The present invention relates to a method and device for forming a mat of material containing lignocellulose, which mat is intended to form at least one board, disintegrated material containing lignocellulose being fed to a feeding out unit and from this being fed in the form of a material flow to a forming unit comprising at least one forming belt, the feeding out unit being positioned at a higher level than the forming unit.
Upon producing boards of material containing lignocellulose, such as particle boards and fibreboards according to the dry method (MDF, HDF, LDF etc.), first the material containing lignocellulose is disintegrated into particles or fibre bundles. Subsequently these are dried and glue-coated and formed to a continuous mat in one or several forming stations. The mat is pre-pressed and subsequently finish-pressed to boards under pressure and heat in a continuous or discontinuous press.
The material containing lignocellulose can be mixed with other materials, for example plastics, waste paper, glass fibres, disintegrated minerals etc., prior to forming or under the forming process. Upon producing boards it is essential that these have homogeneous properties over the whole board surface. These properties are, inter alia, thickness, transverse tensile strength, bending and breaking strength, painting properties etc. Since these properties are dependent on the density of the board, it is important that the forming is effected with a good precision so that the density of the board is the same over the whole board surface. In order to achieve this, during the forming process the particles or fibre bundles must be distributed as homogenously as possible both longitudinally and transversely over the whole formed surface.
Conventional forming equipments for forming boards of material containing lignocellulose are often mechanical. These usually comprise at least one feeding out unit comprising a dosing bin or dosing container where the material is intermediately stored and subsequently is dosed down, free falling, to a forming unit where the material is laid down on a forming belt, i.e. a conveying belt. Further, upon producing fibre boards a scalping roll is often used subsequent to forming, which mills off any unevenness in the mat surface to improve the forming precision.
A drawback of the conventional forming equipments is that the material during its free fall between the feeding out unit and forming unit easily can be affected by surrounding air flows both longitudinally and transversely, whereby the forming precision is impaired. Free fall, where this problem is present, arises, as mentioned above, during the fall between the feeding out unit and forming unit and also, depending on machine type, in the fall from the rolls of the forming unit down onto the forming belt.
During a free fall of a material flow in air, two inconvenient phenomena arise. Firstly, it is prior known that a material flow falling freely in air has a tendency to get together and form several material beams. This tendency increases with an increased height of fall. Secondly, co-ejecting air streaming and decelerating or air-breaking effects arise. These air streams drag long material and also make the fall shaft, which surrounds the material flow, non-transparent due to material whirling about.
A prior method to decrease the effect of the free fall from the rolls arranged at the forming belt, so called forming rolls, down onto the forming belt, is to make these forming rolls vertically movable so that the forming rolls always are positioned close to the formed mat. SE 511259 discloses for example how these rolls are working directly into the mat, whereby the problem with the free fall from the rolls arranged at the forming belt down onto the forming belt is eliminated. However, the problem with the free fall from the feeding out unit to the forming unit is unsolved.
The object of the present invention is to eliminate or at least minimize the problem with deficient homogeneity of the formed mat resulting from the effect of uncontrolled air streams on the free falling material slow between the feeding out unit and forming unit as described above, and resulting from other effects as a result of the free fall of the material flow between said units. Further, the object of the present invention is to solve further problems mentioned above.
The solution of the present invention is to provide a method and a device providing a radical improvement of the forming process by a method of the kind defined in the preamble of claim 1 comprising the special measure that at least one feeding down surface is arranged which extends from the feeding out unit to the forming unit, and that the transport of material between the feeding out unit and the forming unit is effected by feeding the material downwards along this feeding down surface. By feeding the material flow downwards along the feeding down surface essentially along the whole distance between said units, air streams and material flow are separated, whereby a controlled material flow is provided between these units. This controlled material flow in turn enables an increased homogeneity of the formed mat and thus also in the finished board.
According to an advantageous embodiment of the method according to the present invention, the material flow is slowed down and deflected towards the horizontal plane of the forming belt as it approaches the forming unit.
According to a further advantageous embodiment of the method according to the present invention, the width of the material flow is controlled previous to the forming unit. This offers a flexible and uncomplicated variation of the width of the formed mat.
According to another advantageous embodiment of the method according to the present invention, the material flow is laterally controlling by moving adjustable lateral control means in the material flow, said means being positioned in the material flow, and turning said means in relation to the direction of motion of the material flow. Through this the homogeneous properties of the formed mat are strengthened.
According to yet another advantageous embodiment of the method according to the present invention, the distribution of the material transverse to the direction of motion of the material flow is controlled. The purpose of this is also to strengthen the homogeneous properties of the formed mat.
According to an advantageous embodiment of the method according to the present invention, the material is fed to the feeding out unit via a second feeding down surface by feeding said material downwards along this second feeding down surface to the feeding out unit, whereby a controlled material flow is also provided here. This embodiment of the method of the present invention can also be effected independently of and separated from the method according to the present invention involving the feed of material between the feeding out unit and the forming unit, and further comprise one or several of the special measures being taken according to the method of the present invention for feed of material between the feeding out unit and forming unit.
Further, the present invention provides a device for forming a mat of material containing lignocellulose, which mat is intended to form at least one board, comprising a feeding out unit and a forming unit with at least one forming belt, disintegrated material containing lignocellulose being fed to the feeding out unit and subsequently being fed to the forming unit in the form of a material flow, and where the feeding out unit is positioned at a higher level than the forming unit, the device comprising at least one feeding down surface extending from the feeding out unit to the forming unit, the feeding down surface being adapted to transport material between the feeding out unit and the forming unit by feeding the material downwards along this feeding down surface, whereby a controlled material flow is provided between these units.
According to alternative embodiments of the feeding down surface of the device according to the present invention, the feeding down surface comprises a conveying belt, a layer of rolls or a sliding plate. In the case with a sliding plate the gravity affects the downward motion of the material flow while in the case of a layer of rolls or a conveying belt, also their working speed affects the downward motion of the material flow. The sliding plate can comprise several beside one another positioned plates.
According to an advantageous embodiment of the device according to the present invention, the forming unit comprises at least one speed adaptation device, via which the material passes before being laid down onto the forming belt, designed to adapt the speed of the material to the speed of the forming belt. The speed adaptation device comprises for example a diffusion roll which preferably is vertically adjustable.
According to a further advantageous embodiment of the device according to the present invention, width control means adapted to control the width of the material flow previous to the forming unit are arranged along at least one of the longitudinal sides of the feeding down surface.
According to another advantageous embodiment of the device according to the present invention, adjustable lateral control means adapted to laterally control the material flow are positioned in the material flow, the lateral control means being movable in the material flow and pivotally in relation to the direction of motion of the material flow.
According to yet another advantageous embodiment of the device according to the present invention, material distribution means, adapted to control the distribution of the material transverse to the direction of motion of the material flow, are arranged at the feeding down surface.
According to an advantageous embodiment of the device according to the present invention, a second feeding down surface is arranged to feed material to the feeding out unit by feeding said material downwards along this second feeding down surface to the feeding out unit, whereby a controlled material flow is also provided here. This embodiment can also be provided independently of and separated from the device according to the present invention involving the feed of material between the feeding out unit and the forming unit, and further comprise one or several of the special features of the device according to the present invention for feed of material between the feeding out unit and forming unit.
Further, the present invention provides a method for producing boards of material containing lignocellulose, which method comprises the measure of forming a mat from disintegrated material, the method comprising the special measures mentioned in any of the claims 1 to 8.
The present invention also provides a plant for producing boards of material containing lignocellulose, which plant comprises a device for forming a mat, said device comprises the special features mentioned in any of the claims 9 to 22.
Such an arranged method and such a designed plant, respectively, for producing boards present those advantages described above regarding the method for forming a mat.
As described above in the disclosure of the background of the invention, material does not only refer to material containing lignocellulose but also possible addition of any materials, such as plastics, waste paper, glass fibres, disintegrated minerals etc. The material can be of different sizes and forms and for example comprise fibres and/or fibre bundles
Further advantageous embodiments of the present invention emerge from the appended claims.
The present invention will now be described, for exemplary purposes, in more details by way of embodiments and with reference to the enclosed drawings, in which:
Number | Date | Country | Kind |
---|---|---|---|
0300418-1 | Feb 2003 | SE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/SE04/00200 | 2/16/2004 | WO | 8/16/2005 |