CN113840702B

CN113840702B - Method and device for heating and pressing a material mat

Info

Publication number: CN113840702B
Application number: CN202080030977.1A
Authority: CN
Inventors: A·克罗特; B·雷胡伊斯; K-P·施莱茨; G·斯托布
Original assignee: Siempelkamp Maschinen und Anlagenbau GmbH and Co KG
Current assignee: Siempelkamp Maschinen und Anlagenbau GmbH and Co KG
Priority date: 2019-05-24
Filing date: 2020-05-08
Publication date: 2023-01-17
Anticipated expiration: 2040-05-08
Also published as: WO2020239390A1; DE102019114016B4; CN113840702A; DE102019114016A1; WO2020239390A8

Abstract

The invention relates to a method for pre-heating a press material mat prior to entering a press, the press material mat being passed through a double-belt preheating device having an upper, continuously circulating, air-permeable conveyor belt and a lower, continuously circulating, air-permeable conveyor belt, in which the press material mat is subjected to steam or a steam-air mixture by at least one steam supply device and is thereby heated. The method is characterized in that, after the steam preheating in the double-belt preheating device, hot air is applied to the conveyor belt by means of at least one drying device arranged downstream of the steam supply device in the conveying direction during the course of the conveyor belt, so that the hot air flows along the conveyor belt without penetrating the mat, and so that moisture condensed on the conveyor belt by the steam preheating is absorbed by the hot air flowing along the conveyor belt and is discharged together with the hot air.

Description

Method and device for hot-pressing a material mat

Technical Field

The invention relates to a method for pre-hot pressing a material mat prior to entering a press in the manufacturing process of artificial boards, the pressed material mat is passed through a double belt preheating device having an upper continuously circulating gas-permeable conveyor belt and a lower continuously circulating gas-permeable conveyor belt; the press material mat is heated in a double belt preheating device by at least one steam supply device applying steam or a steam-air mixture.

The invention also relates to a double-belt preheating device for heating and pressing a material mat and to an apparatus for manufacturing an artificial board.

Background

The mat of pressing material to be heated (also simply referred to as "mat") is preferably a mat of pressing material for the manufacture of artificial boards. In principle, however, heating of other press material mats or material webs is also included. The press material mats used for manufacturing artificial boards are usually formed from chips or fibres, in particular wood chips or fibres, preferably sized wood chips or fibres, which are spread into a press material mat, for example on a spread belt conveyor or similar. This produces a continuous mat of press material and thus a continuous web of press material mats (Pressgutmattenstrang) which is heated by a double-belt preheating device and subsequently pressed into boards or continuous webs of boards in a press, for example in a continuously operating double-belt press, using pressure and heat. In order to optimize the pressing process, the press material mat or press material is preheated in a preheating device.

Mat preheating has long been practiced in various embodiments during the manufacture of wood-based panels. Thus, for example, double-belt preheating devices are known in which a mat of material is heated with steam, for example saturated steam having a temperature of between 100 ℃ and 130 ℃, by means of a steam supply device, the steam being sprayed onto the mat surface directly before the press inlet, thereby directly heating the covering layer. Where steam can be sprayed into the mat above and below. An endless conveyor belt constructed as a sieve belt holds the mat surface above and below during the steam injection.

Alternatively, the preheating is effected in a double belt preheating device by alternately applying a steam-air mixture to the mat surface, wherein the penetration of the mixture into the mat is assisted by suction or underpressure opposite the application side.

In addition, it is additionally possible in practice to additionally evacuate the mat after preheating and before it enters the continuously operating press, to be precise by means of a separate prepress or by means of a recompressor (compactor) integrated into the preheating device. The compactor expels air through the plurality of rollers out of the mat, thereby enabling higher density access to the inlet of the continuous press and reducing blow-outs

The risk of (c). This enables toHigher feed speeds.

A method and a device for preheating a mat of press material made of sized press material are known, for example, from DE 19701596 C2. The press-fit material mat is subjected to a flow treatment in a preheating device, in which a temperature-controlled fluid consisting of air and water vapor, having a set dew point and a set dew point difference and a temperature of less than 100 ℃ flows through the press-fit material mat.

As regards the production of biodegradable insulating panels, it is known to treat bulk mats with steam-air mixtures (see DE 19635410 A1). The mat or nonwoven is first compacted to the desired thickness and then a steam-air mixture is introduced into the compacted nonwoven in a heating zone over a period of 10 to 20 seconds, specifically while avoiding a pre-curing of the binder. For the purpose of age hardening and drying, in a further process step, a stream of hot air is guided through the compacted nonwoven. The apparatus known in this connection is therefore not used for preheating the mat for subsequent pressing in a separate press, but for preheating by means of a steam-air mixture and for age-hardening and drying the mat by means of hot air in a double belt press.

Furthermore, a method and an apparatus for preheating a mat of compacted material in the manufacturing process of artificial boards are known from EP 2213432 A1 and EP 2588286 B1.

Preheating the mat prior to a continuously operating wood-based board press has proven to be suitable in practice. Of particular importance here is a continuously circulating conveyor belt, which is preferably designed as a sieve belt and through which steam or a steam-air mixture is sprayed into the mat. Since the screen belt undergoes a certain cooling in the return stroke and is heated again to the process temperature and thus to the dew point in the steam injection zone, steam condenses on the screen belt in each cycle. The moisture in the sieve belt increases here until as much moisture is removed from the belt as is supplied to the belt in each cycle. Thus, under unfavorable boundary conditions (for example due to weather conditions or seasons), a large amount of condensate can collect in the belt, forming condensate droplets which are so large that they reach the product surface (i.e. the mat of press material) and there cause soiling of the surface of the final product (i.e. the wood-based board). Therefore, there is a need to avoid contamination of the product surface by condensate.

Since these problems are directly related to the principle of preheating by means of steam or steam-air mixtures, alternative methods for preheating the hot pressed material mat, for example by means of microwaves, have also been proposed (see for example DE 102016110808 A1). Nevertheless, a fundamentally advantageous and economical preheating of the mat by applying steam or a steam-air mixture is of considerable interest.

Disclosure of Invention

Starting from this, the technical task on which the invention is based is to provide a method and a device for the pre-heating of a material mat, which on the one hand takes advantage of the advantages of steam preheating or steam-air mixture preheating and on the other hand avoids or at least greatly reduces the problems of condensate stains on the product surface observed in practice.

To solve the task, the invention proposes the following teaching in a method of the same type for pre-hot pressing a mat of material, in particular before entering a press in the manufacturing process of artificial boards: in the case of a double-belt preheating device, hot air is applied to the conveyor belt (or at least one conveyor belt) after the steam preheating by means of a drying device arranged downstream of the (respective) steam supply device in the conveying direction during the course of the upper and lower conveyor belts, more precisely preferably such that the hot air flows along the upper and lower conveyor belts without penetrating the mat, and such that moisture which has condensed or is condensing on the conveyor belt by the steam preheating is absorbed by the hot air flowing along the conveyor belt and is discharged together with the hot air. The conveyor belt is preferably configured as a sieve belt.

The mat is thus preheated according to the invention in a manner known in principle by applying steam or alternatively a steam-air mixture in a double belt preheating device. But immediately afterwards the belt is dried by means of hot air, which absorbs moisture from the screen belt, so that the problem of condensate stains in the surface of the product can be reliably avoided. The invention is based on the recognition that: it is possible to carry out a simple and effective drying of the conveyor belt (in particular sieve belt) by means of hot air immediately after the application of steam and therefore also during the course of the conveyor belt, in which the mat is held between the belts. For this purpose, hot air is used, which, on the basis of its properties, is able to absorb moisture from the screen belt, i.e. hot air having a high temperature and a low relative air humidity is preferably used.

Preferably, hot air is used at a temperature exceeding 110 ℃, preferably exceeding 120 ℃, for example exceeding 130 ℃. This hot air not only has a strong absorption capacity for the moisture of the screen belt, but also prevents the screen belt from cooling to temperatures below 100 c during the drying process, which would violate the preheating principle of the back-up.

In order to dry the screen belt by means of hot air in a non-removable manner, it is necessary to use hot air with a low relative air humidity. In this respect, the invention proposes that the hot air preferably has a relative air humidity of at most 10%, preferably at most 5%, particularly preferably at most 2%. These values relate to the hot air before contact with the conveyor belt and can be measured as desired, for example in the region of the air inlet, for example shortly before or shortly after its mouth.

In practice, hot air suitable for drying conveyor belts can be provided very simply and economically by extracting, for example, ambient air from a production plant, which typically has a temperature of about 10 ℃ to about 50 ℃ and possibly a higher relative air humidity (at atmospheric pressure) at said temperature. By heating this air (for example by means of a steam-air heat exchanger) to a desired temperature of more than 110 ℃, for example more than 120 ℃, particularly preferably more than 130 ℃, the relative air humidity of the drying air is reduced. In order to achieve the desired very low relative air humidity values, additional air drying may be provided. Air has a very high drying potential by heating (and optionally drying).

In general, it is particularly important to dry the screen belt by means of (dry) hot air in the process region of the conveyor belt of a continuously operating double belt preheating device. The hot air is used only for drying the screen belt and not for treating the product and therefore not for treating the press material mat, since the preheating of the press material mat is carried out only by the steam or steam-air mixture previously introduced into the press material mat. The hot air is thus not blown into or sucked through the product, but is applied to the conveyor belt as follows, namely: the hot air flows only along the conveyor belt and absorbs moisture adhering to the conveyor belt on the basis of the high absorption capacity present by its own low relative air humidity, without penetrating the mat of press material and without affecting the mat temperature through preheating. For this purpose, the drying device may have, for example, an upper hot-air channel for heating the upper conveyor belt and a lower hot-air channel for heating the lower conveyor belt, each hot-air channel having an air inlet at (or near) one channel end and an air outlet at (or near) the opposite channel end, so that each hot-air channel forms a hot-air path for applying hot air to the respective conveyor belt. Thus, instead of being blown in from one side of the mat and sucked away from the other side of the mat, the hot air is supplied and discharged, respectively, on the same side of the mat, so that it flows only along the conveyor belt in the hot air channel without penetrating into the product. For this purpose, it is expedient for the hot air to be conducted through the respective hot air channel under low or excess pressure, which is lower than 10 mbar, preferably lower than 5 mbar. Preferably, the operation is carried out at a very low flow rate of hot air, which relates to a hot air propagation direction oriented parallel (or anti-parallel) to the conveying direction, that is to say the hot air flows along the conveyor belt substantially parallel (or anti-parallel) to the conveyor belt, more precisely preferably at a flow rate of less than 5m/s, particularly preferably less than 3m/s. Overall, the geometry and the mode of operation of the hot channel are selected, which results in a relatively low flow rate and thus a relatively long interaction duration of the hot air with the conveyor belt. The duration of the interaction or contact time between the hot air and the conveyor belt is therefore at least 2 seconds, preferably at least 3 seconds, for example 3 to 5 seconds. The hot air may flow along the conveyor belt on a hot air path having a length of at least 1 meter, preferably at least 2 meters. For this purpose, the length of the upper hot air duct and/or the lower hot air duct in the conveying direction can be at least 1 meter, preferably at least 2 meters, particularly preferably at least 3 meters.

Furthermore, it has proven to be advantageous for the hot air to be guided along the conveyor belt in a flow (main) direction opposite to the conveying direction. This means that the air inlet is arranged in the region of the rear end of the channel and the air outlet is arranged in the region of the front end of the channel, more precisely with respect to the conveying direction of the press material mat. Therefore, the conveyor belt and the hot air preferably contact each other in a counter flow.

The method can preferably be carried out by means of a double belt preheating device comprising an upper continuously circulating air-permeable conveyor belt and a lower continuously circulating air-permeable conveyor belt, between which a treatment gap is formed through which the mat can be guided in the conveying direction (by means of the driven conveyor belt). Furthermore, the double-belt preheating device comprises a steam supply device (arranged between the inlet and the outlet), by means of which the mat can be supplied with steam or a steam-air mixture between the inlet and the outlet in the treatment gap and can thus be heated. According to the invention, the double-belt preheating device has a drying device which is arranged downstream of the steam supply device in the conveying direction, but which is also arranged in the course of the conveyor belt and is therefore arranged between the inlet and the outlet, i.e. the drying device is arranged between the steam supply device and the outlet of the double-belt preheating device. With the aid of the drying device, preferably, hot air can be applied to the conveyor belt as follows: the moisture condensed on the conveyor belt by the steam preheating is absorbed by the hot air flowing along the conveyor belt and discharged together with the hot air. The conveyor belt is designed as an air-permeable and preferably air-permeable and water-vapor-permeable conveyor belt, for example as a screen belt.

It is particularly preferred that the mat is provided with steam supply means in which steam is pressed into the mat from above and from below simultaneously, so that at least one steam supply means is provided above the upper conveyor belt and below the lower conveyor belt, respectively. Preferably, downstream of these steam supply devices, corresponding drying devices for the conveyor belt are provided.

In principle, however, it is possible to assign the steam supply device to only one conveyor belt, and therefore the drying device to this conveyor belt. Finally, the following possibilities also exist in principle, namely: the steam supply device is arranged in the conveying direction on one conveyor belt first and the drying device is arranged downstream, and the other conveyor belt is arranged with the other steam supply device only after the steam supply device in the conveying direction, and then the drying device is arranged for the conveyor belt again at the downstream.

As already mentioned in connection with the method according to the invention, the drying device may have an upper hot air channel for heating the upper conveyor belt and a lower hot air channel for heating the lower conveyor belt, each having an air inlet (at one channel end) and an air outlet (at the opposite channel end), respectively. In terms of construction, the upper and lower hot-air ducts are preferably designed in such a way that the hot air flows through the ducts at a relatively low flow rate and thus has a long interaction duration with the screen belt and at the same time absorbs moisture and mixes air with moisture in the hot ducts without any loss of finger grip.

The hot air channel preferably has a width extending (substantially) over the entire width of the conveyor belt or beyond. The length of the hot air channel in the conveying direction is selected in the manner already described such that a relatively long interaction duration between the hot air and the conveyor belt is ensured. Furthermore, it is optionally expedient for the height of the hot-air channel to also be selected relatively large in order to be able to operate with a large amount of air and air mixed well, so that the moisture-laden hot air does not remain in the immediate vicinity of the conveyor belt over the entire conveying path, but rather is mixed well with the air above or below it in order to increase the moisture absorption.

Based on these considerations, it is optionally suggested: each hot air channel has a plurality of blocking elements, such as partition walls, which reduce the flow cross section and form flow openings in the region of the conveyor belt. The hot air thus flows through the hot air duct from the inlet to the outlet via corresponding obstructions or constriction points, which on the one hand bring the hot air into the region of the conveyor belt at the constriction points and the flow openings formed thereby and on the other hand ensure an increased velocity in the vicinity of the conveyor belt at the constriction points. This can lead to subsequent turbulence in the respective subsequent passage area at the obstacle and thus to an intensive and thorough mixing of the hot air, so that the moisture extracted from the conveyor belt is well distributed over the entire air volume within the passage or within the respective passage area. The drying potential of the air flowing past the screen belt is thus kept high over the entire interaction path, thus ensuring a high degree of drying.

According to a further proposal of the invention, the press material mat is not only preheated in a double belt preheating device but also compacted, more precisely with the aim of degassing the mat prior to the subsequent pressing process. The use of such a compacting device in a twin-belt preheating device is known in principle from the prior art, but according to the invention it is integrated into the claimed twin-belt preheating device, more precisely downstream of the drying device in the conveying direction. Therefore, after steam preheating and subsequent drying of the screen belt, recompaction is performed to vent the mat of compacted material. Structurally, this is achieved by a compacting device which can be configured, for example, as a roller device and can have an upper compacting roller and a lower compacting roller. The upper and/or lower compaction roller may be loaded by at least one suitable force device (kraft), such as at least one pressure cylinder (preferably a hydraulic cylinder), or by a plurality of force devices/pressure cylinders. The compacting rollers are integrated in the course of the conveyor belt, i.e. they act on the conveyor belt from both sides. The compacted material is thus loaded with pressure by the compacting roller with the conveyor belt in between.

Alternatively, the conveyor belt may be preheated by means of belt heating devices respectively arranged upstream of the steam supply device, before the steam is applied to the mat. Such a strip-shaped heating device is arranged, for example, in the return run of the conveyor belt, preferably directly before the transition of the return run into the process and thus directly before the inlet of the double-belt preheating device. The heating of the belt can be accomplished, for example, by applying hot air.

Furthermore, in the context of the invention, the region of the conveyor belt which extends from the inlet to the outlet and in which the mat of press material is therefore guided is referred to as the run and the conveyor belt region which is connected downstream, starting from the outlet to the inlet, forms the return run of the conveyor belt, which then passes back into the run at the inlet.

In a preferred embodiment, the cleaning of the conveyor belts by means of the belt cleaning device is provided, wherein preferably a separate belt cleaning device is associated with each conveyor belt. The belt cleaning device is preferably arranged in the return run of the respective conveyor belt, for example directly after the outlet of the double-belt preheating device. Thus, after the outlet of the mat of compacted material, the conveyor belt is cleaned by removing attached particles of compacted material, such as wood fibres or wood chips. Such a cleaning device may have at least one cleaning brush. Alternatively or additionally, the cleaning device can be operated with (warm) cleaning air, i.e. air is applied for cleaning. For this purpose, an additional suction device is usually provided for the cleaning air, so that the particles removed from the conveyor belt by means of the cleaning air and/or the cleaning brush are sucked away by the suction device. Of particular importance is the fact that the cleaning is optimized by the (prior) drying of the screen belt according to the invention. On the one hand, due to the low moisture of the screen belt, fibre attachment is avoided from the beginning. On the other hand, due to the lower humidity, the attached particles can be more easily removed during the cleaning process. Overall, this contributes to the trouble-free operation of the preheating device.

According to the invention, the described double-belt preheating device and its operation for preheating a hot-pressed material mat are of importance. The invention also relates to an installation for manufacturing artificial boards with at least one spreading device for forming a mat of pressing material, a double-belt preheating device of the type described and a press for pressing the preheated mat of pressing material. This press, which is preferably designed as a continuously operating double belt press, is therefore preferably arranged downstream of the double belt preheating device according to the invention. The double-belt preheating device is therefore not used for producing the finished product, but only for preheating the press material mat within the production process, i.e. the preheated press material mat is subsequently pressed into the finished product in a separate press using pressure and heat.

The press arranged downstream of the preheating device is preferably designed as a double belt press and has, for example, an upper and a lower heating plate and, in the upper part of the press and in the lower part of the press, continuously circulating press belts, such as steel press belts, which are supported on the heating plates or press plates, for example, with roller body units (such as rollers) connected in between. One or both of the heating plates are loaded by a pressure cylinder supported on the press frame (e.g., on the press frame). The preheating device according to the invention can therefore be integrated into conventional manufacturing processes and combined with known double belt presses.

Drawings

The invention is explained in detail below with reference to the drawings, which show only one embodiment. The attached drawings are as follows:

fig. 1 shows, in a simplified diagram, a part of an apparatus for manufacturing artificial boards;

FIG. 2 shows, in a disassembled perspective view, a double belt preheating device according to the invention of the apparatus according to FIG. 1; and is

Fig. 3 shows a schematic simplified side view of the double-belt preheating device according to fig. 1 (partially).

Detailed Description

Fig. 1 shows a simplified illustration of an installation for manufacturing artificial boards in continuous operation. First, a bulk material to be pressed, such as wood fibres or wood chips, is spread onto a belt conveyor by means of a spreading device 1, which is only schematically shown, to form a bulk material mat or pressed material mat 2. The bulk mat produced in this way is pretreated in a double belt preheating device 3 and subsequently pressed in a continuously operating press 4 using pressure and heat into a board or a plate-like continuous web, such as chipboard or fiberboard. The press 4 is preferably designed as a double belt press with upper and lower hot plates and with continuously circulating press belts (e.g. steel press belts) in the upper part of the press and in the lower part of the press, which press belts are supported on press plates (hot plates) with roller elements (e.g. rollers) connected in between. One or both of the heating plates are loaded by a pressure cylinder supported on the press frame (e.g., on the press frame).

In order to optimize the pressing process in the press 4, the press material mat 1 is preheated according to the invention by means of a preheating device 3, which is only schematically illustrated in fig. 1. In the preheating device 3, the pressing material mat 2 is preheated by means of steam or a steam-air mixture, which is injected into the pressing material mat 2 and/or sucked through the pressing material mat 2.

A double belt preheating device 3 is shown in fig. 2 and 3. It has an upper continuously circulating air-permeable conveyor belt 5a and a lower continuously circulating air-permeable conveyor belt 5b. In this embodiment, the

conveyor belts

5a, 5b are configured as

sieve belts

5a, 5b. The conveyor or

screen belts

5a, 5b are each guided around a plurality of rollers or rollers 6, at least one of which is configured as a drive roller for the upper and lower part. Between the

conveyor belts

5a, 5b a process gap is formed, through which the mat 2 is guided in the conveying direction T from the inlet E to the outlet a. The region of the

conveyor belts

5a, 5b which extends from the inlet E to the outlet a and in which the mat of pressing material 2 is therefore guided is referred to as the course V and the region starting from the outlet a to the inlet E connected downstream forms the return path R, which then again merges into the course V at the inlet E.

Directly after the inlet E, the double-belt preheating device 3 has a steam supply device 7 with an upper steam supply tank 8 and a lower steam supply tank 8, by means of which the mat 2 is steamed or, as an alternative, a steam-air mixture and is heated thereby in the treatment gap. It is possible to provide a steam injection box 8 on the upper side of the belt and on the lower side of the belt, respectively, so that steam is pressed into the mat from both sides. But alternatively it is also possible to apply steam to the mat from one side and suck it away from the other side. Details are not shown.

According to the invention, the preheating device 3 has an additional drying device 9, which is also integrated into the double-belt preheating device 3 and is arranged downstream of the steam supply device 7 in the conveying direction T. The drying device 9 is not used for processing the mat of press material 2, but only for drying the conveyor belt and thus the

screen belts

5a, 5b. This is because hot air can be applied to the

screen belts

5a, 5b by the drying device 9, so that moisture condensed on the

conveyor belts

5a, 5b by steam preheating is absorbed by the hot air L flowing along the conveyor belts and discharged together with the hot air L. The drying means 9 are therefore also arranged in the course of the

conveyor belts

5a, 5b and are therefore arranged in the region of the mat of press material between the inlet and the outlet. The drying device 9 has an upper hot air channel 12a and a lower hot air channel 12b, each having an air inlet 13a, 13b at one channel end and an

air outlet

14a, 14b at the opposite channel end. Hot air L having a temperature of 130 ℃, for example, and a relative air humidity of at most 5%, preferably at most 2%, passes by the

screen belts

5a, 5b through the

hot air ducts

12a, 12b, and flows only along the

screen belts

5a, 5b for drying purposes without penetrating into the mat of press material. For this purpose, the drying device is constructed and operated in such a way that the hot air L moves along the

conveyor belts

5a, 5b at a relatively low flow velocity, the flow velocity in the main direction of flow oriented substantially parallel to the conveying direction T preferably being less than 3m/s.

A relatively long contact time for absorbing moisture, which may be, for example, 3 to 5 seconds, and thus an interaction time, between the hot air L and the

conveyor belts

5a, 5b is thereby achieved. The length X of the hot air path, which is defined by the length X of the upper hot air channel 12a and the lower hot air channel 12b, is relatively large here, so that a correspondingly large interaction time is achieved in consideration of the flow rate.

Furthermore, it can be seen in the drawing that each

hot air channel

12a or 12b has a plurality of blocking elements, such as partition walls 15, which reduce the flow cross section and are therefore oriented transversely to the flow direction. In the region of the

conveyor belts

5a, 5b, these blocking elements or separating walls 15 are interrupted so that flow-through openings 16 are formed in the immediate vicinity of the

conveyor belts

5a, 5b. This achieves that, on the one hand, the hot air L is reliably guided directly along the

conveyor belts

5a, 5b. Furthermore, increased velocities and thus turbulences occur in narrow places or in the region of the flow-through openings 16, which result in good thorough mixing of the air at the channel height. This is because although primarily concerned with applying hot air directly to the conveyor belt, the

channels

12a, 12b have a relatively large height H so that sufficient air can be provided for thorough mixing and thus for irreparable removal of moisture from the conveyor belt. Improved thorough mixing and thus improved drying is achieved by the construction with the blocking element 15 and the flow-through openings 16. Furthermore, the

channels

12a, 12b are designed such that the hot air can of course be in high contact with the conveyor belt. For this purpose, the shell-like or box-

like channels

12a, 12b are configured with openings or are configured to be open overall on their side facing the conveyor belt and thus the mat. The channel walls directly adjoining the

respective screen belt

5a, 5b are therefore preferably provided with a large number of openings. It can be constructed, for example, as a grid plate or be equipped with a grid plate. Details are not shown in the drawings.

The hot air L is preferably supplied as ambient air or extracted from the ambient air, for example from a production plant in which the press plant is located. This ambient air typically has a temperature of 10 ℃ to 50 ℃ at atmospheric pressure. The ambient air is heated, for example by a steam-air heat exchanger, not shown, to a desired temperature, for example 130 ℃, and the relative air humidity is thereby reduced very significantly to a defined value, so that the hot air has an excellent moisture absorption capacity. The hot air is guided by suitable means and supplied at a relatively low pressure below 5 mbar via air inlets 13a or 13b into the

respective channels

12a, 12b and discharged at the opposite channel ends via

outlets

14a, 14b. In the embodiment shown, the hot air flows along the conveyor belt in a main flow direction opposite to the conveying direction T of the conveyor belt, i.e. the air is applied in counter-flow. It is always particularly important that the hot air is not pressed into the mat, but that the supply of hot air and the corresponding discharge of hot air are arranged on the same side of the mat 2, so that the hot air flows along the conveyor belt.

Furthermore, the figures show that the double-belt preheating device 3 is additionally equipped in a preferred embodiment with a compacting device 10, which is arranged downstream of the drying device 9, but is also integrated into the double-belt preheating device 3. The mat is compacted (in progress) by means of the compacting device 10 in order to evacuate air from the mat, thereby optimizing the subsequent pressing process in the press 4 and reducing the risk of bursting. In this way, the feed rate of the plant is increased and thus greater economic efficiency is achieved. The compacting device 10 has an upper compacting roller 11 and a lower compacting roller 11, the compacting rollers 11 acting with the

respective screen belt

5a, 5b in between on the press material mat 2. One of the compacting rollers 11, as the compacting roller 11 above, may be equipped for this purpose with suitable force means, such as one or more pressure cylinders 19.

The preheating device 3 is additionally equipped with a belt cleaning device 18, by means of which the

conveyor belts

5a, 5b are cleaned after the outlet a. Such a belt cleaning device 18 can be equipped, for example, with an air supply device and/or a brush and/or suction device. Details are not shown. In the case of belt cleaning with air application, this air application in the return run R should be distinguished from the hot air application during drying and thus in the course V.

Furthermore, an additional belt heating device 17 of the

conveyor belts

5a, 5b is provided in the double-belt preheating device 3, namely before the inlet E of the device in the return run R of the conveyor belts, i.e. the

conveyor belts

5a, 5b are preheated before contact with the mat 2 of press material and therefore also before steam is applied, for example by applying hot air, so that the amount of steam condensing on the conveyor belts is kept low from the beginning.

In addition, suitable devices can be provided in the apparatus or in the double-belt preheating device for detecting, monitoring, controlling and/or regulating important parameters, such as temperature, pressure or humidity. Some sensors are shown by way of example in fig. 3. The temperature of the

respective conveyor belt

5a or 5b can thus be measured by means of the temperature sensor 19, preferably in the return run R. Furthermore, the moisture of the

conveyor belt

5a or 5b can be measured, for example, in the return run R by means of the sensor 20. At least one temperature sensor and/or at least one pressure sensor, which are only indicated by reference numeral 22 in fig. 3, can be integrated in the steam supply device 7. Furthermore, one or more temperature sensors 21 for monitoring the temperature of the hot air can be provided, by means of which the temperature of the hot air can be measured, in particular in the region of the air inlet 13a or 13 b. Fig. 3 shows the sensor only in the upper part of the double-belt preheating device 3 by way of example. Of course, corresponding sensors can be provided in the same way in the lower part.

Claims

1. Method for pre-hot pressing a mat (2) of pressing material before entering a press (4), wherein the mat (2) of pressing material before entering the press (4) is passed through a double belt preheating device (3) having a continuously circulating air-permeable upper conveyor belt (5 a) and a continuously circulating air-permeable lower conveyor belt (5 b); the press material mat (2) is subjected to steam or a steam-air mixture in a double-belt preheating device (3) by means of at least one steam supply device (7) and is thereby heated;

characterized in that, after the steam preheating in the double-belt preheating device (3), hot air (L) is applied to one of the upper conveyor belt (5 a) and the lower conveyor belt (5 b) or to the upper conveyor belt (5 a) and the lower conveyor belt (5 b) in a process (V) of the upper conveyor belt and the lower conveyor belt by means of at least one drying device (9) arranged downstream of the steam supply device (7) in the conveying direction (T), such that the hot air flows along the upper conveyor belt (5 a) and the lower conveyor belt (5 b) without penetrating the press material mat, and such that moisture which has condensed or is condensing on the upper conveyor belt (5 a) and the lower conveyor belt (5 b) by the steam preheating is absorbed by the hot air (L) flowing along the upper conveyor belt (5 a) and the lower conveyor belt (5 b) and is discharged together with the hot air.

2. Method according to claim 1, characterized in that the hot air (L) has a temperature exceeding 110 ℃.

3. Method according to claim 2, characterized in that the hot air (L) has a temperature exceeding 120 ℃.

4. Method according to claim 3, characterized in that the hot air (L) has a temperature exceeding 130 ℃.

5. The method according to any one of claims 1 to 4, wherein the hot air has a relative air humidity of at most 10%.

6. The method of claim 5, wherein the hot air has a relative air humidity of at most 5%.

7. The method of claim 6, wherein the hot air has a relative air humidity of at most 2%.

8. Method according to any one of claims 1 to 4, characterized in that the flow speed of the hot air (L) parallel to the conveying direction (T) is less than 5m/s.

9. Method according to claim 8, characterized in that the flow speed of the hot air (L) parallel to the conveying direction (T) is less than 3m/s.

10. Method according to any of claims 1 to 4, characterized in that the contact time between the hot air (L) and the upper or lower conveyor belt is at least 2 seconds.

11. The method of claim 10, wherein the contact time is 3 seconds to 10 seconds.

12. The method of claim 11, wherein the contact time is 3 seconds to 5 seconds.

13. A method according to any one of claims 1-4, characterized in that the hot air (L) flows along the upper conveyor belt (5 a) and the lower conveyor belt (5 b) on a hot air path having a length (X) of at least 2 meters.

14. Method according to any one of claims 1-4, characterized in that the hot air (L) flows along the upper conveyor belt (5 a) and the lower conveyor belt (5 b) in a flow direction opposite to the conveying direction (T).

15. The method according to any one of claims 1 to 4, characterized in that the mat (2) of press material is compacted by means of a compacting device (10) arranged downstream of the drying device (9).

16. A method according to any one of claims 1 to 4, characterized in that the upper conveyor belt (5 a) and the lower conveyor belt (5 b) are preheated before the application of steam to the mat of compacted material, respectively, by means of a belt heating device (18) arranged upstream of the steam supply device (7).

17. Method according to any one of claims 1 to 4, characterized in that for the hot air (L) ambient air is used, which has a temperature of 10 ℃ to 50 ℃, which is heated to the hot air temperature with a reduced relative air humidity.

18. Double-belt preheating device (3) for heating a mat of pressing material (2) by means of the method according to any one of claims 1 to 17, comprising:

-a continuously circulating air-permeable upper conveyor belt (5 a) and a continuously circulating air-permeable lower conveyor belt (5 b) forming a treatment gap therebetween through which the pad of compacted material (2) can be guided in a conveying direction (T),

at least one steam supply device (7) by means of which the mat of compacted material can be heated by applying steam or a steam-air mixture in the treatment gap,

characterized in that at least one drying device (9) is provided, which is arranged downstream of the steam supply device (7) in the conveying direction (T), by means of which hot air can be applied to one of the upper and lower conveyor belts or to the upper and lower conveyor belts (5 a, 5 b) in the course (V) of the upper and lower conveyor belts (5 a, 5 b), such that it flows along the upper and lower conveyor belts without penetrating the mat of press material, and such that moisture which has condensed or is condensing on the upper and lower conveyor belts (5 a, 5 b) by means of steam preheating is absorbed by and discharged together with the hot air (L) flowing along the upper and lower conveyor belts (5 a, 5 b).

19. The device according to claim 18, characterized in that the upper conveyor belt (5 a) and the lower conveyor belt (5 b) are configured as sieve belts.

20. The device according to claim 18 or 19, characterized in that a compacting device (10) for compacting the mat of compacted material (2) is provided downstream of the drying device (9).

21. Device according to claim 18 or 19, characterized in that for preheating the upper conveyor belt (5 a) and the lower conveyor belt (5 b), a belt heating device (17) is provided upstream of the steam supply device (7), respectively, by means of which the upper conveyor belt (5 a) and the lower conveyor belt (5 b) can be preheated before applying steam to the mat of compacted material.

22. Device according to claim 18 or 19, characterized in that the upper conveyor belt (5 a) and the lower conveyor belt (5 b) are each provided with a belt cleaning device (18).

23. An apparatus according to claim 18 or 19, characterized in that the drying means (9) has an upper hot air channel (12 a) for heating the upper conveyor belt (5 a) and a lower hot air channel (12 b) for heating the lower conveyor belt (5 b), each hot air channel (12 a, 12 b) having an air inlet (13 a, 13 b) at one channel end and an air outlet (14 a, 14 b) at the opposite channel end, respectively.

24. Device according to claim 23, characterized in that each hot air channel (12 a, 12 b) has a plurality of blocking elements of reduced flow cross section, which form or have flow openings (16) in the region of the upper and lower conveyor belts.

25. Device as claimed in claim 22, characterized in that the belt cleaning device is equipped with an air supply device and/or a brush and/or a suction device, respectively.

26. Device according to claim 20, characterized in that the compacting device has an upper and a lower compacting roller (11), which can be loaded by at least one force device.

27. Plant for manufacturing artificial boards having at least one spreading device (1) for forming a mat (2) of press material, a double belt preheating device (3) according to any of claims 18 to 26 for pre-heating a mat (2) of press material and a press (4) for pressing the preheated mat (2) of press material using pressure and heat.