Method and apparatus for the production of a blank for a structural product, and blank so produced

Abstract: Procedure for the fabrication of a blank for a structural product, such as a blank for a structural board, from material (1) comprising longer (L) and shorter (S) particles and possibly also particles (F) smaller than these. The particles are mixed with a binding agent and possible additives and then passed into at least one blank former, from where the particles are brought onto a base (10). Longer particles (L) are brought onto the base (10) to form a first surface layer, onto which is brought at least one layer of smaller particles (F, S), and onto this layer is again brought a layer of longer particles (L) to form a second surface layer, the smallest particles (F) being so brought onto the base that they mainly end up in at least one middle layer in the cross-section of the blank while the amount of smallest particles (F) diminishes towards the surface layers as seen in the cross-section of the blank. The invention also relates to an apparatus implementing the procedure and to a blank for a structural product.

Description: The present invention relates to a procedure as defined in the preamble of claim 1. The invention also relates to an apparatus as defined in claim 15 and to a product as defined in claim 22. DE 9116262 U discloses a multi layer board having a first and a second surface layer and a middle layer between the surface layers. DE 19513306 A1 discloses an apparatus for scattering particles. The apparatus comprises a preliminary roller set and a second roller set below the preliminary roller set. Elongated particles, such as chips or fibres, are used in the manufacture of structural products, e.g. boards made of wood material, especially OSB boards (oriented strand board). OSB boards are fabricated from relatively large chips of different lengths, which are scattered in suitable orientations onto a base together with a binding agent and pressed to produce boards. Short chips should mainly be used in the middle layer of the board, while longer chips should be used in the surface layers. This is advantageous in respect of the board properties, e.g. bending strength. The chips in the surface layers are usually oriented in the longitudinal direction, i.e. in the direction of the longer side of the finished product, while the chips in the middle layer are oriented in the transverse direction or they are not given any particular orientation at all. In prior-art procedures for the production of OSB and waferboards, very short chips, obtained e.g. from a chip cutting machine, are screened out from the process because they have caused deterioration of the dimensional stability and strength properties of the end product as well as a high consumption of binding agent. Typically, about 15% of the chips used as raw material are screened out because they are too short to be included in the product. Prior-art scattering/orienting apparatus are not able to fractionate and/or orient the material being scattered well enough to allow very short particles to be utilised in board manufacture. If admitted into the process, very short chips would impair the board quality because they cannot be scattered on the desired part of the board or oriented accurately enough. The object of the present invention is to achieve a completely new type of procedure and apparatus as well as a product which make it possible to avoid the existing drawbacks of prior art and thus to utilise even very short particles in the fabrication of structural products, such as boards. This object is solved by the features of independent claims 1, 15 and 22. Embodiments of the invention are described by the dependent claims. The procedure and apparatus of the invention have numerous significant advantages. The material to be scattered may contain even relatively short particles and they can be scattered on a desired part of the board and, if necessary, oriented. This allows e.g. the raw material to be more fully utilised. Using the apparatus of the invention, the material can be fractionated better than before and therefore better scattering and orienting results are achieved. These circumstances signify that the quality of the final product is also improved. Thus, in the structural product blank of the invention, smaller particles can be used than at present without impairing the strength or rigidity of the product or its stability against deformation. In the following, an embodiment of the invention will be described by referring to the attached drawing, in which Fig. 1 presents a diagram representing a procedure according to the present invention, Fig. 2 presents a diagram representing a part of the apparatus of the invention in lateral view, Fig. 3 presents detail A of Fig. 2 in magnified form, and Fig. 4 presents a cross-section of a structural product blank according to the invention. A procedure for the fabrication of a blank for a structural product, such as a blank for structural board, from material 1 comprising longer L and shorter S particles, such as longer and shorter chips and/or fibres, and possibly also particles F smaller than these, in which procedure the particles are mixed with a binding agent and possible additives and then passed into at least one blank former, from where the particles are brought onto a base 10, such as a belt conveyor or a mould or a blank coming from a previous apparatus. At first at least one surface layer 11 of longer particles L is brought onto the base 10, and smaller particles F, S are brought onto these to form one or more middle layers 13, 14, upon which longer particles L are again brought to form a second surface layer 12. Thus, the smallest particles F are brought onto the base so that they are mainly placed in a middle layer 13, 14 in the cross-section of the structural product blank and that their amount decreases towards the surface layers 11, 12 as seen in the cross-section of the blank. In the manufacture of structural product blanks, typically three or four blank formers are used, two of which are for the surface layers 11, 12 and one or two for the middle layers 13, 14. From the structural product blank, an actual product is obtained by pressing the blank in a press, thus producing a final product, such as a structural board. Typically, as seen in the cross-section of the blank, the particle size F,S,L increases from the middle towards the upper and lower surfaces 11, 12. Particles F,S,L are brought onto the base 10 either oriented or without orientation. The orientation of the particles L,S,F is preferably improved from the middle of the blank towards its upper and lower surfaces 11, 12 as seen in the cross-section of the blank. Typically, the middle layer 13, 14 is transversely oriented relative to the direction of motion of the base while the surface layers are oriented in the longitudinal direction. The smallest particles F are screened out from the rest of the particles L,S and mixed with a binding agent, whereupon they are brought onto the base either separately or together with larger particles L, S. In previously known solutions, the smallest particles have been screened out from the process altogether. In the procedure of the invention, only part of the smallest particles is rejected while the rest is used in the structural product blank. The structural product blank of the invention is preferably formed by scattering. Fig. 2 presents a blank former. In the procedure of the invention, the material 1 to be processed is conveyed onto a preliminary roller set 3,4 in a blank former, to be screened mainly by particle length. At this stage, most or all of the material being screened falls down below the plane formed by the rollers through the gaps between them. Preferably only part of the material falling down below the set of preliminary rollers 3,4 through the gaps between the rollers is passed onto an intermediate roller set 5 while the rest of the material is conveyed past the intermediate roller set, preferably via an orienting mechanism 6,7,8, onto a scattering base 10. Of the material passed onto the intermediate roller set 5, mainly the shorter particles F, S are passed through the gaps between the intermediate rollers 5 while the longer particles L are passed over the tail end of the intermediate set 5 down below the plane formed by the intermediate rollers 5, preferably via the orienting mechanism 6,7,8, onto the scattering base 10. The longer particles L are fractionated by length before being oriented and/or scattered. The longer particles L are preferably brought onto the scattering base 10 in longitudinal or transverse orientation relative to the track. The shorter particles S and the smallest particles F are fractionated by size before being oriented and/or scattered. The shorter particles S and possibly part of the smallest particles F are brought onto the scattering base 10 in either longitudinal or transverse orientation. The smallest particles F are scattered onto the scattering base 10 in such a way that the shorter they are, the closer to the final middle layer of the board to be pressed they will be positioned in the mat formed on the scattering base. Fig. 1 shows one scattering/orienting station. Typically, scattering/orienting stations are used in pairs, one being used to bestrew the lower side of the board and the other to bestrew the upper side. In the case illustrated by Fig. 2, the lower side has already been bestrewn, so the scattering/orienting station in the figure is used to bestrew the upper side. Fig. 2 thus presents a scattering/orienting apparatus applying the invention, in which the material 1 to be processed, comprising longer L and shorter S particles, preferably such as longer and shorter chips and/or fibres, and possibly even smaller particles F than these, is supplied by means of a feed conveyor onto an accelerating roller 2 rotating at a high speed. The accelerating roller 2 is provided with a suitable rough surface pattern so that it hurls the material to be screened onto a preliminary roller set 3, which consists of at least two substantially parallel rollers, preferably rotating and placed in a substantially horizontal plane with gaps between them, allowing part of the material being processed to fall down through the gaps between the rollers while the rest is passed out via the tail end of the roller set 3, 4. The gaps between the rollers may be individually adjustable, for instance in the way described in patent application FI 922777. In a preferred case, the gap width increases towards the tail end of the preliminary roller set 3, 5. The accelerating roller 2 and the preliminary rollers rotate in the anticlockwise direction as seen in the drawing. The structure of individual rollers in the preliminary roller set 3, 4 may be e.g. like that described in patent application FI 950518. Disposed below the preliminary roller set 3, 4 is a set of intermediate rollers 5, extending through at least part of the length of the preliminary roller set from its beginning as seen in the direction of material supply. The intermediate roller set 5 consists of at least two substantially parallel rollers, preferably rotating and placed in a substantially horizontal plane. Between the rollers there are gaps, so that part of the material being processed falls down through the gaps between the rollers while part of it is passed out over the tail end of the roller set: The gaps between the rollers in the intermediate set may also be individually adjustable, e.g. as in patent application FI 922777. In a preferred case, the gap width increases towards the tail end of the preliminary roller set. The rollers may have a patterned surface, which may be a milled, faced, glued or similar type of grooved and patterned surface. The roller set may also consist of so-called disc rollers, in which case each roller is provided with discs disposed or formed at a distance from each other and having an outer diameter larger than the outer diameter of the rest of the roller. The discs of adjacent disc rollers may be disposed in an interlapping arrangement. The apparatus of the invention works as follows. The material 1 to be processed is brought to the beginning of the preliminary roller set. The accelerating roller 2 hurls the. material onto the preliminary roller set 3, 4, where the rotation and roller structure of the preliminary rollers cause the material to move on. While advancing on the preliminary roller set 3, 4, material of elongated shape tends to be so oriented that even narrow particles cannot fall down through the gaps between the rollers too early. The rotating rollers, especially in the forepart of the preliminary roller set, cause long particles to rise up from the gaps between the rollers, thus preventing them from falling down too soon, whereas shorter particles S, F can fall down through the gaps between the rollers and thus land on the intermediate roller set 5. The shorter particles, such as chips, are fractionated by means of the intermediate roller set 5, preferably by size, so that the smallest particles are allowed to fall down through the gaps between the rollers in the forepart of the roller set into the space below the rollers while the largest particles fall down via the tail end of the roller set. The use of an intermediate roller set 5 makes it possible to prevent the longer chips from being intermingled with the shorter chips and, on the other hand, it allows controlled fractionation of the smallest particles. The apparatus is preferably provided with a chip orienting mechanism 6, 7, 8 placed below the roller sets 3, 4, 5. The orienting mechanism preferably comprises a first set of orienting rollers 6, designed to orient shorter particles S, F, and a second set or orienting rollers 8, designed to orient longer particles L and/or S. The orienting mechanism may also comprise other types of orienting elements besides rollers. It is also possible to use a system that only orients the longer chips, in which case the shorter chips are scattered onto the scattering base without being oriented. In the case illustrated by the figure, the scattering base 10 is a belt conveyor, which moves from the right to the left and may carry on it a blank coming from a previous scattering apparatus. Disposed in conjunction with the orienting mechanism is at least one detector 9 designed to detect the thickness of the blank on the scattering base 10. Based on the data obtained from the detector 9, the elevation of the orienting mechanism is adjusted. The aim is to keep the orienting mechanism as close as possible to the surface on which particles are scattered, so that the orientation of the particles is preserved as well as possible. The invention also relates to a structural product blank, such as a blank for a structural board, which has been formed from material comprising longer L and shorter S particles and possibly particles F smaller than these, such as chips and/or fibres, and a binding agent and which consists of two surface layers 11, 12 and at least one middle layer 13, 14 between them. The surface layers mainly contain longer particles while the middle layer mainly contains shorter particles. The middle layer 13, 14 contains the smallest particles F, the amount of which, in the cross-section of the blank, diminishes from the middle towards the surface layers 11, 12. The particles in the surface layers 11, 12 are typically mainly oriented in the longitudinal direction. The particles in the middle layer are typically mainly oriented in the transverse direction. In a typical case, at least part of the smallest particles is oriented. The structural product blank may naturally be one in which the particles have not been oriented at all but brought onto a base 10 in random orientation during scattering. The smallest particles are generally smaller than about 25 mm (1 "), preferably under 6.25 mm (1/4 "). The longest particles L are typically 75 mm - 150 mm (3" - 6") long. The shorter particles are typically under 25 mm - 75 mm (1" - 3") long. The particle lengths and their distribution in the structural product blank depend on the material used and on the structural product blank and its intended use. It is obvious to a person skilled in the art that the invention is not restricted to the examples of its embodiments described above, but that it can be varied within the scope of the claims presented below. Thus, the principles applied in making the body of the apparatus, providing the rollers with bearings, driving the rollers, and so on, are considered part of the skilled person's ordinary know-how and will not be described here in detail. The widths of the roller sets, the roller diameters, the numbers of rollers and their speeds of rotation are determined according to the capacity needed and the nature of the material to be processed. The thickness of the layers in the structural product blank and the number of layers as well as the sizes and distribution of the particles in different layers depend, among other things, on the intended use and on the material of the particles and its properties.

Claims: Procedure for the fabrication of blank for a structural product, such as a blank for a structural board, from material (1) comprising longer (L) and shorter (S) particles and also particles (F) smaller than these, said particles being e.g. chips and/or fibres, in which procedure the particles are mixed with a binding agent and possible additives and passed into at least one blank former, from where the particles are brought onto a base (10), such as a belt conveyor or a mould or a blank, wherein at least one layer of mainly longer particles (L) is brought onto the base to form a first surface layer (11), onto which is brought at least one layer of mainly smaller particles (F, S), and onto these layers is again brought at least one layer of said mainly longer particles (L) to form a second surface layer (12), the smallest particles (F) being so brought onto the base that they mainly end up in at least one middle layer (13, 14) between said first (11) and said second surface layer (12) in the cross-section of the structural product blank characterised in that the amount of smallest particles (F) decreases towards the surface layers (11, 12) as seen in the cross-section of the blank. Procedure as defined in claim 1, characterised in that the size of the particles (F,S,L) increases from the middle towards the surface layers (11, 12) as seen in the cross-section of the blank. Procedure as defined in claim 1 or 2, characterised in that particles are oriented while being brought onto the base (10). Procedure as defined in any one of claims 1 - 3, characterised in that the orientation of the particles is improved from the middle of the blank towards the surface layers (11, 12) as seen in the cross-section of the blank. Procedure as defined in any one of claims 1 - 4, characterised in that the smallest particles (F) are screened out from the rest of the particles (L, S) and mixed at least with a binding agent, whereupon they are brought onto the base (10) either separately or together with larger particles (L, S). Procedure as defined in any one of claims 1 - 5, characterised in that the blank is formed by scattering. Procedure as defined in claim 6, characterised in that at least part of the particles is fractionated by size in conjunction with blank formation. Procedure as defined in claim 6 or 7, characterised in that the material (1) to be processed is conveyed onto a preliminary roller set (3, 4), to be screened mainly by particle length, permitting at least part of the material being screened to fall down below the plane formed by the rollers through the gaps between them while the possible remainder is passed down over the tail end of the roller set (3, 4), and that at least part of the material falling down below the preliminary roller set (3, 4) through the gaps between the rollers, screened by an intermediate roller set (5) disposed under the preliminary roller set, is passed, preferably via an orienting mechanism (6, 7, 8), onto the scattering base (10), so that, of the material passed onto the intermediate roller set (5), the smallest particles (F, S) are passed through the gaps between the rollers of the intermediate roller set (5) while the longer particles (L) are passed over the tail end of the roller set (5) down below the plane formed by the rollers, preferably by means of the orienting mechanism (6,7,8), onto the scattering base (10). Procedure as defined in claim 8, characterised in that the longer particles (L) are fractionated by length before being oriented and/or scattered. Procedure as defined in claim 8 or 9, characterised in that the longer particles (L) are brought onto the scattering base (10) either in the same orientation as the shorter particles (S, F) or in a different orientation. Procedure as defined in any one of claims 8 - 10, characterised in that the shorter particles (S) and particles (F) smaller than these are fractionated by size before being oriented and/or scattered. Procedure as defined in any one of claims 8 - 11, characterised in that the shorter particles (S) and possibly part of the smallest particles (F) are brought onto the scattering base (10) either in longitudinal orientation or in transverse orientation. Procedure as defined in any one of claims 8 - 12, characterised in that the smallest particles (F) are so scattered onto the scattering base (10) that they will form the middle layer of the board to be pressed from the blank formed on the scattering base. Procedure as defined in any one of claims 8 - 13, characterised in that the material (1) to be processed is acted upon by an accelerating roller (2) at the feed point of the preliminary roller set so that at least part of the particles being processed is hurled onto the preliminary roller set (3, 4). Apparatus for scattering material (1) containing longer (L) and shorter (S) particles and also particles (F) smaller than these, such as chips and/or fibres, preferably together with a binding agent, onto a scattering base (10), said apparatus comprising a preliminary roller set (3, 4) consisting of at least two substantially parallel rollers with gaps between them, and in which apparatus some of the individual rollers consist of bars disposed longitudinally parallel to the rollers at equal distances around the roller circumference and mounted on flanges or the like transverse to the longitudinal direction of the roller, said flanges being fixed to the roller shaft, characterised in that it has a second roller set (5) disposed below the preliminary roller set (3, 4), said second roller set consisting of at least two rollers parallel to each other and extending along at least part of the length of the preliminary roller set as seen in the direction of material supply, with gaps formed between the rollers to permit scattering of particles, and that the gap between individual rollers in the second roller set (5) is smaller than the gap between individual rollers in the preliminary roller set (3,4) at substantially the same horizontal position. Apparatus as defined in claim 15, characterised in that the rollers in the second roller set (5) are cylindrical rollers and/or disc rollers. Apparatus as defined in claim 15 or 16, characterised in that the gaps between the rollers in the second roller set (5) are individually adjustable. Apparatus as defined in any one of claims 15 - 17, characterised in that it comprises an orienting mechanism (6, 7, 8) disposed below the roller sets (3, 4, 5) for scattering the particles in given orientations onto the scattering base (10). Apparatus as defined in any one of claims 15 - 18, characterised in that it is has at least one detector (9) disposed in conjunction with the orienting mechanism (6, 7, 8) to measure the thickness of the mat of particles on the scattering base (10), the elevation of the orienting mechanism (6, 7, 8) being adjusted on the basis of the data obtained from the detector (9). Apparatus as defined in any one of claims 15 - 19, characterised in that the orienting mechanism is provided with mutually different orienting elements (6, 8) for short particles and for long particles. Apparatus as defined in any one of claims 15 - 20, characterised in that it has, in the forepart of the orienting mechanism as seen in the feed direction, elements (6, 7) for orienting short particles (S, F) and after them elements (8) for orienting longer particles (L). Blank for a structural product, such as a blank for a structural board, formed from material comprising longer (L) and shorter (S) particles and also particles (F) smaller than these, such as chips and/or fibres and a binding agent, said blank consisting of at least two surface layers (11, 12) and at least one middle layer (13, 14) between them, characterised in that the middle layer (13, 14) comprises the smallest particles (F), the amount of which diminishes in the cross-section of the blank towards the surface layers. Blank for a structural product as defined in claim 22, characterised in that the surface layers (11, 12) mainly contain longer particles (L, S) while the middle layer mainly contains shorter particles (S, F). Blank for a structural product as defined in claim 22 or 23, characterised in that the particles in the surface layer (11, 12) are mainly oriented in the longitudinal direction, i.e. in the direction of the longer side of the finished product. Blank for a structural product as defined in any one of claims 22 - 24, characterised in that the smallest particles (F) are smaller than about 25 mm (1 "), preferably under 6.25 mm (1/4 "). Blank for a structural product as defined in any one of claims 22 - 25, characterised in that at least part of the smallest particles (F) has been oriented.

Inventors: LAATIKAINEN AARNE, LAITINEN JARMO, LAATIKAINEN, AARNE, LAITINEN, JARMO
Applicants: METSO PANELBOARD OY
Application year: 1998
Main classification: B27N3
IPC codes: B27N3