ES2471382T3 - Procedure and device for the introduction of steam into a mat or in its cover layers - Google Patents

Abstract

Procedure for the steam treatment of a mat or its cover layers in the manufacture of wood material plates, such as chips, fibers, plastics or flakes, from a mixture of particles such as chips, fibers or scales containing lignocellulose and / or cellulose, mixed or not with binders in which the mat is pressed and hardened with application of pressure and heat, characterized in that the vapor pressure and / or the amount of steam in the direction is regulated differently transversal with respect to the work direction through the mat.

Description

Procedure and device for the introduction of steam in a mat or in its cover layers.

The invention relates to a method according to claim 1 and to a device according to claim 6 for the introduction of steam into a mat or in the cover layers of a mat consisting of a mixture of particles such as chips, fibers, plastics or flakes containing lignocellulose and / or cellulose, mixed or not with binders in the manufacture of chip plates.

The application means "mat" a mixture of particles such as chips, fibers or scales containing lignocellulose and / or cellulose, mixed or not with binders spread on a mold tape, which can be spread in several layers or layers and with different orientations. Mats of this type are used in most cases in continuous manufacturing processes for medium density fiberboard (MDF) or oriented chipboard (OSB) English, Oriented Strand Board), although they can also be used in discontinuous processes. These mats are pressed and hardened in continuous processes, in most cases with a double tape press that works continuously. The subject of this application is the introduction of steam into the mat or respectively depending on the procedure only in the corresponding cover layers of a mat during pre-compression in front of a continuous main press or during the main pressing itself. Apart from the introduction of steam into the mat, the problem of steam treatment of mats of different widths must also be solved.

In WO 1998 041 372 A1, as well as DE 101 61 341 A1, a process for steam treatment of cover layers on mats of different widths is described. In the case of a mat width adjustment, during the steam treatment the steam plate area below which there is no mat is disconnected. In addition, it is described that a certain disconnection of the steam treatment is carried out from the edge of the mat in the direction of the center of the mat (approx. 5% of the width of the mat), to minimize steam losses in the edge. The device has a structure such that steam channels, from which steam flows in the direction of the mat, are arranged in the perpendicular direction with respect to the direction of advance. The steam channels are closed at the edge of the mat by cylinders that enter the edge area. The width of the steam treatment inside a channel is therefore adjusted according to the width of the mat and the losses of steam at the edge, being treated by steam in principle almost the entire width of the mat per channel. In WO 1998 041 372 A1 it is further described that the length of the steam treatment zone (seen in the forward direction) is adjusted according to the density profile. The length of the steam treatment zone is controlled by the additional connection of individual channels. In DE 101 61 341 A1 a device is described which allows a steam treatment according to the procedure described above, however, the adjustment of the width and the disconnection at the edge is achieved by rotating correspondingly continuous cylinders.

A device is described in DE 44 47 847 A1, by means of which a steam treatment must be carried out on the cover layers. In the device described, the narrow surface of the mat is sealed by telescopic plates, thus avoiding losses due to steam leakage. For the introduction of steam, boxes are used, which extend in the transverse direction with respect to the direction of advance along the width of the mat.

It has proved to be a disadvantage of the procedures and devices described above that a uniform vapor treatment is not possible in the cover layers along the entire width of the mat. The mat is heated unevenly by steam, so it also turns out that the center of the mat seen along the width is heated less than the edge area. The density profile along the vertical cross-section of the plate is different at the edge and in the center of the plate. The edge area up to 30% towards the center of the mat presents in case of a steam treatment in wider coverage layers (areas with higher density) and higher maximum density values than in the same area from the center. In addition, the center of the mat has a slower temperature increase in the back area of the press than the edge of the mat, so that only a reduced increase in the pressing speed can be achieved. This slower rise in temperature is an indication that less steam is introduced into the center.

Document DE 39 14 106 A1 describes a procedure for a complete flow through the mat or a complete heating of the mat by means of water vapor, the steam being introduced from one side and a vacuum being applied on the opposite side or by introducing the steam at the same time from both sides. It must be treated by steam along the entire width of the mat by steam boxes. However, it has been shown that a simultaneous introduction of steam from above and below does not lead to uniform heating of the mat along the entire width and depth, so that only an insufficient increase in the pressing speed can be achieved.

The reason for the non-uniform steam treatment along the entire width of the mat and depth of the mat in the procedures described above is that the air existing in the mat, which represents a resistance to flow against the entering steam, does not It can come out evenly during steam treatment. Therefore, a high back pressure is opposed in the center of the mat, which is not so marked on the edge of the mat, since here the narrow side of the mat is open and the air can escape. Therefore, with the same pressure, steam enters deeper through the cross section at the edge than in the center of the mat. The result is, therefore, that the process of steam treatment or steam treatment in the cover layers cannot be carried out satisfactorily with the described devices.

It is also a disadvantage that the steam used to inject into the mat condenses in the steam chambers above the mat leading there to water accumulations. Condensed water can drip onto the mat and lead to water stains on the pressed material and, therefore, on the plate of wood material produced itself. This wooden material plate is a piece to be discarded and must be separated in the visual control. Since it is perfectly possible to stop seeing small water spots in the visual control of a plate of wood material of a size of several square meters, this can lead to the supply of defective products and the corresponding loss of image of the producer.

The object of the invention is to improve the process and a device for steam treatment such that the vapor pressure and / or the amount of steam can be adjusted according to the requirements, in particular in the case of differentiated surface densities on a mat .

In an extension of the objective, the steam treatment must be adjusted according to the surface density of the mat.

In addition to the possibility of adjusting a uniform density profile along the entire width of the plate to increase the pressing speed, the procedure of the simultaneous introduction of steam from above and below for the heating of the entire cross section of the mat can be improved in such a way that uniform heating of the entire mat or of the covering layers is possible both along the width and along the thickness. In particular, in case of different surface densities on the mat.

This objective of the invention is achieved in the case of the process because the vapor pressure and / or the amount of steam in the transverse direction are regulated differently from the work direction through the mat.

For a device suitable for carrying out the procedure, but which can also operate autonomously, the objective is achieved because a continuous steam treatment surface is subdivided into different steam treatment fields, several fields being arranged both in the transverse direction as in the longitudinal direction with respect to the working direction and the steam treatment fields can be controlled both individually and in groups and each field or each group being arranged in an adjustable manner in terms of the amount of steam or steam pressure .

With this solution, the vapor pressure in the different chambers can be adjusted differently and by means of variable disconnection and adjustable regulation with respect to the steam pressure or the amount of steam in these fields individually or in groups can different steam treatment zones are regulated with respect to the steam treatment pressure or the amount of steam treatment through the transverse direction of the mat.

It is an advantage that the steam treatment surface is subdivided into different steam treatment fields, and several fields "as a chessboard" can be presented both in the transverse direction and in the longitudinal direction. Thanks to the variable and adjustable regulation of these fields individually or in groups, different steam treatment modes can be regulated for the entire depth of the mat or only for the cover layers. A wedge-shaped steam treatment or an alternating steam treatment is especially advantageous.

With these measures, a uniform heating of both the cover layers along the width and a complete heating is possible. As another point, more steam (condensation front arranged deeper towards the center of the mat) can also be introduced selectively in the center of the mat (seen along the width), the known problem of Low transverse tractions in the center of the plate.

Other measures and advantageous configurations of the object of the invention are indicated in the dependent claims and the description set forth below in the drawing.

They show:

1 shows a possible distribution of the steam chambers in a plan view from above of the mat of pressed material in the work direction;

Figure 2 the introduction of wedge-shaped steam (scratched surface) through the pressure chambers according to Figure 1 and

Figure 3 the alternating introduction of steam only by means of the pressure chambers in row b, d and f according to Figure 1 and

Figure 4 a schematic side view showing the pressure chambers with a heating device.

Figure 1 shows a plan view from above of the pressure chamber fields arranged above a mat of pressed material in the work direction (D.T.) of the press manufacturing facility without steam treatment. The arrow of the work direction is oriented towards the inlet side of the steam treatment section G. The mat of pressed material can be compacted, for example when using the procedure, in a previous press or main press additionally in the direction of job. According to Figure 2, a wedge-shaped steam treatment is now connected in the working direction, which causes the air to move successively from the center of the mat II to the sides of the mat II-II and III- III to be replaced by steam. Depending on the pressure applied to the pressure chambers, a complete flood with air displacement or a pure steam treatment of the cover layers can be carried out with a corresponding preheating of the cover layers.

An additional connection of the steam treatment with the following width grid has proved especially favorable for a preheating of the cover layers: at the beginning of the preheating (approx. 20% of the length of the steam treatment) a steam treatment in 20% of the width of the mat g in the center of the mat II seen along the width, then 40% (again along 20% of the length of the steam treatment), then in 80% (again 20% of the length of the steam treatment) and finally the entire width of the mat g. With this adjustment of steam pressure widths along the length of the steam treatment area G, the mat exhibits even heating of the cover layers after the preheating device, for example respectively the 15% of the dough from above and below along the entire width of the mat g; and the remaining 35% of the possible penetration depth of the steam (per side of the cover layer) is not heated. Therefore, 70% of the mat core remains without the introduction of steam. The manufactured plates, which have been preheated with this procedure, have uniform vertical density profiles both at the edge and in the center of the mat. The properties of the plate correlated with the density profile, such as the resistance to bending is the same at the edges II-II and III-III as in the center of the mat I-I. The pressing speed can be clearly increased in comparison to the procedures indicated above, since heating of the central layer to the adhesive hardening temperature of approx. 100�C in the hot press is made in the center of the mat I-I at the same time as on the edges of the mat II-II and III-

III.

The displacement of the air and, therefore, the uniform treatment by steam can also be favored by adjusting in the center of the mat I-I a higher vapor pressure than at the edges of the mat II-II and III-III. In addition, a different vapor pressure can be adjusted along the steam treatment section G of the steam treatment. This works for the steam treatment of the cover layers in the back area of the steam treatment section G (approximately from doe) preferably with a lower vapor pressure in the center of the mat II, to that the vapor front does not penetrate deeper than at the edges of the mat II-II and III-III.

To introduce a large amount of steam over a short length of steam treatment, a high steam pressure must be applied on mats of a high thickness, at a high pressing speed or if a larger depth of steam treatment is desired. the mat Despite the steam plates that rest on both sides of the mat, this can lead to a lateral blow-out of particles. In the area of the edges of the mat II-II and III-III, therefore, lower vapor pressures can be adjusted than in the center of the mat II, to avoid these problems in the entire steam treatment section G In this way side vents can be avoided by blowing wood particles, such as chips or fibers. This adjustment can be retrofitted as a test with a device according to the invention in the subsequent steam treatment section G, when the gases that are leaving have sought their way through the edges of the mat and an increase in the Exhaust speed no longer causes blow outs.

Naturally, there is the possibility that in special productions (especially in case of different thicknesses of the mat), the center of the mat II has transverse tractions lower than the edges II-II or III-III, seen along the mat width g. In this case, the heating in the center of the mat I-I has been carried out more slowly than at the edges II-II or III-III. Therefore, it may be necessary to control the steam treatment in the cover layers with certain thicknesses of the plate such that in the center of the mat some more steam is added, ie moisture and heat. The heating of the mats along the cross section is, therefore, somewhat deeper in the center of the mat I-I seen along the width of the mat g than at the edges. The edges are heated for example with a depth of 15% of the dough and the center with 20%. With this procedure, plates with almost the same transverse tractions and density profiles could be produced with a high pressing speed. To implement this possibility, wedge-shaped steam treatment is carried out so that 20% of the width of the mat g in the center of the mat II does not correspond to 20% of the steam treatment section G but 40% of the steam treatment section G of the steam treatment. However, as an alternative, the arrangement of the above-mentioned example can also be used, however, a higher vapor pressure is used in the center of the mat I-I than at edges II-II or III-III.

For steam treatment of a mat with a variable mat width g, the external steam treatment fields can be disconnected at edges II-II or III-III, below which no material is found in the case of a narrow mat, to avoid unnecessary steam consumption.

5 The variations in surface density, caused by inaccuracies in the spreading, lead to a locally higher density of the mat, which occurs during a relatively long production time in an area of given width of the mat, eg. in 20% of the width in the center of the mat. This piece of mat with a higher surface density can be detected in a measurement of the surface density before steam treatment. In areas with a higher surface density, a higher vapor pressure can be adjusted to achieve the same depth of the steam treatment or it must be treated by steam over a longer section seen in the work direction.

In the case of a complete flow through the mat to the center of the central layer, a complete heating is not possible either, if steam is introduced from both sides along the entire width of the mat having air inclusions in the center of the mat. The wedge-shaped steam treatment described above or the

The application of a higher vapor pressure along the entire length of the steam treatment also solves this problem, so that in case of a complete flow through the mat, the annoying areas with the air inclusions are eliminated, being ensured a complete uniform heating throughout the width and throughout the thickness of the mat.

The device is made in such a way that the steam treatment surface is subdivided into different steam treatment fields, being able to be distributed both in the transverse direction (v, w, x, y, z) and in the longitudinal direction ( a, b, c, d, e, f) a number of fields to choose freely for an aspect as a chessboard. Thanks to the variable disconnection and the adjustable regulation regarding the steam pressure or the amount of steam in these fields individually or in groups, different steam treatment zones can be regulated with respect to the steam treatment pressure or the amount of steam treatment in the transverse direction of the mat.

It is evident that, depending on the state of the art, a differentially reduced arrangement of steam treatment fields would also be possible and applicable. In the case of a corresponding reduction in the individual steam treatment fields versus a plurality of steam treatment fields in the longitudinal direction and in the transverse direction, a curved steam treatment in the transverse direction along the length of the course would also be The width of the mat.

A schematic side view is shown in Figure 4, in which it is seen, as already explained sufficiently, that a mat 2 is guided on a conveyor belt 1 in the working direction through an arrangement of pressure chambers 3 up and down. Conveyor belt 1 is generally made as a screening belt, so it is vapor permeable. Such a device is usually applied in a previous press for prior compaction and adjustment of the most diverse parameters in front of a double tape press that works continuously.

35 In the pressure chambers 3, a heating device 4 is arranged above the mat 2. In this way it is necessary to prevent condensation from taking place in the pressure chambers 3 proper, thus dropping water drops. on the mat 2. Depending on the force of the steam fluid flow, it may also be reasonable to carry out a heating of the pressure chambers 3 from below, so that the vapor stream cannot carry condensate thus reaching from below to the mat 2. When screening belts are used, it may otherwise be reasonable to provide the conveyor belt 1 in front of the steam treatment fields a, b, c, d, e, f in the working direction DT of the mat 2 with a heating device 5, so that the conveyor belt 1 has a temperature approximately equal to or higher than the condensation temperature of the fluid used for preheating.

It is understood by the expert that the heating of the pressure chambers or the conveyor belt must be completed before the use of the steam pressure chambers.

List of reference signs:

I-I, II-II, III-III Longitudinal lines of the mat in the work direction

a, b, c, d, e, f Arrangement of pressure chambers in the work direction

g Mat width

G Steam treatment section in the work direction

D.T. Work address

1 conveyor belt

2 Mat 3 Pressure chambers 4 Heating device 5 Heating device

Claims (8)

one.

Procedure for the steam treatment of a mat or its cover layers in the manufacture of wood material plates, such as chips, fibers, plastics or flakes, from a mixture of particles such as chips, fibers or scales containing lignocellulose and / or cellulose, mixed or not with binders in which the mat is pressed and hardened with application of pressure and heat, characterized in that the vapor pressure and / or the amount of steam in the direction is regulated differently transversal with respect to the work direction through the mat.

2.

Method according to claim 1, characterized in that the steam pressure and / or the amount of steam are regulated differently in the working direction.

3.

Method according to claim 1, characterized in that the pressure of the steam treatment and / or the amount of the steam treatment are adjusted according to the surface density of the mat.

Four.

Method according to claim 1, characterized in that the steam treatment of the mat in the production direction through a predetermined steam treatment section (G) introduces a decreasing vapor pressure from the center of the mat (II) towards the longitudinal edges (II-II; III-III).

5.

Method according to one or more of the preceding claims, characterized in that a measurement of the surface density is used before the steam treatment surface for the control of the steam treatment.

6.

Device for the steam treatment of a mat or its cover layers in the manufacture of wood material plates, such as chips, fibers, plastics or flakes, from a mixture of particles such as chips, fibers or scales containing lignocellulose and / or cellulose, mixed or not mixed with binders characterized in that a continuous steam treatment surface is subdivided into different steam treatment fields, several fields being arranged both in the transverse direction (v, w, x, y, z) as in the longitudinal direction (a, b, c, d, e, f) with respect to the working direction and the different steam treatment fields being individually adjustable as well as in groups and each field or each group of Adjustable shape in terms of steam quantity or vapor pressure.

7.

Device according to claim 6, characterized in that a device for measuring the surface density is arranged in front of the steam treatment surface with a corresponding feedback possibility for the control of the steam treatment.

8.

Device according to claims 6 � 7, characterized by the use of the device to carry out the procedure.

D.T.

D.T.

D.T.