EP1710061B1 - Method for continuous preheating of a web or a mat, and prepress used therefore - Google Patents

Description

The invention relates to a method for continuously preheating a nonwoven or a mat, especially a mat of elongated or flat wood chips or chips according to the preamble of claim 1 and a pre-press for carrying out the method according to claim 8. Such chips or chips are usually oriented strewn and hot pressed into so-called "OSB" panels (oriented strand boards, woodchips oriented longitudinally and laterally) or "OSL" panels (oriented strand lumber, shreds only longitudinally oriented) or "LSL" panels (long strand lumber, long chips only longitudinally oriented). The method can also be applied to unoriented chips or chips.

A basic method for preheating a nonwoven or a mat is with DE 36 40 682 A1 known. In this case, steam is introduced from at least one broad side of the web and completely or partially passed therethrough. The mat is precompressed before steaming and on the opposite Side of the vapor deposition, a vacuum can be applied. The device is carried out similar to a pre-press and consists of an upper and lower circumferential permeable belt. The preheating of a high mat of chips is not possible with this method and this device, since the mat can not be heated evenly, since the steam can escape laterally at the edge before reaching the middle of the mat. Scattered chips, due to their geometry perpendicular to the mat surface, have a 5 to 30 times higher flow resistance than parallel to the mat surface. This means that the steam introduced perpendicular to the mat surface is preferably diverted into a horizontal steam flow and thus exits from the narrow sides. Regardless of the uneven heating, there are areas in the middle mat section that are not heated. This is because there is no preferred flow direction of the steam in the mat due to the lack of lateral sealing. The flow is divided in the middle of the mat across the width seen in a vertical flow and a horizontal flow, so that individual mat areas are not traversed by the steam. It form air pockets that have a few inches in length, width and thickness. Likewise, no high vapor pressure can be built up. Because the steam can escape sideways immediately after leaving the steam boxes, the steam pressure in the mat is always very low and thus the driving pressure gradient is not sufficient for thicker mats to heat the entire mat.

In the DE 102 07 573 A1 It is suggested that procedures of DE 36 40 682 A1 to optimize further, in which the air is sucked out of the mat during the pre-compression. However, this has not led to a uniform steaming in very high mats with chips, because due to the flow conditions in shavings during air extraction and partially the air leaves the mat on the narrow surfaces of the mat. In the center of the mat, seen across both width and thickness, air remains in the mat. With the upstream suction plates so a Schnitzelmatte can not be vented.

In DE 44 40 997 A1 and DE 44 41 017 A1 (= US 5,762,980 A ) Vorwärmvorrichtungen for mats are described with a side wall to seal the narrow surfaces. In this case, however, targeted hot air to be removed or removed via special gas passage openings in the side wall. The side wall consists of telescopically movable side wall sections which, however, can not be carried out sealingly with one another at higher pressures and are also not provided in this way. If there is a banding of the screen belt, it may happen that the area of the sealing of the screen belt runs outside of the sealing plate. Also, the seal has a high degree of wear which renders permanent operation without reworking of the seal impossible.

The invention is based on the object of specifying a method with which a steam flow can be generated in a mat which has a single flow direction perpendicular to the broad side of the mat and prevents uneven heating of individual mat areas.

The solution to this problem for the method is that the narrow sides of the scattered mat are guided with a side wall and sealed when entering the device for preheating to the atmosphere, the mat from a surface side to a density of 150 - 450 kg / m ³ , preferably 250kg / m ³ , is compressed and the mat is supplied on the same surface side water vapor for preheating while the mat compression is continuously withdrawn and removed on the opposite surface side to the forced guidance of the water vapor through the mat this or vacuum or vacuum is applied and then the mat is compressed again in the outlet of the device.

The solution for a pre-press for carrying out the method according to claim 8 is that the revolving upper screen belt is arranged on the height-adjustable compression rollers between the fixed side walls and that for sealing the upper screen belt to the side walls, a height-adjustable seal and for sealing the lower screen belt a Seal are arranged.

During the pre-compaction of the mat to 20 - 30% of the original mat height, the air in the mat is pressed against the feed direction of the mat. At the beginning of the vapor deposition, the mat has a higher mat density of 150-450 kg / m ³ , preferably 250 kg / m ³ . It has been found that the ratio of vertical to horizontal flow resistance changes with increasing mat density. At a mat density of 100 kg / m ³ , the ratio of horizontal to vertical flow resistance is 30 to 1 and at 350 kg / m ³ mat density only 5 to 1. This means that the pre-compression to 250 kg / m ³ to 350 kg / m ³ mat density, the horizontal flow resistance is increased and thus also a certain sealing of the steam takes place in and against the production direction. This increase in flow resistance is exponential to the increasing mat density. The lateral sealing of the mat narrow surface is made by the continuous side wall. The steam now has no way to escape through the leaking side edges. The air is completely pushed out of the mat during evaporation. Disturbing air pockets can also be seen in the middle of the mat across the width.

A 400 mm thick mat can be heated by this method in less than 10 seconds to a uniform temperature of 100 ° C, which represents the limit for starting the reaction for the normally present reactive adhesive.

The moisture of the entire mat is increased by the vapor condensation by about 5% and the temperature of the mat after the vapor deposition is between 95 and 120 ° C. The temperature level depends on the achieved steam overpressure in the mat and on the degree of overheating of the steam. The increase in mat moisture depends on the mat start temperature. As the mat start temperature increases, less thermal energy is required, which causes less water vapor to condense and lessens the mat's moisture content. The setting of the mat initial temperature can be carried out via a temperature control of the chips in the scattering bin, during the scattering or over preheating devices in front of the device for preheating, for example by means of convection radiation or microwave preheating.

The steaming during a discharge of the mat supports the negative pressure in the mat, since the resulting additional volume of the mat can only be filled by steam. An air access is not possible on the narrow mesh surfaces due to the seal. On the underside either a discharge of water vapor, an exhaust or vacuum is applied, whereby the preferred single flow direction is supported. Likewise, the increase in mat density during precompression and outflow greatly impedes horizontal flow in and against the direction of production, so that neither air from the area in front of the device nor cooled vapor from the area downstream of the device Device can occur in the steaming of the device for preheating. This maximizes the desired vertical flow direction to the production direction in the mat.

The sealing of the upper steam plate and the upper screen belt to the side wall can be done with a pressing bar to achieve a high density. The seal to the continuous side wall is technically easy to implement and reliable in operation. It can be realized with this pre-press steam pressures in the mat up to 4 bar. A Siebbandverlauf, ie a lateral swinging of the band in the production direction, in the region of the steam plate does not affect the seal towards the atmosphere. The upper screen belt does not have to be sealed at the edge either. The lower screen belt may be guided under the side walls in the construction, and means for sealing may be simply and conveniently applied to the underside of the side walls, such as plastic straps or sealing lips. But it can also be performed within the side wall and experience a similar seal as the top guided screen belt. However, the seal on the lower wire is less critical in this area than on the side of the steam supply, since there the pressure is lower or when connecting a suction or a negative pressure (vacuum) entering air is sucked immediately in case of leaks without completely enter the mat to be able to. The short circuit currents in these areas are marginal and change the mat Negative only in the marginal areas, which are removed anyway when trimming after the successful plate production. The steam boxes and extraction boxes must be carried out in principle over the entire length of the Bedampfungsstrecke continuously to apply a high vapor pressure to the mat. To avoid a short circuit flow between the beach and the side wall, several measures can be taken. The mat density at the edge can be increased, which increases the flow resistance. The increase in density can also be carried out on a specially designed steaming plate with low mat height at the edge or by a peripheral circulating separate band. It can also be the evaporation surface only to about 100 - 400 mm to the side edge out. Another possibility is to increase the density on the narrow sides, that the pre-press for preheating has a narrower wire width than the forming belt and thus, for example, a 4-meter-wide mat is scattered, the narrowing by side walls just before the pre-press a reduction in width , for example, learns to 3.6 meters and then enters the pre-press for preheating.

In order to secure the mat against sideways falling off of individual strands with very high mats and to promote the homogeneity of the mat from the spreader to the preheater for preheating, the sidewalls should start from the first spreader (scattering wall) until after the first Preheating be performed continuously. The side wall is made smooth towards the mat.

Immediately prior to transfer of the mat to the continuous press, the mat may be subjected to another shot of steam from below to achieve the same overheating as on the top of the mat when using superheated steam. Thus, plate curvatures can be avoided after the continuous press in the final product.

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

Figur 1

Seitenansicht einer Vorrichtung zur Vorwärmung zwischen einer Streuvorrichtung und einer kontinuierlich arbeitenden Presse,

Figur 2

Schnitt A-A gemäß Figur 1 durch die Vorrichtung zur Vorwärmung und

Figur 3

eine Seitenansicht der Vorrichtung zur Vorwärmung mit Unterstützung der Vorverdichtung.

Show it:

FIG. 1

Side view of a device for preheating between a spreader and a continuously operating press,

FIG. 2

Section AA according to FIG. 1 by the device for preheating and

FIG. 3

a side view of the device for preheating with the support of precompression.

In FIG. 1 is the pre-press 3 for preheating a mat 12 between a spreader 2, possibly consisting of several scatter boxes (not shown), and a continuously operating press 1 (only the Press inlet shown) for the production of plates in section. The pre-press 3 for preheating consists of two height-adjustable compression rollers 6, 6 ', two likewise height-adjustable circulating rollers 4, 4', the rotating screen belts 5, 5 ', compression rollers 15, steam boxes 7 and suction boxes 8. To support the filter belts 5, 5' in the compression zone in each case a plurality of precompression rollers 15 may be arranged. In the vaporization zone, the steam boxes are 7 to just before the rear height-adjustable compression roller 6 ', in which case a sealing lip 13 is arranged here. The suction boxes 8 arranged on the lower screen belt 5 'are likewise provided with a sealing lip 13 for the circulation roller 4'. The sealing lips 13 are designed to be adjustable in height in order to adapt to the respective setting situation of the compaction roller 6 'or circulating roller 4'. At the inlet of the mat 12 in the pre-press 3, the narrow sides of the scattered mat 12 are guided with the side walls 9 and sealed to the atmosphere; Subsequently, the mat 12, starting from a surface side by means of a height-adjustable compression roller 6 and the rotating thereon screen belt 5 to a density of 150 - 450 kg / m ³ , preferably 250kg / m ³ , compressed and then the mat 12 on the same surface side water vapor fed through the steam boxes 7 for preheating while the mat compression is continuously withdrawn. At the same time on the opposite surface side to the forced guidance of the water vapor through the mat 12 it is removed or vacuum or vacuum is applied to the suction boxes 7 and then the mat 12 is again compressed in the outlet of the pre-press 3 with a height-adjustable compression roller 6 '. This compression can still be supported by the circulation roller 4 '. The steam for preheating can be supplied with an overpressure of 0.1 to 10 bar on the steam boxes 7 and in the outlet of the pre-press 3, the mat 12 can be compressed to 150 to 390 kg / m ³ to a certain sealing effect in the mat 12th to evoke oneself. Finally, in the outlet between the pre-press 3 and the continuously operating press 1, a vapor deposition of the (lower) side of the mat can be carried out, which has not been steamed directly in the pre-press 3 itself. This is done to prevent the coming out of the continuous press 1 plates bend unilaterally.

In order to avoid short circuit effects of the steam flow on the side walls 9 in the mat 12, it may be necessary to compress the mat edges (0 to 15% of the total width) up to 1000 kg / m ³ . In order to further support this effect, the steam boxes 7 and / or the suction boxes 8 could be concave in the direction of the mat 12 for higher compression of the outer sides of the mat 12. Incidentally, it may also be helpful not to steam the mat edges (0 to 15% of the total width). Another means of compacting the mat edges is to make the screen belts 5, 5 'narrower than the forming belt 17 under the spreading machines 2 and the side walls 9 between the spreader 2 and the pre-press 3 across the width bring together and then only the mat 12 to take over the screen belt 5 '. In this context, it makes sense to arrange the side walls 9 of the spreader 2 to the outlet of the pre-press 3 just before the continuously operating press 1.

As in FIG. 2 illustrated, the device 3 is characterized in that the circumferential upper screen belt 5 is guided vertically adjustable between the fixed side walls 9, wherein the upper screen belt 5 is sealed by means of a height-adjustable seal 16 to the side walls 9 and the side walls 9 on the lower wire belt 5 'are arranged sealed depending on the version. In this case, the side walls 9 may be arranged with a corresponding seal 18 on the lower wire 5 'standing. For this purpose, it is helpful if the seals 18 are designed as sealing lips and the corresponding counterparts are sealed to the wire 5 'with plastic. But it can also be carried out in a constructive adaptation so that the lower screen belt 5 'is guided between the side walls 9. Then a seal to the suction boxes 8 would be necessary. In this variant, the spreader 2 could also scatter directly onto the lower wire 5 'of the pre-press 3. This would facilitate an external compaction by reducing the passage between the side walls 9 when placed above the lower screen belt 5 '.

In FIG. 3 can be found in a variant of FIG. 1 points drawn in order to further specify the process parameters with regard to the mat density or mat height for uniform heating: Point Matt density mat height a) 60 - 100 kg / m ³ 100% b) 150 - 450 kg / m ³ 15 - 50% c) 150 kg / m ³ 40 - 50% d) 200 - 350 kg / m ³ 20 - 70% e) 80 -100 kg / m ³ 90 - 100%

The mat back pressure at a mat density of 250 kg / m ³ is about 0.2 N / mm ² . This counterpressure leads to springback of the mat 12, so that the upper screen belt 5, despite a belt tension of 5 to 50 N / mm, conforms to the vertically adjustable rear circulation rollers of the device (point cd) and nevertheless maintains contact with the steam boxes 7 , The introduced sealing lips 13 between the steam boxes 7 and the suction boxes 8 and the rear compaction roller 6 'or circulating roller 4' must properly seal and be designed accordingly height adjustable. Also, the lower circulation roller 4 'of the lower wire belt 5' can be made adjustable in height from the mat 12 at too high back pressures in order to achieve an appropriate increase in density at point d) compared to point c). In the pre-press 3, there are a wide variety of possibilities for realizing seals 16, 18 in the vapor-deposition area of the pre-press 3, which each designer is able to work out himself.

In FIG. 3 It is shown that in order to support the screen belts 5 in the initial region of the pre-press 3, a precompression belt 14 is arranged between the precompression rollers 15 and the screen belts 5, 5 '. It is possible to carry out this Vorverdichtungsbänder 14 above and below as further Siebbänder, perform one of the two as impermeable belt or even to design both sealing. In the latter case, the compressed air would escape through the mat 12 opposite to the direction of production. An alternative is also the scattering of the mat 12 on the lower screen belt 5 'of the device 3 in the spreader 2.

In order to adapt the steaming and the extraction to different conditions of production, the steam chambers 7, the suction chambers 8 and the steam boxes 10 are made variable and segmented in length and width and these segments can be individually controlled in their parameters. By a checkerboard-like division, different evaporation modes such as wedge-shaped or line-shaped vapor deposition over the width of the mat 12 can be realized.

LIST OF REFERENCE NUMBERS

1.

continuously working press

Second

spreader

Third

contraption

4th

revolving rollers

5th

screen belt

6th

compaction roller

7th

steam box

8th.

suction

9th

Side wall

10th

steam box

11th

Handover nose

12th

mat

13th

sealing lip

14th

pre-compression

15th

Vorverdichtungswalzen

16th

poetry

17th

forming belt

18th

poetry

Claims (22)

1. A method for the continuous preheating of a mat (12) made of elongated or flat wood chips or shavings scattered in an oriented or non-oriented manner in one or several layers in the production of wooden boards, characterized by carrying out the following method steps:

   1.1 the narrow sides of the scattered mat (12) are guided with a side wall (9) and sealed against the atmosphere during entrance into the prepress (3);

   1.2 the mat (12) is compressed to a density of 150 to 450 kg/m³, preferably 250 kg/m³, starting from one surface side;

   1.3 the mat (12) is supplied with water vapour on the same surface side for preheating, wherein simultaneously the mat compression is continuously removed and on the opposite surface side it is removed or a negative pressure or vacuum is applied for forced guidance of the water vapour through the mat (12), and

   1.4 the mat (12) is subsequently compressed again in the outlet of the prepress (3).
2. A method according to claim 1, characterized in that water vapour is supplied at an overpressure of 0.1 to 10 bars for preheating.
3. A method according to the claims 1 and 2, characterized in that the mat (4) is compressed to 150 to 390 kg/m³ in the outlet of the prepress (3).
4. A method according to the claims 1 to 3, characterized in that the mat side which was not directly supplied with water vapour in the prepress (3) itself is supplied with water vapour between the prepress (3) and the continuously operating press (1).
5. A method according to the claims 1 to 4, characterized in that the edges of the mat are compressed up to 1000 kg/m³ during the prepressing.
6. A method according to the claims 1 to 5, characterized in that the edges of the mat are not supplied with water vapour.
7. A method according to the claims 1 to 6, characterized in that an increase in the density at the edges of the mat is performed by a constriction of the side walls (9) before the prepress (3) or in the inlet thereof.
8. A prepress for the continuous preheating of a mat made of elongated or flat wood chips or shavings scattered in an oriented nor non-oriented manner in one or several layers in the production of wooden boards for performing the method according to claim 1, consisting of screen belts (5, 5') which revolve around revolving rollers (4, 4') and compaction rollers (6, 6', 15) and comprise steam boxes (7) and suction boxes (8) arranged thereon, characterized in that the revolving upper screen belt (5) is arranged between the fixed side walls (9) via the height-adjustable compaction rollers (6, 6'), and a height-adjustable seal (16) is arranged for sealing the upper screen belt (5) towards the side walls (9) and a seal (18) is arranged for sealing of the bottom screen belt (5').
9. A prepress according to claim 8, characterized in that the bottom screen belt (5') is guided with external seals between the side walls (8) via the suction boxes (8).
10. A prepress according to the claims 8 to 9, characterized in that the screen belts (5, 5') are pressed on the outsides of the mat (12) more strongly in the direction of the mat (12) by means of suitable means such as pressure rollers or strips and by taking the sealing into account.
11. A prepress according to the claims 8 to 10, characterized in that the steam boxes (7) and/or the suction boxes (8) are arranged in a concave fashion in the direction of the mat (12) for higher compression of the outside surfaces.
12. A prepress according to claim 8, characterized in that the side walls (9) are arranged vertically with a respective seal (18) on the bottom screen belt (5').
13. A prepress according to the claims 8 to 12, characterized in that one or several steam boxes (10) are arranged beneath the mat (12) in the outlet of the prepress (3) beneath the screen belt (5') and before the inlet of the mat (12) into the continuously operating press (1).
14. A prepress according to the claims 8 to 13, characterized in that the side walls (9) are arranged from the scattering machine (2) up to the outlet of the prepress (3) shortly before the continuously operating press (1).
15. A prepress according to the claims 8 to 14, characterized in that the screen belts (5, 5') are arranged in a narrower fashion than the continuous forming conveyor (17) beneath the scattering machines (2), and the side walls (9) between the scattering machine (2) and the prepress (3) are arranged to reduce the width of the mat (12).
16. A prepress according to the claims 8 to 15, characterized in that the scattering machine (2) scatters directly onto the bottom screen belt (5') of the prepress (3).
17. A prepress according to the claims 8 to 16, characterized in that a revolving pre-compaction belt (14) is arranged between the pre-compaction rollers (15) and the screen belts (5') in the compaction region of the prepress (3).
18. A prepress according to claim 17, characterized in that one or both pre-compaction belts (14) are arranged as screen belts.
19. A prepress according to claim 17, characterized in that one or both pre-compaction belts (14) are arranged as impermeable belts.
20. A prepress according to the claims 8 to 17, characterized in that the steam chambers (7), the suction chambers (8) and the steam boxes (10) are arranged to be variable and in a segmented way with respect to length and width, and said segments can be triggered individually with respect to their parameters.
21. A prepress according to one or several of the claims 8 to 20, characterized in that the revolving roller (4') is arranged in a height-adjustable way.
22. A prepress according to one or several of the claims 8 to 21, characterized in that the sealing lips (13) are arranged in a height-adjustable way depending on the requirements and position of the revolving roller (4') or the compaction roller (6').

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