous furnace, which is preferably designed with sliding plates or several pressure rollers. - A special drive with a targeted torque reserve can be used to apply a tensile or compressive force to the belt in the continuous furnace and / or for the steel belt in the double belt press. - In a double-belt continuous furnace, several and / or different continuous furnaces or chambers can be arranged. With such an arrangement, different radiation modes or couplings of the electromagnetic waves into the pressed material mat can be achieved. A staged power control along the length or width is also more advantageously implemented with this arrangement. - After the double-belt continuous oven, a disposal container for uncured pressed material mats can be arranged and / or the double-belt calibration press could be suitable to transfer uncured pressed material mats to a disposal container in a reversing operation opposite to the transport direction.

[0039] Further general information regarding the purpose or understanding of the invention.

[0040] The double belt press can be designed as an isobaric press or as a conventional continuous press with rolling elements (e.g., a roller belt conveyor) arranged between the heating plates and the steel belts. Typically, the heating plates, which provide the heat, are heated by a hot fluid flowing through them.

[0041] To clarify the structure of the system according to the invention, the individual machines of the device can also be named as: pre-press (optional), top layer press (double belt press), continuous oven (curing) and calibration press (optional).

[0042] Technological differences are seen in the fact that in a pre-press, optional heating is carried out according to the state of the art, preferably during venting, but hardening in the pressing mat does not take place or only takes place in a rudimentary way.

[0043] The top layers cured in the top-layer press serve two purposes: firstly, to facilitate the transport of the pressed material mat, and secondly, to cover the mat and minimize or even prevent springback during transfers between the double-belt press and the continuous oven. Nevertheless, it is possible, and even advisable, to incorporate features between the individual units that minimize springback.

[0044] The upper and lower belts in the individual devices are preferably designed identically at the top and bottom and guided accordingly around deflection rollers.

[0045] The spreading or production of the pressed material mat is sufficiently described in the prior art and can, by and large, be considered independent of the present process. The single- or multi-layered production of the pressed material mat essentially influences the resulting material sheet. The necessary settings in the individual devices are made depending on the pressed material mat, the material used, its moisture content, the layer structure, and similar factors.

[0046] In a particularly preferred and independent embodiment, the material mat is compacted in the double-belt press during the production of the surface layers to 0 to 20%, preferably to 0 to 10%, and most preferably to + / - 5% above the nominal dimension of the material sheet. In other words, the compaction in the double-belt press corresponds to up to 120%, preferably up to 110%, and most preferably 95% to 105% of the height of the finished material sheet.

[0047] In a particularly preferred further embodiment, the springback is limited to less than 25%, preferably less than 15%, and most particularly less than 10% after the double belt press.

[0048] Springback can also be minimized by a separate, relatively small belt recirculation, preferably a double belt recirculation, by covering the surfaces of the top layers with a dense, continuous belt. This belt prevents or minimizes the ingress of air through the top layers, which also inhibits springback. Simultaneously, it would be possible to create a suitable supporting structure between the double belt press and the continuous oven. The belts used can be made of a steel that is comparatively thin compared to the double belt press or of a heat-resistant plastic, which will not be damaged by the high radiant temperature of the steel belts in the double belt press.

[0049] Technologically, the depth of curing or the thickness of the cover layers is essentially determined by the transfer time / steel belt speed, the type of material, the temperature of the steel belts, and the setting temperature of the binder; these are the technological parameters that must be considered or adjusted during production.

[0050] The invention understands compression in the double belt press to also include the pure planar contact of the steel belts with the pressing mat for heat transfer, which would physically result in at least an approximate "compression", even if only infinitesimally.

[0051] A control loop preferably uses the curing of the surface layers or their thickness as a control variable to control and regulate the entire device or manufacturing process. Because the belt or device speed is determined by the device during curing, which in turn determines the amount of energy required for curing in the continuous oven, since the residence time in the chamber or in the area with the electromagnetic waves for heating the pressed material mat is determined by the predetermined transport speed.

[0052] Thus, one possible method for operating a device for producing material sheets from a material spread to form a pressable mat consists of heating the pressable mat in a double-belt press with steel belts that are warmer than the pressable mat by heat conduction, whereby the surface layers in contact with the steel belts are heated to a temperature above the setting temperature of the binder and harden, wherein the unhardened parts of the pressable mat in the middle layer are heated and hardened in a subsequent double-belt continuous oven by means of electromagnetic waves to a temperature above the setting temperature of the binder to produce a material sheet, wherein the thickness of the surface layers to be hardened in the double-belt press is used as a control variable for the control of the device.

[0053] In this context, it would be preferable to determine the thickness of the surface layers after the pressed material mat exits the double belt press, preferably using a non-destructive testing method. Particularly preferably, the measured values ​​are transmitted to a control device for processing and controlling the machine.

[0054] The control device or regulating device is particularly operatively connected with the drives of the individual devices and / or with the control for the production of the electromagnetic waves.

[0055] The invention defines a material sheet as a (nearly) completely hardened pressed mat. By its very nature, this mat emerges from the device as a strand and is cut into material sheets by diagonal saws (not shown in detail, but standard).

[0056] A discharge hopper can be installed after the continuous furnace to collect defective sheets and / or incompletely cured material sheets or pressed mats. This can occur due to incorrect settings or failure of the electromagnetic radiation system. The material sheet would then be unsuitable for processing through the final assembly line. A deflector can be installed to direct the cured surface layers towards the discharge hopper.

[0057] Alternatively or cumulatively, the calibration press can also be switched to a reversing mode to transport material into the discharge container.

[0058] Alternatively or cumulatively, the waste container can also be located after the calibration press.

[0059] The invention understands "in front of, in or opposite to the direction of transport" to refer to a location or direction in which a pressed mat, which is hardened into a material sheet, normally passes through the device.

[0060] Further advantageous measures and embodiments of the subject matter of the invention will become apparent from the dependent claims and the following description with drawing 1631.

[0061] They show: Fig. 1 In a schematic sectional view from the side, a preferred embodiment of the invention with a double belt press for curing the top layers of a pressed material mat and a microwave continuous oven for curing the middle layer or the entire pressed material mat into a material sheet with an optional calibration press and Fig. 2 in a further embodiment a possible enlarged representation of an alternative continuous furnace.

[0062] The same reference numerals are generally used for identical or similar machine elements or fixture parts.

[0063] After Fig. 1. A spread pressed material mat 1 is transferred in the transport direction 8 by a transport device (not shown), usually a forming belt, which runs under spreading devices for creating the pressed material mat, to a double belt press 10. During compaction, or possibly even without compaction, heat is transferred after the steel belts 12 make contact with the pressed material mat 1 from above and below, and the surface layers 2 of the pressed material mat 1 are hardened. The depth of hardening, or the thickness of the surface layers 2, is essentially determined by the transfer time / steel belt speed, the type of material, the temperature of the steel belts, and the setting temperature of the binder.

[0064] The partially cured pressed material mat 1, together with the optionally preheated but not yet cured middle layer 3, is transferred to a continuous oven 20 in a double-belt configuration. The belts 22 are preferably sealed but transparent to electromagnetic radiation. In this embodiment, the electromagnetic radiation is generated by means of capacitor plates 25 and used to cure the middle layer 3 or the uncured areas of the material sheet 9.

[0065] Optionally, a calibration press 30 can be arranged downstream of the double-belt continuous furnace 20, which uses belts to adjust or further compact the thickness of the material sheet 9. Preferably, the belts are made of steel 31. Instead of or in conjunction with the steel belts, a continuous surface of a warp-woven fabric can also be provided, which would be responsible for surface embossing, for example on OSB surfaces.

[0066] The hardening of the pressed material mat was represented as a white area that turns black (hardened).

[0067] Fig. Figure 2 shows a further embodiment with a possible enlarged view of the device and the method using an alternative continuous oven 20, which could primarily be used for microwaves. Individual components of the continuous oven 20 that are independent of microwaves can also be used in a continuous oven 20 with condenser plates 25, for example, a deionization strip 23 for the belts 22. The continuous oven 20 has a chamber 21 for the irradiation / generation of microwaves or other electromagnetic radiation.

[0068] In a process analogous to the previous figure, the pressing mat 1 is introduced into the double belt press 10 in the transport direction 8 into a pressing gap formed between steel belts 12 guided endlessly over deflection drums 14. The steel belts 12 are preferably supported against the heat-emitting heating plates 11 by a roller rod circulation 13, acting like a rolling bearing. The heating plates 11 are preferably adjusted accordingly by hydraulic cylinders (not shown) and are mounted in a press frame (not shown).

[0069] After exiting the double belt press 10, the pressed material mat 1 with the removed top layers 2 is transferred to the continuous oven 20. The belts 22 are also guided over deflection rollers 26 here. The chamber 21 and / or the continuous oven 20 are shielded from the environment by a shield 29 in such a way that the electromagnetic radiation generated by the MW generators 25 cannot be emitted from the chamber 21 into the environment or does not exceed a permissible limit.

[0070] In front of chamber 21, means for compacting the press mat 1 or for recompacting the rebound press mat 1 may be arranged, for example a recompaction 28 with sliding plates or a calender roller arrangement 27.

[0071] A discharge container 7 can be arranged downstream of the continuous furnace 20 to collect defective sheets and / or incompletely cured material sheets 9 or press mats 1. This can occur due to incorrect settings or failure of the electromagnetic radiation. The material sheet would then be unsuitable for processing through the final assembly. A deflector can be arranged to direct the cured surface layers towards the discharge container 6.

[0072] Optionally, a calibration press 30 can be arranged after the continuous oven 20, which performs the final shaping of the material sheet. This can also be arranged after the diagonal saw (not shown) and, if necessary, be operated in cycles. To discharge incompletely cured press mats, the calibration press can be switched to a reversing mode, in which the steel belts 31 in the press gap do not move in the transport direction 8, but transport the material towards the discharge container 7.

[0073] Depending on the solution, the discharge container 7 can also be arranged after the calibration press 1631. Reference numeral list: P1631 1 Pressing mat 2 Top layer 3 middle class 6 deflectors 7 drop containers 8 Transport direction 9 Material board 10 Double belt press 11 heating plates 12 steel bands 13 Roller rod circulation 14 Deflection drum 20 Continuous furnace (double belt) 21st Chamber Volume 22 23 Deionization bar 24 MW generators 25 capacitor plates 26 deflection rollers 27 Calender roller arrangement 28 Recompaction 29 Shielding 30 Calibration press (double belt) 31 steel band 32 Cooling plate

Claims

[1] Method for producing material sheets from a material spread to form a pressable mat, which is mixed with at least one binder that can be cured by heat and / or pressure, characterized by , that The pressing mat (1) is compacted in a double belt press (10) with steel belts (12) that are warmer than the pressing mat (1) and heated by heat conduction, whereby the surface layers (3) in contact with the steel belts (12) are heated to a temperature above the setting temperature of the binder and harden and The uncured parts of the pressed material mat (1) in the middle layer (3) are heated and cured in a subsequent double-belt continuous oven (20) by means of electromagnetic waves to a temperature above the setting temperature of the binder. [2] Method according to one or more of the preceding claims, characterized by, that in the double belt press (10) a pressure of more than 3 N / mm 2 , preferably more than 4 N / mm 2 , especially preferred to be more than 5 N / mm 2 is applied to the pressing mat. [3] Method according to one or more of the preceding claims, characterized by that the hardened top layers (2), after leaving the double belt press (10), have a thickness of more than one mm, preferably more than 2 mm and most preferably more than 4 mm and up to 6 mm. [4] Method according to one or more of the preceding claims, characterized by , that the thickness of both cured cover layers is 15%, particularly preferably 12% and most preferably 6% to 10% based on the thickness of the material plate (9) to be produced. [5] Method according to one or more of the preceding claims, characterized by, that electromagnetic waves in the high frequency range, preferably at 13 or 27 MHz, or in the microwave range, preferably 915 MHz or 2.45 GHz, are used in the double-band continuous oven (20). [6] Method according to one or more of the preceding claims, characterized by , that in the double belt continuous furnace (20) the pressing mat (1) is subjected to a pressure of less than 0.75 N / mm² 2 preferably less than 0.6 N / mm 2 and especially preferably with a pressure of less than 0.5 N / mm² 2 is charged. [7] Method according to one or more of the preceding claims, characterized by , that electromagnetically transparent belts (22) and / or pressure rollers are used in the double belt continuous furnace (20). [8] Method according to one or more of the preceding claims, characterized bythat the setting temperature of a first binder used is above 130°C, preferably above 150°C, most preferably above 160°C. [9] Method according to one or more of the preceding claims, characterized by , that in the top layers (2) finer or dust-like material is used compared to the middle layer(s) (3). [10] Method according to one or more of the preceding claims, characterized by , that the material of the cover layers (2) is mixed with a second binder which has a lower setting temperature than the first binder and preferably cures below 120°C, most preferably below 100°C. [11] Method according to one or more of the preceding claims, characterized by, that after the hardening of the middle layer (3), the material plate (9) is compressed to the nominal dimension in a double-belt calibration press (30) between two steel belts (31), preferably with a pressure of 2 to 3 N / mm² 2 , is compacted and / or held. [12] Method according to claim 11, characterized by , that in the double belt calibration press (30) the top layers of the material plate (9) are smoothed, embossed and / or cooled. [13] Method according to one or more of the preceding claims, characterized by , that material plates (9) are produced with a nominal thickness of more than 10 mm, preferably more than 30 mm and most preferably more than 60 mm. [14] Method according to one or more of the preceding claims, characterized by , that in the pressed material mat (1) the moisture content of the surface layers and the middle layers is essentially the same. [15] Method according to one or more of the preceding claims, characterized by, that when adapting existing manufacturing processes for material sheets (9), preferably double belt presses hardening the pressed material mat by means of heat conduction, the moisture content is increased by 10%, most preferably by 20%, in the top layers and / or the middle layers. [16] Method according to one or more of the preceding claims, characterized by , that the pressing mat (1) is subjected to pre-compression for ventilation before entering the double belt press (10), preferably with at least one air-permeable fabric strip. [17] Method according to one or more of the preceding claims, characterized by , that the material plate (9) exiting the double belt continuous furnace (20) is subjected to a tensile force in the production direction, preferably by the double belt calibration press (30) or a calender roller arrangement. [18] Method according to one or more of the preceding claims, characterized by, that in the double-belt continuous furnace (20) the belts (22) are supported or pressed by capacitor plates (25) to introduce the high frequency. [19] Method according to claim 18, characterized by , that friction-reducing means such as coatings or air cushions are used between the capacitor plates (25) and the tapes (22). [20] Method according to one or more of the preceding claims, characterized by , that the belts (22) together with the pressing mat (9) in the double belt continuous furnace (20) are compressed in the transport direction (8) in front of the continuous furnace (20) by a calender roller arrangement (27) and / or subjected to a thrust force in the transport direction (8). [21] Method according to one or more of the preceding claims, characterized by, that after the double belt continuous oven (20) uncured pressed material mats are disposed of in a disposal container (7) and / or the double belt calibration press (30) in a reversing operation opposite to the transport direction (8) transfers uncured pressed material mats to a disposal container (7). [22] Apparatus for producing material sheets from a material spread to form a pressable mat, which is mixed with at least one binder that can be cured by heat and / or pressure, characterized by , that in the direction of transport (8) a compacting mat (1) for the compressed material and a heating double belt press (20) with two endlessly circulating steel belts (12) for curing the cover layers (2) by means of heat conduction through the steel belts (12) is arranged, and For the curing of the uncured areas of the pressed material mat (1) a double belt continuous oven (20) with a generator for electromagnetic waves in the high frequency range or in the microwave range is arranged below, which The uncured parts of the pressed material mat (1) in the middle layer (3) are heated and cured by means of electromagnetic waves to a temperature above the setting temperature of the binder. [23] Device according to device claim 22, characterized by , that the double belt press (10) is suitable for applying a pressure of more than 3 N / mm 2 , preferably more than 4 N / mm 2 , especially preferred by more than 5 N / mm 2 to be applied to the pressing mat. [24] Device according to one or more of the preceding device claims, characterized by, that in the double-band continuous oven (29) generators for electromagnetic waves in the high-frequency range, preferably at 13 or 27 MHz, or in the microwave range, preferably 915 MHz or 2.45 GHz, are arranged. [25] Device according to one or more of the preceding device claims, characterized by , that the double belt continuous oven (20) is suitable for pressing the mat of material with a pressure of less than 0.75 N / mm² 2 preferably less than 0.6 N / mm 2 and especially preferably with a pressure of less than 0.5 N / mm² 2 to impose... [26] Device according to one or more of the preceding device claims, characterized by that electromagnetically transparent belts (22) and / or pressure rollers are arranged in the double-belt continuous furnace (20). [27] Device according to one or more of the preceding device claims, characterized bythat the double belt continuous furnace (20) with its heat output is suitable to produce a temperature in the pressed material mat that is above the setting temperature of over 130°C of a first binder used, preferably above 150°C, most preferably above 160°C. [28] Device according to one or more of the preceding device claims, characterized by , that in the transport direction (8) after the double-belt continuous furnace (20) for curing the middle layer (3) of the material plate a double-belt calibration press (30) with two endlessly circulating steel belts (31) is arranged, which is preferably suitable for the nominal dimension, preferably with a pressure of 2 to 3 N / mm 2 , to adjust or to keep. [29] Device according to the previous device claim, characterized by , that in the double belt calibration press (30) means for smoothing, embossing and / or cooling the surface layers of the material plate are arranged. [30] Device according to one or more of the preceding device claims, characterized by , that in the transport direction (8) of the press mat (1) a pre-press for venting and compaction, preferably with at least one air-permeable fabric belt, is arranged in front of the double belt press (10). [31] Device according to one or more of the preceding device claims, characterized by , that a double belt calibration press (30) or a calender roller arrangement is arranged to apply a tensile force in the production direction to the material plate exiting the double belt continuous furnace (20). [32] Device according to one or more of the preceding device claims, characterized by , that are arranged in the double-belt continuous furnace (20) to support the endlessly circulating belts (22) and to produce electromagnetic high-frequency capacitor plates (25). [33] Device according to one or more of the preceding device claims, characterized by , that friction-reducing means such as coatings or air cushions are arranged between the capacitor plates (25) and the belts (22). [34] Device according to one or more of the preceding device claims, characterized by , that a calender roller arrangement (27) is arranged in front of the continuous furnace or its chamber (21) for the endlessly circulating belts (22) in contact with the pressed material mat (1) in order to compact the pressing material mat and / or to introduce a thrust force in the double belt continuous furnace (20) in the transport direction (8). [35] Device according to the previous device claim, characterized by that the calender rollers are arranged with a plastic coating. [36] Device according to one or more of the preceding device claims, characterized by, that a deionization bar (23) is arranged for the belts in the double belt continuous furnace. [37] Device according to one or more of the preceding device claims, characterized by , that a compaction zone or a recompaction (28) is arranged in front of the calender roll arrangement (27) and / or the chamber (21) in the double belt continuous furnace (20). [38] Device according to one or more of the preceding device claims, characterized by , that a special drive with a targeted torque reserve is arranged to apply a tensile or compressive force in the continuous furnace for the steel strip in the double-belt press. [39] Device according to one or more of the preceding device claims, characterized by , that in the double-belt continuous furnace (20) several and / or different continuous furnaces (chambers) are arranged, preferably to represent different irradiation powers. [40] Device according to one or more of the preceding device claims, characterized by , that a discharge container (7) for uncured press mats (1) is arranged after the double belt continuous oven (20) and / or the double belt calibration press (30) is suitable to transfer uncured press mats to a discharge container in a reversing operation opposite to the transport direction (8).

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