Process for operating a thermal treatment line for the flexible thermal treatment of metal pre-products

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application is a national stage application, filed under 35 U.S.C. § 371, of International Patent Application PCT/EP2023/076214, filed on Sep. 22, 2023, which claims the benefit of German Patent Applications DE 10 2022 210 161.8, filed on Sep. 26, 2022, and DE 10 2023 200 087.3, filed on Jan. 9, 2023.

TECHNICAL FIELD

[0002]The disclosure relates to a process for operating a thermal treatment line for the flexible thermal treatment of metal pre-products, a thermal treatment line configured and suitable for carrying out the process, and a casting-rolling mill and a process for operating a casting-rolling mill having a thermal treatment line.

BACKGROUND

[0003]The input material in rolling mills is conventionally brought to process temperature by gas-fired reheating furnaces. Generally, the previously primary-formed input material, for example from continuous casting, is cooled on cooling beds and fed to a cold store. The cold input material is then removed from the store and fed into a gas-powered reheating furnace. This process route is known as cold charging.

[0004]An alternative to this is what is known as hot charging. In the case of hot charging, the primary-formed input material, coming from the continuous casting, is fed to the reheating furnace by roller tracks, crane and/or other conveying equipment with only a slight cooling and heated to process temperature. Continuous induction furnaces are used for raising the temperature to the required rolling temperature for small-format primary material, what is known as billets.

[0005]However, this heating process by means of induction furnaces is limited to small square, rectangular or round input materials and is sometimes used in conjunction with a combustion furnace as hybrid heating.

[0006]The disadvantage of gas-powered preheating furnaces is that they cause unwanted emissions such as CO, CO₂, NO_x etc. When using natural gas, there is also the resource consumption of fossil fuels, along with the high operating costs, which depend heavily on the price of gas. Furthermore, a preheating furnace cannot simply be switched on and off, but has to be slowly ramped up and down, which causes additional gas consumption and emissions. Regular ramping up and down causes a reduction in the service life of the brick lining, which in turn results in unwanted downtimes and increases the maintenance costs of the furnace.

[0007]The use of pure induction furnaces for heating to rolling temperature is limited to the above-mentioned small formats and heating from ambient temperature to rolling temperature is not possible or only possible with too low a throughput (e.g., in what is known as pendulum operation). In the event of a malfunction in the rolling mill or the induction furnace, the heated input material might no longer be fed into the rolling mill, such that it has to be cooled down and then processed as scrap in the steel plant.

[0008]The heating process is limited to one or a few heating routes and is only flexible to a limited extent in order to react to any malfunctions.

SUMMARY

[0009]An object of the disclosure is to further develop a known thermal treatment line, a known casting-rolling mill with a thermal treatment line and the known processes for operating the two apparatuses in such a manner that they can be operated more flexibly and emissions and production costs are reduced at the same time.

[0010]The object is achieved by a process for operating a thermal treatment line as disclosed herein, by a thermal treatment line as disclosed herein, by a casting-rolling mill having a thermal treatment line and by a process for operating a casting-rolling mill as disclosed herein.

[0011]A flexible thermal treatment line has at least one loading bed for introducing hot or cold metal pre-products into the thermal treatment line; an unloading bed for discharging hot or cold metal pre-products from the thermal treatment line; at least one first heating device for the thermal treatment of the metal pre-product; at least one second heating device for the thermal treatment of the metal pre-product, in particular for heating to a forming temperature of the metal pre-product; at least three transport devices for transporting and/or temporarily storing the metal pre-product and at least two transfer points for transferring the metal pre-product between the transport devices, wherein the first transport device connects the loading bed at least to the first heating device and the first transfer point; and the second transport device connects the first heating device and the first transfer point with the second heating device and the second transfer point; and the third transport device connects the second heating device and the second transfer point with the unloading bed.

[0020]In a first operating mode, a hot metal pre-product is transported from the loading bed to the unloading bed without thermal treatment by means of the at least three transport devices.

[0021]In a second operating mode, a hot or cold metal pre-product is transported to the second heating device by means of the first two transport devices and the metal pre-product undergoes thermal treatment in the second heating device. By means of the third transport device, the metal pre-product is transported from the second heating device to the unloading bed.

[0022]In a third operating mode, a hot or cold metal pre-product is transported to the first heating device by means of the first transport device and the metal pre-product undergoes thermal treatment in the first heating device. By means of the second transport device, the metal pre-product is transported to the second heating device and the metal pre-product undergoes thermal treatment in the second heating device. By means of the third transport device, the metal pre-product, is transported from the second heating device to the unloading bed.

[0023]In a fourth operating mode, a hot or cold metal pre-product is transported to the first heating device by means of the first transport device and the metal pre-product undergoes thermal treatment in the first heating device. By means of the second and third transport devices, the metal pre-product is transported from the first heating device to the unloading bed.

[0024]A hot metal pre-product has a temperature above 200° C., preferably above 500° C., even more preferably above the material-specific austenitization temperature. The average temperature of the metal pre-product is regarded as the temperature. This can deviate from the surface temperature of the metal pre-product and can either be derived from the surface temperature based on the experience of person skilled in the art or can be determined using appropriate process models.

[0025]A cold metal pre-product has a temperature of less than 200° C. Typically, the temperature of a cold metal pre-product corresponds to the ambient temperature.

[0026]Thermal treatment within the meaning of the disclosure includes all process steps that, in a targeted manner, change, maintain or equalize the temperature of the metal pre-product. In particular, this comprises process steps that equalize the temperature of the core and surface or process steps with which the microstructure of the pre-product is adjusted in a targeted manner.

[0027]A control system selects the operating modes as a function of the process parameters, in particular the parameters of material, material flow, temperature of the metal pre-products on the loading bed, target temperature of the metal pre-products on the unloading bed, energy availability and/or energy costs. The control system optimizes at least the total energy consumption of the thermal treatment line by selecting an operating mode for each metal pre-product.

[0028]The loading and unloading devices are configured as interfaces within the meaning of the disclosure and are suitable for making possible an exchange of material with upstream or downstream systems. These are freely dimensioned as interfaces, to the extent that the interface function of the device according to the disclosure is fulfilled. In particular when a cold metal pre-product is being introduced/discharged, these can interact with external means of transport, such as a crane or floor conveyor vehicle.

[0029]At least one transport device is preferably formed at least partially as a cooling line and/or cooling bed and the metal pre-product is preferably cooled in a targeted manner upon transport by the transport device.

[0030]The second heating device is preferably formed as an induction furnace and preferably heats the metal pre-product inductively.

[0031]The first heating device is preferably formed as a gas-operated furnace and the metal pre-product is preferably heated by means of an exothermic gas conversion. Gases that can be used include natural gas, hydrogen, biogas, coking plant gas or mixtures thereof. These can work directly via a burner flame or indirectly by means of radiant heating pipes.

[0032]A heating device preferably combines various heating methods, more preferably induction with the combustion of gas, upon heating a metal pre-product.

[0033]A separating device is preferably present in the thermal treatment line and the metal pre-product is divided into smaller units by the separating device.

[0034]A connecting device is preferably present in the thermal treatment line and the metal pre-product is connected into larger units by the connecting device.

[0035]Furthermore, the object of the disclosure is achieved by a thermal treatment line for the flexible thermal treatment of metal pre-products which is configured and suitable for carrying out the process.

[0036]At least one transport device preferably has means, preferably driven rollers, conveyor chains and/or pushers, for moving the metal pre-product in different directions on the transport bed, preferably longitudinally and transversely to a main conveyor line. The main conveyor line is the line that has the lowest energy loss in combination with the highest throughput. Energy loss is the energy required to heat/maintain the pre-product at a process temperature.

[0037]A connecting device, preferably a driven roller track, is preferably arranged in the thermal treatment line for connecting the various loading and unloading devices, transport devices, heating devices and/or separating devices.

[0038]The connecting device is preferably formed to be at least partially insulated.

[0039]At least one transport device is preferably formed to be at least partially insulated.

[0040]The thermal treatment line preferably has a cooling line and/or a cooling bed for the targeted cooling of a metal pre-product, and the cooling line and/or the cooling bed is connected to the transport devices, heating devices and/or the loading or unloading bed.

[0041]The object of the disclosure is further achieved by a casting-rolling mill. The casting-rolling mill has a series of units for casting and rolling a metal pre-product into a semi-finished or finished product and a thermal treatment line for the flexible thermal treatment of metal pre-products, wherein the thermal treatment line is arranged at least between a casting mill and a first rolling mill stand. Furthermore, the casting-rolling mill has a higher-level control system for controlling the production process steps on the units and the thermal treatment line.

[0042]The object of the disclosure is further achieved by a process for operating a casting-rolling mill. In the process for operating a casting-rolling mill, the higher-level control system of the casting-rolling mill monitors the material flow through the casting-rolling mill and, in the event of a planned or unplanned deviation from the mass flow through the casting mill to the mass flow through the rolling mill, the higher-level control system uses the thermal treatment line as a temporary storage for metal pre-products or introduces or discharges metal pre-products. Planned or unplanned deviations can result, for example, from a mill malfunction or differences between casting speed and rolling speed due to the materials or dimensions.

[0043]The higher-level control system optimizes the material flow through the casting-rolling mill with regard to the availability of cold pre-products, furnace emissions, costs, material output and/or quality. Furthermore, the higher-level control system optimizes at least the casting speed, the amount of cooling water and the process parameters of the thermal treatment line in relation to the total emissions of the casting-rolling mill and the total production costs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044]FIG. 1 shows possible process routes for the operating modes of a thermal treatment line.

[0045]FIG. 2 shows a material flow through the thermal treatment line.

DETAILED DESCRIPTION

[0046]The invention is described in detail below with reference to the specified figures in the form of exemplary embodiments. In all figures, the same technical elements are designated with the same reference signs.

[0047]FIG. 1 shows the possible process routes within the thermal treatment line as a flow chart. A cold or hot pre-product can be fed into the thermal treatment line as input. In the case shown here, a hot pre-product comes from a continuous casting mill 2. Alternatively, pre-products from, for example, an insulation hood or other devices for controlled cooling can also be fed hot from the casting process.

[0048]The feed of the pre-products to the thermal treatment line is carried out by means of the loading bed 3. The loading bed 3 can be connected to the continuous casting 2 via roller tracks, for example. For the cold charging from a cold store 1, the loading bed 3 is loaded with a crane, for example. The loading bed 3 can also have devices that make it possible to separate or combine pre-products.

[0049]The loading bed 3 is connected to a first transport bed 6, such that the pre-product can be transported from the loading bed 3 to a first transfer point 18 or the first gas furnace 7. The first gas furnace 7 can thermally treat the pre-product in a targeted manner, for example by heating and holding it at a temperature at which the pre-product has a substantially austenitic microstructure.

[0050]The first transfer point 18 connects the first transport bed 6 with the second transport bed 8. As a result, the pre-product can reach the second conveyor bed 8 without passing through the first gas furnace 7. The second conveyor bed 8 can likewise receive the pre-product from the first gas furnace 7. The second transport bed 8 is suitable for transporting the pre-product to a second transfer point 19 or transferring it to a second furnace 9, for example an induction furnace. In the second furnace 9, the surface of the pre-product can be heated to the target temperature in a short time.

[0051]Both the second transfer point 19 and the second furnace 9 can transfer the pre-product to a third conveyor bed 10. The third transport bed 10 has an integrated cooling line 11. The pre-product can be cooled in a targeted manner by means of the cooling line 11. The cooling line 11 is not necessarily in operation upon every transport process through the third transport bed 10.

[0052]The third transport bed 10 transfers the pre-product to an unloading bed 12. The unloading bed 12 can also be formed here as a direct feed to a first rolling mill stand 14 or a scale washer 13. Furthermore, a pre-product can also be discharged by means of the unloading bed 12. The unloading bed 12 can also contain means that make it possible for the pre-products to be separated or combined.

[0053]FIG. 2 shows the schematic structure of an apparatus for carrying out the process. A main conveying direction 15 allows the pre-products to take the shortest route from the continuous casting 2 to a scale washer 13 and the first rolling mill stand 14, thereby undergoing thermal treatment only in the second furnace 9. This makes possible a continuous casting-rolling process with minimal use of additional energy from a furnace.

[0054]A connecting device 4 is arranged between the loading bed 3 and the first transport bed 6. This connecting device 4 can, for example, be formed as an insulated roller track. As a result, the distance between the continuous casting 2 and the separating device 5 can be bridged without major temperature loss. The separating device 5 can separate the previously continuous strand from the continuous casting 2 into individual portions.

[0055]A further conveying direction 16 is arranged parallel to this main conveying direction 15. This connects the cold store I with the scale washer 13 and the first rolling mill stand 14 by the shortest route. On this route, the first furnace 7 is passed through and, if necessary, an integrated cooling line 11 arranged in the third transport bed 10 is used. In addition to the transport function, the transport beds 6, 8, 10 can in each case undertake a parallel displacement between these two conveying directions 15, 16 or discharge the pre-product (17).