INFRARED RADIATOR

The invention relates to an infrared radiator, specifically according to the independent claim.

Generic infrared radiators are used in drying arrangements for heat treatment, such as drying a material web, for example a paper, tissue or cardboard web. These drying arrangements are part of machines for manufacturing and/or treating such material webs. Nonwoven glass fabrics would also be possible. A preferred area of application is the drying of moving paper, tissue or cardboard webs in paper mills, for example behind coating devices, viewed along the running direction of the material web.

Infrared radiators that are known in the art have for example a plurality of rods that are preferably arranged in one plane, i.e. that are coplanar. However, arranging the rods in a plurality of parallel planes spaced from a burner plate is also known. The rods of generic infrared radiators are made of ceramic. Infrared radiators of this kind may be gas-powered. In that case, a burner is associated with them. This burner is operated with a gas-air mixture. The burner has a burner plate that is charged with the gas-air mixture. The gas-air mixture is ignited for example using an electrode. The resulting flame heats the rods. The rods serve as incandescent bodies. They transfer the heat to the material web in the form of infrared radiation. In place of rods, highly heat-resistant metals, for example in the form of grids or porous ceramics, are also known as incandescent bodies.

Infrared radiators of this kind are used as surface radiators in the heat treatment of material webs. For this purpose, a multiplicity of such infrared radiators are arranged next to each other along the width and/or length of the material web to be treated. The required number of radiators is selected based on the width of the material web to be dried and the desired heating power. Using such infrared radiators, surface temperatures of 1100° C. and above may be achieved on the incandescent body.

A drawback of infrared radiators known from the prior art is that their radiation efficiency is not optimal for every application. It has also been shown that the gas-powered infrared radiators that are known in the art produce a very high proportion of nitrogen oxides (NOx) and carbon monoxides (CO) from the combustion of the gas-air mixture.

Further, previous incandescent bodies made from ceramic components such as rods may cause the entire rod to fall onto the material web in the event of a break, which may damage the machine.

The present invention relates to the above-discussed subject matter.

The object of the invention is to create an infrared radiator that is improved over the prior art. In particular, the radiation efficiency and the exhaust gas behavior of the infrared radiator with regard to nitrogen oxides and carbon monoxide should be improved. Also, in the event of a possible break of the incandescent body, parts of the incandescent body should not fall onto the material web and the associated machine damage and downtime should be prevented.

This object is accomplished by an infrared radiator according to the features of the independent claim.

The term “radiation efficiency” refers to the ratio of the power the infrared radiator supplies to the power it radiates—here, in the form of infrared radiation.

An infrared radiator according to the present invention dries a material web, for example in the intended operation (operating state) of the drying arrangement or the machine. This is the state in which the gas-air mixture within the infrared radiator burns and simultaneously heats the (at least one) incandescent body. Combustion may take place in the space bounded by the burner plate and at least one incandescent body—in this case referred to as the combustion chamber.

An incandescent body, in the sense of the present invention, is thus the object through which the gas-air mixture or its combustion products flow, and which is heated as a result of the combustion of the gas-air mixture. It is the part of the infrared radiator that glows due to being heated. Incandescence refers to the emission of radiation that is visible to the human eye. The incandescent body may be that part of the infrared radiator arranged behind the burner plate in the flow direction of the gas-air mixture. It may be at a distance from or in contact with the burner plate. The incandescent body is thus heated by the flames that are generated as a result of the combustion process, for example, on the side of the burner plate facing the incandescent body. The incandescent body could also be said to comprise all those elements that, together with the burner plate, delimit the combustion chamber of the infrared radiator. The at least one incandescent body may represent the outermost surface of the infrared radiator, which is directly opposite the material web to be treated. In such a case, the incandescent body is then arranged between the burner plate and the material web.

As used in the present invention, a “sheet material” is a planar structure such as woven fabric, knitted fabric, crocheted fabric, braided fabric or lace structures. Sheet materials are basically made up of a multiplicity of linear structures such as threads. In such sheet materials, the linear structures form or delimit openings of the sheet material. The sheet material could also be said to be designed in the manner of a net or grid, with the openings representing the interstices of the net or grid. These openings—in a top view of such a sheet material—may take on different geometric shapes, such as polygons, for example rhombuses, rectangles or hexagons. The planar extension of such openings is measured in length and width in the aforementioned top view. Taken together, the openings represent the cavity of the incandescent body and are flowed to or through by the gas-air mixture or the combustion products thereof during operation of the infrared radiator.

“Woven fabric” refers to a sheet material woven from warp and weft threads. These warp and weft threads cross each other. The woven fabric may comprise one or a plurality of different thread systems, preferably a plurality having different mechanical properties. But it is also possible that such woven fabrics may be used in which the warp and weft threads are made of the same material. Threads that serve as warp and weft threads touch each other at the intersections.

A knitted or crocheted fabric may be a mesh. The term mesh is understood to mean such sheet materials in which a loop formed by a thread is interlaced with another loop. Knitted fabrics may be obtained, for example, by knitting or crocheting, with each mesh row being made up of a single thread. Knitted fabrics consist of one or more thread systems. A loop then engages in the loop of the preceding mesh row. In crocheted fabrics, on the other hand, at least two thread systems are used and the meshes of one mesh row are formed simultaneously. The loops define the intersection points at which the threads touch each other.

The term braid refers to an entanglement or interlacing between directly adjacent threads. The threads may be spiral-shaped. The self-supporting sheet material appears as if the individual threads were generated by interlacing the spirals. In other words, it appears as if a thread had been twisted lengthwise into an adjacent thread, so that both spirals interlace with each other and touch at the intersection points. The longitudinal central axes of the spirals then lie parallel to each other in this sheet material. This is referred to as a spiral braid.

In principle, a distinction is made as to whether the sheet materials are capable of supporting themselves after they are produced. This applies to the structures mentioned above, with the exception of scrims. Scrims are also sheet materials that consist of one or more layers of parallel threads. However, these threads are not fixed to each other at their intersection points in a material-fit, force-fit or positive-fit manner. Such a scrim is therefore not self-supporting, i.e. when moved, it loses the shape it has been given. In order for the scrim to retain its shape, the threads laid on top of each other must be held by force. Accordingly, when the infrared radiator according to the invention is ready for operation, the incandescent body is not designed as a scrim. Therefore for the purposes of the invention, scrims should not fall under the concept of a sheet material, i.e. should be free of such a structure. Scrims as intermediate products could be protected by the invention as long as they are subsequently processed in such a way that they are fixed to each other, for example, at their intersection points.

In other words, for the purpose of the present invention, sheet materials exhibit repetitive, preferably regular patterns formed by the threads. In contrast, nonwovens are a random arrangement of fibers that are interlaced with each other or held together by a binder. Therefore, nonwovens do not fall under the term “sheet material” according to the present invention, and thus a nonwoven expressly does not constitute a sheet material. The advantage of using regular pattern-forming sheet materials is that over the entire extension of the sheet material a uniform combustion and thus a uniform exhaust gas behavior takes place when the sheet material is used as an incandescent body.

For purposes of the invention, the term “thread” refers to a linear, long, thin structure. Such a thread is much longer than it is wide, i.e. the diameter of the thread may be between 1 and 10 mm and the thread may have a length of up to 300 mm. The thread may be made of a flexurally rigid material, i.e. a material with comparatively high flexural rigidity such as a ceramic. The term flexural rigidity refers to the product of the elastic modulus with the corresponding geometric moment of inertia. For example, a material having a comparatively higher elastic modulus, or a thread made therefrom, is more flexurally rigid than another thread with the same geometric moment of inertia. The term elastic modulus refers to a material characteristic used in materials engineering that describes the relationship between stress and elongation during the deformation of a solid body with linear-elastic behavior. For purposes of the invention, a long and thin thread as described above is flexurally rigid if it does not change its embossed outer contour as soon as it is removed from the sheet material with at least partial dissolution of the sheet material. Flexurally nonrigid threads may be manufactured by the methods mentioned above, such as weaving or knitting, because the thread is flexible and its outer contour may be freely shaped during the process. On the other hand, flexurally rigid threads cannot be manufactured by such methods without changing or destroying their outer contour. Therefore, according to the invention, such sheet materials are manufactured by means of primary forming. Thus, the entire sheet material—and not just the individual threads—is produced by primary forming. It is therefore preferable that it be monolithic and thus form a single unit.

An articulated connection according to the invention enables the individual threads of the self-supporting sheet material to move relative to each other at the intersection points. The joints are therefore formed by the threads themselves at the intersection points of the threads. The joints are preferably swivel joints.

For the purpose of the invention, a “material web” is a fibrous web, i.e. a scrim or tangle of fibers such as cellulose fibers, plastic fibers, glass fibers, carbon fibers, additives, admixtures or the like. For example, the material web may be a paper web, cardboard web or tissue web. The web may substantially comprise cellulose fibers, with small quantities of other fibers or additives and admixtures being present. This adaptation to a particular application is left to the skilled person.

References to the flow direction of the gas-air mixture in the invention refer to the main flow direction of the particles of the gas-air mixture. This direction corresponds, for example, to a perpendicular to the largest surface of the burner plate of the infrared radiator through which the gas-air mixture flows (the flow-receiving surface of the burner plate). The flow-receiving surface may therefore be at least one delimiting side, i.e. the surface spanned by the spatial length and width of the burner plate. The delimiting side may be spanned by the long and wide edges (of the flow-receiving surface) of the burner plate. Thus, the gas-air mixture may flow through the burner plate at its largest delimiting surface that faces the gas supply or the premixing chamber. If the burner plate is designed as a cuboid, the flow-receiving surface is at least one side face of the cuboid. Because the incandescent body or its envelope may also be designed as a cuboid, the flow-receiving surface of the incandescent body is also a side face (delimiting surface) of the cuboid, which represents a flat surface. Therefore, the above definition also applies analogously to the incandescent body and its flow-receiving surface. Thus the incandescent body is also flowed along this flow-receiving surface together with the gas-air mixture or the combustion products thereof. The flow direction of the gas-air mixture may also be perpendicular to the largest delimiting surface or flow-receiving surface. The flow direction of the gas-air mixture through the incandescent body may be the same as the flow direction through the burner plate. The flow-receiving surface of the incandescent body may be identical to the flow-receiving surface of the burner plate, so that both have the same area. It may be the surface that the incandescent body and the burner plate share when they abut one another directly.

When reference is made in the present invention to one element directly abutting another element, this means that the two elements are in direct contact with each other without anything else—and, preferably, without any distance—between them.

If the invention refers to ceramic, this is understood as a technical ceramic. Examples of this include, for example, silicon carbide and molybdenum silicide. High-temperature-resistant metals such as FeCrAl compounds or heat conductor alloys would also be suitable, in principle, as materials for incandescent bodies.

If reference is made to the incandescent body being made of a plurality of layers arranged one above the other, this means that a plurality of layers of sheet materials may also be provided that are arranged one behind the other in the flow direction of the gas-air mixture. This means that the layers are stacked one above the other, when viewed in the flow direction of the gas-air mixture. This affords, according to the invention, the advantage that the exhaust gas values may be further improved.

The term “at least partially” refers to at least a part of the incandescent body.

If reference is made to one element surrounding another at least partially, this means that it either partially or completely surrounds or envelops the corresponding element.

The term “primary forming” means that the relevant element has been manufactured by a manufacturing process in which a solid body is generated from a formless substance. Examples of this are casting, sintering, 3D printing.

Furthermore, the invention relates to a drying arrangement for heat treatment of a material web, comprising an infrared dryer that has a plurality of infrared radiators according to the invention, preferably arranged in the width and/or length direction of the material web to be treated. Such a drying arrangement may have at least one air dryer for directing hot air and/or a combustion product of the gas-air mixture from the plurality of infrared radiators onto the material web to be treated. In addition, the at least one air dryer and the at least one infrared dryer may be arranged one behind the other as seen in the running direction of the material web to be treated, and the at least one infrared dryer may preferably be connected upstream of the at least one air dryer as viewed in the running direction of the material web to be treated.

The invention also relates to the incandescent body of claim 1 per se, as well as such a body having the features of the dependent claims.

Finally, the invention relates to a machine for manufacturing and/or treating a material web, preferably a paper machine, comprising at least one infrared radiator according to the invention, or such a drying arrangement.

The invention is described in greater detail below with reference to the drawings, without restricting the invention's generality. The drawings show the following:

FIG. 1 a schematic, partially cut-away and not-to-scale representation of one embodiment of an infrared radiator;

FIG. 2 spatial representation of a possible embodiment of an incandescent body according to the invention;

FIG. 3 a highly schematized representation of a drying arrangement in a three-dimensional view according to one embodiment.

FIG. 1 shows an exemplary embodiment of the invention in a schematic, partially cut-away view through a plane that is perpendicular to the material web and parallel to the running direction (indicated by the arrow). The drawing shows an infrared radiator 1, which may be part of a drying arrangement 9. During normal operation, the infrared radiator 1 is arranged at a distance from the material web 8, for example above it. The radiator forms a burner that is arranged in a housing 11.1. This housing has, for example, a rear wall and a plurality of side walls. The rear wall is located on the side (rear side) of the infrared radiator 1 facing away from the material web 8. An opening 2 is provided in this wall, through which a fuel, for example gas and air (an ignitable, combustible gas-air mixture) may enter a mixing chamber 3. The corresponding supply lines outside the infrared radiator 1 are not shown in detail. The mixing chamber 3 is delimited on one side by a gas-permeable burner plate 4 and on the other side by the housing 11.1, here the rear wall thereof. The gas-air mixture flows into the burner plate 4 at a flow-receiving surface corresponding to the rear side of the infrared radiator 1 and passes through the gas-permeable burner plate 4, to be combusted. From there the mixture flows into a combustion chamber 5. This chamber is delimited or formed jointly by the burner plate 4 and an incandescent body 6. The gas-permeable burner plate 4 may be said to separate the mixing chamber 3 from the combustion chamber 5. In the latter chamber, the gas-air mixture ignites. The heat released heats the incandescent body 6 until this body begins to glow. As a result, the body emits infrared rays toward the material web 8 to be dried. Both the burner plate 4 and the incandescent body 6 have a slab-shaped or cuboidal outer contour. In principle, a different outer contour would be possible. In this case, the flow-receiving surface of the incandescent body 6 corresponds to the flow-receiving surface of the burner plate 4. In other words, the two flow-receiving surfaces are the same. They correspond in this case to the clear width of the housing 11.1 that accommodates both the burner plate 4 and the incandescent body 6.

Irrespective of the embodiment shown, the infrared radiator 1 with its incandescent body 6 faces the material web 8; in the case shown, it does so in such a way that the incandescent body 6 runs parallel thereto. However, this need not necessarily be the case. The infrared radiator 1 may also run at an angle thereto. As shown in FIG. 1, the burner plate 4 and the incandescent body 6 are connected in series, viewed in the flow direction of the gas-air mixture. The incandescent body 6 is arranged downstream of the burner plate 4.

According to the embodiment of FIG. 1, the incandescent body 6 is designed as a gas-permeable regular grid. This grid may be formed by at least one sheet material. This structure is made up of a multiplicity of threads that delimit the openings of the grid. Consequently, the gas-air mixture passing through the burner plate 4 may also flow through all openings of the incandescent body 6 (simultaneously).

The incandescent body 6 is arranged at a distance from the burner plate 4, viewed in the flow direction of the gas-air mixture or the combustion products thereof. In other words, the combustion chamber 5 is formed by the space jointly delimited by the burner plate 4 and the incandescent body 6. The burner plate 4 and incandescent body 6 are arranged parallel to each other with regard to their flow-receiving surfaces or delimiting sides.

Although this is not shown in the drawings, it would be possible for the incandescent body 6 to directly abut the burner plate 4. This means that both are arranged without distance from each other and preferably parallel to each other.

Irrespective of the embodiment shown, it would be conceivable in principle, for example to provide a plurality of layers of an incandescent body 6, or more precisely several layers of sheet materials, which could be arranged at a distance from the burner plate 4 in the flow direction of the gas-air mixture or the resulting combustion products.

FIG. 2 shows a spatial representation of a possible embodiment of the incandescent body 6 according to the invention as a sheet material. The incandescent body is made from a multiplicity of threads 15. The sheet material is designed, by way of example, as a spiral braid. For this purpose, the threads 15 are interlaced in the manner of spirals. The longitudinal central axes of the threads 15 run parallel to each other over the entire spatial extent of the resulting sheet material. Threads 15 that are directly adjacent to each other are connected to each other in such a way that the spirals thereof are screwed into one another. As a result, the threads 15 are respectively mounted to each other in an articulated manner at the shared intersection points. This interlocking of the threads 15 results in a loss-proof structure. In other words, if a part of a thread 15 breaks, it is held by the adjacent threads 15 at the intersection points. As a result, the probability that parts of the broken thread will fall onto the material web 8 is significantly minimized. Breakage may occur if the thread 15 is made of a ceramic.

Although not shown, the incandescent body 16 could also be manufactured in the manner of a woven fabric. In that case, two directly-adjacent threads that are designed as weft threads weave the same weaving path through the warp threads, perpendicular to the threads that act as warp threads.

For the production of such sheet materials, primary forming methods such as 3D printing may be used.

Irrespective of the embodiments shown, the increased surface area of the incandescent body 6 may considerably increase the radiation efficiency due to the wavy or spiral outer contour of the threads 15. This is achieved by increasing the surface area for the combustion of the gas-air mixture due to the selected outer contour, which results in a higher energy absorption from the combustion products of the gas-air mixture. This may also reduce the proportion of nitrogen oxides and carbon monoxide in the combustion products.

FIG. 3 shows a possible embodiment of a drying arrangement 11 according to the invention. This may be part of a machine for manufacturing or treating a material web. The drying arrangement 11 here is arranged behind a coating or binder section (not shown) of the machine, in the running direction of the material web 8. Within this section, a coating color or binder is applied to the material web 8. As a result of this application, the material web 8 absorbs moisture and must therefore be dried, or the binder must be cured. This is done in the drying arrangement 11.

The drying arrangement 11 comprises one or, as shown here, a plurality of infrared dryers 12, each of which respectively has a multiplicity of infrared radiators 1 that serve as surface radiators and are preferably arranged parallel to the material web 8. In addition, the drying arrangement 11 also has a plurality of air dryers 13. In the present case, an infrared dryer 12 is respectively downstream of an air dryer 13 when viewed in the running direction of the material web 8, and so forth. Such an infrared dryer 12 and air dryer 13 are respectively referred to as a combination dryer 14. Four combination dryers 14 are furnished, arranged one behind the other in the running direction of the material web 8 to be dried. These combination dryers are, in this case, arranged directly abutting one another. Consequently, when the material web 8 to be dried leaves a first combination dryer 14, it immediately reaches the following combination dryer 14 viewed in the running direction. All combination dryers 14 are set up in such a way that, viewed in the running direction of the material web, drying occurs by infrared radiation from the associated infrared dryer 12, then by convection through the corresponding air dryer 13, by heat radiation and so on alternatingly. As soon as the material web 8 has left the first combination dryer 14 as viewed in the running direction of the web, it is transferred to the second combination dryer 14. There in turn, as viewed in its running direction, the web is first dried by the corresponding infrared dryer 12 and then by the corresponding air dryer 13. In other words, an air dryer 13 assigned to the first combination dryer 14 is arranged between an infrared dryer 12 of a first combination dryer 14 in the running direction and an infrared dryer 12 of another combination dryer 14 immediately following it in the running direction—viewed respectively in the running direction of the material web 8 through the drying arrangement 11. One could also say that the material web 8 is dried along the drying arrangement 11 alternatingly by heat radiation, then by convection, again in turn by heat radiation and so on.

The infrared dryer 12 of a respective combination dryer 14 may be designed as a gas-heated infrared dryer according to the invention. In this case, the infrared dryer 12 may comprise one or more infrared radiators 1 according to the invention (see FIGS. 1a and 1b). The combustion products (exhaust gases) that the infrared radiators 1 generate may then be extracted from the infrared dryer 12 via one or more suction nozzles 12.1 associated with the infrared dryer 12, only one of which is indicated here in a purely schematic manner. The at least one suction nozzle 12.1 may be arranged inside a housing that surrounds the infrared dryer 12.

The respective air dryer 13 may comprise one or more blowing nozzles 13.1, of which only one is shown here, likewise in a purely schematic manner. The at least one blowing nozzle 13.1 serves, among other things, to supply heated air to the material web 8 for drying. For this purpose, the at least one blowing nozzle 13.1 may be connected to a fresh air supply (not shown) in a flow-conducting manner. In addition, a flow-conducting connection may be furnished between the at least one suction nozzle 12.1 and the at least one blowing nozzle 13.1 of the same combination dryer 14. The thermal energy contained in the exhaust gas of the infrared dryer 12 may be used to heat the fresh air or to dry the material web 8 using the thermal energy of the exhaust gas of the respective infrared dryer 12.

INFRARED RADIATOR

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