Pretreatment device

Abstract

Provided is a pretreatment device (10) provided upstream of a reduction furnace (100) for removing an oxide film from a steel strip (S), the pretreatment device (10) comprising: an induction heating device (1) that heats the steel strip (S) by induction heating; a spraying nozzle (2) that is provided upstream or downstream of the induction heating device (1) and directly sprays an atmospheric gas onto the steel strip (S); a circulation flow path (4) that circulates the atmospheric gas in a conveyance path (3) in which the steel strip (S) is conveyed in the induction heating device (1); an oxygen concentration measurement device (5) that measures the oxygen concentration in the circulation flow path (4); and an oxygen-containing gas supply device (6) that adjusts the oxygen supply amount to be supplied to the circulation flow path (4) on the basis of the measurement result of the oxygen concentration measurement device (5), wherein the spraying nozzle (2) sprays, onto the steel strip (S), the atmospheric gas in the circulation flow path (4) to which the oxygen-containing gas has been supplied by the oxygen-containing gas supply device (6).

Description

Pretreatment device

[0001] The present invention relates to a pretreatment device that is provided upstream of a reduction furnace for removing oxide films from steel strips.

[0002] Conventionally, in the annealing process of a steel strip, the steel strip is heated and cooled in a reducing atmosphere in a reducing furnace in order to prevent or remove an oxide film on the surface of the steel strip. As a pretreatment before the heat treatment, Patent Document 1 discloses a configuration in which the surface is slightly oxidized to improve the adhesion of the plating after the heat treatment in the reducing furnace.

[0003] JP-A-51-40016, JP-A-1-262967, JP-A-9-256074, JP-A-2021-91960

[0004] However, the configuration disclosed in Patent Document 1 simply introduces a weakly acidic gas into the pretreatment device, making it difficult to adjust the composition of the atmosphere inside the device or actively produce an oxide film. Furthermore, since the introduced gas is naturally discharged from the inlet and outlet of the device, it is difficult to achieve uniform pretreatment, and there is also the waste of the introduced gas being discharged.

[0005] Therefore, as shown in Patent Document 2, a configuration has been disclosed in which atmospheric gas is circulated by flowing it along the steel strip within an induction heating device to reuse the gas, and as shown in Patent Documents 3 and 4, a configuration has been disclosed in which a dryer or humidifier is installed in the atmospheric gas circulation flow path to adjust the dew point (moisture content) of the atmosphere within the device.However, in either case, it was difficult for the circulating atmospheric gas to come into contact with the surface of the steel strip, making it difficult to adjust the degree of oxidation of the steel strip.

[0006] Therefore, an object of the present invention is to provide a pretreatment device that can adjust the degree of oxidation of a steel strip.

[0007] The present invention is a pretreatment device that is provided upstream of a reduction furnace that removes an oxide film from a steel strip, and includes: an induction heating device that heats the steel strip by induction heating; an injection nozzle that is provided upstream or downstream of the induction heating device and that directly injects atmospheric gas onto the steel strip; a circulation flow path that circulates atmospheric gas within a transport passage in the induction heating device through which the steel strip is transported; an oxygen concentration measuring device that measures the oxygen concentration in the circulation flow path; and an oxygen-containing gas supply device that adjusts the amount of oxygen-containing gas supplied to the circulation flow path based on the measurement results of the oxygen concentration measuring device, and the injection nozzle is configured to inject atmospheric gas from the circulation flow path, to which oxygen-containing gas has been supplied by the oxygen-containing gas supply device, onto the steel strip.

[0008] According to the above configuration, the oxygen concentration of the atmospheric gas sprayed from the spray nozzle can be adjusted by adjusting the amount of oxygen-containing gas supplied to the circulation flow path based on the measurement results of the oxygen concentration in the circulation flow path. Furthermore, the degree of oxidation of the steel strip surface can be adjusted by spraying atmospheric gas with an adjusted oxygen concentration directly onto the steel strip from the spray nozzle. Furthermore, by circulating the atmospheric gas in the conveying passage through which the steel strip is conveyed, the atmospheric gas that oxidizes the steel strip can be used efficiently.

[0009] According to the present invention, a pretreatment device capable of adjusting the degree of oxidation of a steel strip can be provided.

[0010] 6 is a schematic configuration diagram of a pretreatment device according to an embodiment of the present invention; FIG. 7 is an enlarged schematic view of an injection nozzle portion; FIG. 8 is a schematic configuration diagram of a pretreatment device in which circulation fans 411 and 421 are common fans and gas purification devices 412 and 422 are common fans; FIG. 9 is an enlarged schematic view of an injection nozzle portion in which a pair of injection nozzles each inject atmospheric gas in two directions; FIG. 10 is a schematic view showing yet another embodiment of an injection nozzle; FIG. 11 is a schematic view showing a state in which the inner circumferential cylindrical portion is rotated from FIG. 5; FIG. 12 is a schematic view showing a state in which the inner circumferential cylindrical portion is rotated in the opposite direction from FIG. 5;

[0011] FIG. 1 is a schematic diagram of a pretreatment device 10 according to an embodiment of the present invention. As shown in FIG. 1 , the pretreatment device 10 is provided upstream of a reducing furnace 100, which removes an oxide film from a steel strip S to be treated. The pretreatment device 10 includes an induction heating device 1 for inductively heating the steel strip S; an injection nozzle 2 provided downstream of the induction heating device 1 for directly injecting gas onto the steel strip S; a circulation flow path 4 for circulating atmospheric gas within a transport passage 3 through which the steel strip S is transported within the induction heating device 1; an oxygen concentration measuring device 5 for measuring the oxygen concentration within the circulation flow path 4; and an oxygen-containing gas supply device 6 for adjusting the amount of oxygen-containing gas supplied to the circulation flow path 4 based on the measurement results of the oxygen concentration measuring device 5. The oxygen-containing gas may be any gas containing oxygen, and may include pure oxygen or air. In FIG. 1 , the steel strip S is transported from bottom to top within the vertical pretreatment device 10. Although not shown, the transport is achieved by, for example, winding the steel strip S into a coil downstream of the reducing furnace 100.

[0012] The induction heating device 1 includes a solenoid type induction heating device 11 and a transverse type induction heating device 12, and the solenoid type induction heating device 11 is provided upstream of the transverse type induction heating device 12 in the processing direction.

[0013] A plurality of injection nozzles 2 are provided on the downstream side of the solenoid induction heating device 11 and the transverse induction heating device 12. Fig. 2 is an enlarged schematic view of the injection nozzle 2 portion. As shown in Fig. 2, the injection nozzles 2 are provided in pairs so as to face each other perpendicularly to the steel strip S, and the pair of injection nozzles 21a, 21b closer to the solenoid induction heating device 11 are configured so that the gas injection direction forms an acute angle θ1 with respect to the steel strip S (with respect to the conveying direction X of the steel strip S). Further, on the downstream side of the injection nozzles 21a, 21b, a pair of injection nozzles 22a, 22b are arranged so that the gas injection direction is perpendicular to the steel strip S (with respect to the conveying direction X of the steel strip S).

[0014] Similar to the downstream side of the solenoid induction heating device 11, a pair of injection nozzles 2 are provided on the downstream side of the transverse induction heating device 12 so as to face perpendicularly to the steel strip S. The pair of injection nozzles 23a, 23b closer to the transverse induction heating device 12 are configured so that the gas injection direction forms an acute angle θ1 with respect to the steel strip S (with respect to the conveying direction X of the steel strip S). Further, on the downstream side of the injection nozzles 23a, 23b, a pair of injection nozzles 24a, 24b are disposed so that the gas injection direction is perpendicular to the steel strip S (with respect to the conveying direction X of the steel strip S). The injection nozzles 21a, 21b, 22a, 22b, 23a, 23b, 24a, 24b are structured, for example, as cylindrical pipes extending in the width direction of the steel strip S, and the injection ports A are small holes or slits (neither of which is shown) provided in the extending direction of the pipes, and inject the atmospheric gas sent from the circulation flow path 4. For this reason, the injection nozzles 21a to 24b are configured so that, as the state of the atmospheric gas, partitions can be installed inside the pipes and dedicated heaters (not shown) can be installed to vary the temperature across the width of the steel strip S, or the injection amount across the width of the steel strip S can be adjusted by adjusting the position and size of the small holes or slits. The injection direction can also be freely set by rotating the injection nozzles 21a to 24b as a whole. In this embodiment, a pair of injection nozzles whose injection direction is perpendicular to the steel strip S and a pair of injection nozzles whose injection direction forms an acute angle θ1 with the steel strip S are provided. However, another pair of injection nozzles may be provided, the injection direction of which may be perpendicular to the steel strip S or at an acute angle θ1, or the injection direction of which may be in a direction different from the above two directions with respect to the steel strip S. Furthermore, although not shown, the injection nozzles may not be provided as a pair, but may be provided on only one side of the steel strip S.

[0015] An inlet seal device 71 is provided at the inlet 7 of the pre-treatment device 10. The inlet seal device 71 sandwiches the steel strip S while transporting it, thereby preventing outside air from entering the pre-treatment device 10 through the inlet 7 and preventing atmospheric gas within the pre-treatment device 10 from being released to the outside.

[0016] The circulation flow path 4 is configured to circulate the atmospheric gas within the conveying passage 3 through which the steel strip S is conveyed in the induction heating device 1. In this embodiment, the induction heating device 1 is equipped with a solenoid type induction heating device 11 and a transverse type induction heating device 12, and therefore, the induction heating devices 11, 12 are provided with circulation flow paths 41, 42, respectively.

[0017] The circulation flow path 41 circulates the atmospheric gas in the transport passage 31 through which the steel strip S is transported in the solenoid induction heating device 11. The circulation flow path 41 is provided with a circulation fan 411, a gas purification device 412, an oxygen concentration measuring device 51, an oxygen-containing gas supply device 61, a dew point measuring device 413, and a high dew point gas supply device 414. The circulation flow path 41 is provided with a dew point control device 410 that adjusts the dew point of the atmospheric gas, and the dew point control device 410 includes at least one of a deoxidizing device 412a and dehumidifying devices 412b and 412c included in the gas purification device 412, and a high dew point gas supply device 414. In the circulation flow path 41, the atmospheric gas in the conveying passage 31 is sucked in by the circulation fan 411 from the processing upstream side of the solenoid type induction heating device 11, and the oxygen concentration and dew point of the atmospheric gas in the circulation flow path 41 are adjusted by the gas purifier 412, the oxygen concentration measuring device 51, the oxygen-containing gas supply device 61, the dew point measuring device 413, and the high dew point gas supply device 414. The adjusted atmospheric gas is then supplied to the injection nozzles 21a, 21b, 22a, and 22b, and is sprayed from the injection nozzles 21a, 21b, 22a, and 22b directly toward the steel strip S. The atmospheric gas sprayed from the injection nozzles 21a, 21b, 22a, and 22b passes through the conveying passage 31 while being used to oxidize the steel strip S (in this embodiment, it flows in the opposite direction to the conveying direction X of the steel strip S), is sucked in by the circulation fan 411, and circulates through the circulation flow path 41 again.

[0018] The gas purification system 412 includes a deoxidizer 412a and dehumidifying towers 412b and 412c. The deoxidizer 412a removes oxygen from the ambient gas in the transport passage 31 sucked in by the circulation fan 411. The dehumidifying towers 412b and 412c are located downstream of the deoxidizer 412a. The dehumidifying towers 412b and 412c contain desiccants that adsorb (dehumidify) moisture from the gas from which oxygen has been removed by the deoxidizer 412a. In actual use, one of the dehumidifying towers 412b and 412c is used to perform dehumidification, while the other performs a regeneration cycle (heating the desiccant to release the adsorbed moisture) to release the adsorbed moisture. By switching between these operations at regular intervals, the dehumidifying capabilities of the dehumidifying towers 412b and 412c are maintained.

[0019] It is not necessary for the entire amount of the atmospheric gas in the transfer passage 31 to pass through the gas purifier 412, and since the gas purifier 412 is used when the atmospheric gas has a high oxygen concentration or a high dew point, when this is not necessary, part of the atmospheric gas may bypass the gas purifier 412. That is, the circulation passage 41 is provided with a bypass passage 41a that bypasses the gas purifier 412, and by opening the on-off valve 415 or adjusting the flow rate when necessary, the accuracy of adjusting the atmospheric gas circulating through the circulation passage 41 can be improved.

[0020] The oxygen concentration measuring device 51 is disposed downstream of the oxygen-containing gas supply device 61 and is configured to measure the oxygen concentration of the gas flowing through the circulation flow path 41. The oxygen-containing gas supply device 61 is a device that supplies an oxygen-containing gas (including pure oxygen and air) to the circulation flow path 41, and when pure oxygen is used, for example, the oxygen-containing gas supply device 61 is equipped with an oxygen tank 61a and an oxygen supply valve 61b connected to the oxygen tank 61a. Based on the measurement results of the oxygen concentration measuring device 51, the oxygen-containing gas supply device 61 adjusts the opening degree of the oxygen supply valve 61b to adjust the amount of oxygen supplied to the circulation flow path 41.

[0021] In this embodiment, the dew point measuring device 413 is disposed downstream of the oxygen concentration measuring device 51 and measures the dew point of the gas flowing through the circulation flow path 41. The high dew point gas supply device 414 is a device that supplies a high dew point gas to the circulation flow path 41 and includes a humidifier 414a and a high dew point gas supply valve 414b connected to the humidifier 414a. In this embodiment, the high dew point gas supply device 414 is disposed upstream of the oxygen-containing gas supply device 61 and, based on the measurement results of the dew point measuring device 413, operates the humidifier 414a and adjusts the aperture of the high dew point gas supply valve 414b to adjust the amount of high dew point gas supplied to the circulation flow path 41. Note that the dew point measuring device 413 may be disposed upstream of the oxygen concentration measuring device 51, and the high dew point gas supply device 414 may be disposed downstream of the oxygen-containing gas supply device 61.

[0022] The circulation flow path 42 circulates the atmospheric gas in the transport passage 32 through which the steel strip S is transported in the transverse induction heating device 12. The configuration of the circulation flow path 42 is similar to that of the circulation flow path 41. Specifically, the circulation flow path 42 is provided with a circulation fan 421, a gas purification device 422, an oxygen concentration measuring device 52, an oxygen-containing gas supply device 62, a dew point measuring device 423, and a high dew point gas supply device 424. The circulation flow path 42 is provided with a dew point control device 420 that adjusts the dew point of the atmospheric gas, and the dew point control device 420 includes at least one of a deoxidizing device 422a and dehumidifying devices 422b and 422c included in the gas purification device 422, and a high dew point gas supply device 424. In the circulation flow path 42, the atmospheric gas in the transport passage 32 is sucked in by the circulation fan 421 from the processing upstream side of the transverse induction heating device 12, and the oxygen concentration and dew point of the atmospheric gas in the circulation flow path 42 are adjusted by the gas purification device 422, the oxygen concentration measuring device 52, the oxygen-containing gas supply device 62, the dew point measuring device 423, and the high dew point gas supply device 424. The adjusted atmospheric gas is then supplied to the injection nozzles 23a, 23b, 24a, and 24b, and is sprayed from the injection nozzles 23a, 23b, 24a, and 24b directly toward the steel strip S. The gas sprayed from the injection nozzles 23a, 23b, 24a, and 24b passes through the transport passage 32 while being used to oxidize the steel strip S (in this embodiment, it flows in the opposite direction to the transport direction X of the steel strip S), is sucked in by the circulation fan 421, and circulates again through the circulation flow path 42.

[0023] The gas purification system 422 includes a deoxidizer 422a and dehumidifying towers 422b and 422c. The configuration of the gas purification system 422 is similar to that of the gas purification system 412. The deoxidizer 422a removes oxygen from the ambient gas in the transport passage 32 sucked in by the circulation fan 421. The dehumidifying towers 422b and 422c are located downstream of the deoxidizer 422a. The dehumidifying towers 422b and 422c contain desiccants that adsorb (dehumidify) moisture from the gas from which oxygen has been removed by the deoxidizer 422a. In actual use, one of the dehumidifying towers 422b and 422c is used to perform dehumidification, while the other performs a regeneration cycle (heating the desiccant to release the adsorbed moisture) to release the adsorbed moisture. By switching between these operations at regular intervals, the dehumidifying capabilities of the dehumidifying towers 422b and 422c are maintained.

[0024] Like the circulation flow path 41, the circulation flow path 42 is also provided with a bypass flow path 42a that bypasses the gas purification device 422, and by opening the on-off valve 425 or adjusting the flow rate when necessary, the accuracy of adjusting the ambient gas circulating through the circulation flow path 42 can be improved.

[0025] The oxygen concentration measuring device 52 is disposed downstream of the oxygen-containing gas supply device 62 and is configured to measure the oxygen concentration of the gas flowing through the circulation flow path 42. The oxygen-containing gas supply device 62 is a device that supplies an oxygen-containing gas (including pure oxygen and air) to the circulation flow path 42, and when pure oxygen is used, for example, it is equipped with an oxygen tank 62a and an oxygen supply valve 62b connected to the oxygen tank 62a. The configuration of the oxygen concentration measuring device 52 is similar to that of the oxygen concentration measuring device 51, and the configuration of the oxygen-containing gas supply device 62 is similar to that of the oxygen-containing gas supply device 61. The oxygen-containing gas supply device 62 adjusts the opening degree of the oxygen supply valve 62b based on the measurement results of the oxygen concentration measuring device 52, thereby adjusting the amount of oxygen supplied to the circulation flow path 42.

[0026] In this embodiment, the dew point measuring device 423 is disposed downstream of the oxygen concentration measuring device 52 and measures the dew point of the gas flowing through the circulation flow path 42. The high dew point gas supply device 424 is a device that supplies a high dew point gas to the circulation flow path 42 and includes a humidifier 424a and a high dew point gas supply valve 424b connected to the humidifier 424a. The configuration of the dew point measuring device 423 is similar to that of the dew point measuring device 413, and the configuration of the high dew point gas supply device 424 is similar to that of the high dew point gas supply device 414. In this embodiment, the high dew point gas supply device 424 is disposed upstream of the oxygen-containing gas supply device 62 and, based on the measurement results of the dew point measuring device 423, operates the humidifier 424a and adjusts the aperture of the high dew point gas supply valve 424b to adjust the amount of high dew point gas supplied to the circulation flow path 42. The dew point measuring device 423 may be disposed upstream of the oxygen concentration measuring device 52 , and the high dew point gas supply device 424 may be disposed downstream of the oxygen-containing gas supply device 62 .

[0027] Furthermore, the circulation fan 411 and the circulation fan 421 may be a common unit, and the gas purification device 412 and the gas purification device 422 may be a common unit. Figure 3 is a schematic configuration diagram of a pretreatment device 10 in which the circulation fan 411 and the circulation fan 421 are a common unit, and the gas purification device 412 and the gas purification device 422 are a common unit. As shown in Figure 3, when the circulation fan 411 and the circulation fan 421 are a common unit, and the gas purification device 412 and the gas purification device 422 are a common unit, the flow rate of the circulation flow path 41 and the flow rate of the circulation flow path 42 are individually adjusted by multiple flow rate adjustment valves 43. With this configuration, the cost and installation area of ​​the circulation fan and the gas purification device, which are expensive and large, can be reduced.

[0028] (Treatment of steel strip S by pre-treatment device 10) The steel strip S is carried into the pre-treatment device 10 from the entrance 7. The steel strip S is transported into the pre-treatment device 10 through the entrance seal device 71, which prevents outside air from entering the pre-treatment device 10 from the entrance 7 and prevents atmospheric gas within the pre-treatment device 10 from being released to the outside from the entrance 7.

[0029] The steel strip S is first heat-treated in the solenoid induction heating device 11. The steel strip S is heat-treated in the conveying passage 31 of the solenoid induction heating device 11 in the environment of the atmospheric gas in the conveying passage 31. The atmospheric gas in the conveying passage 31 is circulated by the circulation flow path 41. The atmospheric gas in the conveying passage 31 is sucked in by the circulation fan 411 from the treatment upstream side of the solenoid induction heating device 11 and deoxidized and dehumidified by the gas purifier 412. The gas deoxidized and dehumidified by the gas purifier 412 is supplied with an oxygen-containing gas by the oxygen-containing gas supply device 61 and with a high dew-point gas by the high dew-point gas supply device 414, and adjusted to a desired oxygen concentration and dew point. The amount of oxygen-containing gas supplied by the oxygen-containing gas supply device 61 is controlled based on the measurement results of the oxygen concentration measuring device 51, which measures the oxygen concentration of the gas flowing through the circulation flow path 41. Furthermore, the amount of high dew point gas supplied by the high dew point gas supply device 414 is controlled based on the measurement results of a dew point measuring device 413 that measures the dew point of the gas flowing through the circulation flow path 41. In this way, gas with adjusted oxygen concentration and dew point is directly sprayed from the injection nozzles 21a, 21b, 22a, and 22b toward the steel strip S. The injection nozzles 22a and 22b spray atmospheric gas toward the steel strip S from a direction perpendicular to the steel strip S, while the injection nozzles 21a and 21b located upstream of the injection nozzles 22a and 22b spray atmospheric gas toward the steel strip S from a direction forming an acute angle with the steel strip S. The gas sprayed from the injection nozzles 21a, 21b, 22a, and 22b passes through the transport path 31 while being used to oxidize the steel strip S, is sucked in by the circulation fan 411, and circulates again through the circulation flow path 41.

[0030] The steel strip S heat-treated in the solenoid induction heating device 11 is then heat-treated in the transverse induction heating device 12. The steel strip S is heat-treated in the conveying passage 32 of the transverse induction heating device 12 in the environment of the atmospheric gas in the conveying passage 32. The atmospheric gas in the conveying passage 32 is circulated by the circulation flow path 42. The atmospheric gas in the conveying passage 32 is sucked by the circulation fan 421 from the treatment upstream side of the transverse induction heating device 12 and deoxidized and dehumidified by the gas purifier 422. The gas deoxidized and dehumidified by the gas purifier 422 is supplied with an oxygen-containing gas by the oxygen-containing gas supply device 62 and a high dew-point gas by the high dew-point gas supply device 424, and adjusted to a desired oxygen concentration and dew point. The amount of oxygen-containing gas supplied by the oxygen-containing gas supply device 62 is controlled based on the measurement results of the oxygen concentration measuring device 52, which measures the oxygen concentration of the gas flowing through the circulation flow path 42. Furthermore, the amount of high dew point gas supplied by the high dew point gas supply device 424 is controlled based on the measurement results of a dew point measuring device 423 that measures the dew point of the gas flowing through the circulation flow path 42. In this manner, atmospheric gas with adjusted oxygen concentration and dew point is directly sprayed from the injection nozzles 23a, 23b, 24a, and 24b toward the steel strip S. The injection nozzles 24a and 24b spray the atmospheric gas toward the steel strip S from a direction perpendicular to the steel strip S, while the injection nozzles 23a and 23b located upstream of the injection nozzles 24a and 24b spray the atmospheric gas toward the steel strip S from a direction forming an acute angle with the steel strip S. The gas sprayed from the injection nozzles 23a, 23b, 24a, and 24b passes through the transport path 32 while being used to oxidize the steel strip S, is sucked in by the circulation fan 421, and circulates again through the circulation flow path 42.

[0031] The steel strip S that has been heat-treated in the transverse type induction heating device 12 is conveyed to the outlet 9 of the pretreatment device 10 after being changed in its conveying direction to a horizontal direction by, for example, a roll 83, and then sent to a reduction furnace 100 located downstream of the pretreatment device 10 and performing a heat treatment in a reducing atmosphere. Here, an induction heating device that is advantageous for rapidly heating the steel strip S is used for heating, but other heating methods such as an electric heater or a radiant tube burner may also be used.

[0032] In the above embodiment, the steel strip S is transported from bottom to top within the vertical pre-treatment device 10, but it may also be transported from top to bottom, or the steel strip S may be transported from side to side within the horizontal pre-treatment device 10. It may also be transported obliquely within an inclined furnace body. In such cases, the transport is also performed by winding the steel strip S into a coil downstream of the reducing furnace 100.

[0033] The pretreatment device 10 having the above-described configuration can achieve the following effects.

[0034] (1) Based on the measurement results of the oxygen concentration in the circulation flow path 4 by the oxygen concentration measuring device 5, the oxygen concentration of the atmospheric gas sprayed from the spray nozzle 2 can be adjusted by adjusting the amount of oxygen-containing gas supplied to the circulation flow path 4 by the oxygen-containing gas supply device 6. Furthermore, by spraying atmospheric gas with an adjusted oxygen concentration directly from the spray nozzle 2 onto the steel strip S from a short distance, the entire surface of the steel strip S can be reliably oxidized, and the degree of oxidation of the surface of the steel strip S can be actively adjusted, compared to when the steel strip S is simply transported in an atmosphere with an elevated oxygen concentration. Furthermore, by circulating the atmospheric gas within the transport path 3 through which the steel strip S is transported, the atmospheric gas that oxidizes the steel strip S can be used efficiently.

[0035] (2) The injection nozzle 2 injects the atmospheric gas in at least two directions, namely, a direction perpendicular to the steel strip S and directions forming acute angles θ1 and θ2 with respect to the steel strip S, thereby improving the oxidation effect on the surface of the steel strip S while also promoting oxidation by combining the effect of gradual oxidation caused by oblique injection. In addition, when the atmospheric gas is injected in a direction perpendicular to the steel strip S, the atmospheric gas hits the steel strip S over the shortest distance without losing momentum, thereby improving the oxidation effect. In addition, by injecting the atmospheric gas in multiple directions, the opportunity for the atmospheric gas to come into contact with the steel strip S can be increased.

[0036] (3) Deoxygenation devices 412a, 422a are disposed in the circulation flow path 4, and oxygen-containing gas supply devices 61, 62 are disposed downstream thereof, so that when the oxygen concentration of the atmospheric gas in the circulation flow path 4 becomes high, the excess oxygen can be absorbed by the deoxygenation devices 412a, 422a to reduce the oxygen concentration, and when the oxygen concentration of the atmospheric gas in the circulation flow path 4 becomes low, the oxygen-containing gas supply devices 61, 62 can add oxygen to make up for the shortage, to increase the oxygen concentration. Therefore, the oxygen concentration of the atmospheric gas sprayed from the spray nozzle 2 can be more reliably adjusted.

[0037] (4) High dew point gas supply devices 414, 424 are disposed in the circulation flow path 4, and when the dew point of the atmospheric gas in the circulation flow path 4 is low, a high dew point gas can be supplied to the circulation flow path 4 to raise the dew point of the atmospheric gas in the circulation flow path 4. Dehumidifiers 412b, 412c, 422b, and 422c are disposed in the circulation flow path 4, and when the dew point of the atmospheric gas in the circulation flow path 4 is high, the moisture in the atmospheric gas in the circulation flow path 4 can be absorbed by the dehumidifiers 412b, 412c, 422b, and 422c to lower the dew point of the atmosphere in the circulation flow path 4. Therefore, the dew point of the atmospheric gas in the circulation flow path 4 can be more reliably adjusted.

[0038] (5) The induction heating device 1 includes a solenoid induction heating device 11 and a transverse induction heating device 12. The solenoid induction heating device 11 is provided upstream of the transverse induction heating device 12. The solenoid induction heating device 11 provides excellent temperature uniformity across the width of the steel strip S, but its heating efficiency decreases when the steel strip S is thin or at temperatures above the Curie point. On the other hand, the transverse induction heating device 12 is superior in that its heating efficiency does not decrease even when the steel strip S is thin. Taking advantage of these characteristics, an appropriate induction heating device 1 can be selected depending on the heat treatment temperature, material, and shape of the steel strip. Therefore, when using both the solenoid induction heating device 11 and the transverse induction heating device 12, it is preferable to first heat the steel strip S to a temperature near the Curie point using the solenoid induction heating device 11 and then further heat the steel strip S using the transverse induction heating device 12.

[0039] (6) The solenoid type induction heating device 11 is provided with a circulation flow path 41, and the transverse type induction heating device 12 is provided with a circulation flow path 42, so that an appropriate atmosphere for induction heating can be created depending on the type of induction heating device.

[0040] (7) By using the induction heating device 1 as the heating device of the pretreatment device 10, the volume of the conveying passages 31, 32 for the steel strip S within the induction heating device 1 can be reduced, and the atmosphere within the conveying passages 31, 32 can be adjusted more easily, accurately, and quickly. That is, the atmosphere within the conveying passages 31, 32, which has a small volume within the induction heating device 1 and is difficult to circulate, is forcibly circulated by the circulation passages 41, 42, and the atmospheric gas is sprayed onto the steel strip S while controlling the conditions that affect the formation of an oxide film on the surface of the steel strip S. This allows for more accurate and quick control of the atmospheric condition, and stable formation of an oxide film. In this embodiment, the oxygen concentration and dew point of the atmospheric gas are adjusted in the circulation passages 41, 42, but other conditions of the atmospheric gas that affect the surface oxidation of the steel strip S, such as the temperature of the atmospheric gas, may also be adjusted in the circulation passages 41, 42.

[0041] In the above embodiment, each injection nozzle 2 is a nozzle that injects atmospheric gas in one direction, but a pair of injection nozzles 2 may each inject atmospheric gas in two directions. Figure 4 is an enlarged schematic view of the injection nozzle portion of a pair of injection nozzles 25a, 25b, each of which injects atmospheric gas in two directions. As shown in Figure 4, injection nozzles 25a, 25b include inner cylindrical portions 25a1, 25b1 and outer cylindrical portions 25a2, 25b2. The inner cylindrical portions 25a1, 25b1 and the outer cylindrical portions 25a2, 25b2 are each configured to be rotatable about their centers.

[0042] In the injection nozzle 25a, the inner cylindrical portion 25a1 has two openings 26a1 and 26a2, and the outer cylindrical portion 25a2 has two openings 27a1 and 27a2. By rotating the inner cylindrical portion 25a1 and the outer cylindrical portion 25a2, the openings 26a1 and 26a2 of the inner cylindrical portion 25a1 are connected to the openings 27a1 and 27a2 of the outer cylindrical portion 25a2, respectively, so that atmospheric gas is injected in two directions. The openings 26a1 and 26a2 of the inner cylindrical portion 25a1 have larger opening areas than the openings 27a1 and 27a2 of the outer cylindrical portion 25a2.

[0043] Similarly, in the injection nozzle 25b, the inner cylindrical portion 25b1 has two openings 26b1 and 26b2, and the outer cylindrical portion 25b2 has two openings 27b1 and 27b2. By rotating the inner cylindrical portion 25b1 and the outer cylindrical portion 25b2, the openings 26b1 and 26b2 of the inner cylindrical portion 25b1 are connected to the openings 27b1 and 27b2 of the outer cylindrical portion 25b2, respectively, so that atmospheric gas is injected in two directions. Note that the openings 26b1 and 26b2 of the inner cylindrical portion 25b1 have larger opening areas than the openings 27b1 and 27b2 of the outer cylindrical portion 25b2.

[0044] The rotation of the inner cylindrical portions 25a1, 25b1 and the outer cylindrical portions 25a2, 25b2 may be performed automatically or manually. The rotation of the inner cylindrical portions 25a1, 25b1 and the outer cylindrical portions 25a2, 25b2 may be fixed at a predetermined angle so that one of the two spray directions of the spray nozzles 25a, 25b is perpendicular to the steel strip S and the other is set to a direction forming an acute angle θ2 with respect to the steel strip S.

[0045] Furthermore, each of the pair of injection nozzles 25a, 25b that inject atmospheric gas in two directions may be configured so that the two injection directions can be changed. The injection nozzles are preferably provided as a pair so as to face each other perpendicularly to the steel strip S, and it is further preferable that the injection angles of the injection nozzles provided as a pair are symmetrical with respect to the steel strip S. According to this configuration, the injection direction of the injection nozzles 25a, 25b is configured to be changeable, so that oxygen can be directly injected at a desired position on the surface of the steel strip S.

[0046] Yet another embodiment of the injection nozzle is shown in Figures 5 to 7. In Figures 5 to 7, only one side of the injection nozzle is shown as a representative example.

[0047] Figure 5 shows the initial state of the injection nozzle 28. The injection nozzle 28 comprises a fixed outer peripheral cylindrical portion 101 and a rotatable inner peripheral cylindrical portion 111. In order to inject the atmospheric gas perpendicularly to the steel strip S, an opening 102 is provided in the outer peripheral cylindrical portion 101, and an opening 112 is provided in the inner peripheral cylindrical portion 111. The opening 112 in the inner peripheral cylindrical portion 111 is formed to be longer in the circumferential direction than the opening 102 in the outer peripheral cylindrical portion 101, as indicated by X in Figures 5 to 7, so that the atmospheric gas can be injected even when the inner peripheral cylindrical portion 111 is rotated.

[0048] Furthermore, in order to spray the atmospheric gas obliquely onto the steel strip S, an opening 103 is further provided in the outer cylindrical portion 101, and an opening 113 is further provided in the inner cylindrical portion 111. The opening 103 in the outer cylindrical portion 101 is formed to be longer in the circumferential direction than the opening 113 in the inner cylindrical portion 111, as shown by Y in Figures 5 to 7, so that the atmospheric gas can be sprayed even when the inner cylindrical portion 111 is rotated.

[0049] Furthermore, in order to supply the atmospheric gas to the injection nozzle, an opening 104 is further provided in the outer cylindrical portion 101, and an opening 114 is further provided in the inner cylindrical portion 111. The opening 114 in the inner cylindrical portion 111 is formed to be longer in the circumferential direction than the opening 104 in the outer cylindrical portion 101, as indicated by Z in Figures 5 to 7, so that the atmospheric gas can flow into the injection nozzle 28 even when the inner cylindrical portion 111 is rotated.

[0050] Figure 6 is a schematic diagram showing a state in which the inner peripheral cylindrical portion 111 has been rotated from the state shown in Figure 5, and Figure 7 is a schematic diagram showing a state in which the inner peripheral cylindrical portion 111 has been rotated from the state shown in Figure 5 in the opposite direction to that shown in Figure 6. With the above-mentioned configuration, as shown in Figures 6 and 7, the inner peripheral cylindrical portion 111 can be rotated to change the oblique injection direction of the injection nozzle 28 as shown in θa, θb, and θc in Figures 5 to 7. Therefore, by configuring the injection nozzle so that the injection direction can be changed, atmospheric gas can be directly injected at a desired position on the surface of the steel strip S.

[0051] In the above embodiment, the solenoid induction heating device 11 and the transverse induction heating device 12 are provided as the induction heating device 1, but only one of the induction heating devices may be provided, or three or more induction heating devices may be provided. However, when both the solenoid induction heating device 11 and the transverse induction heating device 12 are provided, it is preferable that the solenoid induction heating device 11 be provided upstream of the transverse induction heating device 12 for the reasons described above.

[0052] In the above embodiment, each induction heating device 1 is provided with a circulation flow path 4 (the solenoid type induction heating device 11 is provided with a circulation flow path 41, and the transverse type induction heating device 12 is provided with a circulation flow path 42), but if the heating atmosphere of the induction heating devices 1 is the same, the circulation flow paths may be shared. Furthermore, although not shown, the temperature of the steel strip S may be monitored and the atmospheric gas in the circulation flow path of only the necessary induction heating device may be adjusted.

[0053] In the above embodiment, the injection nozzle 2 is provided downstream of the induction heating device 1, but it may also be provided upstream of the induction heating device 1. In this case, the gas injected from the injection nozzle 2 flows through the transport passage 3 from the upstream side to the downstream side. Furthermore, when a plurality of induction heating devices 1 are provided, the injection nozzle 2 may be provided downstream of one induction heating device and upstream of the other induction heating device.

[0054] The present invention and embodiments can be summarized as follows.

[0055] (1) One embodiment of the present invention is a pretreatment device provided upstream of a reduction furnace for removing an oxide film from a steel strip, the pretreatment device comprising: an induction heating device for heating the steel strip by induction heating; an injection nozzle provided upstream or downstream of the induction heating device for injecting gas directly onto the steel strip; a circulation flow path for circulating atmospheric gas within a transport passage through which the steel strip is transported in the induction heating device; an oxygen concentration measuring device for measuring the oxygen concentration in the circulation flow path; and an oxygen-containing gas supply device for adjusting the amount of oxygen-containing gas supplied to the circulation flow path based on the measurement results of the oxygen concentration measuring device, and the injection nozzle is configured to inject the atmospheric gas in the circulation flow path, to which oxygen-containing gas has been supplied by the oxygen-containing gas supply device, onto the steel strip.

[0056] According to the above-mentioned configuration (1), the oxygen concentration of the gas injected from the injection nozzle can be adjusted by adjusting the amount of oxygen-containing gas supplied to the circulation flow path based on the measurement results of the oxygen concentration in the circulation flow path. Furthermore, by directly injecting gas with an adjusted oxygen concentration from the injection nozzle onto the steel strip, the surface of the steel strip can be reliably oxidized and the degree of oxidation can be adjusted. Furthermore, by circulating the atmospheric gas in the conveying passage through which the steel strip is conveyed, the atmospheric gas that oxidizes the steel strip can be used efficiently.

[0057] (2) In the above configuration (1), a dew point control device for adjusting the dew point of the atmospheric gas is disposed in the circulation flow path.

[0058] According to the above configuration (2), the dew point control device controls the dew point of the atmospheric gas in the circulation flow path, thereby making it possible to adjust the oxidation of the steel strip.

[0059] (3) In the configuration (2), the dew point control device includes at least one of a deoxidizer, a dehumidifier, and a high dew point gas supply device.

[0060] According to the configuration (3), the dew point control device includes at least one of a deoxidizer, a dehumidifier, and a high dew point gas supply device, so that the dew point of the ambient gas in the circulation flow path can be controlled.

[0061] (4) In the configuration (2), the dew point control device includes a deoxidizer and a dehumidifier, and includes a bypass flow path that bypasses the deoxidizer and the dehumidifier.

[0062] According to the configuration (4), by providing a bypass flow path that bypasses the deoxidizer and dehumidifier, when there is no need to lower the dew point of the atmospheric gas in the circulation flow path, the deoxidizer and dehumidifier are not used, thereby extending their lifespan.

[0063] (5) In the above-mentioned configuration (1), the injection nozzle is configured to inject the atmospheric gas toward the steel strip in at least two directions.

[0064] According to the above configuration (5), the injection nozzle injects the atmospheric gas toward the steel strip in at least two directions, thereby increasing the opportunities for the atmospheric gas to come into contact with the steel strip.

[0065] (6) In the above configuration (5), at least one of the spray directions of the spray nozzle is perpendicular to the steel strip.

[0066] According to the above configuration (6), when the atmospheric gas is injected in a direction perpendicular to the steel strip, the atmospheric gas hits the steel strip over the shortest distance without losing momentum, thereby improving the oxidation effect.

[0067] (7) In the above configuration (1), the injection direction of the injection nozzle is configured to be changeable.

[0068] According to the above configuration (7), the injection direction of the injection nozzle is configured to be changeable, so that the atmospheric gas can be injected directly onto a desired position on the surface of the steel strip.

[0069] (8) In any one of the configurations (1) to (7), the induction heating device includes a solenoid type induction heating device and a transverse type induction heating device, and the solenoid type induction heating device is provided upstream of the processing of the transverse type induction heating device.

[0070] According to the above configuration (7), it is possible to heat a thin steel strip to a high temperature while making the temperature uniform in the width direction of the thin steel strip.

[0071] Various modifications and variations may be made without departing from the spirit and scope of the present invention as set forth in the following claims.

[0072] The present invention can provide a pretreatment device that can adjust the degree of oxidation of a steel strip, and is therefore of great industrial value.

[0073] REFERENCE SIGNS LIST 1 induction heating device 11 solenoid type induction heating device 12 transverse type induction heating device 2 injection nozzle 21a injection nozzle 21b injection nozzle 22a injection nozzle 22b injection nozzle 23a injection nozzle 23b injection nozzle 24a injection nozzle 24b injection nozzle 25a injection nozzle 25a1 inner peripheral cylindrical portion 25a2 outer peripheral cylindrical portion 26a1 opening 26a2 opening 27a1 opening 27a2 opening 25b injection nozzle 25b1 inner peripheral cylindrical portion 25b2 outer peripheral cylindrical portion 26b1 opening 26b2 opening 27b1 opening 27b2 opening 28 injection nozzle 101 outer peripheral cylindrical portion 111 inner peripheral cylindrical portion 102 opening 112 opening 103 opening 113 Opening 104 Opening 114 Opening 3 Transfer passage 31 Transfer passage 32 Transfer passage 4 Circulation passage 41 Circulation passage 41a Bypass passage 410 Dew point control device 411 Circulation fan 412 Gas purification device 412a Deoxidation device 412b Dehumidification tower 412c Dehumidification tower 413 Dew point measurement device 414 High dew point gas supply device 414a Humidification device 414b High dew point gas supply valve 415 On-off valve 42 Circulation passage 42a Bypass passage 420 Dew point control device 421 Circulation fan 422 Gas purification device 422a Deoxidation device 422b Dehumidification tower 422c Dehumidification tower 423 Dew point measurement device 424 High dew point gas supply device 424a Humidification device 424b High dew point gas supply valve 425 On-off valve 43 Flow rate adjustment valve 5 Oxygen concentration measuring device 51 Oxygen concentration measuring device 52 Oxygen concentration measuring device 6 Oxygen-containing gas supply device 61 Oxygen-containing gas supply device 62 Oxygen-containing gas supply device 61a Oxygen tank 61b Oxygen supply valve 62a Oxygen tank 62b Oxygen supply valve 7 Inlet 71 Inlet sealing device 83 Roll 9 Outlet 10 Pretreatment device 100 Reduction furnace S Steel strip A Injection nozzle

Claims

1. A pre-treatment device provided upstream of a reduction furnace for removing an oxide film from a steel strip, comprising: an induction heating device which heats the steel strip by induction heating; an injection nozzle provided upstream or downstream of the induction heating device which directly injects atmospheric gas onto the steel strip; a circulation flow path in the induction heating device which circulates atmospheric gas within a transport passage through which the steel strip is transported; an oxygen concentration measuring device which measures the oxygen concentration in the circulation flow path; and an oxygen-containing gas supplying device which adjusts the amount of oxygen-containing gas supplied to the circulation flow path based on the measurement results of the oxygen concentration measuring device, wherein the injection nozzle is adapted to inject atmospheric gas from the circulation flow path to which oxygen-containing gas has been supplied by the oxygen-containing gas supplying device onto the steel strip; and a dew point control device which adjusts the dew point of the atmospheric gas is provided in the circulation flow path.

2. The pretreatment device of claim 1, wherein the dew point control device comprises at least one of a deoxidizer, a dehumidifier, and a high dew point gas supply device.

3. The pretreatment device according to claim 1, wherein the dew point control device comprises a deoxidizer and a dehumidifier, and further comprises a bypass passage that bypasses the deoxidizer and the dehumidifier.

4. A pre-treatment device provided upstream of a reduction furnace for removing an oxide film from a steel strip, comprising: an induction heating device for heating the steel strip by induction heating; an injection nozzle provided upstream or downstream of the induction heating device for directly injecting atmospheric gas onto the steel strip; a circulation flow path for circulating atmospheric gas within a transport passage through which the steel strip is transported in the induction heating device; an oxygen concentration measuring device for measuring the oxygen concentration in the circulation flow path; and an oxygen-containing gas supply device for adjusting the amount of oxygen-containing gas supplied to the circulation flow path based on the measurement results of the oxygen concentration measuring device, wherein the injection nozzle is configured to inject atmospheric gas from the circulation flow path to which oxygen-containing gas has been supplied by the oxygen-containing gas supply device onto the steel strip, and the injection nozzle is configured to inject atmospheric gas in at least two directions toward the steel strip.

5. The pretreatment device according to claim 4, wherein at least one of the spray directions of said spray nozzles is perpendicular to the steel strip.

6. A pre-treatment device provided upstream of a reduction furnace for removing an oxide film from a steel strip, comprising: an induction heating device for heating the steel strip by induction heating; an injection nozzle provided upstream or downstream of the induction heating device for directly injecting atmospheric gas onto the steel strip; a circulation flow path for circulating atmospheric gas within a transport passage through which the steel strip is transported in the induction heating device; an oxygen concentration measuring device for measuring the oxygen concentration in the circulation flow path; and an oxygen-containing gas supply device for adjusting the amount of oxygen-containing gas supplied to the circulation flow path based on the measurement results of the oxygen concentration measuring device, wherein the injection nozzle is configured to inject atmospheric gas from the circulation flow path to which oxygen-containing gas has been supplied by the oxygen-containing gas supply device onto the steel strip, and the injection direction of the injection nozzle is configured to be changeable.

7. A pretreatment device as described in any one of claims 1 to 6, wherein the induction heating device comprises a solenoid type induction heating device and a transverse type induction heating device, and the solenoid type induction heating device is provided upstream of the processing of the transverse type induction heating device.

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