Method and apparatus for the production of engineered panels from particleboard

Abstract

Method for producing material panels from chip material, wherein the chip material is produced by crushing annual or perennial plants, is subsequently provided with a binder in the further course of the process, is then spread onto a forming belt via at least one spreading device (6) to form a mat and is finally compacted into panels in a continuous or indexed press (8), which are last cut to the desired material panel size, characterized in that a measurement of chip geometries is carried out at least after the step of providing with a binder.

Description

[0001] The invention relates to a method for producing material panels from chip material, wherein the chip material is produced by shredding annual or perennial plants, is subsequently provided with a binder in the further course of the process, is then spread onto a forming belt via at least one spreading device to form a mat, and is finally compacted into panels in a continuous or indexed press, which are then cut to the desired material panel size.

[0002] The invention further relates to a device for the production of material panels from chip material, with - at least one device for shredding annual or perennial plants into wood chips - at least one device for coating the chips with a binding agent - at least one spreading device with which the chip material coated with binder can be spread onto a forming belt to form a mat, - a continuous or clocked press with which the mat can be compacted into slabs, and - a cutting or milling device with which the plate can be brought into a final shape of a material plate.

[0003] The term "material panels" refers to panels that contain at least a large proportion of lignocellulose-based material, usually wood chips, but may also contain other particles, such as fibers, including those made of plastic. To simplify the description, the terms "chip material" or "chips" include all particles from annual and perennial plants used in the construction of the material panel.

[0004] The shredding of annual or perennial plants is usually first done with chippers, and then with (knife ring) chippers and / or refiners, such as those distributed by Pallmann Maschinenfabrik GmbH & Co. KG in Zweibrücken. However, devices are also known that use sound shock waves to shred wood chips into shavings or fibers.

[0005] The binder can be sprayed onto the chip surfaces via so-called glue nozzles in a drop chute for the chips, a blowline or a mixer, so that the chip surface is at least partially wetted.

[0006] From hoppers, the binder-coated chips are fed via known spreading heads onto a continuous forming belt, which transports the spread mat to a press where the mat or cut sections thereof are pressed. Particularly after continuous pressing, the emerging sheet strand is processed into panels of the desired dimensions using suitable saws and grinding equipment.

[0007] It has been found that measuring chips after shredding is beneficial. For this purpose, 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 adjustments to the shredding equipment, such as resharpening or adjusting the spacing of the knives. Precise knowledge of the chip geometry also allows for the calculation of its total surface area. This, in turn, enables the calculation of the required amount of binder in the subsequent process step. Such chip sampling and measurement can even provide limited insights into the quality of the subsequently produced material panel. This is described, for example, in the article "Advantages of Image-Analytical Measurement of Chip Thickness" in Holz-Zentralblatt No. 50 of December 13, 2019, pages 1101 to 1103.

[0008] An example of determining material density before dosing with a binder is described in detail in DE 20 2017 100 935 U1.

[0009] The problem, however, is that during the process steps of transport, sieving, and screening, and especially during the application of binder, the chips are often subjected to further stress that they lose their size, for example, due to breakage in the mixer or friction in blow lines. The quality characteristics previously determined using state-of-the-art measurement methods are therefore inaccurate.

[0010] The purpose of the invention is therefore to provide an improved measurement method and thus more reliable statements about the expected material plate quality.

[0011] The problem is solved methodically with the features of claim 1 and in particular by measuring the clasp geometries at least after the step of applying a binder.

[0012] This provides a cross-section of chip geometries that more closely resembles those found in the mat actually pressed into the material panel than a measurement of the raw chips before gluing. The inventors recognized that the application of the binder plays virtually no role in determining the chip geometry. If the inventive method allows for the use of a representative cross-section of chip geometries after gluing as a basis for calculations of the wood particle-adhesive matrix, predictions regarding the quality properties of the material panel, such as flexural strength and transverse tensile strength, can be significantly more reliable. This is because all processes that alter the geometry of the chips during gluing can now be taken into account. The measurement is performed using optoelectronic sensors with measurement results that are ideally 3D evaluable.

[0013] It is preferred that, after the chips have been coated with a binding agent, a subset is removed from the conveying stream and the chips are separated for measurement.

[0014] This method makes it possible to obtain a representative cross-section of chip geometries from only a small quantity of chips. This allows, for example, the adjustment of classifiers, sieves, and / or spreading devices. To illustrate this, the air volume and / or velocity can be adjusted during air classification 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.

[0015] Preferably, the dust content is determined and separated before measurement.

[0016] This means that great care is taken to extract a small sample of chips, perhaps weighing 5 to 100 g, from the chip flow after the binder has been applied. This may involve dividing a larger quantity of extracted chips into smaller portions to measure a representative proportion, while separating out the very small particles. Their proportion in relation to the total weight of the extracted chips should be determined as accurately as possible. However, since they contribute little or nothing to the strength of the resulting material sheet, it is important to only capture and measure chips above a relevant size. Furthermore, separating out dust has the advantage of making the measurement more precise, as even with a low-resolution sensor, the dust content is difficult to determine.If the dust content is separated and measured, for example via vibrating screen, the material panel manufacturer has the opportunity to influence it, for example by using an extraction system in a viewing device, because he wants to avoid the dust components in the material panel that absorb too much binder relative to their size.

[0017] It is also advantageous to measure chips that are joined by adhesive.

[0018] In many cases, different chip geometries are specified for the individual layers of a material sheet. For example, it may be desirable for relatively large and long chips in the outer top layer to increase the flexural strength of the produced sheet, or for very small chips in the top layer to improve the smoothness of the material sheet after grinding for a surface coating, such as filling and varnishing, paper coating, or paint. If different spreading devices are then used for different layers in the overall mat build-up on the forming belt, the method now implemented offers a significantly better prediction of which particle or chip sizes will be fed to the respective spreading device by sieving or screening.For example, an image analysis measuring system using laser profile scanning technology can detect whether it is a large, heavy chip or many small chips stuck together.

[0019] It is advantageous that the clasp geometry measurement is also carried out before the application of a bonding agent.

[0020] Changes in the conditions during the grinding process often result in differences between the chip geometries before and after the application of a binder. In addition to the type of wood, the moisture content also plays a role here.

[0021] This second measurement allows for a comparison of chip geometries before and after gluing, enabling improved adjustment or at least better control within the chipping device. This could involve changing the blade projection or resharpening the blades to achieve more uniform chips after chipping. The dual measurement of chip geometry also allows for the determination and potential adjustment of chip changes during the process and their impact on the quality of the finished material sheet. This provides several early intervention options, such as adjustments before or during gluing.

[0022] Preferably, the chip geometry measurement is carried out repeatedly at predetermined time intervals and the measured chips are returned to the manufacturing process.

[0023] This results in a regulated manufacturing process that can be continuously adjusted. The predetermined time intervals can be set from a quarter of an hour to a day.

[0024] To determine and measure the exact clasp geometry, it is advantageous to use a laser line triangulator and receiving optics for clasp geometry measurement that have a resolution of less than 15 µm, preferably less than 5 µm.

[0025] Using such a measuring device, the dimensions of chips can be precisely determined in this process. The generated laser line is typically significantly longer than the chip, and the receiving optics measure at an angle that also allows the chip height to be determined. In the resolution range below 5 µm, it is even possible to clearly identify clumped chips. This enables a direct correlation between the measured chip sizes and the subsequent material sheet quality.

[0026] The object of the invention is achieved by means of the device according to the features of claim 8 and in particular by the fact that a device for measuring chip geometries in the chip flow direction is provided downstream of the device for applying a binding agent to the chips.

[0027] The further device claims correspond by analogy largely to the method claims and represent preferred embodiments of the protected device.

[0028] In particular, the features associated with the measuring device represent an improvement over the state of the art.

[0029] For example, the technical equipment for additional measurement of the dust content via a dust separation device is crucial for the design of the quality characteristics of the material sheet to be produced.

[0030] The invention will be explained in more detail below with the help of the figures. These figures show Fig. 1. A rough schematic sketch showing the units used for the production of material sheets, Fig. 2 a measuring device, Fig. 3 a mixer usable for the invention and Fig. 4 a classifier usable for the invention.

[0031] In Fig. Figure 1 shows a diagram of the equipment used to manufacture material sheets. The following plant components for individual process steps are depicted in the continuous sequence indicated by process arrows: a chipper 2, a chip dryer 3, a screening device 4, a device for applying a binder to the chips with mixers 5a, 5b, which also represent other devices for applying binder to the chips, furthermore spreading devices 6, which may spread the glued chips in several layers of different chip sizes from several spreading heads 6a, 6b onto a 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 panels.

[0032] The chippers 2 also symbolically represent the general process of reducing wood to chips. The five indicated knife-ring chippers are fed from a hopper above via screw conveyors and produce different chip sizes depending on the knife setting. The resulting chips of varying sizes and moisture content are then conveyed to the dryer 3.

[0033] The following screening device 4 can be used in different versions at various production points. It is required to separate fine particles (e.g., dust) or coarse particles (e.g., unwanted minerals or glue lumps) from the flow of chips. Screening devices 4 are also used, for example, to achieve fractionation according to chip size during the spreading process, so that different layers of the final material sheet are produced from chips of varying sizes.

[0034] In the embodiment according to Fig. For example, roughly speaking, two different chip size ranges are produced, which are fed from hoppers to a mixer 5a and a mixer 5b respectively. In these mixers, the chips are at least partially wetted with binder.

[0035] This makes it possible to supply different chip sizes to the spreading heads 6a for the top layers of the mat to be spread and pressed than to the spreading heads 6b for the middle layer(s).

[0036] The double belt press 8, as used for the production of engineered wood panels, especially wood-based panels, has in its basic structure an upper press section with an upper heated pressure plate and a lower press section with a lower heated pressure plate. Frames, in which pressure transmitters for applying pressure are also supported, connect the upper and lower press sections. In both the upper and lower press sections, endless circulating steel belts are guided around belt deflection drums, forming a press gap for applying pressure and temperature to the mat.

[0037] Furthermore, one can recognize in Fig. 1. A chip size measuring device 10 is also installed downstream of the mixer 5. Optionally, a chip size measuring device 11 is also provided upstream of the mixer. A representative selection of chips, i.e., a very small quantity of chips extracted from the transport process at a sampling point 20, is measured in this chip size measuring device 10, 11. This measurement allows conclusions to be drawn about the quality properties of the resulting material plate or provides indications of useful parameter changes at the individual units. These settings can be made manually or via a computer-aided evaluation unit 12.

[0038] An exemplary embodiment for the chip size measuring device 10, 11 is shown in Fig. Figure 2 illustrates this. At the sampling point 20, a small quantity of chips is diverted from the chip flow onto the vibrating trough 14. The chips are already at least partially coated with binder at the chip size measuring device 10. At least one eccentric drive 15 vibrates the screen of the vibrating trough, causing irrelevant wood dust to fall through onto the dust disposal belt 16a of a dust separation device 16, where it can be weighed and removed via a disposal 19. The chips remaining in the vibrating trough 14 are conveyed by the vibration to a singulation device, in this example a singulation chute 18, and are passed by the measuring conveyor belt 17 by the laser line triangulator 13 with 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.

[0039] The following describes two examples of how the results of chip size measurement can be used for parameter settings in the process. These examples are illustrated using... Fig. 3 and Fig. 4.

[0040] Fig. Figure 3 shows a device for applying a binding agent 5 to the chips, i.e., for wetting the chips with the binding agent. The exemplary design of a mixer 5a, 5b is irrelevant to the invention. It could, for example, also be a mixing device using a blow line or a drop chute equipped with glue nozzles.

[0041] 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 moistened with a binding agent via glue nozzles 25 along the way.

[0042] Depending on the results of the chip geometry measurement after the device for applying a binding agent 5 to the chips 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 quantity of chips supplied at inlet 23, c) the speed at which chips pass through the mixer 5a, 5b (where 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).

[0043] These parameters, mentioned as examples, have an extremely strong impact on the quality properties of the finished material panel when changed. Quality prediction can be performed using statistical and / or physical models. The binder supply provides strength up to a certain limit, which is now easier to define; larger chips in the surface layer contribute to flexural strength, while smaller chips in the surface layer allow for a smoother coating. Thus, the desired properties of the finished material panel can be achieved by measuring the chip geometry after the device for applying a binder (5) to the chips.Finding a compromise in favor of the material plate quality between slow throughput through a mixer 5a, 5b and thus the risk of the chips permanently breaking due to the high mechanical stress, and fast throughput with the risk of insufficient wetting by binder, can be simplified by determining the chip size.

[0044] A second example of how the results of chip size measurement can be used for parameter settings in the process shows Fig. 4.

[0045] This is a screening device 4. In the exemplary embodiment, chips from a hopper 26 are fed 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 then forwarded. Dust is removed, for example, via an extraction system 29. A similar screening process can also be carried out directly at the screening devices 6, in which only a desired range of chip sizes is ultimately used.

[0046] The invention allows for a more precise determination of how, for example, the wind speed and volume flow should be set by measuring the chip geometry. This enables much better control of the allocation of specific chip sizes to the individual material plate layers.

[0047] In both cases, it is therefore advisable to control the transport speed of the transport medium for the chips. This transport medium can be mechanical, such as a conveyor belt or the tools in a mixer. However, it can also be a gas or liquid in which the chips are transported, as in a classifier. Reference symbol list 1 Plant for the production of material panels 2 Device for shredding wood, wood chipper 3 dryers 4. Viewing device 5 Device for applying a binding agent to the chips 5a, 5b Mixer 6 Spreading device with multiple spreading heads 6a Spreader head top layer 6b Spreader head middle layer 7 Conveyor belt, forming belt 8 Continuous Press 9 Cutting and milling device 10 Chip size measuring device (optoelectronic) after mixer 11 Chip size measuring device (optoelectronic) in front of mixer 12 Computer-aided evaluation unit 13 laser line triangulator with optical sensor 14 vibrating trough 15 eccentric drive 16 Dust separation device 16a Dust disposal conveyor belt with scale 17 Measuring conveyor belt for chips 18 Singling shaft 19 Disposal 20 Sample collection point 21 Mixing room 22 shaft with transport and mixing tools 23 Admission 24 Controlled exhaust 25 glue nozzle 26 bunkers 27 blowers 28 wind streamlines 29 Extraction 30 conveyor belt

Claims

[1] A process for producing material panels from chip material, wherein the chip material is produced by comminuting annual or perennial plants, is provided with a binding agent in the further course of the process, is then spread onto a forming belt via at least one spreading device (6) to form a mat and is finally compacted into panels in a continuous or cycle-controlled press (8), which are finally cut to the desired material panel size, characterized by that chip geometries are measured at least after the step of applying a binding agent. [2] Method according to claim 1, characterized by that after the chips have been provided with a binding agent, a partial quantity is removed from the conveyor flow. [3] Method according to claim 1 or 2, characterized by that the chips are separated for measurement. [4] Method according to one of claims 1 to 3, characterized bythat the dust content is determined and separated before measurement. [5] Method according to one of claims 1 to 4, characterized by that chips bonded together by adhesive bonding are measured. [6] Method according to one of claims 1 to 5, characterized by that the chip geometry measurement is also carried out before applying a binding agent. [7] Method according to one of claims 1 to 6, characterized by that the chip geometry measurement is carried out repeatedly at predetermined intervals and the measured chips are fed back into the manufacturing process. [8] Method according to one of claims 1 to 7, 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. [9] Device for the production of material plates from chip material, with - at least one device for shredding annual or perennial plants (2) into chip material, - at least one device for providing the chips with a binding agent (5), - at least one spreading device (6) with which the chip material provided with binding agent can be spread to form a mat on a forming belt (7), - a continuous or cycle-controlled press (8) with which the mat can be compacted into plates, and - a cutting or milling device (9) with which the plate can be brought into a final shape of a material plate, characterized by that a device for measuring chip geometries (10) in the chip flow direction is provided after the device for providing the chips with a binding agent (5). [10] Device according to claim 9, characterized by that a sampling point (20) is provided for chips from the chip flow of the chips provided with binding agent. [11] Device according to claim 10, characterized by that between 5 and 50 grams of chips can be removed via the sampling point (20). [12] Device according to claim 9 to 11, characterized by that the device for measuring chip geometries (10) is suitable for isolating a representative cross-section of chip sizes. [13] Device according to one of claims 9 to 12, characterized by that individual and / or bonded chips can be measured via a laser line triangulator (13) and a receiving optics of the device for measuring the chip geometry (10) and the measurement results can be forwarded to an evaluation unit (12) [14] Device according to one of claims 9 to 13, characterized by that a dust separation device (16) is provided in front of the device for measuring chip geometries (10). [15] Device according to claim 14, characterized bythat the separation device (16) comprises a dust disposal belt with scales (16a).

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