Irradiation device, hardening module and method for hardening or gelling coating material on a workpiece

Abstract

Irradiation device (5) for a workpiece (2) with radiation-curing coating, comprising an elongated radiation source designed to emit electromagnetic radiation in the ultraviolet spectrum, and a housing (7) which partially surrounds the radiation source (6) and has at least one cooling channel (8) which is at least partially bounded by the housing and is in thermally conductive contact with the radiation source (6), wherein the cooling channel (8) is designed to guide a cooling gas and the power output of the radiation source (6) is selected such that a quantity of heat that can be generated by the radiation source (6) can be dissipated essentially by means of a gas flow in the cooling channel (8), so that the irradiation device (5) is in particular exclusively gas-cooled.

Description

[0001] The invention relates to an irradiation device for a workpiece with a radiation-curing coating, as well as a curing module and a method for gelling or curing a radiation-curing coating on a workpiece.

[0002] In the industrial production of workpieces, such as those used in furniture or interior building construction, it is common practice to apply a surface coating. This provides the workpieces with special protection against abrasion and moisture penetration. Furthermore, the optical and tactile properties can be tailored to specific requirements. Such coatings are used particularly in the production of wood-based composite components, such as medium-density or high-density fiberboard (MDF), but also on workpieces made of stone, glass, metal, or plastic whose surfaces need to be optimized in terms of their optical or functional properties.

[0003] The coating material is typically in a liquid state during application to the workpiece surface and must be cured or at least gelled after application, especially if a further coating is to be applied. The aforementioned irradiation device can be used for this purpose. Such an irradiation device generally has several radiation sources designed to emit electromagnetic radiation, which initiates one or more chemical reactions in the coating associated with the curing process. These processes are usually based on polymerization of the coating, in which at least partial cross-linking of the molecules within the coating material takes place. This can be supported by the addition of so-called photoinitiators, which absorb the radiation from the irradiation device and decompose into reactive radicals that enable polymerization.

[0004] Alternatively, polymerization can be initiated directly by the radiation itself, eliminating the need for photoinitiators.

[0005] Common coating materials often contain components that can be harmful to the human body and the environment, especially when the coating is not fully cured. Therefore, it is standard practice to select radiation source power levels high enough to ensure the desired degree of coating cure with a sufficiently high probability. However, this is disadvantageous because high power output is required from the irradiation equipment to achieve the desired process parameters. This negatively impacts the overall complexity of the irradiation equipment's design and operation, as well as its energy efficiency.

[0006] The object of the invention is to propose means by which, on the one hand, good curing of surface coatings on workpieces is possible and, on the other hand, good energy efficiency can be achieved with a simple design of the devices used.

[0007] The problem is solved with an irradiation device according to claim 1, a hardening module according to claim 6 and a method according to claim 16. Advantageous further developments are each the subject of dependent subclaims.

[0008] The irradiation device according to the invention serves to cure or gel a radiation-curing coating that may be located on the surface of a workpiece. The irradiation device comprises an elongated radiation source configured to emit electromagnetic radiation in the ultraviolet spectrum, and a housing that partially surrounds the radiation source. A cooling channel extends at least partially between the radiation source and the housing and is in thermally conductive contact with the radiation source. The cooling channel serves to guide a cooling gas. The power output of the radiation source is selected such that the amount of heat generated by the radiation source can be dissipated essentially by means of a gas flow guided in the cooling channel. In particular, the irradiation device is exclusively gas-cooled.

[0009] The invention is based on the finding that conventional radiation-curing coatings can be cured or gelled at such low power levels per unit length that simple air cooling is sufficient to dissipate the heat generated. This simplifies the design of the irradiation device, as other cooling media, particularly cooling liquids, can be completely dispensed with. In other words, the irradiation device preferably has only one or more cooling channels for conveying cooling gases and, in particular, no channel for conveying cooling liquid. At the same time, reliable curing of the coating is possible, especially when more than one irradiation device is used.

[0010] The workpiece can be a so-called MDF / HDF material board, which is provided with the radiation-curing coating. However, the invention is not limited to the use of the irradiation device on specific types or geometries of workpieces. The electromagnetic radiation emitted by the radiation source can be in the wavelength range between approximately 100 nm and 400 nm. It is also within the scope of the invention that the workpiece is provided with more than one radiation-curing coating, whereby, in particular, several coatings can be arranged above or below one another, each of which is to be cured or gelled.

[0011] The radiation source itself has an elongated body and a power output per unit length, which can be specified in watts per centimeter and thus relates to the length of the radiation source. In a preferred embodiment, the radiation source is a mercury vapor lamp, for example, a medium-pressure or high-pressure UV lamp. These lamps are characterized by a broad emission spectrum in the UV range and offer radiation intensities sufficient to cure or gel coatings in relatively compact dimensions. Alternatively, doped mercury vapor lamps can be used, in which the spectrum is specifically tailored by the addition of metals, preferably iron, gallium, or indium. The radiation source can also be a metal halide lamp, which can likewise be doped, preferably with iron, gallium, indium, or lead.One advantage of using the aforementioned types of radiation sources is that the workpiece is subjected to only minimal thermal stress during the hardening process, and the radiation, in particular, has no damaging effect. If a conveying system is used to move the workpiece into the effective range of the irradiation device, this also has a positive effect on the conveying system, as cooling can be completely eliminated or at least designed for minimal cooling capacity.

[0012] It is within the scope of the invention that the length-related power of the radiation source results from the nominal power of the radiation source, in particular corresponds to it, or that the radiation source can be operated with a power that is lower than its nominal power, in particular by means of a ballast by means of which the length-related power can be adjusted.

[0013] Within the scope of the invention, the housing can be considered a component or an assembly of several components, which is arranged adjacent to the radiation source, in particular at a distance. The cooling channel, as described above, is formed between the radiation source and the housing and can in particular be directly bounded by the radiation source and the housing.

[0014] The cooling channel serves to guide the cooling gas, which can be ambient air or another gas that may be enriched with additional components, particularly as a result of the curing process or the operation of the radiation source, and which can be discharged along with these components. In particular, the cooling gas can be a mixture of several gases that can be supplied to the cooling channel together or separately. Specifically, it can be a mixture of ambient air with another gas, especially nitrogen, which is preferably present in the mixture in a higher proportion than in ordinary ambient air, i.e., above approximately 78% by volume.

[0015] The cooling channel preferably extends along the radiation source and surrounds it circumferentially in certain areas, whereby the gas flow can be guided in a longitudinal direction along the radiation source and / or in a circumferential direction around the radiation source.

[0016] Preferably, the cooling channel comprises several sub-channels, which can extend in particular along two opposite sides of the radiation source.

[0017] In particular, the housing can be arranged and designed such that an opening is provided through which radiation from the radiation source can be emitted radially and out of the housing. Preferably, the irradiation device can be arranged such that the opening defines an effective area of ​​the irradiation device, in particular the radiation source, within which the workpiece with the surface coating can be irradiated. Furthermore, this opening can serve for the supply of cooling gas to the cooling channel. In other words, the cooling channel can be fluidically connected to the opening.

[0018] In an advantageous embodiment, the cooling channel is limited by the radiation source and the housing, wherein the housing has at least one, preferably several, cooling fins, particularly on a side facing away from the cooling channel.

[0019] The advantageous embodiment described above exhibits a high degree of functional integration. On the one hand, the housing serves to enclose the radiation source and thus protect it from external influences. On the other hand, the housing directly defines the cooling channel and thus determines its path, so that the gas flowing within it can be guided past the radiation source in the necessary manner to absorb the heat it emits. It is further advantageous that the gas flow does not only carry away the absorbed heat from the radiation source by moving through the cooling channel, but can also transfer it convectively to the housing. The housing can itself advantageously be provided with one or more cooling fins on the side facing away from the cooling channel, through which the heat can also be dissipated.

[0020] It is conceivable that a further cooling flow can be routed along a side of the housing facing away from the radiation source. This makes it possible to dissipate the heat absorbed by the cooling gas not only through the movement of the cooling gas out of the cooling channel, but also via the housing itself to a second cooling flow. In particular, the housing defines a second cooling channel on a side facing away from the radiation source, which is preferably formed by one or more housing components.

[0021] In an advantageous further development, the housing is designed as a reflector on one side facing the radiation source.

[0022] It is advantageous for the housing to have a reflective surface on one side facing the radiation source. This reflective surface can result from the material and / or surface finish of the housing itself and / or be achieved by means of a reflective component attached to it. This makes it possible not only to direct the radiation emitted directly from the radiation source onto the workpiece surface, but also to deflect radiation components that are not emitted directly towards the workpiece. A reflective surface can be paraboloid, elliptical, or free-form to ensure optimal focusing or homogenization of the radiation distribution.

[0023] In an advantageous further development, the radiation source extends essentially along a principal axis of extension and the housing is curved around the principal axis of extension.

[0024] With this further development described above, it is possible to enclose the radiation source in at least one radial direction from the housing and to release it in a second radial direction, in particular in the area of ​​the opening explained above, so that on the one hand the radiation emitted directly from the radiation source and on the other hand radiation reflected from the housing is directed into an effective area of ​​the irradiation device, in particular the radiation source.

[0025] In an advantageous embodiment, the housing defines a ventilation gap into which the cooling channel opens. Preferably, the housing has at least two housing parts between which the ventilation gap is formed, into which the cooling channel opens. In particular, several partial channels are joined in the area of ​​the ventilation gap and open, in particular, into the ventilation gap.

[0026] Advantageously, the housing components are arranged essentially symmetrically with respect to the main axis of extension of the radiation source. In particular, the two housing components can each be arranged on one side of the radiation source with respect to the main axis of extension and, together, form the ventilation gap in a common apex region. In this way, the cooling channel extends, particularly in the form of two sub-channels, to two sides of the radiation source, so that the gas flow can be concentrated and discharged in the area of ​​the ventilation gap.

[0027] In an advantageous embodiment, the ventilation gap is fluidically connected to a flow resistance which runs essentially parallel to the main axis of extension of the radiation source. In particular, the flow resistance is arranged downstream of the ventilation gap, especially with respect to a nominal flow direction of the gas flow.

[0028] The advantageous further development described above is based on the understanding that, ideally, a gas flow for cooling the radiation source should be directed around its circumference for a substantial portion of its total length, particularly its entire length. This is complicated by the fact that fans or other flow generators, which may be located upstream or downstream of the radiation source, can create comparatively inhomogeneous flow conditions within the cooling channel. In particular, different flow velocities can occur within the cooling channel and along the radiation source, resulting in certain areas of the radiation source being cooled more or less effectively than others.By installing a flow resistance, which extends essentially along the main axis of the radiation source and can be simply designed as a deflector plate, it is possible, particularly downstream of the radiation source, to create a backwater area. This ensures that the gas flow guided in the cooling channel is better distributed along the entire length of the radiation source. In this context, it is important to note that uniform cooling of the radiation source has a particularly positive effect on the radiation spectrum along the source and, in particular, creates uniform radiation conditions along the main axis.

[0029] In an advantageous further development, the length-specific power of the radiation source is at most 160 W / cm, preferably at most 150 W / cm, most preferably at most 140 W / cm, in particular at most 130 W / cm.

[0030] The aforementioned length-specific performance characteristics of the radiation source have proven particularly advantageous in the applicant's investigations for reliably curing or gelling common types of coatings. At the same time, it is possible to operate the radiation source exclusively with gas cooling and to dispense with other cooling media.

[0031] In an advantageous further development, the radiation has a spectral focus between 100 nm and 280 nm.

[0032] The aforementioned wavelength range lies within the so-called UVC spectrum, which has proven particularly advantageous for fully or partially curing common radiation-curing coatings. This wavelength range corresponds to so-called UVC radiation (also: ultraviolet-C), which is characterized by its high photon energy and strong interaction with organic molecules. In an advantageous embodiment of the invention, the radiation emitted by the radiation source has a spectral focus in the range between 180 nm and 280 nm.

[0033] A spectral focus can be defined as the average wavelength of a radiation source, taking into account the spectral intensity distribution within that wavelength range. Such a spectral focus is particularly advantageous for applications requiring direct, initiator-free polymerization, as UVC radiation is capable of breaking chemical bonds in unsaturated monomers or oligomers without the addition of photoinitiators, thus directly triggering crosslinking. Furthermore, radiation in this range can contribute to disinfection or the destruction of biological contaminants – a potentially beneficial side effect in sensitive production environments. Regarding the curing of radiation-curing coatings on MDF / HDF workpieces, UVC radiation enables rapid and complete surface curing, resulting in a hard, scratch-resistant, and chemical-resistant layer.

[0034] In an advantageous further development, the irradiation device comprises at least one temperature sensor which is in thermally conductive contact with the radiation source and / or the cooling channel and / or the housing and / or the ventilation gap.

[0035] The temperature sensor enables the monitoring of heat generation from the irradiation device, particularly the radiation source, and its use in controlling the device or associated components, especially the radiation source. The temperature sensor can be, for example, an infrared thermometer, a thermocouple, or a resistance thermometer. It is understood that temperature measurement for controlling the irradiation device or associated components does not necessarily have to be performed directly at the radiation source, but can also be taken at adjacent components. It is particularly advantageous if the temperature sensor can be connected, or is connected, to a control unit that is designed to control and / or regulate the irradiation device or an associated component, especially the radiation source.In particular, the temperature sensor is configured to output a sensor input to the control unit, which processes the sensor input and, depending on this, outputs a control signal to one of the other components. Preferably, the temperature sensor is arranged such that, when a cooling gas is guided in the cooling channel, it is in thermally conductive contact with the cooling gas. In particular, the temperature sensor can have a spatial detection range and be arranged such that the radiation source and / or the cooling channel and / or the housing and / or the ventilation gap are at least partially located within the detection range.

[0036] As described above, the problem is also solved by a curing module for curing or gelling a radiation-curing coating on a workpiece according to claim 6. The curing module has a conveying means which is designed to receive the workpiece and move it along a conveying direction. Furthermore, the curing module has an irradiation device according to the invention or an advantageous embodiment thereof. At least between the conveying means and the irradiation device, in particular the radiation source, a passage area is formed in which the workpiece provided with the coating can be exposed to electromagnetic radiation in the ultraviolet spectrum.

[0037] Regarding the possible configurations of the curing module, the descriptions of the irradiation device according to the invention, or an advantageous embodiment thereof, apply accordingly. The conveying means can preferably be an endlessly circulating conveyor belt, the upper run of which is designed as a support for the workpiece. The irradiation device can have an effective area extending between the radiation source and the conveying means in order to expose workpieces and their coatings to electromagnetic radiation in the ultraviolet spectrum. It is conceivable that the curing module comprises one or more irradiation devices.

[0038] In an advantageous further development, a conveying device is configured to move the workpiece in the conveying direction at a conveying speed above 25 m / min. Preferably, the conveying speed is at least 30 m / min, particularly at least 40 m / min, and preferably at least 80 m / min.

[0039] The further training described above is based on the finding that comparatively high conveying speeds of at least 25 m / min up to over 80 m / min are achievable with the hardening module and that reliable hardening of the workpiece coating is possible.

[0040] In an advantageous further development, the radiation source is tilted relative to the direction of conveyance.

[0041] An inclined position of the radiation source relative to the conveying direction can be understood, in the context of this advantageous development, as such that the principal axis of extension of the radiation source and the conveying direction enclose an angle between 0° and 90° at least in one support plane of the workpiece on the conveying medium. Investigations have shown that, with such an arrangement, the irradiated workpiece can be treated with higher power densities, particularly compared to an orthogonal orientation. This allows the radiation source to have a comparatively low nominal power or to be operated with low power and exclusively gas-cooled, while still achieving the desired curing state of the coating. This improves the efficiency of the curing module. Advantageously, the width of the conveying medium is less than the length of the radiation source along its principal axis of extension.It is conceivable that the conveying medium has a width of 1300 mm and the radiation source a length of 1600 mm.

[0042] In an advantageous further development, the cooling channel is fluidically connected to at least one gas source, in particular a nitrogen source.

[0043] The aforementioned further development is based on the understanding that, instead of ambient air, other gases can be used to generate the gas flow for cooling the irradiation device. In particular, advantages arise when the gas flow is generated with an inert gas that produces few or no substances requiring safe removal during cooling of the irradiation device, such as ozone. Furthermore, the cooling gas can be selected such that, compared to ambient air, lower flow rates are required due to differing thermal conductivities and heat capacities. Moreover, surface oxidation can be avoided, thereby extending the service life of the irradiation device and, in particular, its metallic housing components.Furthermore, hardening under partially or completely inert conditions requires less power and can produce better workpiece surfaces, particularly with regard to scratch resistance or chemical resistance, compared to reactive conditions. It is conceivable that the cooling channel or its sub-channels are connected to more than one gas source to create a mixture with different gas components.

[0044] The gas source can advantageously be any device for supplying a suitable cooling gas, in particular an inert gas such as nitrogen or a noble gas such as argon, helium, neon, xenon, or krypton. Examples include pressurized gas cylinders, central supply systems in industrial plants, or vaporizers for cryogenically liquefied nitrogen. The gas can be introduced into the cooling channel via the flow-controlled connection either directly or via an intermediate storage tank. This can be achieved using rigid pipes or flexible hoses. Valves, pressure reducers, or flow meters can be integrated into the connection to regulate the gas flow. Automatic control of the gas supply based on temperature, pressure, or other process parameters is also possible, ensuring precise and demand-based cooling.

[0045] In an advantageous further development, the hardening module includes a hardening sensor, which is specifically designed to detect the degree of hardening of the coating on the workpiece.

[0046] The curing sensor can be based on physical, chemical, or optical measurement principles and enables continuous or discrete-time monitoring of the coating's curing state on the workpiece surface. By measuring the degree of curing, the curing process can be monitored and, if necessary, controlled to ensure uniform and reliable curing of the workpiece. This contributes to achieving high quality and allows for application-specific, optimized process control.

[0047] The curing sensor could, for example, be based on near-infrared spectroscopy (NIR spectroscopy), where spectral characteristics of the coating are used to determine the curing state. Alternatively, the degree of curing can also be analyzed indirectly by evaluating other physical or chemical measurements, such as temperature profiles or the composition of the discharged cooling gas.

[0048] The result of determining the degree of curing can be used to control the operating parameters of the curing module, in particular to adjust the UV output or the supply of cooling gas as needed. In this way, the curing process can be dynamically controlled and adapted to different workpiece conditions or process fluctuations, ensuring consistently high product quality and energy-efficient operation.

[0049] It is particularly advantageous if the curing sensor is connected via signal transmission to a control unit, which is configured to control and / or regulate the irradiation device and / or curing module or one of its components. In particular, the curing sensor is configured to output a sensor input to the control unit, which processes the sensor input and outputs a control signal to one of the other components.

[0050] Preferably, the hardening sensor has a detection range and is positioned relative to the conveying device such that a workpiece picked up by the conveying device, when moving in the conveying direction, at least partially enters the detection range. The hardening sensor can be located in the passage between the irradiation device, in particular the radiation source, and the conveying device. It is also conceivable that the hardening sensor is located upstream of the irradiation device with respect to the conveying direction. It is also possible that the hardening sensor is located downstream of the irradiation device with respect to the conveying direction in order to verify a hardening state after the workpiece has been exposed to radiation.This can be advantageous if, on the one hand, the hardening state of the workpiece is to be checked as part of quality assurance and, on the other hand, the data collected are to be used for power control of the radiation source when irradiating subsequent workpieces, in particular to enable workpiece-discrete power control.

[0051] In an advantageous further development, the irradiation device, in particular the radiation source, is arranged to be adjustable relative to the conveying means in order to change the height of the pass-through area by means of an adjustment.

[0052] By adjusting the height of the irradiation device, or at least the radiation source, it is possible to change the height of the passage area. This allows workpieces of varying thicknesses to be fed into the curing module, enabling the surface coating to be cured or gelled. In particular, the height of a focal point within the irradiation device, which is predetermined by the design, can be adjusted accordingly. This allows the height of the focal point within the passage area to be adapted as needed to different workpiece thicknesses, especially to the height of the workpiece surface.

[0053] Advantageously, the hardening module, particularly with regard to the conveying direction upstream of the irradiation device, has at least one workpiece sensor configured to detect the presence of a workpiece and / or its dimensions. This sensor can be, in particular, an optical or acoustic sensor.

[0054] Furthermore, the curing module can include a control unit and an actuator, each of which is connected to the workpiece sensor via a signal and is configured to adjust the passage height based on a signal input from the workpiece sensor. The actuator can be any type of adjustment device, arranged to move the irradiation device or just the radiation source as needed, thereby setting a desired height position relative to the conveying device. Additionally or alternatively, the workpiece sensor itself or another measuring device can be configured to detect the presence and / or dimensions of a workpiece to be coated. The control unit is specifically designed to control and, in particular, regulate the radiation source based on sensor input.This makes it possible to supply power to the radiation source according to demand, so that it can be operated at a lower power level than during the curing process, especially when no workpiece needs to be cured, and can even be switched off completely if necessary.

[0055] In an advantageous embodiment, the curing module comprises at least one, preferably several, shielding elements, which are arranged in front of and / or behind the irradiation device with respect to the conveying direction. Preferably, the shielding element has an air inlet opening, which is connected to the cooling channel, particularly in terms of airflow.

[0056] The shielding element can be understood as a component or an assembly of several components that serve to separate the working area of ​​the irradiation device within the curing module from the environment. In particular, the shielding element is designed to protect the working area of ​​the irradiation device from external light influences and, conversely, to prevent the escape of UV light, thus protecting the operator's eyes. Additionally or alternatively, it is possible to create an atmospheric separation of the curing module from its surroundings. This is particularly advantageous because gases, such as ozone, can be generated during the curing of the coating and the cooling of the irradiation device, and these gases should be removed with the cooling gas flow.One way to achieve this is to equip the shielding element with an air intake opening through which the cooling gas can be introduced into the working area of ​​the irradiation device and extracted and discharged via the cooling duct. If a shielding element is positioned both in front of and behind the irradiation device, flows of the extracted cooling gas, e.g., ambient air, can be generated. These flows move from the respective air intake openings towards the irradiation device and are discharged in a concentrated stream after heating. This prevents them from escaping through the inlet or outlet of the curing module, ensuring that any gases produced, such as the aforementioned ozone, are safely removed. In particular, it is possible for the air intake opening to be fluidically connected to an air supply fan and / or to the gas source.The air inlet can be equipped with an air inlet grille, through which ambient air is drawn into the passage area as a result of a negative pressure created by an exhaust fan.

[0057] In an advantageous further development, the irradiation device has a power supply unit which is connected to the radiation source in terms of energy technology and the length-specific power can be variably adjusted by means of the power supply unit.

[0058] The power supply unit provides electrical power and controls the radiation source and, in particular, enables precise adjustment of the length-specific power, i.e., the emitted radiant power per unit length of the radiation source. It is also possible to set and, if necessary, modify a spectral property of the emitted radiation, especially its intensity and / or wavelength-dependent intensity distribution.

[0059] The variable power output via the power supply allows the radiation intensity to be adapted to different process requirements. This is particularly advantageous when processing different workpiece materials, coating thicknesses, coating materials, curing speeds, or conveying speeds. For example, a reduction in power may be necessary to prevent overheating temperature-sensitive substrates, while a reduction in power can be beneficial for particularly reactive or thin-film coatings, or an increase in power for comparatively less reactive or thicker coatings.

[0060] The power supply can be implemented as a separate unit or as part of an analog or digital control unit. In particularly preferred embodiments, the power supply can be integrated into a higher-level control unit that also takes into account other parameters of a coating or conveying system, in particular line speed, temperature, and coating type. Power control can be stepless or in discrete steps, thus enabling dynamic process control with high energy efficiency and consistent curing quality.

[0061] In an advantageous embodiment, the cooling duct is fluidically connected to at least one exhaust air fan and / or one supply air fan. In particular, the exhaust air fan and / or the supply air fan is configured to generate a minimum power-related volume flow of 70 m³ / h per kilowatt, depending on the length-specific power, preferably at least 50 m³ / h per kilowatt, and particularly at least 30 m³ / h per kilowatt.

[0062] The aforementioned blower units are preferably used for the targeted generation and guidance of an airflow through the cooling duct, so that the amount of heat generated by the radiation source can be effectively dissipated by the moving cooling gas.

[0063] The exhaust fan is preferably arranged to extract and remove heated air from the cooling duct, while a supply air fan can introduce fresh, cool ambient air or filtered process air. Alternatively or additionally, recirculation mode can also be provided.

[0064] The length-specific power refers to the emitted radiant power per unit length of the radiation source. This relationship ensures sufficient heat dissipation even at high radiant power levels, preventing overheating of the components and maintaining the radiation source at an optimal operating temperature, which can influence the emittable radiation.

[0065] The fan-assisted airflow thus allows for demand-based, scalable cooling capacity that can be automatically or manually adjusted to the operating conditions. Such control can be achieved, for example, by linking it to the control system of the radiation source's power supply, so that the airflow rate increases accordingly when the radiation intensity increases. Alternatively, temperature-controlled regulation can be implemented using sensors in the vicinity of the cooling duct or the radiation source.

[0066] This design ensures thermally stable operation, extends the service life of the radiation source and reduces the risk of thermally induced process deviations, especially with temperature-sensitive workpieces or substrates such as MDF or HDF boards.

[0067] In particular, the power supply and / or a separate frequency converter, each of which may be part of a control unit, are connected to both the radiation source and the exhaust fan and / or the supply air fan via power supply connections. Specifically, the power supply is connected to the control unit via signal connections. This control unit is configured to set the linear power output of the radiation source and, depending on this, to adjust the fan speed or related parameters of the exhaust fan and / or the supply air fan. This makes it possible to adjust both the radiation intensity and the cooling capacity required, particularly in relation to and / or interaction with each other.

[0068] In an advantageous further development, the hardening module comprises a control device which is set up to adjust, depending on a sensor input, the length-specific power of the radiation source and / or the height of the passage area and / or a power of the exhaust fan and / or the supply air fan and / or a conveying speed of the workpiece.

[0069] According to the advantageous embodiment described above, it is conceivable that the control unit receives sensor input from the temperature sensor and / or the workpiece sensor and / or the hardening sensor, each of which is connected to the control unit via signal transmission. It is also conceivable that the control unit outputs a control signal to the radiation source and / or the actuator and / or at least one of the blowers and / or the conveying device in order to regulate them. In particular, a control routine is implemented in the control unit which processes the sensor input(s) and outputs the control signal(s) accordingly.

[0070] As explained above, the invention also relates to a method for hardening or gelling a radiation-curing coating on a workpiece according to claim 16. In this method, the workpiece with its coating is placed in the effective area of ​​an irradiation device, which may in particular be an irradiation device according to the invention or one of its advantageous embodiments. The irradiation device comprises a radiation source that is partially surrounded by a housing and a cooling channel that runs between the radiation source and the housing. The cooling channel is in thermally conductive contact with the radiation source. The radiation source emits electromagnetic radiation in the ultraviolet spectrum and thereby generates heat, which is dissipated essentially by means of a gas flow, in particular air, guided in the cooling channel.In particular, this results in the radiation source being cooled exclusively by gas cooling.

[0071] The method described above can be carried out, in particular, with an irradiation device according to the invention or an advantageous embodiment thereof, or with a curing module according to the invention or an advantageous embodiment thereof, and vice versa. In particular, the descriptions of the irradiation device according to the invention or an advantageous embodiment thereof, or the descriptions of the curing module or an advantageous embodiment thereof, apply accordingly to the method known from experience or an advantageous embodiment thereof and are transferable.

[0072] Possible embodiments of the invention are explained below by way of example with reference to a model embodiment and a figure. It shows Figure 1 shows a hardening module with several irradiation devices.

[0073] Engineered wood panels, such as medium-density fiberboard (MDF) or high-density fiberboard (HDF), are often coated with radiation-cured finishes. These types of wood-based panels are widely used in furniture making, interior design, and flooring, where they are subjected to high mechanical and chemical stresses while also meeting aesthetic requirements.

[0074] To meet this requirement, it is common practice to apply protective coatings to the surfaces of the panels. These coatings protect against abrasion, moisture, and chemical influences, and also improve optical and tactile properties. On an industrial scale, coatings based on radiation-curing materials are of great importance. Curing the applied coating by radiation results in a rapid and uniform cross-linking of the reactive components it contains.

[0075] In Figure 1A curing module 1 is shown, which enables the reliable and energy-efficient curing of a radiation-curing coating (not shown) on a workpiece 2. The curing module 1 comprises a conveying element 3, which in the embodiment shown is designed as an endlessly circulating conveyor belt. The upper run of the conveyor belt is designed to receive the workpiece 2 and convey it along a conveying direction 4 into the working area of ​​several irradiation devices 5. For clarity, only one of the irradiation devices 5 and its components are indicated with reference numerals; however, the following descriptions apply to the other irradiation devices shown.

[0076] The irradiation device 5 has a radiation source 6, which in this case is designed as an elongated mercury vapor lamp and has a main axis of extension that lies in the image plane of the Figure 1 The main axis of extension of the radiation source 6 is inclined relative to the conveying direction 4 in a manner not shown in detail here. Furthermore, the irradiation device 5 also has a housing 7. In the embodiment shown here, the housing 7 is formed in two parts and extends partly parallel to the main axis of extension of the radiation source 6 and partly circumferentially around it. A cooling channel 8 is formed between the radiation source 6 and the housing 7, which is divided into two sub-channels and serves to guide a gas flow with which the irradiation device 5 is cooled.

[0077] As demonstrated by Figure 1As shown, the radiation source 6 is surrounded on two sides by a gas flow, which in this embodiment is an air flow drawn from the vicinity of the hardening module 1. Not shown here, the cooling gas can also be a gas other than ambient air, e.g., nitrogen, or a mixture of several gases taken from one or more gas sources.

[0078] As demonstrated by Figure 1 It is also apparent that the housing parts of the housing 7 are curved around the main extension axis of the radiation source 6 and enclose a ventilation gap in a common apex area, from which the heated gas flow can escape in order to convectively dissipate the amount of heat it has absorbed.

[0079] To ensure good distribution of the cooling air along the main axis of the radiation source 6, a flow resistance in the form of a deflector plate 9 is arranged downstream of the ventilation gap. This creates a dynamic pressure that ensures the air in the cooling channel 8 is distributed along the main axis of the radiation source 6. The housing 7 has a reflective surface on one side facing the radiation source 6 (not shown). This allows the light radiation emitted by the radiation source to be directed not only directly onto the surface of the workpiece 2 to be cured, but also reflected from an area facing away from the workpiece and directed onto the workpiece 2 through an opening on the underside of the housing 7.

[0080] On one side facing away from the radiation source 6, the housing 7 has a plurality of cooling fins 10, which ensure optimized heat distribution within the housing 7. In a manner not shown here, the cooling fins 10 can also serve to guide a further gas flow to cool the irradiation device 5.

[0081] It is advantageous that the curing module 1 and the irradiation devices 5 are exclusively air-cooled, so that no additional coolants, in particular cooling liquids, are required to regulate the heat generation in the irradiation devices 5. In the embodiment shown here, the gas flow, which is indicated by arrows and is required for cooling the radiation sources 6, is partially generated for each irradiation device 5 by means of an exhaust fan 11. This fan is arranged downstream of the cooling channel 8 and behind the radiation source 6 and extracts the heated air, along with any process gases that may have been generated, from the cooling channel 8. The resulting negative pressure ensures that fresh air is drawn in through one or more air inlets 12 on the shielding elements 14 and directed towards the radiation sources 6.

[0082] As demonstrated by Figure 1As also shown, the curing module 1 also has a supply air fan 13, which is arranged in such a way that it conveys the air drawn in from its surroundings towards the cooling channel 8, and this air is then also discharged via the exhaust air fan 11. This makes it possible to provide additional fresh air and to increase the cooling capacity as needed, which is particularly advantageous if the curing module 1 has several irradiation devices 5. In a manner not shown in detail here, a curing module 1 can also have only one irradiation device 5 and only one exhaust air fan 11.

[0083] The exhaust fan 11 can be connected to a frequency converter and operated at different speeds and thus different delivery rates. Investigations have shown that the supply air fan 13 does not need to be frequency-controlled; its delivery rate can be adjusted manually as needed using a supply air damper. In an alternative embodiment, however, all fans can be frequency-controlled.

[0084] As demonstrated by Figure 1As shown, a shielding element 14 is arranged in front of and behind the radiation source 6 with respect to the conveyance direction 4. Each shielding element is designed as an enclosure and contains an air inlet opening 12 with an air inlet grille. The air inlet opening can be connected to the air inlet fan 13 in a manner not shown in detail here. The shielding element 14 serves, on the one hand, to protect the effective area of ​​the irradiation device 5 from external light influences and, on the other hand, to prevent unwanted emission of UV radiation.

[0085] In the example shown here, the irradiation device 5 and the shielding element 14 are enclosed in a common housing, which is height-adjustable. This makes it possible to adjust the passage height 16 as required, thus enabling the surface curing or gelling of workpieces of two different thicknesses. For this purpose, the curing module 1 has an actuator 17, by means of which the housing can be moved and the passage height 16 can be changed as needed. Alternatively, it is also possible to adjust the height of only the irradiation device 5 or its radiation source 6.

[0086] As demonstrated by Figure 1As also shown, the curing module 1 has a workpiece sensor 15 in an entry area, which in this case serves to detect the presence and thickness of the workpiece 2. This makes it possible to control the power of the radiation sources 6 depending on the detected absence or presence of a workpiece 2. Furthermore, it is possible to automatically adjust the passage height 16 by means of a drive device (not shown here) depending on the detected workpiece thickness. This is particularly advantageous because adjusting the irradiation device 5 shifts the focal point of the emitted radiation, which can thus be adapted to the workpiece thickness. This allows optimal curing quality to be achieved for any workpiece thickness.

[0087] In addition to the workpiece sensor 15, the curing module 1 also includes curing sensors 18, which are designed as near-field infrared spectroscopy sensors and which, in the embodiment shown here, are arranged between the irradiation devices 5 of the curing module 1. These serve to detect the curing state of the coating on the surface of the workpiece 2. The data obtained can be used, as needed, to increase or decrease the power of one of the irradiation devices 5, adjust the passage height, set the workpiece feed speed, or adjust the required cooling volume flow rate.

[0088] The curing module 1 further comprises temperature sensors 19, which, in the embodiment shown here, are each arranged in the cooling channel 8 of the irradiation devices 5. In this embodiment, the temperature sensor 19 serves to monitor the heat development in the cooling channel 8, so that the volume flow rate of the cooling gas or the power of the radiation source can be adjusted, or both measures can be taken simultaneously to regulate the heat balance of the irradiation device 1. It is also possible to adjust the conveying speed of the conveying medium 3. The temperature sensor can also be arranged in the area of ​​the ventilation gap, but this is not shown here.

[0089] A control unit 20 is provided to receive sensor signals from the workpiece detection unit 15, at least one of the hardening sensors 18, or one of the temperature sensors 19. In the embodiment shown here, the control unit 20 is connected to the workpiece sensor 15, the hardening sensors 18, and the temperature sensors 19 via signal transmission, as indicated by the dashed lines. An evaluation routine implemented on the control unit 20 is configured to evaluate the sensor signals individually or together and to output one or more control signals to the conveying device 3, the irradiation device 5, the supply air blower 13, one or more exhaust air blowers 11, or the actuator 17. In particular, it is possible to flexibly control the operation of the hardening module 1 and to positively influence the hardening process or the process of the workpiece 2 becoming gel-like.

Claims

1. Irradiation device (5) for a workpiece (2) with a radiation-curing coating, comprising an elongated radiation source designed to emit electromagnetic radiation in the ultraviolet spectrum, and a housing (7) which partially surrounds the radiation source (6) and has at least one cooling channel (8) which is at least partially bounded by the housing and is in thermally conductive contact with the radiation source (6), wherein the cooling channel (8) is designed to guide a cooling gas and the power output of the radiation source (6) is selected such that a quantity of heat that can be generated by the radiation source (6) can be dissipated essentially by means of a gas flow in the cooling channel (8), so that the irradiation device (5) is in particular exclusively gas-cooled.

2. Irradiation device (5) according to claim 1, wherein the cooling channel (8) is limited by the radiation source (6) and the housing (7), wherein the housing has, in particular, at least one, preferably several, cooling fins (10) on a side facing away from the cooling channel (8) and / or wherein the housing is designed as a reflector on a side facing the radiation source (6), wherein the radiation source (6) extends, in particular, substantially along a principal axis of extension and the housing (7) is curved about the principal axis of extension.

3. Irradiation device (5) according to one of the preceding claims, wherein the housing (7) defines a ventilation gap into which the cooling channel (8) opens, in particular by means of two housing parts between which the ventilation gap is formed, wherein the ventilation gap is preferably connected in terms of flow technology to a flow resistance (9), in particular a deflector plate, which runs substantially parallel to the main axis of extension of the radiation source (6).

4. Irradiation device (5) according to one of the preceding claims, wherein the length-specific power of the radiation source (6) is at most 160W / cm, preferably at most 150 W / cm, most preferably at most 140W / cm, in particular at most 130 W / cm and / or wherein the radiation has a spectral center point between 100 and 280 nm, in particular between 180 and 280 nm.

5. Irradiation device (5) according to one of the preceding claims, comprising at least one temperature sensor (19) which is in thermally conductive contact with the radiation source (6) and / or the cooling channel (8) and / or the housing (7) and / or the ventilation gap.

6. Curing module (1) for curing or gelling a radiation-curing coating on a workpiece (2), comprising a conveying means (3) which is provided to receive the workpiece (2) and move it along a conveying direction (4), and comprising at least one irradiation device (5) according to one of claims 1 to 5, wherein at least between the conveying means (3) and the irradiation device (5), in particular the radiation source (6), a passage area is formed in which the workpiece (2) provided with the coating can be exposed to electromagnetic radiation in the ultraviolet spectrum.

7. Hardening module (1) according to claim 6, wherein the conveying means (3) is configured to convey the workpiece (2) at a conveying speed above 25 meters per minute, preferably at least 30 meters per minute, in particular at least 40 meters per minute, most preferably at least 80 meters per minute in the conveying direction (4).

8. Hardening module (1) according to one of claims 6 or 7, wherein the radiation source (6) is inclined relative to the conveying direction (4), wherein in particular a width of the conveying means (3) is less than a length of the radiation source (6).

9. Hardening module (1) according to one of claims 6 to 8, wherein the cooling channel (8) is fluidically connected to at least one gas source, in particular a nitrogen source.

10. Hardening module (1) according to one of claims 6 to 9, comprising at least one hardening sensor (18) which is in particular configured to detect the degree of hardening of the coating on the workpiece (2).

11. Hardening module (1) according to one of claims 6 to 10, comprising at least one workpiece sensor (15) which is configured to detect the presence of a workpiece and / or a workpiece dimension.

12. Hardening module (1) according to one of claims 6 to 11, in which the irradiation device (5), in particular the radiation source (6), is arranged adjustably relative to the conveying means (3) in order to change a height (16) of the passage by means of an adjustment, in particular by means of an actuator (17).

13. Curing module (1) according to one of claims 6 to 12 with at least one shielding element which is arranged in front of and / or behind the irradiation device (5) with respect to the conveying direction (4) and in particular has an air inlet opening (12) which is connected to the cooling channel (8) in particular in terms of flow technology.

14. Curing module (1) according to one of claims 6 to 13, wherein the cooling channel (8) is fluidically connected to an exhaust air blower (11) and / or a supply air blower (13), which are in particular configured to provide a minimum power-related volume flow of 70 m³ depending on the length-specific power. 3 / h / kW, especially 50 m 3 / h / kW, preferably 30 m 3 to generate / h / kW.

15. Hardening module (1) according to one of claims 6 to 14, with a control device (20) which is configured to adjust, depending on a sensor input, the length-specific power of the radiation source (6) and / or the height (16) of the passage area and / or a delivery rate of the exhaust air blower (11) and / or the supply air blower (13) and / or a delivery speed of the conveying medium.

16. Method for hardening or gelling a radiation-curing coating on a workpiece (2), wherein the workpiece (2) with its coating is brought into an effective area of ​​an irradiation device (5), in particular an irradiation device (5) according to one of claims 1 to 5, which comprises a radiation source (6) which is partially surrounded by a housing (7) and has at least one cooling channel (8) which is at least partially limited by the housing (7) and is in thermally conductive contact with the radiation source (6), wherein the radiation source (6) emits electromagnetic radiation in the ultraviolet spectrum and a quantity of heat generated thereby is dissipated substantially by means of a gas flow guided in the cooling channel (8).

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