EP2275239A2 - Method and apparatus for introducing steam in a mat, especially in the covering layers - Google Patents

Abstract

The method involves pressing and hardening a mat under utilization of pressure and heat, and controlling vapor pressure and/or steam amount transverse to a working direction in dependence of a surface weight of the mat. The vaporization of the mat is performed over a steaming sector (G) from a middle section to long edges through decreasing vapor pressure, during manufacturing of wood-based panels made of cellulose-containing particles such as chips or fiber. An independent claim is also included for a device for vaporization of a mat and outer layers of the mat during manufacturing of wood-based panels such as chip board, fiber board, plastic board and scrap board.

Description

The invention relates to a method and a device for introducing steam into a mat or into the cover layers of a mat consisting of a mixture of lignocellulose and / or cellulose-containing particles, such as chips, fibers, plastics or chips, mixed with or without binder of chipboard.

The application means by a "mat" a mixture of lignocellulosic and / or cellulosic particles, such as shavings, fibers or chips, dispersed with or without binder, which can be scattered in several layers and with different orientations. Such mats are usually used in continuous production processes for chipboard (MDF) or chipboard (OSB), but can also be used in discontinuous processes. These mats are usually pressed in continuous processes with a continuous double belt press and cured. Subject of this application is the introduction of steam into the mat or due to the process only in the respective outer layers of a mat during precompression before a continuous main press or during the main pressing itself. In addition to the introduction of steam into the mat and the evaporation of different width mats is a problem solved shall be.

In the WO 1998 041 372 A1 as well as the DE 101 61 341 A1 describes a process for covering layer coating in mats of different widths. In this case, during vapor deposition in the case of a width adjustment of the mat, the area of the steam plate below which is not a mat is switched off. In addition, it is described that a certain deactivation of the vapor deposition from the edge of the mat in the direction of the center of the mat (about 5% of the mat width) is made in order to minimize vapor losses at the edge. The device is constructed so that steam channels are arranged perpendicular to the feed direction from which steam flows out in the direction of the mat. The steam channels are closed at the edge of the mat by retracting cylinders in the edge area. The steaming width within a duct is thus set according to the width of the mat and the steam losses at the edge, with basically virtually the entire width of the mat being steamed per duct. In the WO 1998 041 372 A1 is further described that the length of the evaporation zone (seen in the feed direction) is set according to the density profile. The length of the evaporation zone is controlled by switching on individual channels. In the DE 101 61 341 A1 becomes describes a device that allows the method described above, a vapor deposition, but the width adjustment and the edge shutdown is achieved by turning correspondingly continuous cylinders.

In the DE 44 47 847 A1 a device is described by means of which a top layer vapor deposition is to take place. In the described device, the mat narrow surface is sealed by means of telescopic plates, whereby steam leakage losses are to be avoided. For steam introduction, boxes which run across the width of the mat transverse to the feed direction are used.

A disadvantage of the above-described methods and devices has been found that no uniform vapor deposition of the outer layers over the full width of the mat is possible. The mat is unevenly heated by the steam which also results in the mat center being seen less heated than the edge area when seen across the width. The density profile across the vertical plate cross-section differs at the edge and from the plate center. Thus, the area from the edge to 30% to the center of the mat in a topcoat vaporization has broader cover layers (areas with higher density) and greater density maxima than in the same area from the center. In addition, the center of the mat in the rear press area has a slower temperature rise than the mat edge, resulting in only one low gain in press speed can be achieved. This slower temperature rise is a sign that less vapor is being introduced in the middle.

In the DE 39 14 106 A1 For example, a method is described for fully flowing or completely heating the mat by means of water vapor, wherein the steam is introduced from one side and a vacuum is applied on the opposite side or steam is introduced simultaneously from both sides. It should be steamed over the entire width of the mat using steam boxes. However, it has been found that a simultaneous introduction of steam from above and below does not lead to a uniform heating of the mat over the full width and depth and thus only an insufficient increase in the pressing speed can be achieved.

The cause of the uneven vapor deposition across the full mat width and mat depth of the processes described above is that the air present in the mat, which is a flow resistance to the penetrating vapor, can not escape evenly during vapor deposition. The incoming steam is thus counteracted by a high back pressure in the center of the mat, which is not so pronounced at the edge of the mat, since the open narrow side of the mat is open here and the air can escape. Therefore, at the same pressure, the steam penetrates deeper over the cross-section at the edge than in the center of the mat. As a result, so the process of vapor deposition or the Deckschichtevampfung with the described devices unsatisfactory possible.

It is also a disadvantage that the steam used and to be injected into the mat condenses in the steam chambers above the mat where it leads to water accumulation. The condensed water can drip onto the mat and lead to water spots only on the pressed material and thus on the produced wood-based panel itself. This wood-based panel is broke and must be discarded during visual inspection. However, since small water spots can be overlooked in the visual inspection of a wood-based panel several square meters in size, this can lead to the delivery of defective goods and the corresponding image loss of the producer.

The aim and the object of the invention is to further develop the method and a device for vapor deposition in such a way that the vapor pressure and / or the amount of vapor can be adjusted in accordance with the requirements, in particular for different basis weights in a mat.

In an extension of the task, the vapor deposition should be adjustable depending on the basis weight of the mat.

In addition to the possibility of setting a uniform density profile over the entire plate width to increase the pressing speed, this can

Simultaneous steam injection from the top and bottom to heat the full mat cross-section can be improved so that a uniform heating of the entire mat or the cover layers both across the width and the thickness is possible. In particular, at different occurring basis weights in the mat.

This object of the invention is achieved for the method according to that the vapor pressure and / or the amount of steam are controlled differently across the mat transversely to the working direction.

For a device suitable for carrying out the method, but also independently operable, the object is achieved in that a continuous vapor deposition surface is divided into different Bedampfungsfelder, wherein both in the transverse and in the longitudinal direction to the working direction several fields are arranged and the individual Bedampfungsfelder both individually, as well as in groups controlled and each field or each group is arranged controllable in the amount of steam or in the vapor pressure.

With this solution, the vapor pressure in the individual chambers can be set differently and by the variable shutdown and controllable control with respect to the vapor pressure or the amount of steam of these fields individually or in groups can be different Steaming zones with respect to the steaming pressure or the amount of steaming across the mat einsteuern.

It is advantageous that the vapor deposition surface is divided into different Dampfungsfelder, wherein both in the transverse and in the longitudinal direction several fields "checkered" may be present. Due to the variable and controllable control of these fields individually or in groups, different evaporation modes for the entire mat depth or only the outer layers can be controlled. Particularly advantageous is the wedge-shaped vapor deposition or an alternating vapor deposition.

With these measures, a uniform heating of both the outer layers across the width as well as a complete heating is possible. As a further point, it is also possible to introduce more steam (condensation front lying deeper in the middle of the mat) in the middle of the mat (seen across the width), whereby the known problem of low transverse forces in the center of the board can be solved here.

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

Figur 1

Mögliche Einteilung der Dampfkammern in einer Draufsicht der Pressgutmatte über die Arbeitsrichtung,

Figur 2

Keilförmige Einleitung (schraffierte Fläche) des Dampfes über die Druckkammern gemäß Figur 1 und

Figur 3

Alternierende Einleitung des Dampfes nur über die Druckkammern in Reihe b, d und f gemäß Figur 1 und

Figur 4

eine schematische Seitenansicht mit Darstellung der Druckkammern mit einer Heizeinrichtung.

Show it:

FIG. 1

Possible division of the steam chambers in a plan view of the pressed material mat over the working direction,

FIG. 2

Wedge-shaped introduction (shaded area) of the steam over the pressure chambers according to FIG. 1 and

FIG. 3

Alternate introduction of steam only via the pressure chambers in series b, d and f according to FIG. 1 and

FIG. 4

a schematic side view showing the pressure chambers with a heater.

FIG. 1 shows the top view of the arranged above a Pressgutmatte pressure chamber fields in the working direction (AR) of the press manufacturing plant without steaming. The arrow of the working direction points to the inlet side of the Bedampfungsstrecke G. The Pressgutmatte can be compressed in addition, for example, when using the method in a pre-press or main press in the working direction. To FIG. 2 Now a wedge-shaped vapor deposition is switched in the direction of work, which causes the air is successively pushed from the middle of the mat II to the mat side II-II and III-III and replaced by steam. Depending on the applied pressure in the pressure chambers, a complete flow with displacement of the air can be carried out, or a pure cover layer vaporization with appropriate cover layer preheating.

As a particularly favorable for a cover layer preheating, a connection of the evaporation has been found with the following width grid: At the beginning of the preheating (about 20% of the steaming length), steaming of 20% of the mat width g in middle of the mat II across the width, then 40% (again 20% of the steaming length), then 80% (again 20% of the steaming length), and finally the full mat width g. With this width adjustment of the vapor pressure over the length of the vapor deposition zone G, the mat, after passing through the preheating device, uniformly heats the cover layers by, for example, 15% of the mass from above and below over the entire width of the mat g; and the remaining 35% of the possible penetration depth of the vapor (per topcoat side) are not heated. This leaves 70% of the mat core without steam. The sheets produced, which were preheated by this method, have uniform vertical density profiles both at the edge and in the center of the mat II. The density profile correlated plate properties such as the bending strength is the same at the edges II-II and III-III as in Mattenmitte II. The pressing speed can be significantly increased compared to the above methods, since the heating of the middle layer on the curing temperature of the adhesive of 100 ° C in the hot press in Mattenmitte II at the same time as at the mat edge II-II and III-III.

The air displacement and thus the uniform steaming can be further supported by the fact that in the middle of the mat II, a higher vapor pressure is set than at the mat edge II-II and III-III. Furthermore, can still on the Bedampfungsstrecke G of the steaming a different vapor pressure can be set. Thus, for the covering layer coating in the rear area of the steaming section G (for example from d or e), preferably a lower vapor pressure is used in the center of the mat II, so that the steam front does not penetrate deeper than at the mat edge II and III.

In order to apply a large amount of steam to a short steaming length either with thick mats, with a high pressing speed or with a greater desired steaming depth, a high vapor pressure must be applied to the mat. This can lead to side blowers of particles despite lying on both sides of the mat steam plates. Therefore, in order to avoid these problems, lower vapor pressures can be set in the mat edge area II-II and III-III on the entire steaming section G than in the middle of the mat I-I. This makes it possible to avoid lateral blowouts of wood particles such as chips or fibers. This setting can also be adapted again with a device according to the invention in the back steaming section G, if the escaping gases have searched their way through the edges of the mats and an increase in the outflow speed no longer causes blowouts.

Of course, there is the possibility that in special productions (especially with different mat thicknesses) the middle of the mat II seen over the mat width g lower cross-trains than the edge II-II or III-III. In this Case, the warming in mid-mat II is slower than at the edge of II-II and III-III. Thus, it may be necessary for certain plate thicknesses to conduct the topcoat vapor deposition so that in the middle of the mat a little more steam, ie moisture and heat, is added. The warming of the mats across the cross section is thus seen slightly deeper in the center of the mat II over the mat width g than at the edge. For example, the rim is heated 15% deep of the mass and the middle 20%. With this method, plates with nearly equal cross-sections and density profiles could be produced at high press speeds. To implement this possibility, the vapor deposition is performed wedge-shaped so that 20% of the mat width g in mat center II not 20% on the Bedampfungsstrecke G but 40% on the Bedampfungsstrecke G of steaming are performed. Alternatively, however, the classification from the above example can be used, but in the middle of the mat II, a higher vapor pressure than at the edges II-II and III-III is used.

For steaming a mat with different mat width g, the outer Bedampfungsfelder at the edges II-II and III-III under which there is no material in a narrow mat, can be switched off to avoid unnecessary steam consumption.

Surface weight fluctuations, which are caused by scatter inaccuracies, lead to locally higher mat density, which over a longer production time in a certain width range of the mat, for example 20% of the width in the middle of the mat. This piece of mats higher basis weight can be seen in a basis weight measurement before the evaporation. In the areas with a higher basis weight, a slightly higher vapor pressure can be set in order to achieve the same depth of vapor deposition or it must be vaporized a longer distance in the transport direction.

Likewise, when the mat is completely flowed through to the middle of the middle layer, complete heating is not possible if steam is introduced from both sides in the full width of the mat and air pockets are present in the center of the mat. The above-described wedge-shaped vapor deposition or the application of a higher vapor pressure over the entire vaporization length also solves this problem, so that at a complete flow through the mat, the disturbing areas of air bubbles are cleaned and a complete uniform heating across the width and thickness of the mat is secured.

The device is designed so that the vapor deposition surface is subdivided into different vapor deposition fields, wherein both transverse (v, w, x, y, z) and longitudinal (a, b, c, d, e, f) any number of fields for a checkerboard-like appearance can be distributed. Due to the variable shutdown and controllable control with regard to the vapor pressure or the amount of steam of these fields individually or in groups, different Steaming zones with respect to the steaming pressure or the amount of steaming across the mat einsteuern.

It is of course obvious that, depending on the state of the art, a differential reduction arrangement of the vapor deposition fields would be possible and applicable. Thus, with a corresponding reduction of the individual vapor deposition fields against a multiplicity of vapor deposition fields in the longitudinal direction and in the transverse direction, a curved vapor deposition across the width of the mat would be conceivable.

In FIG. 4 is a schematic side view shown in the already sufficient as can be seen that a mat 2 is guided on a conveyor belt 1 in the working direction by an array of pressure chambers 3 above and below. The conveyor belt 1 is usually designed as a sieve belt and thus vapor-permeable. Such a device is usually used in a pre-press for precompression and adjustment of various parameters in front of a continuously operating double belt press application. In the pressure chambers 3, a heater 4 is disposed above the mat 2. This is to prevent condensation from taking place in the pressure chambers 3 themselves, and thus drops of water from falling onto the mat 2. Depending on the strength of the fluid flow of the steam, it may also be useful to carry out a heating of the pressure chambers 3 below, so not condensate in the Steam flow can be taken and so passes from below to the mat 2. When using screen belts, it may also be useful to provide the conveyor belt 1 before the Bedampfungsfelder a, b, c, d, e, f in the working direction AR of the mat 2 with a heater 5, so that the conveyor belt 1 to an approximately equal or be brought higher temperature than the condensation temperature of the fluid used for preheating.

It goes without saying for the person skilled in the art that the heating of the pressure chambers or of the conveyor belt must be completed with steam before the use of the pressure chambers.

List of Reference Numerals: DP1408EP

I-I, II-II, III-III

Longitudinal lines of the mat in the working direction

a, b, c, d, e, f

Arrangement of the pressure chambers in the working direction

G

Matt width

G

Bedampfungsstrecke in the working direction

AR

working direction

1

conveyor belt

2

mat

3

pressure chambers

4

heater

5

heater

Claims (8)

Process for steaming a mat or its cover layers in the production of wood-based panels, such as chip, fiber, plastic or chipboard panels, from a mixture of lignocellulosic and / or cellulosic particles, such as shavings, fibers or shavings, mixed with or without binder wherein the mat is pressed and cured using pressure and heat, characterized in that
the steam pressure and / or the amount of steam is controlled differently across the mat across the working direction. A method according to claim 1, characterized in that the vapor pressure and / or the amount of steam in the working direction is controlled differently. A method according to claim 1, characterized in that the vapor deposition pressure and / or the amount of vapor deposition is set as a function of the basis weight of the mat. A method according to claim 1, characterized in that the vapor deposition of the mat in the direction of production over a predetermined Bedampfungsstrecke (G) from the middle of the mat (II) to the longitudinal edges (II-II, III-III) towards a decreasing vapor pressure is introduced. Method according to one or more of the preceding claims,
characterized in that a basis weight measurement in front of the vapor deposition surface is used for the vapor deposition control. Device for steaming a mat or its outer layers in the manufacture of wood-based panels, such as chip, fiber, plastic or Schnitzelplatten, from a mixture of with or without binder added lignocellulosic and / or cellulose-containing particles, such as chips, fibers or chips, characterized characterized in that a continuous vapor deposition surface is subdivided into different vapor deposition fields, wherein a plurality of fields are arranged both in the transverse direction (v, w, x, y, z) and in the longitudinal direction (a, b, c, d, e, f) are and the individual Bedampfungsfelder both individually, and controlled in groups and each field or each group in the amount of steam or in the vapor pressure is arranged controllable. Apparatus according to claim 6, characterized in that a device for measuring the basis weight is arranged in front of the Bedampfungsfläche with appropriate Rückmeldungsmöglichkeit for Bedampfungssteuerung. Device according to claims 6 or 7, characterized by the use of the device for carrying out the method.

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