EP3403816B1 - Method for pressing a pressed material mat - Google Patents

Description

• wobei die Presse ein Pressengestell (z. B. mit mehreren hintereinander angeordneten Pressenrahmen), zumindest eine (beheizbare/beheizte) obere Pressenplatte und zumindest eine (beheizbare/beheizte) untere Pressenplatte aufweist, wobei die obere Pressenplatte und/oder die untere Pressenplatte zur Einstellung eines zwischen den Pressenplatten angeordneten Pressspaltes mit am Pressengestell abgestützten Presszylindern beaufschlagt wird,
• wobei von den Pressenplatten einlaufseitig ein Einlaufbereich gebildet wird, in dem die in den Pressspalt einlaufende Pressgutmatte während einer Verdichtungsphase verdichtet wird.

The invention relates to a method for pressing a pressed material mat in the course of the production of wood-based panels in a continuous press according to claim 1,

• wherein the press has a press frame (e.g. with several press frames arranged one behind the other), at least one (heatable/heated) upper press platen and at least one (heatable/heated) lower press platen, the upper press platen and/or the lower press platen for adjustment a press gap arranged between the press plates is acted upon by press cylinders supported on the press frame,
• an inlet area being formed by the press plates on the inlet side, in which the pressing material mat entering the press gap is compacted during a compaction phase.

In this case, endlessly circulating press belts, e.g. As steel strips, provided with the interposition of rolling element assemblies, z. B. roll bars, are supported on the press plates. The mat of pressed material is guided into the press gap with the aid of the press belts and passed through the press gap and pressed into a wood-based panel or a (continuous) wood-based panel strand using pressure and heat. Wood-based panel means in particular fiberboard or chipboard. In a fiberboard it can be z. B. be an MDF board or an HDF or LDF board.

In principle, there is the possibility that the press plates each have a constant thickness over their entire length, so that an inlet-side Section of such a press plate forms the inlet area in which the pressing material mat (to nominal size) is compacted. However, it is preferably provided that the press plates in the inlet area have increased flexibility or bending elasticity compared to the adjoining main press area, so that a flexible contour of the upper press plate or lower press plate can be adjusted at least in the inlet area. For this it is expedient if the upper press platen and/or the lower press platen (in the entry area) has a smaller thickness than in the main pressing area. In a particularly preferred embodiment, it is provided that as the upper press plate, on the one hand in the infeed area, an upper infeed press plate and on the other hand an upper main press plate arranged downstream of this in the working direction are provided and/or that as the lower press platen on the one hand in the infeed area a lower infeed press plate and on the other hand a lower main press plate arranged downstream of this in the working direction is provided. The inlet press plates, which in practice are also often referred to as inlet plates, preferably have a smaller thickness and thus higher flexural elasticity than the main press plates, which in practice are often also simply referred to as press plates. Both the main press plate and the inlet plates are preferably heatable, e.g. B. provided with heating channels for a heating medium.

The method therefore preferably relates to a continuously operating double belt press with a so-called flexible press infeed, in which the infeed contour of the infeed gap or infeed mouth can be adjusted steplessly and practically to produce any continuous bending lines.

Such a continuous press is z. B. from the DE 197 40 325 C5 known. Double-acting differential cylinders are connected (in several rows) to the inlet plates, so that tensile and compressive forces can be adjusted continuous bending lines are connected in a predetermined distribution to the upper inlet plate or to the lower inlet plate.

Based on such a press is in the DE 199 18 492 C1 a method for pressing a pressed material mat is described, in which the pressed material mat is compressed below the nominal size at the beginning of the run-in phase in the entry area of the inlet mouth and as a result of which its heat transport capacity is increased with accelerated heat supply, and the pressed material mat after a specified compression phase with the expansion of the press gap between the inlet plates for generation is relieved of a decompression. The background to this state of the art is the consideration that the flexible or highly flexible design of the infeed mouth makes it possible to variably design the area of the highest compaction in the longitudinal direction of the press, depending at least on the respective pressing material properties, the respective mat height, the respective spreading density of the pressing material in the longitudinal direction of the press , so that the narrowest gap between the upper and lower sheet steel strip and consequently the upper and lower inlet plate does not always have to be at the same point and seen relatively far in the press in the direction of production. Rather, according to DE 199 18 492 C1 an early compaction of the respective pressing material mat can be realized by compression below the nominal size already taking place in the inlet gap.

Incidentally, in practice with continuous presses, the problem has been dealt with that arises due to the construction of the frame construction of the press frames, since pressure fluctuations can occur, so that glue bridges that have already formed are broken up again. This can lead to a loss of strength in the wood-based panel produced. In order to avoid such pressure fluctuations as a result of the frame construction of a continuous press, in the DE 199 26 258 B4 the application of so-called "bevel principle". For this purpose, in the calibration zone of the pressing section, the support lines on the press platen of the fixed press beam should be offset from the support lines on the press platen of the movable press beam, so that in the main pressing area both the upper press platen and the lower press platen parallel to each other in a corrugated manner, forming a Press lengths constant press gap are deformed.

In the DE 103 20 741 B4 and the EP 2 514 585 A1 the use of pressure distribution plates between adjacent press frames in the longitudinal direction of the press, with corresponding supports for the press plates, is described in order to implement the oscillating principle in conventional frame constructions. Such pressure distribution plates with supports can, for. g. in the area of the lower press platen and also in the area of the lower inlet plate (cf. EP 2 514 585 A1 ). Furthermore, the US4017248A ,the EP 1323 509 A1 as well as the EP 185 993 A2 Prior art method of pressing a pressed material mat.

However, these considerations regarding the bevel principle relate primarily to the main pressing area, which is formed by the usual main pressing plates. Such constructions are intended to reduce pulsations in the material to be pressed, particularly in the main pressing area, in particular from the point of view of saving glue.

The object of the invention is to create a method for pressing a pressed material mat in the course of the production of wood-based panels in a continuous press of the type described above, which is characterized by particularly high cost-effectiveness and high panel quality at the same time.

To solve this problem, the invention teaches that the upper press platen and/or the lower press platen, at least in the infeed area, is lowered and raised cyclically in a pulsating manner, at least in certain areas, so that the pressed material mat entering the infeed gap (at least in the compaction phase) is repeatedly compressed and cyclically Relieving by means of the press cylinders connected to the upper press platen and/or the lower press platen in the inlet area, several pulsingly varying compression phases and decompression phases are successively passed through.

The infeed area or the infeed mouth of the continuous press is consequently opened and closed in a cyclically pulsating manner, so that the mat to be pressed is compressed and relieved in a cyclically pulsating manner, at least in the infeed area and possibly also in a section of the main pressing area, so that the actual compaction process in the infeed area is accompanied by pulsating compaction and Relief is superimposed. As a result, the pressed material mat is not continuously compacted down to a nominal size (compaction size) in the compaction phase, as has been the case up to now, but is instead cyclically relieved again and again during the compaction phase. According to the invention, the method includes cyclically compressing the pressed material mat several times to the nominal size in several compression phases or even cyclically several times below the nominal size and consequently to realize an overcompression, with relief in the decompression phases taking place between the compression phases, specifically beyond the nominal size. The pressing material mat is preferably completely relieved of pressure in the decompression phases and is consequently depressurized, ie the pressure in the pressing material mat is reduced to zero or almost zero. In the context of the invention, nominal dimension means the thickness of the compressed mat at the end of the pulsating inlet area. This nominal size (compaction size) is usually slightly larger (e.g. up to 20% or up to 15% larger) than the finished size (final size) of the panel leaving the press, since there is still residual compaction/calibration in the press and thus, if necessary, residual compression from the nominal size to the finished size.

The invention is based on the surprising finding that the pressing process can be optimized, in particular with regard to economic efficiency, if a pulsation of the pressing material, which has been disruptive in the main pressing area in particular, is specifically and actively generated in the area of the inlet. Because while pulsations in the rear area of the press, in which the compacted plate is consolidated, must be avoided, the invention has recognized that a targeted and active pulsation in the infeed area (and possibly in a first part of the main pressing area) has a positive effect on the economy affects. In principle, the aim is to heat the mat to be pressed as quickly as possible (up to the inside of the mat) in the press, since the glues usually used at a certain temperature of e.g. B. about 100 ° C can be activated. Surprisingly, it has been found that a higher temperature in the mat can be reached much more quickly if the mat to be pressed is cyclically pulsatingly compressed and decompressed in the inlet area and, if necessary, in a part of the adjoining main pressing area, with the surprising effect that a heat can be introduced into the mat very quickly and the respective critical temperature (e.g. 100 °C) is reached in the press much earlier than with conventional infeed constructions or infeed settings. The pulsating compression and decompression allows the steam to penetrate the mat interior very quickly, so that it heats up very quickly. The interim relief is important here, in that the press is (almost) depressurized or opened at least in the infeed area, so that the mat can cyclically pulse again to a greater thickness than in the previously compacted and preferably over-compacted state. When the pressure is relieved, the mat becomes more porous, allowing the steam to penetrate more easily. During the over-compaction, an improved heat transfer from the press to the product or the mat is produced.

It is within the scope of the invention that the press nip pulsates in the inlet area with a predetermined constant pulse amplitude by z. B. the upper press platen is raised and lowered with a constant pulse amplitude. Constant pulse amplitude means that the inlet mouth always pulsates constantly with the same pulse amplitude, although the pulse amplitude does not have to be the same over the length of the inlet area. It is therefore within the scope of the invention that e.g. the upper press plate, e.g. inlet plate (or the lower press plate, e.g. inlet plate) is periodically raised and lowered with always the same pulse amplitude, with this pulse amplitude then being able to decrease in relation to the working direction, e.g. from pulse to pulse can decrease. This means that with a periodically pulsating upper press plate, e.g. infeed plate, each point of the mat of pressed material entering is compressed and decompressed with decreasing pulse amplitude, e.g. pulse amplitude decreasing from pulse to pulse. The pulse amplitude can, for example, be between 1 mm and 10 mm over the entire pulsating area of the press platen, but then decrease in the working direction.

It is fundamentally within the scope of the invention that the pressure generated in the pressed material mat is always identical in the compression phases or at the maximum of the compression phases and consequently remains constant, namely for several or all pulse maxima. However, the invention has recognized that a Heat input into the pressing material mat is particularly rapid if the pressure generated in the pressing material mat decreases in the compression phases from compression phase to compression phase, i.e. the pressure in the pressing material mat is reduced in the pulse maxima from pulse maximum to pulse maximum. The decreasing pressure can result in the pressing material mat as a result of the constantly decreasing counter-pressure, specifically as a result of the product, which essentially consists of wood, becoming constantly softer as a result of the steam. Thus, the resistance of the not yet consolidated part of the mat decreases.

Since the effect according to the invention is achieved to a particular degree by a pumping effect of the water/steam into the interior of the mat, it is expedient to provide the pressing material mat with a sufficient moisture content or water content. Particularly preferably, the liquid required for generating the steam can be made available by moistening the pressing material mat on the mat surface, specifically preferably from both sides onto both plate surfaces. In combination with the measures according to the invention, a very rapid introduction of heat can be realized in this way. In contrast to conventional methods of steam preheating or the like, applying water to the mat surface is very easy and inexpensive. Another advantage is the fact that the water remains in the system due to the steel press belts circulating in the continuous press and is therefore inherent to the system. This means that the use of screens, textile belts or perforated heating plates can be dispensed with.

As already explained, the press design must allow for cyclic pulsation of the press platen, at least in the infeed area. This can e.g. B. realized in that in the inlet area at least one upper Press plate or at least a lower press plate is provided with sufficient bending elasticity. It may be useful to provide press plates with a thickness of up to 70 mm, preferably up to 60 mm, in the inlet area, while the thickness of the press plates in the main pressing area is greater than 80 mm, e.g. 80mm to 120mm, e.g. B. can be 100 mm. In principle, this can be achieved with uniform press plates that have different thicknesses in sections. However, it is particularly preferred to provide main press plates in the main press area and (separate) infeed press plates with a correspondingly smaller thickness in the infeed area. It is within the scope of the invention that the pulsation is realized exclusively in the area of the upper and/or lower inlet press plate. Depending on the length of this inlet press plate, however, it is expedient if the pulsation also extends into the area of the main press plates. Alternatively, however, there is also the possibility of designing the infeed press plates with a correspondingly large length, so that the pulsation can then be restricted to the area of the (flexible) infeed press plates. In this case it may then be possible to reduce the length of the main press plates in which no pulsation is realized.

Alternatively, there is also the possibility of realizing the press plates over the entire length of the press with a constant thickness, in which case only an inlet-side area of these uniform press plates is designed to pulsate in the manner according to the invention.

Since, according to the invention, the active pulsation in the infeed area results in very rapid heating of the pressed material mat, there is the possibility of significantly reducing the overall length of the press while the press speed remains the same. Alternatively, there is the possibility of staying the same Press length to work at a significantly higher speed, so that the production capacity is increased. In addition, in the prior art it is necessary, in order to avoid temperature-related damage to the surfaces of the mat, not to select the temperatures of the press plates too high, since relatively long temperature rise times are used. Due to the shorter temperature exposure time on the surface achieved according to the invention, it is now possible to further increase the temperature of the press plates, e.g. B. to temperatures of over 200 ° C, optionally to over 220 ° C. This significantly reduces the heating time factor.

In practice, the method described can basically be implemented with a continuous press of known design. It may be useful to work with relatively long inlet plates that are provided with a large number of rows, each with several inlet cylinders. However, the press can also be modified in the manner described above. It also goes without saying that with an overall cyclically pulsating inlet gap, a suitable transition to the non-pulsating areas of the press, e.g. B. the pulse amplitude decreases successively in a transition range. This corresponds e.g.

The (respective) pulsating press platen can have a (constantly) curved contour or can be set with a constantly curved contour via the press cylinder, so that this curved contour is then raised and lowered in a pulsating manner overall.

Fig. 1

eine kontinuierliche Presse in einer vereinfachten Seitenansicht,

Fig. 2

(stark vereinfacht) den Einlaufbereich einer kontinuierlichen Presse gemäß der Erfindung,

Fig. 3

die Temperaturentwicklung einer Pressgutmatte im Vergleich.

The invention is explained in more detail below with reference to a drawing that merely shows an exemplary embodiment. Show it:

1

a continuous press in a simplified side view,

2

(greatly simplified) the inlet area of a continuous press according to the invention,

3

the temperature development of a pressing material mat in comparison.

In 1 a continuously operating press for the production of wood-based panels, in particular fiberboard, is shown. In this continuous press, a pressed material mat entering the press in working direction A with the input thickness (E) made of glued wood particles, e.g. B. glued wood fibers, continuously pressed to form a wood-based panel or a wood-based panel strand. The press has a press frame 1 . In this exemplary embodiment, an upper main press platen 2 is arranged in the upper part of the press and a lower main press platen 3 is arranged in the lower part of the press. These main press plates 2, 3 can be heated and are consequently designed as heating plates with integrated heating channels. The press frame 1 consists of a plurality of press frames 4 arranged in a row in the longitudinal direction of the press. The press also has an upper infeed press plate 5 arranged in front of the upper main press platen 2 on the inlet side and a lower infeed press plate 6 arranged in front of the lower main press platen 3 on the inlet side. The inlet press plates 5, 6 are also designed as heatable plates with integrated heating channels. They are also designed to be flexible in order to set an inlet contour.

Press cylinders 7 , which are supported on the press frame 1 , are connected to the upper main press platen 2 in order to set the press gap in the main press area. In addition, inlet cylinders 8 are connected to the upper inlet press platen 5, which are also supported on the press frame 1 and via which the inlet gap or the press gap in the inlet area can be adjusted. In addition, endlessly circulating press belts 9 (e.g. steel press belts) are provided in the upper part of the press and in the lower part of the press. B. roll bars on the inlet press plates 5, 6 and the main press plates 2, 3 are supported.

In 1 a press is shown in a fundamentally known embodiment, in which five rows of infeed cylinders 8 are provided in the infeed area. The inlet cylinders 8 and/or the main cylinders 7 are designed as double-acting differential cylinders within the scope of the invention, so that tensile forces and compressive forces can (at least) be transferred to the upper inlet plate 5, so that a continuous bending line of the upper inlet plate 5 can be set. In the exemplary embodiment, the lower inlet plate 6 is fastened to the press frame (e.g. with a fixed radius).

According to the press according to 1 now operated in such a way that the upper infeed press plate 5 (and possibly also a first section of the main press plate 2) via the infeed cylinders 8 (and possibly the press cylinders 7) in the infeed area (and possibly also in a first section of the main press area) with a specific pulse amplitude overall cyclically is lowered and raised in a pulsating manner. This causes the pressed material mat entering the infeed gap to pulsate several times in succession, at least in the compression phase (in the infeed area) by means of multiple cyclic compression and relief by means of the press cylinders/infeed cylinders connected to the upper infeed press platen in the infeed area undergoes varying phases of compression and decompression. This will be in the 2 clearly.

In 2 the inlet area of a continuous press is shown with the inlet plates 5, 6, which form an inlet mouth or inlet gap tapering in the working direction A. In the exemplary embodiment for the upper inlet plate, this inlet contour can be extended via that of 2 Set the intake cylinder, not shown, variably. In the exemplary embodiment, the lower inlet plate is fastened to the press frame with a predefined contour. The press belts/steel belts and the rotating roller bars are not shown. However, the respective thickness of the mat is limited by the upper steel strip and the lower steel strip. This is in 2 shown only greatly simplified without depicting the steel bands and rolling rods. In 2 it can now be seen that the upper infeed press plate 5 is lowered and raised in a cyclically pulsating manner via the infeed cylinder 8 (with the curved contour). where is in 2 the neutral position of the curved upper inlet plate 5 is shown, which corresponds to the usual setting of an inlet mouth. In addition, the upper maximum position on the one hand and the lower maximum position on the other hand of the inlet plate in the course of the pulsation are shown as examples. It can be seen that after an initial compaction, the pressed material mat is then compacted below the nominal size within the inlet mouth, the nominal size N in this case meaning the thickness of the mat at the end of the pulsating inlet area. This nominal size N is slightly larger (e.g. up to 20% larger) than the finished size of the panel leaving the press, since calibration and thus residual compaction to the final size takes place further down the line behind the infeed area. where is in 2 also recognizable that not only the upper inlet plate 5 is raised and lowered in a pulsating manner, but also a part of it subsequent upper press plate 2, so that the pulsating area can extend into the area of the main press plates 2, 3 inside. This is particularly useful if the method according to the invention is to be implemented with presses of conventional design. Optionally, however, it is also within the scope of the invention to limit the pulsating area to the inlet plates, in which case it is expedient to work with extended inlet plates. Anyway, it's in 2 indicated that the pulsating raising and lowering of the inlet plate 5 (and possibly the press plate 2) can be represented as a quasi pulsating pivoting movement of the plate about a (virtual) pivot point P. This also means that the (absolute) pulse amplitude decreases from pulse to pulse when viewed spatially in the working direction A and then assumes the value zero in the area of the virtual pivot point.

With the measures according to the invention, the heat can be introduced into the pressing material mat particularly efficiently and quickly, so that a very rapid temperature rise is realized in the inlet area. This can be done using the 3 clarify. Shown is the temperature development for, on the one hand, a conventionally shaped (non-pulsating) inlet mouth and, on the other hand, for an inlet mouth pulsating according to the invention. The temperature T is shown as a function of the time t. While curve K1 shows the temperature development for a conventionally designed inlet mouth as a reference, curve K2 shows the temperature development in pulsation operation by way of example and it can be seen that the heat input is significantly faster. This can be seen, for example, from the time difference Δt drawn in the figure at a critical temperature of 100° C., for example.

Claims (9)

1. Method for pressing a press material mat during the process of producing wood based boards, more particularly fibreboards, in a continuous press,

   wherein the press comprises a press frame (1), at least one upper press plate (2, 5) and at least one lower press plate (3, 6), wherein in order to adjust a press gap arranged between the press plates, the upper press plate (2, 5) and/or the lower press plate (3, 6) are acted upon by press cylinders (7, 8) supported at the press frame (1),

   wherein on the inlet side, the press plates (5, 6) form an inlet area in which the press material mat (M) entering into the press gap is compressed during a compression phase,

   characterised in that

   at least in the inlet area, the upper plate (5) and/or the lower press plate (6) is at least in parts lowered and raised in a cyclically pulsating manner so that by means of the press cylinders connected to the upper press plate and/or the lower press plate in the inlet area, the press material mat entering the inlet gap consecutively passes through several pulsating, varying compression phases and decompression phases,

   wherein in several compression phases, the press material mat is on multiple occasions cyclically compressed to nominal size or over-compressed to under nominal size and each time between the compression phases is unpressurised above nominal size in the decompression phases.
2. Method according to claim 1, characterised in that the pressure in the press material mat is reduced to zero or almost zero in the decompression phases by, for example, depressurising the press cylinders.
3. Method according to claim 1 or 2, characterised in that in the compression phases, the pressure generated in the press material mat decreases from compression phase to compression phase.
4. Method according to any one of claims 1 to 3, characterised in that in the inlet area, the upper and/or lower press plate is at least in parts periodically raised and lowered in a pulsating manner with a pulse amplitude that is constant in time.
5. Method according to any one of claims 1 to 4, characterised in that the pulse amplitude decreases from pulse to pulse along the upper and lower press plates in the working direction (A).
6. Method according to any one claim 1 to 5, characterised in that that press material mat is moistened before the inlet.
7. Method according to any one of claims 1 to 6, characterised in that a press is used, which, as the upper press plate (2, 5), on the one hand in the inlet area, comprises an upper inlet press plate (5) and, on the other hand, arranged downstream thereof in the working direction (A), an upper main press plate (2), and or as the lower press plate (3, 6), on the one hand comprises a lower inlet press plate (6) in the inlet area and, on the other hand, arranged downstream thereof in the working direction (A), a lower main press plate (3) .
8. Method according to claim 7, characterised in that the pulsating area extends over the entire length of the upper inlet press plate or the lower inlet press plate and over a partial section of the upper main press plate or the lower main press plate.
9. Method according to any one of claims 1 to 8, characterised in that the pulsating area of the upper press plate extends over a length of more than 20% of the total length of the upper press plate or the lower press plate.

Images