Patent Grant
11759972
Applicant claims priority under 35 U.S.C. § 119 of German Application No. 10 2018 218 512.3 filed Oct. 29, 2018, the disclosure of which is incorporated by reference.
The present invention relates to a gypsum fiberboard panel or fiber-reinforced gypsum plasterboard panel, in particular in accordance with DIN EN 15283-2, as well as to a method and an apparatus for production of such a gypsum fiberboard panel.
Gypsum fiberboard panels are used as construction panels, fire-protection panels, noise-protection panels and wet-room panels, for planking (load-bearing) and cladding (non-load-bearing) of components, for example walls, ceilings, pillars or girders. Gypsum fiberboard panels serve, in particular, also as finished-part/dry-floor elements, hollow-floor elements and double-floor elements, to form floor constructions.
In the production of gypsum fiberboard panels, a dry mixture is formed from calcined gypsum, fibers, and, if applicable, admixtures. After addition of water, without further binders, the dry mixture is formed into panels and dried. The gypsum sets due to the water, and penetrates and sheathes the fibers. The setting process therefore has a decisive influence on the quality of the gypsum fiberboard panels. In particular, it has been shown that greater panel strength can be achieved by means of setting that is as uniform as possible.
The difficulty in bringing about a uniform setting process is ensuring that the most complete and uniform wetting of the dry mixture takes place with the setting water that is to be added, if at all possible without allowing an excess of water to occur in this regard. Methods that are directed at achieving setting that is as uniform as possible are known.
WO 93/04830 A1 discloses a method for the production of gypsum fiberboard panels according to a semi-dry process. In this regard, at least one layer of a mixture of gypsum, fibers, and water is spread onto a continuously moving belt. Subsequently, the spread layer is pre-compacted in a pre-press that has pressing rolls that lie opposite one another, to 110 to 180% of the desired panel thickness; subsequently, it is wetted again with an upper and lower spraying apparatus, and finally it is pressed to the panel thickness in the main press. The spray apparatuses disposed between pre-press and main press are combined with a vacuum box having a fan, in each instance.
EP 0 260 342 A1 relates to a method for the production of molded parts composed of gypsum and fibers that contain lignocellulose, using a dry process. In this method, gypsum powder is mixed with the fibers as a hemihydrate; this dry mixture is poured into the desired mold, pre-compacted in a press, and subsequently pressed, in the same press, to form the molded parts, wherein the gypsum powder is converted from the hemihydrates to dehydrate, using water, and the pressed molded parts are dried by means of the action of heat. The water required for conversion of the gypsum is added to the gypsum/fiber mixture after it has been pre-compacted.
In practice, it has been shown that it cannot be ensured, using the pre-compaction techniques that are usually used, for example by means of pressure rolls, that uniform and complete wetting of the gypsum/fiber mixture (called a cake) will always take place during the subsequent pressing process. In particular in the production of gypsum fiberboard panels that are supposed to have a thickness of 30 mm, for example for use as floor elements, the water can penetrate into the cake only in part. This can lead to a considerably greater proportion of water in the upper region of the panel, and during the pressing process, this can lead to squeezed areas in the upper region and/or dry spots in the lower region.
This is a known problem. Currently, two thinner panels are connected with one another for the production of thicker gypsum fiberboard panels.
The present invention is based on the task of creating a method for the production of a gypsum fiberboard panel, by means of which complete and uniform wetting and setting of the gypsum/fiber mixture is guaranteed, and by means of which it is also possible, in particular, to produce panels having a thickness>25 mm.
It is a further task of the invention to make available an apparatus for the production of such a gypsum fiberboard panel, by means of which complete and uniform wetting and setting of the gypsum/fiber mixture is guaranteed, and by means of which it is also possible to produce panels having a thickness>25 mm.
Furthermore, it is a task of the invention to make available a gypsum fiberboard panel that can be produced using a uniform wetting and setting process, wherein in particular, the formation of squeezed areas or dry spots is supposed to be prevented during production, also in the case of panels having a thickness>25 mm.
These tasks are accomplished by means of a method having the characteristics according to one aspect of the invention, as well as by means of an apparatus having the characteristics according to another aspect of the invention, as well as by means of a gypsum fiberboard panel having the characteristics according to a further aspect of the invention. Advantageous further developments of the invention are indicated below.
The method according to the invention comprises the following method steps:
According to the invention, the method is characterized in that for pre-compaction, the mixture is sprayed with a water mist, and, preferably at the same time, a partial vacuum is applied to it.
It is advantageous, in the case of the method according to the invention, that the water mist is drawn into the gypsum/fiber mixture during pre-compaction, in such a manner that the mixture can be uniformly wetted over its entire cross-section. As a result, gypsum and fibers are made more capable of absorbing water, so that the mixture is uniformly and completely wetted with the amount of setting water that is added later.
The gypsum fiberboard panels produced in this manner are characterized by great strength, in particular bending resistance according to DIN EN 15283-2, and great raw density, depending on the settings of the overall system.
Furthermore, in the case of the method according to the invention, the pre-compaction can be adapted to the panel thickness to be produced, in that water mist and/or partial vacuum are coordinated accordingly. The method according to the invention thereby makes possible the production of different panel thicknesses and an increase in advancing speed depending upon the panel thickness. As a result, the throughput and the production sequence in the production of gypsum fiberboard panels are improved.
In particular, gypsum fiberboard panels having great strength, with a panel thickness>25 mm, can be reliably and reproducibly produced using the method according to the invention. The method thereby makes possible the production of floor elements that are composed of a single thick gypsum fiberboard panel, instead of two thin panels that are connected with one another.
Within the scope of the invention, the gypsum used can be a gypsum obtained from gypsum rock, called natural gypsum, in particular building plaster or stucco, as well as industrially produced calcium sulfate or calcium sulfate that occurs as a byproduct in technical processes, called technical gypsum, in particular gypsum derived from flue gas desulfurization systems (FGD gypsum). Also, calcium sulfate modifications from dismantling and recycling (recycled gypsum) can be used.
Within the scope of the invention, all fibers suitable for the production of gypsum fiberboard panels can be used, in particular fibers that contain cellulose, for example recycled paper fibers or artificial mineral fibers, for example glass fibers.
Furthermore, it lies within the scope of the invention that an aggregate, preferably expanded perlite and/or mica, and/or an additive, preferably pigment, can be added to the mixture, and/or that an admixture, preferably a setting accelerator or setting delay agent and/or hydrophobic agent, can be added to the mixture and/or to the setting water.
According to an advantageous embodiment of the method, a first surface of the mixture, preferably its free top side facing away from the conveying means, is sprayed with the water mist for pre-compaction, and the partial vacuum is applied on a second surface of the mixture, which lies opposite the first, preferably on its underside that faces the conveying means. Preferably, this takes place at the same time.
Preferably, a water/solid value w/s of 0.05 to 0.25, preferably of 0.1, is produced in the mixture for pre-compaction with the water mist.
The water mist is an aerosol, in particular composed of liquid aerosol particles in ambient air, having an average particle size of 0.1 to 60 μm, preferably 15 μm.
Preferably, a partial vacuum of 5 to 20 mbar, preferably of 10 to 15 mbar, preferentially of 10 mbar is applied to the mixture for pre-compaction.
According to a further advantageous embodiment, the mixture also has a partial vacuum applied to it for post-compaction. In particular, in this regard, a partial vacuum of 10 to 25 mbar, preferably of 15 to 20 mbar, preferentially of 20 mbar is generated. Particularly preferably, the partial vacuum is applied to increase slowly in the advancing direction of the conveying means, for example in that the amount of air drawn off to generate the partial vacuum is increased section by section in the advancing direction.
Preferably, the partial vacuum is applied to an underside of the conveying means or on the conveying means underside, in each instance, for pre-compaction and/or post-compaction, so that the partial vacuum acts on the mixture through the conveying means.
Preferably, gypsum fiberboard panels having a thickness of 6 to 50 mm are produced using the method according to the invention. In particular, gypsum fiberboard panels in the usual thickness range, having a thickness of 10 to 25 mm, particularly preferably of 10 to 18 mm, or thick gypsum fiberboard panels having a thickness of 25 to 40 mm, particularly preferably of 30 mm, are produced.
In this regard, the gypsum fiberboard panel that can be produced or has been produced according to the invention preferably has the following material properties:
The apparatus according to the invention for the production of a gypsum fiberboard panel comprises:
According to the invention, the apparatus is characterized in that the pre-compaction device has means for spraying the mixture with a water mist, as well as means for preferably simultaneous application of a partial vacuum to the mixture.
The apparatus is particularly suitable for carrying out the method according to the invention, and also has the advantages described above.
In particular, in the case of the apparatus according to the invention, the pre-compaction device can be adapted to the panel thickness to be produced, in that water mist and/or partial vacuum are coordinated accordingly. By means of the apparatus according to the invention, it is possible to increase the advancing speed as a function of the panel thickness. The apparatus thereby guarantees higher throughput and an improved production sequence during production.
In particular, it is also possible to produce gypsum fiberboard panels having great strength, with a panel thickness>25 mm, in reliable and reproducible manner, using the apparatus according to the invention, for example floor elements that are composed of a single thick gypsum fiberboard panel.
According to a preferred embodiment, the apparatus is configured in such a manner that with the pre-compaction device, a first surface of the mixture, preferably its free top side that faces away from the conveying means, can be sprayed with the water mist, and the partial vacuum can be applied to a second surface of the mixture that lies opposite the first, preferably to its underside that faces the conveying means.
Preferably, the pre-compaction device comprises means for spraying, by means of which the mixture can be sprayed with fine water droplets having an average droplet size of 0.1 to 60 μm, preferably 15 μm, in particular depending upon thickness with a water amount of 1 to 10 l/h.
Preferably, the means for spraying have at least one mist nozzle, preferably 1 to 35 mist nozzles, particularly preferably 14 to 28 mist nozzles, with which the water mist can be sprayed at an air pressure of 2 to 4 bar, preferably 3 bar, and a liquid pressure of 1 to 3 bar, preferably 2 bar, and a jet angle of 40° to 80°, preferably 60°. In particular, the mist nozzles are pneumatic atomizer nozzles.
Preferably, the pre-compaction device comprises means for applying a partial vacuum to the mixture, wherein the means are configured for applying a partial vacuum of 5 to 20 mbar, preferably of 10 to 15 mbar, preferentially of 10 mbar to the mixture. Preferably, the means are configured in such a manner that the partial vacuum can be applied at an underside of the conveying means, wherein the partial vacuum can be applied to the mixture through the conveying means.
According to a further advantageous embodiment, the post-compaction device also has means for generating a partial vacuum, wherein preferably, a partial vacuum of 10 to 25 mbar, preferably of 15 to 20 mbar, preferentially of 20 mbar can be applied to the mixture.
Preferably, the post-compaction device follows the wetting device in the advancing direction of the conveying means, wherein the partial vacuum that can be generated by the means of the post-compaction device can be applied to an underside of the conveying means, so that the partial vacuum can be applied to the mixture through the conveying means. Particularly preferably, the means for generating a partial vacuum are configured in such a manner that the amount of air drawn off to generate the partial vacuum can be increased, section by section, in the advancing direction of the conveying means.
Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.
In the drawings,
In the individual figures, the same parts are always provided with the same reference symbols. Furthermore, in connection with the figure description, it is explicitly emphasized that the invention is not restricted to the exemplary embodiments shown and thereby not to all or multiple characteristics of the combinations of characteristics that are described. Instead, each individual partial characteristic of the exemplary embodiment or of each exemplary embodiment can also have inventive significance even dissociated from all the other partial characteristics described in connection with it, by itself and also in combination with any desired characteristics of another exemplary embodiment, and also independent of the claims and their antecedents.
An apparatus 1 according to the invention, for production of a gypsum fiberboard panel 2, is shown in
The conveying device 3 is configured as a driven conveyor belt and, in particular, has a screen belt 3a as the conveying means (
The raw material application device 4 has a mixing device 4a and a feed device 4b. The raw material application device 4 is a spreading machine, for example.
The mixing device 4a is connected with a supply container 17 for gypsum 14, a supply container 18 for paper fibers 15, and further supply containers 19 for aggregates, additives, and admixtures 16. The mixing device 4a can be filled from the containers 17, 18, 19 with an amount of gypsum 14, fibers 15, and other materials 16 determined for production of the mixture 13. The mixing device 4a thereby serves for mixing and producing the mixture 13.
It is advantageous if a paper processing device 20 is assigned to the fiber container 15 of the mixing device 4a, by means of which former device scrap paper 21, which can be passed to the processing device 20, can be recycled to produce the paper fibers 15. The paper processing device 20 involves hammer mills and fiber mills.
The feed device 4b is connected with the mixing device 4a. The feed device 4b is configured in such a manner that the mixture 13 that can be produced by the mixing device 4a can be spread onto the screen belt 3a with a predeterminable mixture height or mixture thickness.
The pre-compaction device 5, which is shown in greater detail in
The means for spraying 22 comprise a water supply container 25, a spray chamber 26 having at least one mist nozzle 27 for producing the water mist 23, as well as a water feed line 28, by means of which the water can be fed to the mist nozzle 27 from the water supply container 25.
The spray chamber 26 has a preferably block-shaped housing 29, which is disposed above the screen belt 3a. The housing 29 is preferably disposed so as to surround or enclose the screen belt 3a, so that the screen belt can move through a housing interior or spray chamber interior. In particular, the housing 29 has two opposite side walls 29a, which extend parallel to the advancing direction A in a longitudinal direction B, as well as two end walls 29b, which run perpendicular to these and extend in a width direction C, as well as a ceiling wall 29c that extends perpendicular to the walls 29a, 29b and extends in a height direction D. The end walls 29b have a passage opening 30, in each instance, through which the screen belt 3a, with the mixture 13 lying on it, can be conveyed into the housing 29 or into the spray chamber 26 on one housing side, and conveyed out again on the opposite housing side. The passage opening 30 has a width in the width expanse of the screen belt 3a or in the width direction C, and, perpendicular to this, a height in the height direction D. The width is dimensioned in such a manner that the screen belt 3a can be moved through the passage opening 30 with the smallest possible distance, preferably of 1 to 5 mm, from the respective side wall 29a. The height of the passage opening 30 corresponds to the distance of a lower edge of the side wall 29b from the screen belt 3a or from the mixture 13. Preferably, the height of the passage opening 30 can be adapted to the height of the mixture 13 determined to be spread onto the screen belt 3a. In particular, the end wall 29b can be moved up and down, in driven manner, in the height direction D, so that the height of the passage opening 30 can be increased or reduced.
The mist nozzles 27 are disposed within the housing 29, preferably on the ceiling wall 29c. Preferably, 1 to 35, preferentially 14 to 28 mist nozzles 27 are provided. It is practical if the mist nozzles 27 are disposed in the spray chamber 26 distributed at a regular distance from one another, and directed in the direction of the screen belt 3a, so that a first free top side 13a of the mixture 13, facing away from the conveying means, can be uniformly sprayed with the water mist 23. Preferably, the mist nozzles 27 are configured, in each instance, for spraying an aerosol consisting of gas, for example nitrogen, or air and of water particles, having a droplet path configured in cone-like manner, i.e. an aerosol cone 31. For example, the aerosol cone 31 can be generated with an air pressure of 2 to 4 bar, preferably 3 bar, and a liquid pressure of 1 to 3 bar, preferably 2 bar, and a jet angle of 40 to 80°, preferably 60°, wherein the water particles have an average droplet size, in particular, of 0.1 to 60 μm, preferably 15 μm. The mist nozzles 27 are, for example, pneumatic atomizer nozzles, type Lechler 136.231.35 A2.
The water mist 23 that can be sprayed onto the mixture 13 by the means 22 for spraying is thereby preferably formed of multiple aerosol cones 31. Preferably, the mixture 13 can be continuously sprayed with the water mist 23.
The means 24 for applying a partial vacuum to the mixture 13 have a partial vacuum generation device (not shown), by means of which a partial vacuum can be generated and can be applied to an underside 13b that lies opposite the free top side 13a and faces the conveying means. Preferably, the means 24 are structured in such a manner so as to apply the partial vacuum on an underside of the screen belt 3a, so that the partial vacuum can be applied to the mixture 13 through the screen belt 3a. Preferably, a partial vacuum of 5 to 20 mbar, preferably of 10 to 15 mbar, preferentially of 10 mbar can be applied to the mixture 13. By means of applying the partial vacuum, the water mist 23 can be drawn into the mixture 13. Preferably, the means 24 are a vacuum tray.
The wetting device 6 has means 32 for watering the mixture 13 with the setting water required for setting of the gypsum/fiber mixture, as well as a water supply container 33 connected with the water supplying means 32, for feed of the setting water. The water supplying means 32 is preferably configured as a water curtain.
The post-compaction device 7 preferably has means for generating a partial vacuum, by means of which the setting water can be drawn into the mixture, post-compacting the mixture 13. Preferably, the means for generating a partial vacuum are formed analogous to the means 24 of the pre-compaction device 5 and have a partial vacuum generation device for applying a partial vacuum to the underside 13b of the mixture 13. Preferably, the partial vacuum can also be applied to the underside of the screen belt 3a, so that the partial vacuum can be applied to the mixture 13 through the screen belt 3a. Preferably, a partial vacuum of 10 to 25 mbar, preferably of 15 to 20 mbar, preferentially of 20 mbar can be applied to the mixture 13, using the post-compaction device 7. In particular, the partial vacuum can be applied in such a manner that the amount of air drawn off to generate the partial vacuum can be increased section by section along the conveyor belt underside, viewed in the advancing direction A. Preferably, the post-compaction device comprises a vacuum tray.
The pressing device 8 has means for pressing or compaction of the mixture 13 to produce a gypsum fiberboard panel strand, in particular a continuous one, having a thickness corresponding to the gypsum fiberboard panel 2 to be produced. The pressing device 8 is preferably a cycle press or ContiRoll press.
The cutting device 9 has means for disaggregation, for example cutting blades or water-jet cutters, of the gypsum fiberboard panel strand along the width direction C, to produce individual gypsum fiberboard panels 2. The cutting device 9 thereby serves for separating the gypsum fiberboard panel strand to produce the gypsum fiberboard panels 2.
The drying device 10 has means for drying the gypsum fiberboard panels 2. This is preferably a multi-level dryer.
The finishing device 11 has means for finishing the gypsum fiberboard panels 2, such as, for example, a grinding device, an edge profiling device or the like.
The coating device 12 has means for coating the gypsum fiberboard panel 2 with a coating agent, for example a hydrophobic agent and/or a dust-binding agent.
In the following, production, according to the invention, of a gypsum fiberboard panel 2, in particular continuous production, using the apparatus 1 according to the invention, will be described.
Gypsum 14, fibers 15, and, if applicable, aggregates and/or additives and/or admixtures 16 in accordance with a composition to be produced are placed into the mixing device 4a. In the mixing device 4a, these raw materials are mixed to produce the mixture 13, in particular the dry mixture 13.
In the method, a gypsum 14 made from natural gypsum, preferably building plaster or stucco, and/or technical gypsum, preferably FGD gypsum, and/or gypsum-like calcium sulfate modifications, preferably RC [recycled] gypsum, is used. In particular, FGD gypsum is used. Preferably, gypsum having a grain size of 1 μm to 1 mm, preferably of 10 to 200 μm is used.
Fibers that contain cellulose, preferably recycled paper fibers and/or artificial mineral fibers, preferably glass fibers and/or rock wool fibers are used as fibers 15. In particular, recycled paper fibers are used. Preferably, fibers 15 having an average fiber length of 63 μm to 2 mm are used.
In addition, usual aggregates, additives and/or admixtures can be used.
Preferably, a mixture 13 having the following composition is produced in the mixing device 4a:
The advancing speed VA of the screen belt 3a of the conveying device 3 in the advancing direction A is preferably set to 5 to 500 mm/s (depending upon the thickness of the mixture 13).
The mixture 13 is applied to the screen belt 3a by means of the feed device 4b. Preferably, the mixture 13 is spread onto the screen belt 3a with a thickness or mixture height of 20 to 350 mm.
The mixture 13 is conveyed into the pre-compaction device 5 for pre-compaction, through the passage opening 30 of the spray chamber 26, which faces the mixing device 4a.
In the pre-compaction device 5, the free top side 13a of the mixture 13 is uniformly sprayed with the water mist 23, using the means 22. In this regard, the water mist 23 is preferably set in such a manner that the mixture 13 is sprayed with fine water droplets having an average droplet size of 0.1 to 60 μm, preferably 15 μm. In particular, aerosol cones 31 forming the water mist 23 and consisting of gas, for example nitrogen, or air and water particles, are produced using the mist nozzles 27. Preferably, in this regard, the aerosol cones 31 are produced with an air pressure of 2 to 4 bar, preferably 3 bar, and a liquid pressure of 1 to 3 bar, preferably 2 bar, and a jet angle of 40 to 80°, preferably 60°. Depending on the mixture height, the mixture 13 is sprayed with an amount of water of 1 to 10 l/h. For production of a panel thickness of 30 mm, the mixture is sprayed with an amount of water or amount of water mist of 7 l/h, for example.
Preferably, a water/solid value w/s of 0.05 to 0.25, preferably of 0.1, is produced in the mixture 13, using the means 22 for spraying.
In the pre-compaction device 5, a partial vacuum is furthermore applied to the underside 13b of the mixture 13, using the means 24, in particular at the same time with spraying of the mixture 13 with the water mist 23. With the partial vacuum, the water mist 23, i.e. the water particles contained in the water mist 23 are drawn into the mixture 13, and thereby the mixture 13 is compacted and made capable of absorbing water. Preferably, a partial vacuum of 5 to 20 mbar, preferably of 10 to 15 mbar, preferentially of 10 mbar is applied to the mixture 13 for pre-compaction. In particular, the partial vacuum is applied on the underside of the conveying means, so that the partial vacuum acts on the mixture 13 through the screen belt 3a.
After pre-compaction, the mixture 13 is passed to the wetting device 6 or conveyed into the wetting device 6. In the wetting device 6, the mixture 13, in particular the top side 13a of the mixture, is wetted or watered with the setting water required for setting the gypsum/fiber mixture, by means of the water curtain 32. Preferably, in this regard, a water/solid value w/s of 0.4 to 0.6, preferably of 0.5, is produced.
After wetting, the mixture 13 is conveyed into the post-compaction device 7 or the mixture 13 passes through the post-compaction device 7. A partial vacuum is applied to the underside 13b of the mixture 13, using the post-compaction device 7. The setting water is drawn into the mixture 13 with the partial vacuum, wherein the mixture 13 is further compacted or post-compacted. Preferably, a partial vacuum of 10 to 25 mbar, preferably of 15 to 20 mbar, preferentially of 20 mbar is applied to the mixture 13 for post-compaction. In particular, the partial vacuum is applied to the underside of the screen belt 3a, so that the partial vacuum is applied to the mixture 13 through the screen belt 3a. In particular, the partial vacuum is applied in such a manner that the amount of air drawn off to generate the partial vacuum is increased section by section along the underside of the screen belt, viewed in the advancing direction A.
However, it also lies within the scope of the invention that wetting and post-compaction take place simultaneously, in particular that a device configured analogous to the pre-compaction device is used for wetting and post-compaction.
The post-compacted mixture 13 is conveyed to the pressing device 8 and pressed to form a gypsum fiberboard panel strand having a thickness in accordance with the gypsum fiberboard panel 2 to be produced, using the means for pressing. Preferably, a pressure of 100 to 350 bar, in particular 300 bar is applied for pressing the mixture 13.
The gypsum fiberboard panel strand is conveyed to the cutting device 9 and separated into individual gypsum fiberboard panels 2 using the means for disaggregation.
The separated gypsum fiberboard panels 2 are conveyed into the drying device 10 and dried using the means for drying. Preferably, the gypsum fiberboard panels 2 are dried at a temperature of 80 to 260° C. for 40 to 100 minutes.
If necessary, the gypsum fiberboard panels 2 are profiled and/or reworked in the finishing device 11. For example, the gypsum fiberboard panels 2 can be provided with sharp-edged or profiled edges, or an edge can be produced having a flattened region that runs toward the panel edge.
After drying and finishing, the gypsum fiberboard panels 2 are coated with a coating agent, for example a hydrophobic agent or an agent for binding dust, in the coating device 12, if applicable.
In advantageous manner, the gypsum fiberboard panels 2 described above are produced with the following dimensions and material properties:
In particular, one-part or one-piece gypsum fiberboard panels 2 having a panel thickness>25 mm can also be produced in reliable manner.
Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.
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|---|---|---|---|
| 10 2018 218 512.3 | Oct 2018 | DE | national |
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| 20200130227 A1 | Apr 2020 | US |
