Apparatus and method for pressure board manufacturing

Abstract

A method (M) of producing a pressed sheet (1) for electrical insulation comprises, in any order: a) mechanically compressing (M1) at least one pressed sheet precursor (2) suitable for electrical insulation, and b) emitting (M2) electromagnetic waves (EM) towards the pressed sheet precursor (2). The mechanical compression (M1) of the press plate precursor (2) comprises passing the press plate precursor (2) sequentially through a plurality of compression stations (S1, S2, S3), each compression station (S1, S2, S3) comprising at least one pair of rollers (3) which together compress the press plate precursor (2) as the press plate precursor passes through the gap between the respective pair of rollers (3), where the gaps of each station (S1, S2, S3) become smaller sequentially.

Description

Technical Field

[0001] The present disclosure relates to the manufacture of pressed board for electrical insulation in transformers. Pressed board can be made from pure unbleached cellulose extracted from wood, such as long-fiber softwood. Due to its high chemical purity, mechanical strength, and good oil-immersibility, pressed board is suitable for use as an insulating material for motors and capacitors, for example, in oil-filled power transformers and distribution transformers. Background Art

[0002] Pressboard can be made using a hot pressing operation, in which multiple wet fiber precursor sheets are inserted between press plates to form a stack, which is then pressed and heated to dry the precursor into a finished pressboard. The time required for batch pressing can range from 10 minutes to 3 hours, depending primarily on the thickness and moisture content of the pressboard. Furthermore, the process requires a significant amount of energy to heat the press plates and the hot press chamber.

[0003] Conventional drying methods typically remove moisture from the wood from the surface to the inside. It's not uncommon for the surface to be completely dry, but the inside of the wood or pressed board remains wet. As water drains from the wood, it causes shrinkage and cracks, which reduces the quality of the product.

[0004] It is therefore an object of the present disclosure to provide an improved method of manufacturing pressed board that enables faster production, improved surface finish, and greater energy efficiency. Summary of the Invention

[0005] According to a first aspect, this and other objects are achieved by a method as defined in independent claim 1, alternative embodiments being specified in the dependent claims. The method is suitable for producing pressed board and comprises, in any order:

[0006] a) mechanically compressing at least one pressed board precursor, and

[0007] b) emitting electromagnetic waves toward the (one or more) pressed board precursors. The mechanical compression of the pressed board precursors may include sequentially passing the pressed board precursors through a plurality of compression stations, each compression station comprising at least one pair of rollers that together compress the pressed board precursors as the pressed board precursors pass through a gap between the corresponding pair of rollers, wherein the gap at each station becomes successively smaller.

[0008] When producing pressed board, the pressed board precursor must be dried. The mechanical compression of the pressed board precursor forces the liquid to be discharged from the wet pressed board precursor. By emitting electromagnetic waves to the pressed board precursor, the liquid is heated in the precursor, thereby promoting the drying of the material inside. This can reduce the time required to dry the pressed board. In addition, this can reduce energy consumption compared to using convection drying only in a heating chamber (i.e. without any electromagnetic waves). In addition to emitting electromagnetic waves, ultrasonic waves can also be emitted to the pressed board precursor. Emitting ultrasonic waves to the pressed board precursor accelerates the phase change of moisture in the pressed board from the liquid phase to the gas phase.

[0009] The electromagnetic waves may be microwaves having a frequency in the range of 1 GHz to 300 GHz. Electromagnetic waves having such wavelengths provide deep penetration into the pressed board precursor and generally provide a high rate of heat generation within the body of the pressed board.

[0010] The electromagnetic waves may be radio waves with a frequency in the range of 1 MHz to 100 MHz. Electromagnetic waves with this wavelength generate heat in the pressed board by interacting with water molecules. However, the rate of heat generation is lower than that of microwaves and is proportional to the water content in the pressed board.

[0011] The method may further include providing one or more electromagnetic shielding members configured to at least partially surround one or more spaces around one or more portions of the pressed board precursor, wherein microwaves are emitted within or into the one or more spaces. The electromagnetic shielding members contain a majority of the electromagnetic waves, wherein the pressed board precursor absorbs energy in the electromagnetic waves.

[0012] The method may further comprise removing water and / or water vapor from the one or more spaces. By removing water and / or water vapor from the one or more spaces, saturation of the moisture content within the spaces is reduced, thereby enabling a longer drying period or a continuous drying operation. Water may be removed through a drain in the lower portion of the space(s), thereby reducing the accumulation of liquid water or water vapor in the space(s).

[0013] The method (M) according to any one of claims 1 to 4, further comprising reducing the ambient pressure around the pressed board precursor (2) to a pressure below atmospheric pressure. Reducing the ambient pressure results in a lower boiling point temperature, thereby initiating the phase change from liquid to vapor earlier.

[0014] The emission of electromagnetic waves can include emitting intermittent pulses of the emitted electromagnetic waves, or can include repeatedly varying the power of the emitted electromagnetic waves between a higher power level and a lower power level over time. By emitting electromagnetic waves intermittently, or by varying the power over time, the energy provided by the electromagnetic waves varies over time. In the absence of, or with minimal energy supplied to, the pressed board precursor, heat conduction within the pressed board precursor has time to equalize any hot spots that may be caused by the electromagnetic waves. Hot spots can cause the pressed board to overheat and cause surface burns, cracking, or weakening.

[0015] The mechanical compression of the pressed board precursor may include passing the pressed board precursor between at least one pair of rollers, wherein the pair of rollers together compress the pressed board precursor as the pressed board precursor passes through the gap between the respective pair of rollers. The rollers provide a gap between the rollers that is smaller than the thickness of the pressed board precursor passing between the rollers. Thus, the rollers provide a robust and reliable method for compressing the pressed board precursor to a given thickness to remove liquid from the pressed board precursor.

[0016] The method may further include heating at least one roller to heat the pressed board precursor. By supplying heat to the pressed board precursor, liquid in the pressed board precursor is more easily evaporated. By heating at least one roller, heat is supplied from the heated roller(s) to the pressed board precursor, making it easy to control the speed of the rollers to control the amount of heat transferred to the pressed board precursor.

[0017] The power of the electromagnetic waves emitted may be reduced sequentially for each compression station. As the pressed board is compressed, its moisture content and mass are locally reduced, which means that less heating power is required to heat the pressed board later in the sequence / process. By reducing the power of the electromagnetic waves used for each compression station, overheating and surface burning, cracking, or weakening of the pressed board can be reduced. The power reduction can be achieved by reducing the impact and / or by intermittently operating the power supply to reduce the total power supplied over time. Electromagnetic waves with time-varying power can also be used for this purpose.

[0018] As an alternative or in addition to compression using a pair of rollers, the mechanical compression of the pressed board precursor may include compressing the pressed board precursor between a plurality of press plates. Press plates provide an alternative means for compressing the pressed board precursor. A plurality of press plates may be used together as a stacked array of press plates for receiving the pressed board precursor sandwiched between the press plates.

[0019] At least one of the plurality of press plates can be heated, thereby heating the pressed board precursor. By supplying heat to the pressed board precursor, liquid in the pressed board precursor evaporates more easily. By heating at least one of the plurality of press plates, heat can be supplied to the pressed board precursor from the heated press plate(s).

[0020] Electromagnetic waves can be emitted toward a first region of the pressed sheet precursor upstream of the pair of rollers and / or toward a second region of the pressed sheet precursor downstream of the pair of rollers. By emitting more electromagnetic energy, the drying effect is improved. It is beneficial to apply electromagnetic energy upstream and downstream of the rollers to ensure that the heating effect is continuously provided at both stages. Figure 5 As shown, additional electromagnetic shielding members 9 may be provided around any components that should be protected from electromagnetic waves, such as the rollers 2 .

[0021] The power of the emitted ultrasonic waves may be configured to cause at least some of the water of the pressed board precursor to change from a liquid phase to a vapor or gas phase.

[0022] According to a second aspect, this and other objects are also achieved by the device as defined in independent claim 11, alternative embodiments being specified in the dependent claims.The device according to the following embodiments performs at least some of the functions described above with reference to the corresponding embodiments of the method.

[0023] The apparatus is suitable for dehydrating a pressed board precursor and comprises a compression assembly configured to compress the pressed board precursor and at least one electromagnetic wave emitter configured to emit electromagnetic waves toward the pressed board precursor and / or the compressed pressed board.

[0024] The electromagnetic wave transmitter may be configured to transmit microwaves having a frequency in the range of 1 GHz to 300 GHz.

[0025] The apparatus may further include one or more electromagnetic shielding members configured to at least partially surround one or more spaces around the one or more portions of the pressed board precursor.

[0026] The electromagnetic wave transmitter is configured to transmit radio waves having a frequency in the range of 1 MHz to 100 MHz.

[0027] The apparatus may also include vents and / or drains configured to enable moisture (such as water and / or water vapor) to escape from the one or more spaces.

[0028] It will be apparent to one of ordinary skill in the art that the above-mentioned aspects, the appended claims, and / or the examples disclosed herein above and later below may be appropriately combined with each other.

[0029] Additional features and advantages are disclosed in the following description, claims, and drawings, and in part will be apparent to those skilled in the art or learned by practicing the disclosure described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1-5Different embodiments of an apparatus for dehydrating a pressed board precursor using one or more pairs of rollers and various embodiments of an electromagnetic wave transmitter are schematically shown.

[0031] Figure 1 An apparatus is shown in which an electromagnetic wave transmitter is suspended upstream of a compression assembly comprising a single pair of rollers. The transmitter is surrounded by an optional electromagnetic shield comprising a plurality of shield members forming a housing with openings for the input and output of the pressed board precursor.

[0032] Figure 2 An apparatus is shown in which the compression assembly comprises a plurality of pairs of rollers and the electromagnetic wave transmitter comprises a plurality of transmitters distributed along the production line. This embodiment does not include electromagnetic shielding, but other embodiments may include electromagnetic shielding instead.

[0033] Figure 3 Shown with Figure 2 but further comprising an ultrasonic transmitter configured to transmit ultrasonic waves toward the pressed board precursor.

[0034] Figure 4 Shown with Figure 3 The apparatus shown corresponds to that shown but also includes an optional electromagnetic shielding member around each pair of rollers and around the corresponding electromagnetic wave transmitter. The shielding member contains the energy from each transmitter to a specific part of the pressed board precursor.

[0035] Figure 5 Corresponding to Figure 4 The equipment shown in Figure 1 is similar to the one shown in Figure 2, but with a different electromagnetic shielding design. Here, the electromagnetic shielding surrounds the main part of the production line, including all electromagnetic wave emitters. Alternatively, the shielding can be a room-like shielding around the equipment, so that workers can move within the shielded space, at least when the equipment is stopped and / or not emitting electromagnetic waves.

[0036] The number and type of electromagnetic and ultrasonic transmitters may be freely varied as appropriate, for example depending on the type of waves to be transmitted and therefore on the design and range of the transmitter(s) used. Furthermore, the design of the compression assembly may affect the positioning and design of the transmitters.

[0037] Figure 6a -e and 7a-d schematically show two similar embodiments of apparatus for producing pressed boards; Figure 6a -e, the device includes an electromagnetic wave transmitter and / or an ultrasonic wave transmitter outside the platen, and Figure 7a -d, the electromagnetic wave transmitter and / or ultrasonic wave transmitter is integrated with the pressing plate.

[0038] Figure 8a-b schematically illustrates an arrangement using more than two plates to provide more than one intermediate space between the platens so that more than one pressed board precursor can be sandwiched between the platens and compressed simultaneously by compression of the entire sandwich stack of platens and pressed board precursors; Figure 8a shows a plurality of press plates before a press plate precursor is placed between the press plates, Figure 8b The press plates are shown with the pressed board precursor placed between the press plates before compressing the pressed board precursor.

[0039] It will be appreciated that suitably arranged electromagnetic shielding members may be placed around or partially around a press plate or stack of press plates.

[0040] Figure 9 A first embodiment of the method according to the present disclosure is schematically illustrated.

[0041] For identical features appearing in several figures, the same reference numerals are generally not repeated. DETAILED DESCRIPTION

[0042] An embodiment of a method for producing a pressed board will be described below with reference to the accompanying drawing, which shows an apparatus for carrying out such a method.

[0043] As mentioned above, the pressed board 1 is typically made of pure unbleached cellulose from wood, such as long-fiber softwood. Alternatively, the pressed board 1 can be made of cellulose fibers from other sources, such as cotton, hemp, and jute, or other tree types. Alternatively, polymer fibers can be used as aramid fibers, or a combination of cellulose and polymer fibers. Furthermore, additives such as binders and fillers can be used.

[0044] Pressed board 1 is typically manufactured using a hot pressing operation in which a plurality of wet fiber precursor sheets 2 are placed between press plates 4 to form a hanging stack that is pressed and heated to remove water and dry the pressed board precursors 2 into the finished pressed board 1 .

[0045] The dewatering and drying process can be a process in which the press plates 4 remain closed until the heated press plates 1 are dry. Alternatively, the drying process can use a cycle of repeatedly separating and closing the press plates 4. Separation allows moisture to leave the press plate material more easily, and additional compression and any further heating can then be performed by closing the press plates 4 again and compressing the stack of press plates 4.

[0046] According to the present disclosure, one or more electromagnetic wave emitters 6 are provided to emit electromagnetic waves EM toward the pressboard precursor 2, thereby accelerating drying and enabling drying at a lower temperature, thereby improving the water removal and drying process. Optionally, in addition to the electromagnetic wave emitters 6, one or more ultrasonic wave emitters 14 are provided, wherein in addition to the electromagnetic waves EM, ultrasonic waves U are also emitted toward the pressboard.

[0047] The present disclosure also proposes an alternative to using a press plate 4, suggesting the use of a process comprising at least a pair of rollers 3, wherein the pressed board precursor 2 is fed between the pair of rollers 3 to compress the pressed board precursor 2, thereby removing liquid from the pressed board material. The rollers 3 can be permeable to liquids, such as liquid water or water vapor, so that the liquid water or water vapor can more easily leave the pressed board precursor 2 when it is compressed between the rollers 3. The liquid water or water vapor can then be removed from the rollers 3 using any suitable arrangement, such as ventilation, drainage, and / or suction removal.

[0048] Compression using the nip rollers 3 enables a continuous compression and drying process, wherein a continuous feed of pressboard precursor 2 / pressboard 1 material is directed to the nip rollers 3. Downstream of the nip rollers 3, i.e., the area into which the pressboard material enters after passing through the nip rollers 3, the pressboard material is typically further dried, for example, during transport on a conveyor system. The pressboard material on the conveyor system has a large surface area exposed to the surrounding atmosphere and is therefore suitable for allowing evaporated liquid to leave the pressboard material.

[0049] It will be appreciated that electromagnetic wave emission EM can be used both when compression is performed using the platen 4 and when compression is performed between the rollers 3. The material of the platen 4 or rollers 2 is preferably selected so as not to interact with EM waves.

[0050] Furthermore, it will be appreciated that heating of the pressed sheet material may be provided both when compression is performed using the platens 4 and when compression is performed between the rollers 3. For example, one or more of the rollers 3 may be heated, or one or more of the platens 4 may be heated, or radiant heaters or hot air heaters may be provided to heat the pressed sheet material.

[0051] The electromagnetic waves EM can be emitted to the pressed sheet material before, after, or during compression. Therefore, the electromagnetic wave emitter 6 can direct the electromagnetic waves toward the pressed sheet material upstream of the rollers 3 or downstream of the rollers 3, or toward the gap between the rollers 3 where the pressed sheet material is compressed.

[0052] exist Figure 1 In the first exemplary embodiment shown, there is provided an apparatus 5 for dehydrating a pressed board precursor 2. The apparatus 5 includes a compression assembly configured to compress the pressed board precursor 2. The apparatus 5 also includes an electromagnetic wave emitter 6 configured to emit electromagnetic waves toward the pressed board 1 (in this case, toward the pressed board precursor 2).

[0053] In this embodiment, the electromagnetic wave emitter 6 is located upstream of the compression assembly. However, any other suitable arrangement and positioning of the electromagnetic wave emitter 6 may be used. By placing the electromagnetic wave emitter 6 upstream of the compression assembly (where the moisture content of the pressed board precursor is higher), early heating of the pressed board precursor 2 is promoted, thereby shortening the overall drying time and energy consumption.

[0054] In other embodiments, the electromagnetic wave emitter 6 may be provided downstream of the compression assembly. Providing the electromagnetic wave emitter 6 downstream of the pair of rollers 3 is advantageous because the remaining moisture in the pressed board continues to receive the energy required to boil / evaporate the moisture in the pressed board precursor, thereby promoting faster drying.

[0055] As described above, in addition to mechanical compression and EM emission, the pressboard 2 can also be heated by convection or conduction heating. For example, the pair of rollers 3 can be provided with heating means for heating the rollers 3, which in turn heat the pressboard material. In other embodiments, the heating means can alternatively be omitted or replaced with some other suitable heating means, such as an infrared heater.

[0056] Other possible embodiments of the apparatus include at least one pair of rollers 3 and a plurality of press plates 4, wherein the apparatus provides for the pressing sheet to pass between the rollers 3 before being compressed between the press plates 4. Such an embodiment combines the advantages of efficient and continuous removal of liquid from the pressed sheet material as it passes between the rollers 3, with the press plates 4 subsequently providing improved control over the dryness of individual portions of the pressed sheet 2 or separate sheets of the pressed sheet 2.

[0057] Figure 6a Two separate press plates 4 are shown, with an uncompressed press plate 2 placed between them. Figure 6b The pressure plate 4 is shown partially closed. Figure 6c The full compression of the press plates 2 resulting from further closing of the press plates 4 is shown (closing = moving the press plates 4 closer to each other, ie reducing the spacing or gap between the press plates 4). Figure 6d The separation of the pressing plates 4 and the removal of the compressed sheets of the pressing plates 2 are shown. Figure 6e The use of an array of suitable transmitters 6 to transmit electromagnetic waves EM and / or ultrasonic waves U to the compressed sheet of press plates 2 is shown. The press plates 4 are typically suspended vertically, with the sheet of press plates 2 suspended vertically between the press plates 4. The stack 7 of press plates 4 is then compressed using any suitable compression / clamping device, such as a hydraulic cylinder.

[0058] Figure 7a-d corresponds essentially to the embodiment of FIG. 6 , but the electromagnetic wave emitter 6 and / or the ultrasonic wave emitter 14 are integrated into the press plate(s) 4 , so that the sheets of compressed press plate 2 are not removed before being subjected to the electromagnetic waves EM and / or ultrasonic waves U.

[0059] Figure 8a illustrates the fact that several press plates 4 are often used together as a "stack" 7, so that a plurality of press plate sheets can be compressed at once once they are clamped between the press plates 4, e.g. Figure 8b shown.

[0060] In all embodiments of the method according to the present disclosure, the method for producing a pressed board comprises, in any order: a) mechanically compressing M1 at least one pressed board precursor 2 , and b) emitting M2 electromagnetic waves EM towards the pressed board precursor 2 .

[0061] When producing a pressed board 1, the pressed board precursor 2 must be dried. Mechanical compression of the pressed board precursor 2 forces liquid out of the wet pressed board precursor 2. By emitting electromagnetic waves EM toward the pressed board precursor 2, the liquid is heated in the precursor 2, thereby promoting drying out of the material. This can reduce the time required to dry the pressed board precursor 2. Furthermore, it can reduce energy consumption compared to using only convection drying in a heating chamber, i.e., without any electromagnetic waves EM. In addition to emitting electromagnetic waves EM, ultrasonic waves U can also be emitted toward the pressed board precursor 2. Emitting ultrasonic waves U toward the pressed board precursor 2 enables the liquid to leave the material at a lower temperature, for example, by changing from a liquid phase to a gas phase.

[0062] The power of the electromagnetic wave EM emission and / or ultrasonic wave U emission is preferably adjusted according to the size, thickness, and mass of the pressed board material, so that the electromagnetic wave EM emission and / or ultrasonic wave U emission has a positive effect on the evaporation of liquid from the pressed board material, which means that at least part of the water in the pressed board material changes from the liquid phase to the vapor phase or gas phase.

[0063] In this embodiment, the electromagnetic wave EM includes microwaves with a frequency ranging from 1 GHz to 300 GHz.

[0064] In other embodiments, the electromagnetic waves may alternatively or additionally include radio waves having a frequency in the range of 1 MHz to 100 MHz.

[0065] like Figure 1 、 Figure 4 ,and Figure 5As shown, the method may include providing one or more electromagnetic shielding members 9 configured to at least partially surround one or more spaces V1, V2, V3 around one or more portions of the pressed board precursor 2, wherein electromagnetic waves EM are emitted into or within the one or more spaces. The electromagnetic shielding members 9 contain most of the electromagnetic waves so that the electromagnetic waves are absorbed by the pressed board precursor 2. If a plurality of electromagnetic wave emitters 6 are provided, it may be beneficial to contain the emission from each electromagnetic wave emitter 6, for example, to avoid stronger emissions from thicker portions adjacent to the pressed board reaching thinner portions of the pressed board that have passed through the compression assembly. This isolation is Figure 4 It is schematically shown in FIG.

[0066] The method may also include removing water and / or water vapor from one or more spaces. By removing water and / or water vapor from one or more spaces, the saturation of the water content in the space is reduced, thereby allowing for a longer drying period. Water can be removed through the drain port 10 in the lower portion of the space(s), thereby reducing the accumulation of liquid water or water vapor in the space(s). Figure 5 As shown, for example, water can be removed by providing a drain 10 in the lower portion of the electromagnetic shielding space so that water can drain from the electromagnetic shield due to gravity. Alternatively or additionally, water vapor can be removed by providing vents to allow air to enter and leave the space surrounded by the electromagnetic shielding member 9. An optional ventilation fan / air pump 12 is provided to enable forced air ventilation through the vents. The vents 11 and / or drains 10 can be provided in any electromagnetic shielding member 9 or other housing, not just in Figure 5 In the embodiment shown.

[0067] The method may further comprise reducing the ambient air pressure surrounding the pressed board precursor 2 to a pressure below atmospheric pressure. Reducing the ambient pressure results in a lower boiling point temperature, thereby initiating the phase change from liquid to vapor earlier. For example, the ambient air pressure may be controlled by enclosing part of the production line / apparatus 5 or the entire production line / apparatus 5 and operating an air pump 12 to draw air from the enclosed portion of the production line, thereby reducing the air pressure. The air pump 12 may be used to provide forced ventilation through vents, preferably adjustable / controllable vents 13, provided through the inlet (see FIG. 1 ). Figure 5 ), which allows the ambient air pressure to be reduced and maintained at a low level by closing or restricting the airflow to the inlet.

[0068] The transmitting of the electromagnetic waves may include transmitting intermittent pulses of the transmitted electromagnetic waves.

[0069] like Figure 1-5As shown, mechanical compression of the pressed board precursor 2 may include passing the pressed board precursor 2 between at least one pair of rollers 3 and compressing the pressed board precursor 2 together as it passes through the gap between the corresponding pair of rollers 3. The rollers 3 provide a gap between the rollers 3 that is smaller than the thickness of the pressed board precursor 2 passing between the rollers 3. Thus, the rollers 3 provide a robust and reliable means for compressing the pressed board precursor 2 to a given thickness to remove liquid or vapor from the pressed board precursor 2.

[0070] The method may further include heating the at least one roller 3, thereby heating the pressed board precursor 2. By supplying heat to the pressed board precursor 2, the liquid in the pressed board precursor 2 is more easily evaporated. By heating the at least one roller 3, heat is supplied from the heated roller(s) 3 to the pressed board precursor 2, and the speed of the roller can be easily controlled to control the amount of heat transferred to the pressed board precursor 2.

[0071] like Figures 3 to 5 As shown, the mechanical compression of the pressed board precursor 2 may comprise passing the pressed board precursor 1 sequentially through a plurality of compression stations S1, S2, S3 (see Figure 2 ), each compression station includes at least one pair of rollers 3, and when the pressed board precursor 2 passes through the gap between the corresponding pair of rollers 3, these rollers compress the pressed board precursor 3 together, wherein the gap at each station becomes smaller successively. If the thickness of the pressed board precursor 2 is to be significantly reduced, it may be appropriate to compress the pressed board precursor 2 in steps so as to facilitate the introduction of the pressed board precursor 2 between the rollers 3 in the gap between the rollers 3. Instead of passing the pressed board precursor 2 back and forth between the rollers 3 and reducing the gap between the rollers 3 each time, a plurality of compression stations may be used, wherein the gap becomes smaller at each station through which the pressed board precursor 2 passes.

[0072] The power of the electromagnetic waves emitted can be reduced sequentially for each compression station S1, S2, and S3. As the pressed board is compressed, its moisture content and quality are locally reduced, which means that less heating power is required to heat the pressed board later in the sequence / process. By reducing the power of the electromagnetic waves used for each compression station, overheating and surface burning, cracking, or weakening of the pressed board can be reduced. The power reduction can be achieved by reducing the impact and / or by intermittently operating the power supply to reduce the total power supplied over time. Electromagnetic waves with time-varying power can also be used for this purpose.

[0073] As an alternative or in addition to compression using a pair of rollers 3, the mechanical compression of the pressed board precursor 2 may include pressing the pressed board precursor 2 between a plurality of press plates 4, as shown in Figures 6, 7, and 8. The press plates 4 provide an alternative method for compressing the pressed board precursor 2. The plurality of press plates 4 may be used together as a stacked array 7 of press plates 4 for receiving the pressed board precursor 2 sandwiched between the press plates 4.

[0074] At least one of the plurality of press plates 4 may be heated, thereby heating the pressed board precursor 2. By supplying heat to the pressed board precursor 2, liquid in the pressed board precursor 2 evaporates more easily. By heating at least one of the plurality of press plates 4, heat is supplied from the heated press plate(s) 4 to the pressed board precursor 2.

[0075] At least after the step of mechanically compressing the pressed board precursor 2, electromagnetic wave emission may be performed in the pressed board precursor 2. By emitting electromagnetic waves toward the pressed board precursor 2 after mechanical compression of the pressed board precursor 2, the electromagnetic waves strike the relatively dry pressed board precursor, thereby wasting less energy on heating liquid, which can be more easily removed by compression.

[0076] Alternatively or additionally, electromagnetic wave emission may be performed on the pressed board precursor 2, at least during the step of mechanically compressing the pressed board precursor 2. The electromagnetic wave emission will produce a phase change, resulting in a high vapor concentration in the pressed board. The subsequent mechanical compression will allow for rapid and efficient extraction of moisture and diffusion through the pressed board.

[0077] Following the above description of the method, this method is provided by a suitably designed production line, herein referred to as apparatus for dewatering a pressed board precursor 2. The apparatus according to the following embodiments performs at least some of the functions described above with reference to the respective embodiments of the method.

[0078] The apparatus comprises a compression assembly configured to compress the pressed board precursor 2 and at least one electromagnetic wave transmitter 6 configured to transmit electromagnetic waves to the pressed board precursor 2 and / or the compressed pressed board.

[0079] The electromagnetic wave transmitter 6 is configured to transmit microwaves with a frequency in the range of 1 GHz to 300 GHz.

[0080] like Figures 1 to 5 As shown, the apparatus may further comprise one or more electromagnetic shielding members 9 configured to at least partially surround one or more spaces V1 , V2 , V3 around one or more parts of the pressed board precursor 2 .

[0081] The electromagnetic wave transmitter 6 may alternatively or additionally be configured to transmit radio waves having a frequency in the range of 1 MHz to 100 MHz.

[0082] The apparatus may further comprise a vent 11 and / or a drain 10 configured to enable moisture (such as water and / or water vapor) to exit the one or more spaces.

[0083] like Figure 1As shown, the electromagnetic waves may be emitted toward a first area A1 of the pressed sheet precursor 2 upstream of the pair of rollers 3 and / or may be emitted toward a second area A2 of the pressed sheet precursor 2 downstream of the pair of rollers 3 .

[0084] like Figures 1 to 5 As shown, the compression assembly may comprise at least a pair of rollers 3 defining a respective gap between the rollers 3. The gap is suitable for compressing the pressed board precursor according to its thickness and is typically in the range of 1-30 mm.

[0085] like Figures 3 to 5 As shown, one or more ultrasonic transmitters 14 may be provided, which are configured to transmit ultrasonic waves U toward the pressed board precursor. At least one ultrasonic transmitter 14 may be attached to a corresponding nip roll 3 such that the ultrasonic transmitter 14 rotates together with the corresponding nip roll 4.

[0086] The ultrasonic transmitter 14 may be suspended within the interior space of the corresponding roller 3 so that the ultrasonic transmitter 14 does not rotate with the corresponding roller 3. Alternatively, the ultrasonic transmitter 14 may be located outside the roller 3, mounted on the roller 3, or suspended so that the ultrasonic transmitter 14 does not contact the roller 3 and does not move with the roller 3.

[0087] The compression assembly may include a platen stack 7 comprising a plurality of platens 4 operable between a separation configuration P1 in which the pressed board precursors 2 are movable into respective intermediate spaces 8 between adjacent platens 4, and a compression position P2 in which the platens 4 are pressed closer to each other to reduce the intermediate spaces 8, thereby compressing the pressed board precursor(s) 2. Such a platen stack 7 may be configured as Figure 8a -b as shown.

[0088] It should be understood that any of the methods described herein for mechanically compressing a pressed board precursor may be used in conjunction with any of the methods described herein for emitting electromagnetic waves at a pressed board precursor.

[0089] Specifically, the present disclosure includes embodiments defined by the following clauses:

[0090] Item 1. A method (M) for producing a pressed sheet (1) for electrical insulation, the method comprising, in any order: a) mechanically compressing (M1) at least one pressed sheet precursor (2) suitable for electrical insulation, and b) emitting (M2) electromagnetic waves (EM) towards the pressed sheet precursor (2).

[0091] Clause 2. The method (M) according to clause 1, wherein the electromagnetic waves (EM) are microwaves with a frequency in the range of 1 GHz to 300 GHz.

[0092] Clause 3. The method (M) of clause 1, wherein the electromagnetic waves (EM) are radio waves having a frequency in the range of 1 MHz to 100 MHz.

[0093] Item 4. The method (M) according to Item 2 further includes providing one or more electromagnetic shielding members (9) configured to at least partially surround one or more spaces (V1, V2, V3) around one or more parts of the pressed board precursor (2), wherein microwaves are emitted within or into the one or more spaces (V1, V2, V3).

[0094] Clause 5. The method (M) according to clause 4, further comprising removing water and / or water vapor from one or more spaces (V1, V2, V3).

[0095] Clause 6. The method (M) according to any one of clauses 1 to 5, further comprising reducing the ambient pressure around the pressed board precursor (2) to a pressure below atmospheric pressure.

[0096] Clause 7. Method (M) according to any one of clauses 1-5, wherein emitting (M2) electromagnetic waves comprises emitting intermittent pulses of the emitted electromagnetic waves, or comprises repeatedly changing the power of the emitted electromagnetic waves between a higher power level and a lower power level over time.

[0097] Item 8. A method (M) according to any one of items 1 to 6, wherein the mechanical compression (M1) of the pressed board precursor (2) comprises passing the pressed board precursor (2) between at least one pair of rollers (3) while compressing the pressed board precursor (2) as it passes through the gap between the corresponding pair of rollers (3).

[0098] Item 9. A method according to Item 8, wherein the mechanical compression (M1) of the pressed board precursor (2) includes passing the pressed board precursor (2) through a plurality of compression stations (S1, S2, S3) in sequence, each compression station (S1, S2, S3) including at least one pair of rollers (3), and compressing the pressed board precursor (2) while passing through the gap between the corresponding pair of rollers (3), wherein the gap of each station (S1, S2, S3) becomes smaller in sequence.

[0099] Clause 10. Method (M) according to any one of the preceding clauses, wherein the emitted electromagnetic wave power is configured to cause at least some of the water of the pressed board precursor (2) to change from a liquid phase to a vapor or gas phase.

[0100] Item 11. An apparatus (5) for dewatering a pressed board precursor (2), the apparatus comprising a compression assembly configured to compress the pressed board precursor, at least one electromagnetic wave emitter (6) configured to emit electromagnetic waves toward the pressed board precursor (2) and / or the compressed pressed board (1).

[0101] Clause 12. The apparatus (5) according to clause 11, wherein the electromagnetic wave transmitter is configured to transmit microwaves with a frequency in the range of 1 GHz to 300 GHz.

[0102] Clause 13. The apparatus (5) of clause 12, further comprising one or more electromagnetic shielding members (9) configured to at least partially surround one or more spaces (V1, V2, V3) around one or more portions of the pressed board precursor (2).

[0103] Clause 14. The device (5) according to clause 11, wherein the electromagnetic wave transmitter is configured to transmit radio waves with a frequency in the range of 1 MHz to 100 MHz.

[0104] Clause 15. The apparatus (5) according to any one of clauses 11-14, further comprising a vent (11) and / or a drain (10) configured to enable moisture (such as water and / or water vapor) to leave the one or more spaces (V1, V2, V3).

[0105] The terms used herein are only used to describe specific aspects and are not intended to limit the present disclosure. Unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" used herein also include plural forms. As used herein, the term "and / or" includes any and all combinations of one or more associated listed items. It should also be understood that the terms "include", "comprise", "have", and / or "contain" when used herein specify the presence of the features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0106] It should be understood that although the terms first, second, etc. can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, without departing from the scope of this disclosure, a first element can be referred to as a second element, and similarly, a second element can be referred to as a first element.

[0107] As shown in the figures, relative terms such as "below" or "above" or "upper" or "lower" or "horizontally" or "vertically" may be used herein to describe one element's relationship to another. It should be understood that these terms and the above-described terms are intended to encompass different orientations of the device in addition to the orientations shown in the figures. It should be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

[0108] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that the terms used herein should be interpreted as having a meaning consistent with their meaning in this specification and the context of the relevant art, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0109] It should be understood that the present disclosure is not limited to the aspects described above and shown in the accompanying drawings; on the contrary, those skilled in the art will recognize that many changes and modifications are possible within the scope of the present disclosure and the appended claims. In the drawings and the description, the aspects disclosed are for illustration only and not for limitation, and the scope of the inventive concept is set forth in the appended claims.

[0110] 1 Pressed board 2 Pressed board precursor 3 Roller 4 pressure plate 5 Apparatus for dewatering pressed board precursors 6 electromagnetic wave transmitter 7 Platen stacking 8 In-between Space 9 Electromagnetic shielding components 10 Drain 11 vents 12 Ventilation fan / air pump 13 Adjustable / controllable vents 14 Ultrasonic transmitter M Method for producing pressed board M1 Mechanical compression M2 Emitting electromagnetic waves EM electromagnetic waves U ultrasound A1 Area upstream of the rollers A2 Area downstream of the rollers

[0111] Reference numerals

Claims

1. A method (M) for producing a pressed sheet (1) for electrical insulation, said method comprising, in any order: a) mechanically compressing (M1) at least one pressed board precursor (2) suitable for electrical insulation; as well as b) emitting (M2) electromagnetic waves (EM) towards said pressed board precursor (2), The mechanical compression (M1) of the pressed board precursor (2) includes passing the pressed board precursor (1) through a plurality of compression stations (S1, S2, S3) in sequence, and each compression station (S1, S2, S3) includes at least one pair of rollers (3). When the pressed board precursor (2) passes through the gap between the corresponding pair of rollers (2), the pair of rollers (3) compress the pressed board precursor together, wherein the gap of each station (S1, S2, S3) becomes smaller in sequence.

2. The method (M) according to claim 1, wherein The electromagnetic waves (EM) are microwaves with a frequency ranging from 1 GHz to 300 GHz.

3. The method (M) according to claim 1, wherein The electromagnetic waves (EM) are radio waves with a frequency in the range of 1 MHz to 100 MHz.

4. The method (M) according to claim 2, further comprising providing one or more electromagnetic shielding members (9) configured to at least partially surround one or more spaces (V1, V2, V3) around one or more parts of the pressed board precursor (2), in, The microwaves are emitted within or into the one or more spaces (V1, V2, V3).

5. Method (M) according to claim 4, further comprising removing water and / or water vapor from the one or more spaces (V1, V2, V3).

6. The method (M) according to any one of claims 1 to 5, further comprising reducing the ambient air pressure around the pressed board precursor (2) to a pressure below atmospheric pressure.

7. The method (M) according to any one of claims 1 to 5, wherein Said emitting (M2) electromagnetic waves comprises emitting intermittent pulses of the emitted electromagnetic waves, or comprises repeatedly varying the power of the emitted electromagnetic waves between a higher power level and a lower power level over time.

8. Method (M) according to any one of the preceding claims, wherein The power of the emitted electromagnetic waves is configured to cause at least some of the water of the pressed board precursor (2) to change from a liquid phase to a vapor phase or a gas phase.

9. An apparatus (5) for dehydrating a pressed board precursor (2), the apparatus comprising a compression assembly configured to compress the pressed board precursor (2) and comprising at least one electromagnetic wave emitter (6) configured to emit electromagnetic waves towards the pressed board precursor and / or the compressed pressed board (1). in, The compression assembly includes a plurality of compression stations (S1, S2, S3), each compression station (S1, S2, S3) includes at least one pair of rollers (3), and the at least one pair of rollers is suitable for compressing the pressed board precursor (3) when the pressed board precursor (2) passes through the gap between the corresponding pair of rollers, wherein the compression stations (S1, S2, S3) are arranged in sequence so that the pressed board precursor can pass through the plurality of compression stations (S1, S2, S3) in sequence, wherein the gap of each compression station becomes smaller in sequence.

10. The device (5) according to claim 9, wherein The electromagnetic wave transmitter is configured to transmit microwaves with a frequency ranging from 1 GHz to 300 GHz.

11. The apparatus (5) according to claim 10, further comprising one or more electromagnetic shielding members (9) configured to at least partially surround one or more spaces (V1, V2, V3) around one or more parts of the pressed board precursor (2).

12. The device (5) according to claim 9, wherein The electromagnetic wave transmitter is configured to transmit radio waves with a frequency in the range of 1 MHz to 100 MHz.

13. The apparatus (5) according to any one of claims 9 to 12, further comprising a vent (11) and / or a drain (10) configured to allow moisture, such as water and / or water vapor, to leave the one or more spaces (V1, V2, V3).

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