Infrared radiation emitter, welding system, in particular plastic welding system, with such an infrared radiation emitter, as well as welding process with such an infrared radiation emitter

Abstract

Infrared radiation emitter with an emitter body (1) comprising a ceramic material and wherein the emitter body (1) has a working area (2) which emits incoherent infrared radiation (R) when an electric current is applied, wherein the ceramic material comprises a first material component (A) which has an electrical conductivity that increases with increasing temperature and wherein the ceramic material has a second material component (B) which increases the electrical conductivity of the ceramic material in a lower temperature range,wherein at least the working area (2) is essentially dimensionally stable and self-supporting and is designed as an elongated body and wherein the longitudinal extent of the emitter body (1) comprises a multiple or multiple of a width and a height of an emitter body cross-section lying or arranged transversely to the longitudinal extent and wherein the working area (2) has one or more curvatures or bends along its longitudinal extent (L).

Description

[0001] The present invention relates to an infrared radiation emitter, a welding system, in particular a plastic welding system, with such an infrared radiation emitter, and a welding process, in particular a plastic welding process with such an infrared radiation emitter.

[0002] In conventional welding of thermoplastic materials, the joining zone is typically melted by a heating element. The two components are brought into contact with one side of the heating element at a time. Once sufficient material has transitioned into the molten phase, the process known as "switching over" takes place. During this process, the two component halves are lifted from the heating element, the heating element itself is retracted, and the two (still) molten thermoplastics are brought into contact.

[0003] A further development of this process is contactless heating element welding and the infrared welding based on it. Two different concepts are used specifically in infrared welding: welding with metal foil emitters and welding with quartz glass emitters. Metal foil emitters consist of a metal foil or a resistive sheet made of suitable alloys such as constantan. The maximum operating temperature is 800°C, resulting in an emission maximum at a wavelength of approximately 3 µm. Higher temperatures must be avoided because they would lead to strong oxidation effects with the surrounding air. To construct a welding fixture, a carrier is provided with a groove. A metal foil is placed in this groove in a zigzag pattern and secured.

[0004] In contrast, welding devices with quartz glass emitters are used. Similar to an incandescent light bulb, the glass body is evacuated and a tungsten filament is inserted. Due to the vacuum, oxidation processes are largely prevented, allowing for the use of higher energy levels. While this significantly increases the radiation output compared to metal foil emitters, some of the light is absorbed by the quartz glass body and therefore no longer contributes to the welding process. Another disadvantage of this widespread technology is the limited design freedom. Although the glass tubes can be bent manually, the radii are limited, and manufacturing tolerances are very critical.

[0005] Publication WO 2014 / 160156 A1 describes a ceramic heating element for plastic welding, which comprises a silicon carbide material. The heating element described in this publication is operated by means of a chemical combustion process.

[0006] Publication JPH04174990A discloses an electrically operated, ceramic heating element made of silicon carbide, which emits radiation in the infrared range.

[0007] Publication WO 2017 / 089494 A1 describes an electric heating element made of silicon carbide that can be manufactured using a 3D printing process.

[0008] However, the latter two publications do not reveal that the ceramic heating elements described therein could be suitable for applications in the welding sector.

[0009] Document US 2,941,962 A discloses a heating element comprising a ceramic material and having a working area that emits incoherent infrared radiation when an electric current is applied, wherein the ceramic material comprises a first material component that has increasing electrical conductivity with increasing temperature, and a second material component that increases the electrical conductivity of the ceramic material in a lower temperature range.

[0010] The publication EP 0 787 349 B1 describes a ceramic electrical resistance material produced by ceramicizing a filler embedded in a matrix of at least one organosilicon polymer. The specific electrical resistance of the ceramicized material can be adjusted by the type and proportion of the filler.

[0011] German patent application DE 197 48 209 A1 describes a method for fusion bonding of plastics, in which the interfaces are heated independently of one another to the fusion temperature using an external heating source. The parts with the heated interfaces are then joined under pressure and held against each other until a solid fusion bond is formed. The interfaces of the parts are heated without contact using a dark infrared emitter. The surface temperature of the infrared emitter is maintained at a constant value of at least 590°C, in particular at least 630°C, regardless of control-related deviations, and the heating time is limited to a period specific to each part.

[0012] The publication DE 10 2011 055 460 A1 describes a method for welding plastic components along a joining area running around the circumference, wherein the plastic components to be welded are first brought into their joining position and fixed there, and then the plastic components are transported past a stationary heat source for welding.

[0013] The German patent application DE 10 2005 028 661 A1 describes a process for producing a two-layer film by joining two thermoplastic films, wherein a single film made of a thermoplastic material is continuously passed by heat radiation sources with a second single film made of thermoplastic material, but with a smaller film thickness, with their film surfaces to be joined, wherein the energy supply is such that the surfaces to be joined of both single films are softened or melted to between 1 and 50 of the film thickness and the softened or melted film surfaces are brought together over the entire width and pressed together under pressure.

[0014] It is an object of the invention to provide an infrared radiation emitter which offers advantages over known emitters for welding applications, especially for plastic welding.

[0015] Furthermore, it is an object of the invention to provide an advantageous welding system, in particular an advantageous plastic welding system.

[0016] Furthermore, it is an object of the invention to provide an advantageous welding process, in particular a plastic welding process.

[0017] The problem is solved according to the invention by an infrared radiation emitter with an emitter body comprising a ceramic material, wherein the emitter body has a working area which emits incoherent infrared radiation when an electric current is applied, wherein the ceramic material comprises a first material component which has an electrical conductivity that increases with increasing temperature, and wherein the ceramic material has a second material component which increases the electrical conductivity of the ceramic material in a lower temperature range.

[0018] By comprising a first material component of a ceramic material exhibiting increasing electrical conductivity with increasing temperature, the infrared radiation emitter according to the invention can be excited by applying an electric current to emit incoherent infrared radiation, with the heat flux radiated by the emitter increasing with the temperature of the emitter body. In this way, a rapid increase in temperature and thus in the radiated heat flux is achieved. To further accelerate the temperature increase, a second material component is added, which increases the relatively low electrical conductivity of the ceramic material at lower temperatures, i.e., in a cold state or at room temperature. In this way, an infrared radiation emitter is created that can very quickly reach an operating temperature of up to 1700° Celsius.Furthermore, such an emitter is not susceptible to corrosion and can be manufactured easily. By increasing the electrical conductivity in a lower temperature range, it is possible to forgo preheating the emitter and heat it by current flow even at room temperature. A lower temperature range is defined as a temperature range in which the electrical conductivity of the ceramic material is lower than in a higher temperature range. Specifically, the lower temperature range can be understood as the range between room temperature and approximately 700°C.

[0019] According to the invention, at least the working area is dimensionally stable and / or self-supporting. Preferably, the entire emitter body can be essentially dimensionally stable and / or self-supporting.

[0020] In this way, the emitter body does not require a supporting housing or frame structure to maintain its shape, as is the case with metal foil or quartz glass emitters. Because no support or frame elements are necessary to hold the emitter body, there is also no need to dissipate heat transferred from the emitter body to these elements. This allows cooling measures to be reduced or eliminated. Furthermore, it is possible to move the emitter body into and out of a working position using dedicated machine elements, such as feed or handling elements, without the movement causing any unwanted deformation of the emitter body.

[0021] According to the invention, at least the working area is designed as an elongated body. Preferably, the entire emitter body can be designed as an elongated body.

[0022] In this way, the emitter body can be designed according to an area of ​​a workpiece surface to be heated or welded, and its elongated shape defines the length of at least one area of ​​the weld or the entire longitudinal extent of the weld.

[0023] According to the invention, the longitudinal extent of the emitter body comprises a multiple or multiple of a width and height of an emitter body cross-section lying or arranged transversely to the longitudinal extent.

[0024] Furthermore, it is advantageous if the working area is designed such that, during operation of the infrared radiation emitter, infrared radiation can be emitted or is emitted in at least two opposite directions, in particular additionally in at least a third direction, preferably essentially in exactly four directions, and / or wherein the working area is designed such that, during operation of the infrared radiation emitter, infrared radiation can be emitted or is emitted radially from the working area.

[0025] In this way, during a plastic welding process where the working area is positioned between two plastic parts to be joined, the joining zones of both parts can be heated simultaneously by the emitted infrared radiation. The working area is then moved out of the space between the parts, and the plastic parts are brought into contact. This can advantageously accelerate the plastic welding process. It is also possible to assign a separate heating working area to each of the plastic parts to be joined or to each of the joining zones. If a separate heating working area is used for each of the plastic parts or joining zones to be joined, the at least two working areas can be integrated into one infrared radiation emitter, or two or more infrared radiation emitters, each with one working area, can be used.Particularly advantageous is the ability to adapt the shape of the working area to the shape and path of the weld. For example, if a joining partner has a recess within which the weld is to be formed, radial radiation from a working area with a corresponding cross-section can heat the welding area effectively.

[0026] In a further advantageous embodiment, the working area has flat surfaces from which infrared radiation can be emitted or is emitted orthogonally during operation of the infrared radiation emitter.

[0027] In a welding application, a work area with flat surfaces, for example a work area with a square cross-section, can be positioned closer to the surface to be melted with a larger radiating surface area than a work area with a curved surface, for example a work area with a round cross-section.

[0028] Furthermore, in an advantageous embodiment, the working area is designed such that the emitted infrared radiation is emitted essentially within an angular range of 180° or within an angular range of 120° or within an angular range of less than 120°.

[0029] In this way, various emitter bodies can be provided, each adapted to a specific positioning of the joining partners within a welding system. If infrared radiation is emitted essentially within an angular range of 180°, i.e., within an angle between 0° and 180°, and thus particularly in opposite directions, then parallel joining surfaces of the joining partners can be heated simultaneously and with the same radiant power. Conversely, emission within an angular range of less than 180° is particularly suitable if joining surfaces are not, or cannot be, arranged parallel to each other before joining.

[0030] Furthermore, it can be advantageous if the working area is rod-shaped or tubular and / or has a round, in particular circular or non-circular, or tubular or omega-shaped cross-section and / or a U-shaped, V-shaped, W-shaped, or C-shaped profile. A polygonal, in particular a substantially triangular or quadrilateral, cross-section can also be advantageous, especially if the cross-section has a width and a thickness.

[0031] A rod-shaped working area allows for very simple emitter manufacturing. A tubular working area, for example, allows for the integration of cooling measures within the working area, which could be beneficial for temperature control at high temperatures. Furthermore, the cross-section of the working area can be adapted to the welding task. In particular, it is possible for the working area to have at least two or more different cross-sections, or for the cross-section of the working area to vary in shape and / or dimensions along its length. A rectangular cross-section of the working area is particularly advantageous for flat joining zones, as it ensures uniform heating of the flat joining zone.

[0032] Furthermore, it can be advantageous if the working area comprises a hollow profile having at least one opening, in particular if the at least one opening extends substantially over the entire or complete longitudinal extent of the working area. The working area can simultaneously be configured in different regions with different profile shapes or cross-sectional shapes. It is also possible for the entire working area to be configured with essentially a uniform profile shape or cross-sectional shape, the dimensions of which may be constant or may vary within a specific region of the working area.

[0033] According to the invention, the working area has one or more curves or bends in or along its longitudinal extent. In particular, the working area can extend in or along its longitudinal extent within two spatial dimensions, or the working area can extend in or along its longitudinal extent within three spatial dimensions.

[0034] This allows the working area to be advantageously adapted to the shape and / or dimensions of the weld. Particularly advantageous is the welding of joining zones of welds that extend on or along free-form surfaces with curves, steps, or similar geometric structures using emitters specifically adapted to these joining zones.

[0035] In a further embodiment, the infrared radiation emitter is designed to heat a limited area of ​​a workpiece surface, and the working area is shaped according to the shape of the limited area, in particular wherein the working area has one or more curves or bends that correspond to one or more curves or bends of the limited area.

[0036] This design also allows the emitter's working area to be adapted favorably to the intended shape of the weld. This makes it possible to weld seams with complex shapes.

[0037] In a further embodiment of the invention, the emitter body has a working area and at least, preferably exactly, two, in particular integrally connected, contacting areas which are provided for the connection of electrical contacts, in particular wherein the contacting areas each have larger cross-sections or larger cross-sectional areas than the cross-section or a cross-sectional area of ​​the working area.

[0038] Since the heat generation within the working area depends on the ratio of its cross-sectional area to its specific conductivity, it is advantageous to provide the contact areas, which are also carried by the operating current, with a larger cross-sectional area, thus reducing heat generation in the contact areas. In this way, undesirable excessive heating in the electrical contact area can be avoided.

[0039] In a further advantageous embodiment, the contact areas are spaced apart from each other by an opening, preferably wherein the distance between the contact areas is less than the wall width and wall thickness of a working area cross-section. The opening ensures the electrical separation of the at least two contact areas, which can accordingly be connected to the respective poles of the electrical power source. To ensure a hermetic seal of the weld between the half-shells, particularly when welding housings, for example by joining two half-shells, the distance between the contact areas should be chosen to be as small as possible.

[0040] Alternatively or additionally, the emitter body has a working area and retaining areas connected directly or indirectly, in particular integrally, to the working area, which are provided for the arrangement and / or fixing of the working area to machine elements, in particular feed elements or handling elements or retaining elements of a machine, in particular a welding system, preferably a plastic welding system, in particular wherein the retaining areas each have larger cross-sections or larger cross-sectional areas than the cross-section or a cross-sectional area of ​​the working area and / or wherein the retaining areas are thermally insulated from the working area.

[0041] It is also advantageous for the holding areas to heat up less than the working area, or to be thermally insulated from the machine in which the emitter is used. This prevents machine areas adjacent to the working area from overheating.

[0042] Alternatively or additionally, it is possible that at least one, and in particular all, contact areas are designed as holding areas.

[0043] This is particularly advantageous when the emitter body needs to be compact and small, for example for producing a weld seam from several welding points or a short linear weld seam.

[0044] In a further embodiment of the invention, the first material component is a semiconductor material, in particular silicon carbide, or the first material component exhibits oxygen ion conductivity, in particular wherein the first material component comprises zirconium oxide doped with yttrium oxide.

[0045] It has been found that emitter bodies can be made particularly advantageously from silicon carbide or doped zirconium oxide. These materials exhibit a suitable temperature dependence of electrical conductivity. In the case of a silicon carbide emitter body, the conductivity in the cold state can be optimized by adding a material that acts as an electrical conductor, such as graphite, particularly by doping with graphite. In the case of an emitter body made of zirconium oxide, especially doped with yttrium oxide, which exhibits oxygen ion conductivity, graphite can also be added to achieve the same effect. Alternatively or additionally to graphite, a metallic conductor can also be added. Furthermore, the aforementioned materials are sufficiently robust, dimensionally stable, and temperature-resistant.

[0046] In a further advantageous embodiment of the invention, the second material component increases the electrical conductivity of the ceramic material in a temperature range below 700° Celsius, in particular wherein the second material component comprises carbon, preferably graphite.

[0047] In an alternative advantageous embodiment, yttrium oxide can be provided as the second material component, in particular wherein zirconium oxide is doped with yttrium oxide as the first material component.

[0048] Particularly with silicon carbide, the electrical conductivity at low temperatures, for example below 700°C, can be increased by adding carbon, especially in the form of graphite. The same effect is achieved with zirconium oxide by doping it with yttrium oxide. By increasing the electrical conductivity at low temperatures, the infrared radiation emitter can be heated by an electric current without the need for preheating. This allows the desired operating temperatures of the emitter to be reached very quickly.

[0049] It can be particularly advantageous if the work area has a non-white color, in particular a grey color, preferably a dark grey color, or a black color.

[0050] A dark work area, especially one colored gray, dark gray, or black, has a higher emissivity for infrared radiation than a light or white work area. A dark coloration is achieved, for example, by a mixture of silicon carbide and graphite.

[0051] Furthermore, it can be advantageous if the infrared radiation emitter is connected to an electrical current source or electrical voltage source and can be operated or is operated with a variable defined operating current or a variable defined operating voltage, in particular a defined direct current or a defined direct voltage, preferably with a current in a range between 20 amperes and 40 amperes, and wherein the infrared radiation emitter can be operated or is operated in at least one upper temperature range with a lower operating current or a lower operating voltage than in a lower temperature range.

[0052] In this way, it can be ensured that the emitted infrared heat radiation, which can increase avalanche-like in an upper temperature range in the infrared radiation emitter according to the invention, does not increase indefinitely, so that the emitted heat energy can be kept constant at least within a certain bandwidth.

[0053] In a further advantageous embodiment of the invention, the infrared radiation emitter is connected to an electric current source or an electric voltage source and comprises an active control of the electric current source or an electric voltage source, in particular wherein the active control is implemented as a control loop in which a temperature sensor, in particular a pyrometer, is provided which determines the actual temperature of the emitter body, wherein the actual temperature is compared with a preset or preset target temperature and wherein the current source or the voltage source is actively controlled according to a deviation of the actual temperature from the target temperature resulting from the comparison, in particular automatically by means of an actuator.

[0054] Since the electrical conductivity of the infrared radiation emitter increases with rising temperature, and the heat flux radiated by the emitter also increases with rising temperature, it is advantageous to provide automatic control of the operating current so that the radiated heat flux can be kept constant. This allows the infrared radiation emitter to deliver a consistently high welding energy, thus ensuring the quality of the welding process.

[0055] The object of the invention is further achieved by a welding system, in particular a plastic welding system, with an infrared radiation emitter according to the invention.

[0056] Furthermore, the object of the invention is achieved by a welding process, in particular a plastic welding process, using an infrared radiation emitter according to the invention or for carrying out in a welding system according to the invention, which comprises the following steps: • Selection of an emitter body temperature depending on an absorption coefficient of the material to be welded for infrared radiation emitted by the emitter body and depending on a desired penetration depth of the emitted infrared radiation into the material to be welded; • Heating the emitter body to the selected temperature; • Melting of the material to be welded by the infrared radiation emitted by the emitter body at the selected temperature;

[0057] By selecting the temperature, the emission spectrum can be modified so that more or less energy is absorbed at the surface of the plastic component. This is described by the optical penetration depth. Increasing the temperature shifts the wavelength spectrum towards shorter wavelengths. In other words, increasing the temperature shifts the maximum of the emitted infrared radiation into a region of shorter wavelengths. Unpigmented plastics absorb longer wavelengths more strongly than shorter wavelengths. Therefore, with unpigmented plastics, a lower emitter temperature allows the material to be melted to a greater depth than with a higher emitter temperature. Thus, selecting a lower emitter temperature can optimize the absorption behavior of unpigmented plastics.By adjusting the temperature to the specific material properties, it is therefore possible to control how much material is melted for the welding process. This also increases the efficiency of the infrared radiation emitter.

[0058] It is advantageous if a defined operating current or a defined operating voltage is applied to the working area to heat the emitter body, whereby the defined operating current or defined operating voltage is regulated or controlled upon reaching the selected temperature or a defined temperature below the selected temperature in such a way that the selected temperature is not exceeded or the temperature of the working area remains constant, in particular within a defined temperature band.

[0059] In an emitter body according to the invention, the electrical conductivity increases with increasing temperature. Since the temperature rises during operation, the increasing conductivity would cause the temperature to rise abruptly or rapidly if the operating current or voltage remained constant. To reach or maintain a defined temperature, at least for a certain period, it is advantageous to control or regulate the operating current or voltage accordingly.

[0060] In a further embodiment, the emitter body heats the workpiece(s) to be welded without contact. In particular, the emitter body can be arranged at a distance of at least 2 mm from the surface of the workpiece to be welded. Preferably, the emitter body can be moved closer to the surface of the workpiece to be welded, or the workpiece(s) to be welded can be moved closer to the emitter body.

[0061] In this way, the emitter according to the invention can be used for contactless welding. The workpiece area intended for the weld seam can thus be heated very quickly. The contactless process prevents molten material from adhering to the welding elements that contact the workpiece surface. Furthermore, the emitter according to the invention can be moved out of the space between the joining partners very quickly, so that the time required for moving the tools and bringing the joining partners together, during which the molten areas cool down again, is kept to a minimum.

[0062] A manufacturing process for an infrared radiation emitter according to the invention is also advantageous, wherein the emitter body, in particular the complete infrared radiation emitter, is produced from a ceramic powder using a 3D printing process, particularly wherein the ceramic powder comprises graphite powder or graphite granules. In the 3D printing process, an open-pored green compact comprising graphite powder is printed and bonded using a phenolic resin. Subsequently, the green compact is impregnated or infiltrated with liquid silicon. The impregnated green compact is then heated, whereby the silicon reacts to form silicon carbide and solidifies.

[0063] In this way, infrared radiation emitters can be manufactured whose shape is tailored to the intended shape of the weld seam in a welding process. This makes it possible to realize very complex weld seam shapes.

[0064] In an advantageous embodiment of the manufacturing process, the infrared radiation emitter is intended for a welding application and the manufacturing process includes the following additional steps: a) Determining the geometric shape of a weld geometry to be heated, in particular three-dimensional, especially by derivation from a CAD drawing or by measurement on a sample component; b) Generating a data set with geometric data from the determined geometric shape, in particular by adding further geometric data to generate a data-based representation of an emitter body to be manufactured, and transferring this data set to a 3D printing machine; c) Performing a 3D printing manufacturing process according to the specified geometric data using the 3D printing machine and producing at least the emitter body, preferably the complete infrared radiation emitter, from the ceramic powder;

[0065] In this way, an integrated manufacturing process for the infrared radiation emitter can be provided. In particular, it is possible to derive the desired weld geometry from a manufacturing drawing of the joining partners to be welded, and from this weld geometry, in turn, to define the geometry of the emitter body for generating the weld, and then to manufacture the corresponding emitter body automatically.

[0066] Advantageous embodiments and further developments according to the invention result from the respective dependent patent claims and also from the following description.

[0067] The invention will be further explained below with reference to exemplary embodiments and the drawings. The drawings show, in schematic representation: Fig. 1. A diagram illustrating the electrical conductivity of various materials as a function of temperature; Fig. 2 a perspective view of an emitter body according to the invention; Fig. 3 a representation of several embodiments of cross-sectional shapes for emitter bodies according to the invention; Fig. 4 a top view of a further embodiment of an emitter body according to the invention; Fig. 5 a side view representation of the emitter body according to Fig. 4;

[0068] Corresponding parts and sizes are found in the figures. Fig. Label items 1 to 3 with the same reference symbols.

[0069] Fig. Figure 1 shows a diagram illustrating the electrical conductivity σ as a function of temperature T for a first material component A, a second material component B and a composite material comprising both a first and a second material component A + B.

[0070] The first material component A can be or comprise a semiconductor material, for example silicon carbide. When an electric current is applied, the current is converted into heat in a silicon carbide body due to its electrical resistance, thus increasing the body's temperature.

[0071] A body made of silicon carbide emits a heat flux Q that depends on the temperature T of the body, with an intensity maximum in the infrared spectral range at a defined wavelength.

[0072] As the temperature T of a body increases, so does its electrical conductivity σ, which in turn amplifies the temperature increase. It has been observed that at temperatures above 700°C, the electrical conductivity σ of a body made of silicon carbide as the primary material component A is significantly higher and increases much faster than at temperatures below 700°C. In particular, it has been observed that at temperatures around 700°C, the increase in the material's electrical conductivity rises sharply. Correspondingly, the temperature T of the body also increases sharply in this range.

[0073] For example, carbon, especially in the form of graphite as the second material component B, exhibits a significantly higher electrical conductivity than the first material component A in a temperature range below 700°C. While the electrical conductivity of graphite B also increases more sharply in a temperature range above 700°C than below, this increase is not abrupt.

[0074] It was observed that a material comprising silicon carbide as a first material component A and graphite as a second material component B exhibits a favorable conductivity-temperature profile A+B. The electrical conductivity is significantly increased by graphite in a lower temperature range below 700°C compared to a material consisting solely of silicon carbide.

[0075] This allows the body to reach a temperature of 700°C more quickly when a corresponding operating current is applied. In an upper temperature range above 700°C, the electrical conductivity of silicon carbide is very high, allowing a further rapid increase in the body's temperature T and thus the emission of infrared radiation R from the body's surface.

[0076] Fig. Figure 2 shows a perspective view of an emitter body 1 according to an embodiment of the invention. The emitter body 1 has an elongated working region 2 with a hollow, tube-like cross-section. The cross-section has an opening 5 that extends along the entire length of the working region 2 parallel to the longitudinal axis of the working region 2. Of course, it is also possible for the opening 5 to extend not parallel to the longitudinal axis, but, for example, spirally or in some other way around it.

[0077] The opening 5 is bounded by contact areas 4, which extend radially away from the hollow, tube-like cross-section. The contact areas 4 are arranged at opposite edges of the opening 5.

[0078] In the illustrated embodiment, the contact areas 4 also extend parallel to the longitudinal axis of the working area 2 over the entire length of the working area 2. However, it is possible that the contact areas 4 extend only in a part of the working area 2 or are arranged exclusively in an end region of the working area 2.

[0079] For the purpose of connecting an electrical contact to the contacting areas 4, these can, for example, have a bore for receiving a contact screw or another contact structure.

[0080] Furthermore, in the illustrated embodiment, the contact areas 4 have a larger cross-sectional area relevant for the flow of electric current than the cross-sectional area relevant for the flow of electric current of the hollow, tubular cross-section of the working area 2. This means, in particular, that, in the illustrated embodiment, the width t1 of the contact areas 4 relevant for the flow of electric current can be greater than the wall thickness t2 of the hollow, tubular cross-section. This measure allows the temperature of the contact areas 4 to be reduced when an operating current is applied, compared to the temperature of the working area 2. This, in turn, protects less thermally resilient contact elements, such as metallic screws or claws, which are fixed to the contact areas 4 for electrical contact.

[0081] The contacting areas 4 can also be designed as holding areas, which can be provided for the arrangement and / or fixing of the working area 2 on machine elements such as feed elements or handling elements or holding elements of a welding system, preferably a plastic welding system.

[0082] The holding areas can each have larger cross-sections or cross-sectional areas than the cross-section or cross-sectional area of ​​the working area. The holding areas can also be thermally insulated from the working area.

[0083] In an embodiment not shown, it is also possible to provide holding areas that are separated from or different from the contacting areas.

[0084] The cross-section of the working area 2 is also designed such that, during operation, infrared radiation R is emitted in at least two opposite directions in the radial direction. This allows an emitter body 1 according to the invention to be used in a welding system in such a way that the emitter body 1 can simultaneously heat and melt the weld zones of two joining partners arranged on opposite sides of the emitter body 1.

[0085] Fig. Figure 3 shows several embodiments of cross-sectional shapes for emitter bodies 1 according to the invention. Contacting areas 4 and holding areas can be provided in a suitable form on each of the cross-sectional shapes shown.

[0086] Embodiment a) shows a circular cross-section of a working area 2 made of solid material. This cross-section is suitable for a rod-shaped working area.

[0087] Embodiment b) shows a round, hollow cross-section. Such a cross-section is suitable for a tubular working area 2.

[0088] Embodiment c) shows an omega-shaped cross-section with an opening 5. The feet of the omega-shaped cross-section can serve as contact areas 4. Essentially, a working area 2 with an omega-shaped cross-section radiates uniformly in a range of 0° to 180° around a cross-sectional center point.

[0089] Embodiment d) shows a U-shaped cross-section with an opening 5. A U-shaped cross-section can have straight legs, so that infrared radiation is emitted uniformly from the straight legs. Such a cross-section can be suitable when a relatively wide area is to be heated.

[0090] Embodiment e) shows a V-shaped cross-section, embodiment f) a W-shaped cross-section. Such cross-sections can be advantageous, for example, if the joining surfaces cannot be arranged parallel to each other before welding or, in the case of the W-shaped cross-section, if more than two joining partners are to be welded together.

[0091] Embodiment g) shows an alternative omega-shaped cross-section with an opening 5 that is smaller in height and wider compared to embodiment c). With this cross-section, the working area 2 also radiates in a range of 0° to 180° around a cross-sectional center point. However, with this cross-section, a significantly larger proportion of the total radiation is emitted in a central area around 90°, and a significantly smaller proportion in the peripheral areas near 0° and near 180°.

[0092] Fig. 4 shows the top view and Fig.Figure 5 shows a side view of another specific embodiment of an emitter body 1 according to the invention. The emitter body 1 also has a working area 2. The working area 2 has the shape of a very short, circular tube. The tube comprises a wall with a rectangular cross-section, a wall width t2, and a wall thickness t3. The wall width t2 is greater than the longitudinal extent L of the working area along the Z-axis, and the wall thickness t3 corresponds to the longitudinal extent L.

[0093] Such an emitter body 1 is advantageously designed to connect pipes or pipe sections together. The emitter body 1 is adapted to the pipes or pipe sections to be connected such that its diameter rx 2 and wall thickness t2 essentially correspond to the diameter and wall thickness t2 of the pipes or pipe sections.

[0094] In the welding process, the emitter body 1 is positioned between the pipes or pipe sections to be joined, so that the infrared radiation R emitted along the Z-axis heats or melts the end faces of the pipes or pipe sections. In the illustrated embodiment, infrared radiation R is also emitted in a radial direction, but in this case it does not contribute to the welding process or only contributes negligibly.

[0095] After melting, the emitter body 1 is moved out of the area between the pipes or pipe sections to be joined, and the melted end faces of the pipes or pipe sections are brought into contact with each other and, if necessary, joined together under defined pressure.

[0096] Working area 2 comprises two opposing contact areas 4, each with two contact openings or contact bores 6 in which screws can be fixed for electrical contacting the emitter body 1. Each contact area 4 has a width t1 that is greater than the wall thickness t2 of the tube wall of working area 2. This ensures that the cross-section of the contact areas 4, which is relevant for the conversion of the electric current into heat, is larger than the cross-section of the tube wall. This results in the contact areas 4 being heated to a lesser extent than the tube wall of working area 2.

[0097] The contact areas 4 are also separated from each other by an opening 5, so that the working area does not form a completely closed tube. Since the weld seam must be hermetically sealed in the application of pipe welding, the distance between the contact areas 4 formed by the opening 5 is designed to be as small as possible and is 1 mm in the illustrated embodiment.

[0098] In order to produce a completely closed and hermetically sealed weld seam between the pipes or pipe sections to be welded during the welding process, it is also necessary to ensure that the working area around the area of ​​opening 5 is heated sufficiently so that over-radiation in the area of ​​opening 5 melts the material to be melted to a sufficient degree. Reference symbol list 1 emitter body 2 Work area 3. Work area surface 4 contact areas 5 Opening 6 contact holes r radius A first material component B second material component σ electrical conductivity Temperature Infrared radiation t1 Width of a contact area t2 Wall width of a work area cross-section t3 Wall thickness of a work area cross-section L Longitudinal extent of the work area X X-axis Y Y-axis Z Z-axis

Claims

[1] Infrared radiation emitter with an emitter body (1) comprising a ceramic material and wherein the emitter body (1) has a working area (2) which emits incoherent infrared radiation (R) when an electric current is applied, wherein the ceramic material comprises a first material component (A) which has an electrical conductivity that increases with increasing temperature and wherein the ceramic material comprises a second material component (B) which increases the electrical conductivity of the ceramic material in a lower temperature range,wherein at least the working area (2) is essentially dimensionally stable and self-supporting and is designed as an elongated body and wherein the longitudinal extent of the emitter body (1) comprises a multiple or multiple of a width and a height of an emitter body cross-section lying or arranged transversely to the longitudinal extent and wherein the working area (2) has one or more curvatures or bends along its longitudinal extent (L). [2] Infrared radiation emitter according to claim 1, wherein the entire emitter body (1) is substantially dimensionally stable and / or self-supporting and / or wherein the entire emitter body (1) is designed as an elongated body. [3] Infrared radiation emitter according to one of the preceding claims, wherein the working area (2) is configured such that, in operation of the infrared radiation emitter, infrared radiation (R) can be emitted or is emitted in at least two opposite directions, in particular additionally in at least a third direction, preferably substantially in exactly four directions, and / or wherein the working area (2) is designed such that in an operation of the infrared radiation emitter infrared radiation (R) can be emitted radially from the working area (2) or is emitted, and / or wherein the working area (2) has planar surfaces from which infrared radiation (R) can be emitted or is emitted orthogonally in an operation of the infrared radiation emitter. [4] Infrared radiation emitter according to one of the preceding claims, wherein the working area (2) is rod-shaped or tubular. and / or having a round, in particular circular or non-circular, or tubular or omega-shaped or polygonal, in particular a substantially triangular or quadrilateral, cross-section, in particular wherein the cross-section has a width (t2) and a thickness (t3) and / or has a U-shaped, V-shaped, W-shaped, or C-shaped profile and / or wherein the working area (2) comprises a hollow profile which has at least one opening (5), in particular wherein the at least one opening extends substantially over the entire longitudinal extent (L) of the working area (2). [5] Infrared radiation emitter according to any of the preceding claims, wherein the working area (2) extends along its longitudinal extent (L) within two spatial dimensions or wherein the working area (2) extends along its longitudinal extent (L) within three spatial dimensions. [6] Infrared radiation emitter according to one of the preceding claims, wherein the infrared radiation emitter is provided to heat a limited area of ​​a surface of a workpiece and wherein the working area (2) is shaped according to a shape of the limited area, in particular wherein the working area (2) has one or more curvatures or bends corresponding to one or more curvatures or bends of the limited area. [7] Infrared radiation emitter according to one of the preceding claims, wherein the emitter body (1) has a working area (2) and at least, preferably exactly, two, in particular integrally, contact areas (4) connected to the working area (2), which are provided for the connection of electrical contacts, in particular wherein the contact areas (4) each have larger cross-sections or larger cross-sectional areas than the cross-section or a cross-sectional area of ​​the working area (2) and / or in particular wherein the contact areas (4) are spaced apart from each other by an opening (5), preferably wherein the distance between the contact areas (4) is less than a wall width (t2) and a wall thickness (t3) of a working area cross-section, and / or wherein the emitter body (1) has a working area (2) and retaining areas connected directly or indirectly, in particular integrally, to the working area (2), which are provided for the arrangement and / or fixing of the working area (2) to machine elements, in particular feed elements or handling elements or retaining elements of a machine, in particular a welding system, preferably a plastic welding system, in particular wherein the retaining areas each have larger cross-sections or larger cross-sectional areas than the cross-section or a cross-sectional area of ​​the working area (2) and / or wherein the retaining areas are thermally insulated from the working area (2), and / or wherein at least one, in particular all, contact area(s) (4) is / are designed as holding area(s). [8] Infrared radiation emitter according to any of the preceding claims, wherein the first material component (A) comprises a semiconductor material, in particular silicon carbide, or wherein the first material component (A) has oxygen ion conductivity, in particular wherein the first material component (A), in particular yttrium oxide-doped, comprises zirconium oxide and / or wherein the second material component (B) increases the electrical conductivity of the ceramic material in a temperature range below 700° Celsius, in particular wherein the second material component (B) comprises carbon, preferably graphite. [9] Infrared radiation emitter according to one of the preceding claims, wherein at least the working area (2) has a non-white coloration, in particular a grey or black coloration, preferably a dark grey coloration. [10] Infrared radiation emitter according to one of the preceding claims, wherein the infrared radiation emitter is connected to an electrical current source or an electrical voltage source and can be operated or is operated with a variable defined operating current or a variable defined operating voltage, in particular a defined direct current or a defined direct voltage, preferably with a current in a range between 20 amperes and 40 amperes, and wherein the infrared radiation emitter can be operated or is operated in at least one upper temperature range with a lower operating current or a lower operating voltage than in a lower temperature range. [11] Infrared radiation emitter according to one of the preceding claims, wherein the infrared radiation emitter is connected to an electric current source or an electric voltage source and comprises an active control of the electric current source or an electric voltage source, in particular wherein the active control is implemented as a control loop in which a temperature sensor, in particular a pyrometer, is provided which determines the actual temperature of the emitter body (1), wherein the actual temperature is compared with a preset or preset target temperature and wherein the current source or the voltage source is actively controlled according to a deviation of the actual temperature from the target temperature resulting from the comparison, in particular automatically by means of an actuator. [12] Welding system, in particular plastic welding system, with an infrared radiation emitter according to one of the preceding claims. [13] Welding process, in particular plastic welding process, using an infrared radiation emitter according to any one of claims 1 to 11 or for carrying out in a welding system according to claim 12, comprising the following steps: • Selection of a temperature (T) of the emitter body (1) depending on an absorption coefficient of the material to be welded for infrared radiation emitted by the emitter body (1) and depending on a desired penetration depth of the infrared radiation (R) emitted by the emitter body (1) into the material to be welded; • Heating the emitter body (1) to the selected temperature (T); • Melting of the material to be welded by the infrared radiation (R) emitted by the emitter body (1) at the selected temperature (T); [14] Welding method according to claim 13, wherein a defined operating current or a defined operating voltage is applied to the working area (2) to heat the emitter body (1), wherein the defined operating current or the defined operating voltage is regulated or controlled upon reaching the selected temperature (T) or a defined temperature below the selected temperature (T) in such a way that the selected temperature (T) is not exceeded or the temperature of the working area (2), in particular within a defined temperature band, remains constant. [15] Welding method according to claim 14, wherein the emitter body (1) heats the workpiece(s) to be welded without contact, in particular wherein the emitter body (1) is arranged at a distance of at least 2 mm from the surface of the workpiece to be welded, preferably wherein the emitter body (1) is moved towards the surface of the workpiece to be welded or wherein the workpiece(s) to be welded are moved towards the emitter body (1).

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