Method for the production of engineered panels from particleboard

Abstract

Method for producing material panels from chip material, wherein the chip material is produced by comminuting lignocellulosic material, in the further course of the process this chip material is conveyed with different transport media and at different transport speeds through individual treatment units (3, 4, 5) to a spreading device (6), by means of which it is spread into a mat onto a forming belt (7), wherein the mat is finally compacted into panels in a continuous or indexed press (8), which are last cut to the desired material panel size in a cutting and / or milling device (9), wherein a quantity of chips separated from the transport flow is geometrically measured during the manufacturing process of the material plates and wherein the chip geometry measurement takes place before the application of a binder, characterized by the fact that the chip material is provided with a binder in a device for applying a binder to the chips (5, 5a, 5b) at a first transport speed through a first transport medium and / or is fractionated in a viewing device (4) at a second transport speed through a second transport medium, and the results of the measurement of the clamp geometry are supplied to an evaluation unit (12), and from this the transport speed of the first and / or second transport medium is set.

Description

[0001] The invention relates to a method for producing material boards from chip material, wherein the chip material is produced by comminuting annual or perennial plants, in particular from lignocellulose-containing material, in the further course of the method this chip material is transported with different transport media and at different transport speeds through individual treatment units to a spreading device, by means of which it is spread onto a forming belt to form a mat, wherein the mat is finally compacted into boards in a continuous or cycle-controlled press, which are finally cut to the desired material board size in a cutting and / or milling device, wherein a quantity of chips separated from the transport flow is geometrically measured during the manufacturing process of the material plates and wherein the chip geometry measurement is carried out before the material is provided with a binding agent.

[0002] The term "material boards" refers to boards that contain at least a large proportion of lignocellulose-containing material, usually wood chips, but may also contain other particles, such as fibers, including plastic. To simplify the description, the terms "chip material" or "chips" include all particles from annual and perennial plants used to construct the material board.

[0003] The wood is usually first shredded with chippers, followed by (knife-ring) chippers and / or refiners, such as those sold by Pallmann Maschinenfabrik GmbH & Co. KG in Zweibrücken. However, devices are also known that use sonic shock waves to reduce wood chips into shavings or fibers.

[0004] From bunkers, the chips, coated with binding agents, are finally transferred via spreading heads to a continuous forming belt, which transports the spread mat to a press, where the mat or cut parts of it are pressed. Especially after a continuous press, the emerging sheet strand is processed into material sheets of the desired dimensions using suitable saws and grinding equipment.

[0005] It has already been established that it is useful to measure chips after comminution. To do this, a representative sample of chips is taken from the process and measured using a device such as that described in DE 10 2005 019 986 A1. This allows conclusions to be drawn about necessary measures on the comminution device, such as resharpening or adjusting the distance between the blades. With precise knowledge of the chip geometry, their total surface area can also be calculated. This allows the amount of binding agent required in the subsequent process step to be calculated. Such separation of chips from the process and their measurement can, to a limited extent, even allow conclusions to be drawn about the quality of the subsequently produced material board. This is described, for example, in Holz-Zentralblatt No. 50 of 13.

[0006] December 2019, pages 1101 to 1103 in the article “Advantages of image-analytical measurement of chip thickness”.

[0007] The object of the invention is to provide improved control of the manufacturing process from chip size measurement and thus higher material plate quality.

[0008] The object is achieved in accordance with the method with the features of claim 1 and in particular in that the results of the measurement of the chip geometry are fed to an evaluation unit, and from there onwards at least one transport speed of a transport medium is set.

[0009] The inventors recognized that the transport speed of the chips during the manufacturing process, especially in screening devices and devices for applying a binding agent to the chips, has a decisive influence on the final quality. They then realized that the average size of the chips is of great importance in this context. Measurement is carried out using optoelectronic sensors with measurement results that can be evaluated in 3D, if possible.

[0010] Therefore, the invention now aims to adapt the transport speed of the chips to the manufacturing process by adjusting the speed of the transport media for the chips.

[0011] Changes in the speed of the transport media can produce very different results during fractionation or wetting with binders. Using empirical and / or mathematical-physical data stored in memory, the evaluation unit can determine the optimal current speed of the transport media. This would allow a relatively accurate idea of ​​the board quality to be obtained during the production of the material boards.

[0012] It is therefore preferably provided that the chip material is produced by comminuting wood, is provided with a binding agent in a further course of the method in a device for providing the chips with a binding agent at a first transport speed through a first transport medium and / or is fractionated in a screening device at a second transport speed through a second transport medium, and the results of the measurement of the chip geometry are fed to an evaluation unit, and from this at least the transport speed of the first and / or second transport medium is set.

[0013] Transport media can therefore be mechanically driven machine components as the first transport media (e.g. conveyor belts, mechanical pushers, rotating drums, etc.), as well as gaseous or liquid carriers of the chips as the second transport media (e.g. gas streams in air classifiers).

[0014] The binder can be sprayed onto the chip surfaces via so-called glue nozzles in a chip chute, a blowline, or a mixer, so that the chip surface is at least partially wetted. The chips have a transport velocity, which in a blowline is determined by the velocity of the carrier gas, and in a mixer, for example, by the speed and angular position of the mixing tools.

[0015] In screening devices, the chips are divided into size ranges, which are later fed to the individual scattering heads, for example. Here, too, the chips are moved via a transport medium, namely a gas stream.

[0016] It is advantageous that the evaluation unit influences the control or regulation of the speed of a mixer and thus the first transport speed based on the chip geometry measurement.

[0017] Alternatively or additionally, it is advantageously provided that the evaluation unit influences the throughput of gases at at least one fan of a screening device and thus the second transport speed based on the chip geometry measurement.

[0018] The first or second transport speed can be influenced either in a controlled or regulated manner. In both cases, but especially in the controlled version, the quality of the material sheet to be produced becomes significantly more consistent over a longer production period.

[0019] It is preferred that a portion of the chips is removed from the conveying stream and the chips are separated for measurement.

[0020] This makes it possible to create a representative cross-section of chip geometries with only a small amount of extracted chips. This can then be used, for example, to adjust sifter and / or screening devices and / or spreading devices. To illustrate this, for example, in air separation, the air volume and / or speed can be adjusted to separate the chips from the middle layer and the top layer in such a way that specific and desired chip geometries are fed to the spreading devices.

[0021] Preferably, the dust content is determined and separated before measurement.

[0022] This means that great care is taken to remove a small sample of chips, perhaps weighing 5 to 100 g, from the chip transport flow. If necessary, this can be done by portioning out a larger amount of the removed chips in order to measure a representative proportion of the chips, but to separate out the very small particles. Their proportion of the total weight of the removed chips should be recorded if possible. However, since they contribute little or no to the strength of the final material plate, it is important to only record and measure chips above a relevant size. The separation of dust also has the advantage of making measurements more precise, because even with a low resolution of the measuring sensor, the dust content is difficult to determine.If the dust content is separated and measured, for example, using a vibrating chute, the material board producer has the opportunity to influence the process, for example by means of extraction in a screening device, because he wants to avoid, as far as possible, dust components in the material board that absorb too much costly binder relative to their size.

[0023] It is advantageous that the chip geometry measurement is carried out before a binding agent is applied.

[0024] Changes in the conditions during shredding often result in differences between the chip geometries before and after the application of a binding agent. In addition to the type of wood, the moisture content also plays a role here. In this respect, this second measurement allows the chip geometries before and after gluing to be compared, which allows for improved readjustment or at least improved control within the shredding device. In this case, changing the knife projections used or resharpening the knives can be considered in order to achieve more uniform chips after shredding. By measuring the chip geometry before the chips are applied with a binding agent, the chip changes during the process and their effect on the quality of the finished material board can be determined and, if necessary, changed. This then offers several options for early intervention, i.e. settings before or during gluing.Here, determining the speed of the transport medium for the chips in a classifier or a device for providing the chips with a binding agent is a new approach to quality-improving control of the entire manufacturing process.

[0025] Alternatively or additionally, it is advantageous if chip geometries are also measured after the step of applying a binding agent.

[0026] This yields a cross-section of the chip geometries that are much closer to the actual mat pressed into the material board than when measuring the raw chips before applying a binding agent, i.e., before gluing. The inventors recognized that the application of the binding agent plays a negligible role in determining the chip geometry. If, using the method according to the invention, a representative cross-section of the chip geometries after gluing can be used as a basis for calculations, the predictions regarding the quality properties of the material board, such as flexural strength and transverse tensile strength, can be assessed with significantly greater certainty. This is because all processes that change the geometry of the chips during gluing can now be taken into account.In particular, it is easy to achieve a precise distribution of the chips intended for the different material plate layers by regulating the speed of the chip transport media.

[0027] It is advantageous to measure chips that are bonded together.

[0028] Different chip lengths are often required for the individual layers of a material board. For example, it may be desirable to have relatively large and long chips in the outer layer to increase the flexural strength of the produced board, or it may be desirable to have very small chips in the outer layer to improve the smoothness of the material board after sanding for filling and varnishing, paper coating, or painting. If different scattering devices are then used for different layers for the overall structure of the mat on the forming belt, the process now in practice offers a significantly better way of predicting which particle or chip sizes will be fed to the respective scattering device via sieving or sifting. For this purpose, an image analysis measuring system using laser profile scanning technology, for example, detects whether it is a large, heavy chip or many small chips stuck together.

[0029] Preferably, the chip geometry measurement is carried out repeatedly at predetermined intervals and the measured chips are fed back into the manufacturing process.

[0030] This creates a controlled manufacturing process that can be continuously intervened in. Predefined time periods can be set from a quarter of an hour to a day.

[0031] To determine and measure the exact chip geometry, it is advantageous to use a laser line triangulator and receiving optics with a resolution of less than 15 µm, preferably less than 5 µm.

[0032] Using such a measuring device, the dimensions of chips can be clearly determined in this process. Typically, the generated laser line is significantly longer than the chip, the width of the line is narrower than the length or width of a particle, and the receiving optics measure at an angle that also allows the height of the chip to be determined. In the resolution range below 5 µm, it is even possible to clearly identify stuck chips. This allows a clear correlation between the measured chip sizes and the subsequent material sheet quality.

[0033] The invention is explained in more detail below with the aid of the figures. Fig. 1 a rough schematic sketch with the units used to produce material plates, Fig. 2 a measuring device, Fig. 3 a mixer usable for the invention and Fig. 4 a viewing device usable for the invention.

[0034] In Fig. Figure 1 shows a diagram of units used to produce material plates. The following system components are shown for individual process steps in a continuous sequence, indicated by process arrows: a chipper 2, a dryer for the chips 3, a screening device 4, a device for providing the chips with a binding agent 5 with mixers 5a, 5b, which also represent other devices with which binding agent is applied to the chips, furthermore scattering devices 6, which scatter the glued chips, if necessary in several layers of different chip sizes, from several scattering heads 6a, 6b onto a forming conveyor belt 7 to form a mat, a continuous press 8 and a cutting or milling device 9 for the precise dimensioning of the finished material plates.

[0035] The chippers 2 also symbolically represent the general reduction of wood into chips. The five knife-ring chippers shown are fed from a bunker above via screw conveyors and produce different chip sizes depending on the knife setting. The resulting chips, which vary in size and moisture content, are then passed on to dryer 3.

[0036] The following screening device 4 can be used in various designs at various production points. They are required to separate fine particles (e.g., dust) or coarse particles (e.g., unwanted minerals or glue lumps) from the flow of chips. However, screening devices 4 are also used, for example, to achieve fractionation according to chip size during scattering, so that different layers of the final material sheet are created from chips of different sizes.

[0037] In the embodiment according to Fig. 1, for example, two different chip size ranges are roughly generated, which are fed from bunkers to a mixer 5a and a mixer 5b, respectively. In these mixers, the chips are at least partially wetted with binding agent.

[0038] This makes it possible to supply different chip sizes to the spreading heads 6a for the outer layers of the mat to be spread and pressed than to the spreading heads 6b for the middle layer(s).

[0039] The double-belt press 8, as used for the production of material boards, particularly material boards made of wood-based materials, has a basic design consisting of an upper press section with an upper, heatable pressure plate and a lower press section with a lower, heatable pressure plate. Frames, which also support pressure transducers for pressure application, connect the upper and lower press sections. In both the upper and lower press sections, endlessly circulating steel belts are guided around belt deflection pulleys, forming a press nip for applying pressure and temperature to the mat.

[0040] Furthermore, one can see in Fig. 1 also shows, by way of example, a chip size measuring device 10 downstream of the mixer 5 and a chip size measuring device 11 upstream of the mixer. A representative selection of chips, i.e., a very small quantity of chips discharged from the transport process at a sampling point 20, is measured in this chip size measuring device 10, 11 in order to be able to draw conclusions about the quality properties of the subsequent material plate from this measurement or to obtain indications for useful parameter changes in the individual units. These settings can be made manually or via a computer-assisted evaluation unit 12.

[0041] The evaluation unit 12 can be used to control many process parameters in the material plate manufacturing process, the settings of which can or should be changed based on the chip size measurement. According to the invention, the speed of the transport medium for the chips in screening devices 4 and devices for applying a binding agent 5 to the chips is to be adjusted based on the obtained chip size measurement results.

[0042] An exemplary embodiment of the chip size measuring device 10, 11 is shown in Fig. 2. A small amount of chips is diverted from the chip flow at the aforementioned sampling point 20 onto the vibrating chute 14. The chips are already at least partially wetted with binding agent at the chip size measuring device 10. With at least one eccentric drive 15, the sieve of the vibrating chute is shaken in such a way that irrelevant wood dust falls through onto the dust disposal belt 16a of a dust separation device 16, can be weighed with a scale, and removed via a disposal device 19. The chips remaining in the vibrating chute 14 are transported by vibration to a separation device, in this example a separation shaft 18, and are moved by the measuring conveyor belt 17 past the laser line triangulator 13 with an optical sensor and measured with a resolution of less than 15 µm, preferably less than 5 µm. The measured data are fed to an evaluation unit 12.

[0043] The following two examples describe how the results of chip size measurement can be used for parameter settings in the process. Fig. 3 and Fig. 4.

[0044] Fig. Figure 3 shows a device for providing the chips with a binding agent 5, i.e., for wetting the chips with a binding agent. The exemplary design of a mixer 5a, 5b is irrelevant to the invention. It could also be, for example, a mixing device using a blow line or a chute equipped with glue nozzles.

[0045] The illustrated mixer 5a, 5b has a mixing chamber 21 in which a shaft with transport and mixing tools 22 is rotatably mounted. The mixing chamber 21 has an inlet 23 on one side and an outlet 24 on the other side, which can be controlled by a flap (not shown). The chips are transported from the inlet 23 to the outlet 24 by means of the mixing tools and are wetted with binding agent via glue nozzles 25 along the way.

[0046] Depending on the results of the measurement of the chip geometry for providing the chips with a binding agent 5 and its evaluation in the evaluation unit 12, the influencing parameters of the mixing device 5 can now be displayed and changed. These include, for example, a) the amount of binder supplied via the glue nozzles 25 , b) the feed quantity of chips at the inlet 23, and - essential for this invention - c) the speed at which the chips pass through the mixer 5a, 5b (whereby the variation of the rotational speed of the shaft with transport and mixing tools 22 or the position of the controlled outlet 24 can have an influence).

[0047] When changed, these parameters, given as examples, have an extremely strong impact on the quality properties of the subsequently finished material board. The binder supply provides strength up to a certain limit, which is now easier to define; larger chips in the covering layer contribute to flexural strength; smaller chips in the covering layer allow for a smoother coating, so that the result of the chip geometry measurement after the device for providing the chips with a binder 5 can meet the desired requirements for the finished material board. Finding a compromise in favor of material board quality between slow throughput through a mixer 5a, 5b and the associated risk of permanent chip breakage due to the high mechanical stress, and fast throughput with the risk of insufficient wetting by the binder can be simplified by determining the chip size.

[0048] A second example of how the results of the chip size measurement can be used for parameter settings in the process is shown Fig. 4. This is a screening device 4. In the exemplary embodiment, chips from a hopper 26 are scattered via a conveyor belt 30 into a wind stream generated by a blower 27, which carries the chips a varying distance depending on their weight (indicated by lines 28). In this way, specific chip sizes that appear suitable for the material panel production process can be filtered out and, if necessary, sieved and forwarded. Dust is removed, for example, via an exhaust system 29. A similar screening process can also take place directly at the scattering devices 6, in which only a desired chip size range is ultimately used. By measuring the chip geometry, the invention allows for more precise determination of how, for example, the wind speed and volume flow should be adjusted. This allows for much better control of the allocation of specific chip sizes to the individual material plate layers.

[0049] In both cases, it makes sense to control the speed of the transport medium for the chips. The transport medium can be mechanical, such as a conveyor belt or the tools in a mixer. It can also be a gas or liquid in which the chips are transported, as in a separator. List of reference symbols 1 plant for the production of material boards 2 Device for shredding wood, chipper 3 dryers 4 viewing device 5 Device for providing the chips with a binding agent 5a, 5b mixer 6 Spreading device with several spreading heads 6a Spreading head cover layer 6b Spreading head middle layer 7 Conveyor belt, forming belt 8 Continuous press 9 Cutting and / or milling device 10 Chip size measuring device (optoelectronic) after mixer 11 Chip size measuring device (optoelectronic) before mixer 12 Computer-assisted evaluation unit 13 Laser line triangulator with optical sensor 14 vibrating trough 15 Eccentric drive 16 Dust separation device 16a Dust disposal belt with scale 17 Measuring conveyor belt for chips 18 Separation shaft 19 Disposal 20 sampling points 21 Mixing room 22 shaft with transport and mixing tools 23 Entrance 24 Regulated outlet 25 Glue nozzle 26 bunkers 27 blowers 28 wind streamlines 29 Extraction 30 conveyor belt

Claims

[1] A method for producing material boards from chip material, wherein the chip material is produced by comminuting lignocellulose-containing material, in the further course of the method this chip material is brought with different transport media and at different transport speeds through individual treatment units (3, 4, 5) to a spreading device (6), by means of which it is spread to a mat on a forming belt (7), wherein the mat is finally compacted in a continuous or cycle-controlled press (8) to boards, which are finally cut in a cutting and / or milling device (9) to the desired material board size, wherein a quantity of chips separated from the transport flow is geometrically measured during the manufacturing process of the material plates and wherein the chip geometry measurement is carried out before the material is provided with a binding agent, characterized by , that the chip material is provided with a binding agent in a device for providing the chips with a binding agent (5, 5a, 5b) at a first transport speed by a first transport medium and / or is fractionated in a screening device (4) at a second transport speed by a second transport medium, and the results of the measurement of the chip geometry are fed to an evaluation unit (12), and from this at least the transport speed of the first and / or second transport medium is adjusted. [2] Method according to claim 1, characterized by that the chip material is produced by crushing wood. [3] Method according to claim 1 or 2, characterized by that the evaluation unit (12) influences the control or regulation of the speed of a mixer (5a, 5b) and thus the first transport speed based on the measurement of the chip geometry. [4] Method according to one of claims 1 to 3, characterized by that the evaluation unit (12) influences the throughput of gases at at least one fan of a screening device and thus the second transport speed based on the measurement of the chip geometry. [5] Method according to one of claims 1 to 4, characterized by that the chips are separated for measurement. [6] Method according to one of claims 1 to 5, characterized by that the dust content is determined and separated before measurement. [7] Method according to one of claims 1 to 6, characterized by that chip geometries are also measured after the step of applying a binding agent. [8] Method according to claim 7, characterized by that chips bonded together by adhesive bonding are measured. [9] Method according to one of claims 1 to 8, characterized bythat the chip geometry measurement is carried out repeatedly at predetermined intervals and the measured chips are fed back into the manufacturing process. [10] Method according to one of claims 1 to 9, characterized by that a laser line triangulator (13) and a receiving optics are used for the chip geometry measurement, which have a resolution of less than 15 µm, preferably less than 5 µm.

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