BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to an infrared radiator as well as a method of assembling such a radiator, specifically according to the independent claims.

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 arranged at a distance 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. A burner is then 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. Instead of rods, highly heat-resistant metals, for example in the form of grids or porous ceramics, have also become 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.

In addition, 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.

SUMMARY OF THE INVENTION

The object of the invention is to create an infrared radiator and a method of assembling such a 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 and a method according to the features of the independent claims.

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 or connecting elements that serve as warp and weft threads touch each other at the intersections.

A knitted or crocheted fabric may be meshware. The term meshware 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, mesh by mesh. 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 and the connecting elements touch the threads.

The term braid refers to an entanglement or interlacing between the connecting element and, for example, two threads directly adjacent to it. The threads as well as the connecting elements may be spiral-shaped. The self-supporting sheet material is then generated by interlacing the spirals. This may be achieved, for example, by twisting a connecting element lengthwise into a 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 it 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. An example in which a woven fabric is made from a scrim is examined in greater detail in the drawings and should fall within the scope of the invention.

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 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. The geometric moment of inertia is related to the cross-sectional area of the thread perpendicular to the longitudinal extension thereof. 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. Nonrigid threads may be processed into sheet materials 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 processed by such methods without changing or destroying their outer contour. For this reason, these sheet materials must alternatively for example be built up thread by thread, by joining them together by hand, by the method according to the invention. For this purpose, a plurality of (flexurally rigid) threads are initially furnished, the outer contour of which is predetermined. The threads are then connected to each other by connecting elements. At least one connecting element engages at least indirectly into two adjacent threads and connects these at the intersection points, for example, in an articulating manner. The joints are accordingly formed at the intersection points of the threads with the connecting elements. Such an articulated connection makes it possible for the threads of the self-supporting sheet material to move relative to each other. Thus the individual threads may expand differently to each other within the sheet material during heat input.

For purposes of the invention, “connecting elements” refers to structures that connect threads with each other at least indirectly, to produce a self-supporting sheet material. This latter term denotes both alternatives: with mediation, i.e. indirectly, and immediately, i.e. directly. In the first case, the threads are connected indirectly via the connecting element (directly adjacent thereto) if the connecting element itself does not engage in these two threads, but rather via additional threads. An example of this is woven fabric or meshware. In the second case, a connecting element engages in both threads directly adjacent to it and forms a plurality of intersection points (or articulated connections) with them. This is the case for a spiral fabric: Here, a connecting element always alternates with a thread.

Such connecting elements may be designed in such a way that they form a positive and/or nonpositive fit between the threads to be connected (or between each other). A positive fit is achieved when the connecting elements at least partially encompass themselves or the threads, as is the case with the formation of the intersection points. In principle, the connecting element could connect the threads positively, in the manner of a snap closure. It may be advantageous if the connection between the connecting element and the thread is detachable. Then individual threads or connecting elements within the sheet material may be removed and replaced without the need to recreate the entire sheet material. The connection should preferably be non-destructively detachable. This is the case if at least the thread (or the connecting element) is not changed or destroyed in the outer contour that it has within the sheet material. A non-destructively detachable connection has the advantage that the sheet material may be restored after its disassembly (in reverse order to this).

The connecting elements themselves may be designed as threads.

If the connection may be released and reconnected by hand, little force is required to join it. The connection in this case may also be freely disconnected and re-created using a tool.

The connection, i.e. the positive fit, may be designed in such a way that the threads cannot fall out of the connecting elements during operation of the infrared radiator, and thus they are held in the connecting elements in such a way that they cannot be lost. Thus, a self-supporting sheet material is achieved at all times during the operation of the infrared radiator.

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 the largest delimiting surface thereof 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.

The present invention also relates to a method of assembling an infrared radiator according to the invention. Assembly may be performed in the ascending sequence of steps a) and b) as claimed. A corresponding disassembly may be carried out in the opposite sequence. When such an incandescent body is repaired, the sheet material may first be dissolved by disassembling the relevant elements to be replaced, such as threads and connecting elements, and may then be restored by assembling the replacement threads or connecting elements.

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 as claimed, 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.

