Method for operating at least one heating element in a thermal process device
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- SMS GROUP GMBH
- Filing Date
- 2024-08-15
- Publication Date
- 2026-07-08
Smart Images
Figure EP2024072968_06032025_PF_FP_ABST
Abstract
Description
[0001] Method for operating at least one heating element in a thermal processing device
[0002] The invention relates to a method for operating at least one heating element in a thermal processing device, such as a furnace, in particular a preheating furnace, a strip processing plant with a preheating device and / or a furnace for adjusting the metallurgical properties of the strip, or a Compact Strip Production (CSP) plant for heating a heating material, in particular a metallic heating material, more particularly a metal strip. The invention further relates to said thermal processing device with a control device for controlling the heating element according to the method and to the use of the information determined according to the method in production planning for the products produced with the thermal processing device. The thermal processing device can be used in the production and / or processing of semi-finished products and / or preliminary products, in particular made of metallic materials or non-metallic materials.Metallic materials can be iron, steel, or non-ferrous metals. Non-metallic materials can be glass, ceramics, or other non-metallic materials.
[0003] Heating elements, particularly electric heating elements, as used in the aforementioned thermal processing devices, are well known in the art. However, their service life is limited and depends in particular on the temperature or power at which they are operated, as well as on the changes in temperature and / or power at which the heating elements are operated.
[0004] Temperature, especially the temperature of the heating element's heat conductor, has a non-linear influence on the service life of the heating elements. The criterion for this is usually creep strength, which is easily determined at constant temperatures and is available for many materials. The influence of thermal load changes on service life is greater than the influence of the absolute temperature level. At constant temperature, creep deformation is lower, sometimes significantly lower, than during temperature changes, even when the temperature changes occur at a low absolute temperature level.
[0005] Lifetime consumption is a cost factor in the operating costs of a thermal processing device. This is particularly true because the failure of heating elements leads to a reduction in the performance of the thermal processing system, with adverse effects on its productivity, product quality, and / or the performance requirements of other heating elements or their service life in the thermal processing system. This is true because these other heating elements then typically have to be subjected to greater demand to at least partially compensate for the performance of the failed heating element. The failure of heating elements also leads to downtime or production loss, especially if the heating elements require unscheduled replacement. This leads to increased operating costs for spare parts and replacement labor.
[0006] The service life of heating elements is therefore already receiving special attention in the state of the art. This is particularly evident in the fact that various prediction models for predicting the (remaining) service life of heating elements are known in the state of the art. Examples:
[0007] An example of a physically based model for the damage and lifetime development of metallic components, even if not directly related to electrical resistance heating, is described by Schwing et al. in “Lifetime of metallic furnace components at
[0008] Thermal cycling (Part 3)”, see Process Heat, Issue 07, 2019, pp. 63-69). This is done on the basis of a Graham-Wallace model approach, as presented in the article “Relationship between long and short time creep and tensile properties of a commercial alloy” in the Journal of the Iron and Steel Institute, 1955, pp. 104-121.
[0009] Nikitina and Rybnikova take a similar approach, as explained in "Parametric Methods for Determining the Characteristics of Long-Term Metal Strength Thermal Engineering," 2018, Vol. 65, No. 6, pp. 379-386. All approaches include coefficients derived from regression of experimental data. These coefficients are suitable for improving models with growing data sets (self-learning models).
[0010] The application of a predictive model for heating element wear is illustrated by Pogrebisskiy et al. in their work "Modelling of degradation processes for refractory metallic heating elements of vacuum resistance furnaces," IOP Conf. Series: Materials Science and Engineering 313 (2018) 012011. They demonstrate that the resistance of the heating element material changes significantly with increasing lifetime wear and is a suitable parameter for monitoring lifetime wear. Vacuum chamber furnaces are furnaces operated in batches, allowing the replacement of a heating element after each batch. In "A Failure Time Prediction Method for Condition-Based Maintenance, Quality Engineering," 26, 2014, pp. 335-349, Arda Vanli presents a combined model for lifetime prediction. The model uses concrete operating data on the element's lifetime with statistical values from experimental data.The outlook includes the expansion to a self-learning model.
[0011] The maintenance status of heating elements can be monitored by monitoring their electrical resistance. The electrical resistance depends on the cross-section and the resistivity of the conductor material. The cross-section changes due to corrosive or mechanical wear or the elongation of the heating wire. Corrosion changes the resistivity of a layer close to the surface, and thus both the average resistivity of the heating element across its entire cross-section and across the cross-section of the non-corroded portion of the material.
[0012] The measurement of resistance for the purpose of determining the condition of resistance heating elements is claimed in US2008183404 and US20220390404. The diagnosis is based on a comparison of the resistance of a heating element with a reference value in an unused state. US2008183404 describes the responses to a low remaining service life as issuing a warning and blocking the operation of the affected heating element.
[0013] All of the prior art publications mentioned have the disadvantage that they do not provide any recommendations on how such a heating element can be operated in order to extend its service life.
[0014] The invention is therefore based on the object of further developing a known method for operating at least one heating element in a thermal processing device, as well as a known thermal processing device with such a heating element, in such a way that the service life of the heating element is extended. A further object of the invention is to appropriately utilize information about a desired or necessary extension of the service life of the heating element.
[0015] This object is achieved with respect to the method by the method claimed in patent claim 1. Accordingly, the method according to the invention is characterized in that the remaining service life of the heating element is predicted, and that the power at which the heating element is operated is controlled as a function of the predicted remaining service life.
[0016] The expression "operating the heating element at a .... power" means that the power at which the heating element is operated is controlled by a control device. The terms "control device" and "control" can also refer to a control device and "regulate." Furthermore, the terms also include the setting of constant values.
[0017] The claimed consideration of the predicted remaining service life during operation of the heating element advantageously enables an extension of the service life of the heating element, preferably at least until a scheduled replacement of the heating element, which is already due. In this way, for example, an unscheduled replacement of the heating element can be prevented, thereby avoiding the aforementioned disadvantages, which are particularly associated with an unscheduled failure of the heating element.
[0018] In other words: It is the merit of the inventors to have recognized that through suitable control or regulation or automation of the thermal processing device and in particular of the heating element, the predicted lifetime consumption of the heating element can be reduced considerably.
[0019] The above-mentioned object of the invention is further achieved by a thermal processing device according to claim 7 and by the use of the information determined according to the method according to the invention according to claim 10. The advantages of these solutions correspond to the advantages mentioned above with reference to the claimed method.
[0020] Advantageous embodiments of the method according to the invention, the thermal processing device according to the invention and the claimed use are the subject of the dependent claims.
[0021] As already mentioned above, the special feature of the method according to the invention for operating a heating element in a thermal processing device for heating a material to be heated is that a) the service life of the heating element is predicted and that b) the power with which the heating element is operated is controlled as a function of the predicted remaining service life.
[0022] The invention is described in detail below in the form of exemplary embodiments for the process steps a) and b).
[0023] Examples of implementation for process step a):
[0024] According to the invention, the remaining service life of the heating element is predicted using at least one remaining service life prediction model. The prediction model can be a physical model, a regression model, a data-based model, such as a statistical model or a neural network, or a hybrid model. A hybrid model combines a physical model with a data-based model.
[0025] The prediction models typically predict the remaining service life of the heating element based on information that is suitable as an indicator of the remaining service life of the heating element. Some examples include:
[0026] - A first suitable indicator of the remaining service life of the heating element is, for example, a detected change in its electrical resistance over time. The electrical resistance of the heating element is a measurement parameter that is easy to measure. In addition to the specific resistance of the heating element material and the material properties of the heating element, it also depends on the cross-section of the heating element through which current flows. A change in the resistance allows conclusions to be drawn about corrosion, i.e. a change in the material property, and / or material loss, i.e. a change in the cross-section. The electrical resistance can be measured by the control device, typically power electronics, which supplies power to the heating element. For more precise measurement data, separate resistance measurements can also be carried out; these must be installed separately.The use of resistance measurements could reduce the requirements for wire breakage detection on thyristor controllers and thus advantageously reduce the capital expenditure for longer-term operating components.
[0027] - Another indicator of the remaining service life of the heating element can be a geometric change in the heating element detected over time, particularly compared to its original state. For example, monitoring the cross-section of the heating element provides direct feedback on its wear. Monitoring the cross-section can be done visually, but is then challenging and prone to errors. Changes in the length of the heating element are easier to detect, particularly in the case of wound or meandering heating wires. When lengthened or stretched in this way, the wires leave their mounting position and sag. Monitoring is possible visually for continuously operated thermal processing devices, e.g., using cameras. For thermal processing devices operated in batches, there may be points in time that allow direct access.Installed process cameras can continuously perform this monitoring task, provided they have sufficient resolution and a sufficient focal range. If this is not the case, additional inspections are conceivable or necessary. For example, discontinuously operated thermal processing devices, especially furnaces, can be regularly inspected with appropriate high-resolution cameras, for which the camera is inserted into the thermal processing device. This approach is particularly suitable for bell furnace batteries. Within the thermal processing device, "inspection bases" with high-resolution cameras can be provided, on which a heating hood is regularly positioned for camera-based inspection of its heating elements. Continuously operated furnaces, such as roller-hearth furnaces or walking beam furnaces, can be traversed by an appropriate inspection system during a production shutdown.Alternatively, openings for inspection or the lifting or opening of lids, for example, with optionally directly attached heating elements, are possible. During these inspections, a comparison is made with reference images. The evaluation can be gradient-based or absolute, based on one or more references.
[0028] - Another indicator of the remaining service life of the heating element can be a detected change in the emissivity of the heating element over time. Such a change in emissivity is determined by comparing a non-contact and a contact temperature measurement. If these two types of temperature measurement are available for a heating element simultaneously, the two measurements differ by the emissivity of the heating element. A detected change in emissivity is particularly an indication of wear and thus a reduced service life of the heating element.
[0029] - Another indicator of the remaining service life of the heating element is a detected change in the heating element's response over time, specifically in the form of a change in the temperature generated by the heating element in response to a change in the power supplied to it. The heating element's response can be particularly well monitored by recording a time-temperature curve in which the temperature that develops after a change in the power supplied is plotted. Changes in the heating element's response detected with the curve can also be an indication of wear and thus of a reduced remaining service life of the heating element.
[0030] - A further indication of a reduction in the remaining service life can be a detected reduction in the power consumption and / or the energy balance of the heating element over time while the process requirements or conditions remain the same.
[0031] - Finally, a detected change in the temperature profile and / or the temperature distribution within the thermal processing device and / or a change in the temperature profile and / or the temperature distribution or a target temperature not being reached for the material to be heated after passing through the thermal processing device and / or a detected change in the quality of the properties to be set by the heat treatment, for example the metallurgical properties, the mechanical properties, the physical properties, the surface quality or the properties of applied coatings of the material to be heated after passing through the thermal processing device can be an indication of a reduced remaining service life.
[0032] The forecast models are typically designed to determine the remaining service life of the heating element based on at least one of the above-mentioned indicators. For this purpose, at least one of the indicators is fed to the respective forecast model as an input variable. For indicators or data that are directly related to the wear of the heating element, such as a change in its cross-section or a change in its electrical resistance, the forecast of the remaining service life may be possible using simple, i.e. linear, polynomial or exponential models. These models can be based on physical model assumptions, on regression from measured data, or a combination thereof. Other information, i.e.In particular, information that does not show a direct connection to the wear of the heating element can be used in the context of a statistical forecast and / or in data-based models of artificial intelligence, e.g. so-called neural networks.
[0033] All models can be continuously "fed" with new data obtained from repeated and updated evaluations of the indicators. In self-learning models, the continuously updated data or information about the remaining service life of the asset is used to improve the model. In neural networks, the additional or updated data is added to a training dataset of the neural network, and training is then continued in the future using the updated training dataset. In statistical models, the additional updated data is used to update and improve the calculated means and standard deviations.Linear, polynomial, and exponential models derived from regression can be adjusted based on the additional data by rerunning the interpolation / regression of linear, polynomial, or exponential functions on a larger database. This allows improved coefficients to be determined.
[0034] In hybrid models, which, as mentioned, combine a data-based approach with a physical model approach, coefficients of physical model equations can be multiplied by respective correction factors, which enable a data-based adjustment. These correction factors are improved as the data set grows.
[0035] If not all heating wires are accessible with suitable measuring devices, e.g., if resistance measurement is not possible and there is no optical access for a camera to the heating elements, a combination of random measurement data acquisition and static or database-based models can be used to predict service life. To improve the accuracy of service life prediction, maintenance intervals and / or downtimes of the elements can also be regularly used, e.g., in the form of a feedback loop.
[0036] Having previously shown various embodiments for the execution of method step a), various embodiments for method step b) according to the method according to the invention are described below:
[0037] In the event of a currently determined reduced remaining service life of the heating element, for example compared to when it was new, the method according to the invention provides, in particular according to method step b), for example that the heating element is only operated at a reduced power output compared to its target power and / or at a reduced temperature compared to its target temperature for the material to be heated and / or with a reduced number of load changes per unit of time compared to a predetermined target number. Specifically, the heating element in question can, for example, only be operated with a constant load, i.e. without load changes, or only at a constant temperature, i.e. without temperature changes. All of the measures mentioned result in a reduced load on the heating element in question and therefore lead to an extension of its remaining service life.
[0038] Particularly in a continuously operated thermal processing device, the heating element in question could, for example, be operated with a less stressful mode, as described in the previous paragraph, and at the same time at least one additional heating element could be provided to heat the material to be heated. The additional heating element could then provide the additional power, temperature increase or the specified number of load cycles that may be required to heat the material to be heated. With such simultaneous operation of the two heating elements, the heating of the material to be heated can be ensured according to a specified heating characteristic, i.e. with a required target power, a required target temperature and / or a specified target number of load cycles. At the same time, by operating the original heating element with only a lower load, its service life is extended as desired.
[0039] This significantly reduces the risk of unscheduled heating element failures before they are due to be replaced during the next scheduled maintenance shutdown. This allows more heating elements to be replaced during planned downtimes than during unplanned downtimes, reducing the number of unplanned downtimes and increasing the utilization of the thermal processing equipment.
[0040] The thermal processing device has a control device for operating the heating element for which the reduced remaining service life has been determined in a less stressful operating state and / or for controlling the additional heating element, as described above. According to the invention, the control device is designed such that it can control the heating elements according to the method according to the invention. In particular, the control device is designed to control the heating element affected by the reduced remaining service life and the additional heating element such that, when these two heating elements are operated together, the desired heating characteristic for a particular material to be heated can be reliably achieved. The power, the temperature and / or the target number of load changes correspond to the intended or desired heating characteristic and are designated in the claims with the preceding attribute "target".Finally, the present invention recommends using the information on the remaining service life of the heating element determined according to the method according to the invention, in particular according to method step a), in production planning for a product to be manufactured for which the heating material is an intermediate product. For example, this information can be used to initially plan and / or run only production campaigns with heating materials that require a lower temperature than the maximum temperature of the heating element or a lower number of temperature changes per unit of time than the maximum possible number of temperature changes with the heating element within its intended heating characteristics.With such production planning, the heating element with the predicted reduced service life can then continue to be used without any problems, at least until it is replaced during an already scheduled maintenance shutdown of the production facility. These production campaigns can then be run in at least one area of the thermal processing device in which at least one heating element with the reduced predicted remaining service life is installed.
[0041] The method according to the invention is explained below by way of example with reference to Figures 1 and 2.
[0042] The figures show possible applications of the method in a thermal processing plant or a zone of a thermal processing plant with n heating elements, referred to simply as "elements" in the figures. The remaining service life, i.e., the remaining lifetime of the heating elements used, is calculated, for example, using a forecast model.
[0043] Figure 1 shows the process flow for changes in the predicted remaining service life of a heating element. Figure 2 shows the power curve over time with several changes in the power requirement and the predicted remaining service life of heating element 1.
[0044] If the predicted remaining lifetime of an element, in the figures the heating element 1, falls below a threshold value (TH1, TH2), the load on the element is reduced in order to extend the remaining lifetime. The reduction in the load occurs in Figures 1 and 2 by reducing the power of the first heating element P r The total power P supplied to the process tis kept constant by increasing the power output of the other elements Pj V i + 1. The increase can, for example, be proportionally linear. If it is not possible to keep the power constant by increasing the power of the other elements, the process can continue to operate at a reduced power. In this case, further adjustments to the process may need to be made, for example extending the treatment time of the material being treated. The load can be further reduced by reducing the number of cycles. In the examples in the figures, this is achieved by keeping the power of the first heating element P1 constant once the second threshold value TH2 is exceeded. Temperature and / or product changes that are accompanied by a change in the power requirement are only realized by changing the power of the other heating elements.
Claims
Patent claims: 1 . A method for operating at least one heating element in a thermal processing device for heating a material to be heated, comprising the following steps: - Operating the heating element at a predetermined power; characterized in that the remaining service life of the heating element is predicted; and in that the power at which the heating element is operated is controlled as a function of the predicted remaining service life.
2. The method according to claim 1, characterized in that the remaining service life of the heating element is predicted using at least one remaining service life prediction model; and that the prediction model is a physical model, a regression model, a data-based model, for example a statistical model or a neural network, or a hybrid model, wherein the hybrid model combines the physical model with the data-based model.
3. Method according to claim 2, characterized in that at least one of the following information is determined as an indicator of the remaining service life of the heating element: - a change in the electrical resistance of the heating element over time; - a geometric change of the heating element over time, in particular compared to its original state; - a change in the emissivity of the heating element over time by comparing a contactless and contact temperature measurement; - a change in the response of the heating element over time in the form of a change in the temperature generated by the heating element in response to a change in the power supplied; - a change in the power consumption and / or energy balance of the heating element over time with constant process requirements; and / or - a change in the temperature profile within the thermal processing device, and / or a change in the temperature profile of the material to be heated after passing through the thermal processing device and / or the quality of the material to be heated after passing through the thermal processing device; and / or - the failure to reach a target temperature for the heating product under known conditions; and that the forecast model is designed to forecast the remaining service life of the heating element on the basis of at least one of these items of information about the heating element supplied to the forecast model as an input variable.
4. Method according to one of the preceding claims, characterized in that the prognostic model is designed to be self-learning in that the at least one piece of information determined repeatedly or continuously during the service life of the heating element is used to improve the model or - in the case of a neural network - to train it.
5. Method according to one of the preceding claims, characterized in that - in the case of a remaining service life that is currently higher than that determined at an earlier point in time, for example when new, determined reduced remaining service life of the heating element - the heating element is only operated with a reduced power compared to a target power, and / or with a reduced temperature compared to a target temperature for the material to be heated and / or with a reduced number of load changes per unit of time compared to a predetermined target number of load changes per unit of time, for example with a constant load, further for example with a constant temperature.
6. Method according to one of the preceding claims, characterized in that at least one further heating element is provided for heating the material to be heated; and that the further heating element is operated in addition to the heating element such that, upon combined operation of the two heating elements, the target power, the target temperature, and / or the target number of load cycles are achieved.
7. A thermal processing device for heating a material to be heated, comprising a heating element for heating the material to be heated; and a control device for controlling the heating element; characterized in that the control device is designed to control the heating element according to the method according to one of the preceding claims.
8. Thermal processing device according to claim 7, characterized in that at least one further heating element is provided for heating the heating material; and that the control device is further designed to control the further Heating element in addition to the heating element to be controlled in such a way that when the two heating elements are operated together, the target power, the target temperature and / or the target number of load changes for the material to be heated are achieved.
9. Thermal processing device according to claim 7 or 8, characterized in that the heating element is an electrical heating element, in particular a resistance heating element.
10. Use of the information on the remaining service life of the heating element determined according to the method according to the invention according to one of claims 1 to 6 in the production planning for a product to be produced for which the heating material is an intermediate product, in such a way that - in the case of only a short forecast remaining service life of the heating element - only production campaigns with heating materials are planned and / or run which require a temperature which is lower than a maximum temperature of the heating element or a number of temperature changes per unit of time which is lower than a maximum possible number of temperature changes with the heating element.