Continuous processing equipment for metal strips

Abstract

To realize efficient high-temperature heating and to suppress or control scale generation on the metal strip surface by appropriately using induction heating to heat the metal strip under atmospheric control.SOLUTION: There is provided a continuous treatment facility for metal strips in which metal strips continuously conveyed are treated, which is equipped with atmosphere control means for controlling the atmosphere in the space through which the metal strips pass, heating means for heating the metal strips by induction heating using both the LF and TF methods in the space, and cooling means for cooling the metal strips heated in the space.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an installation for the continuous treatment of metal strips. [Background technology]

[0002] In furnaces that heat treat metal materials in high-temperature atmospheres, reducing gases such as hydrogen and carbon monoxide are used to heat the material, or indirect heating using radiant tubes is used to prevent oxidation of the material. Furthermore, for continuous annealing of steel sheets, such as stainless steel sheets, which have low emissivity surfaces but require high-temperature heating, atmospheric annealing using gas burners has been used.

[0003] However, when using radiative heat transfer (e.g., gas burners) to heat the steel sheet, the heat transfer capacity decreases as the temperature difference between the steel sheet and the ambient temperature decreases. Therefore, a longer heating length is required for high-temperature heating. Furthermore, when annealing in air, a tough oxide film called scale forms on the steel sheet surface, necessitating a descaling process (hereinafter also referred to as descaling) to remove the scale after annealing. When the scale is tough, descaling is performed using mechanical descaling, a salt bath using molten salt, or pickling. However, when the scale is tough, strong acids are used for pickling, which results in a significant wastewater treatment burden. On the other hand, when reducing gases such as hydrogen or carbon monoxide are used to prevent oxidation of the material during heat treatment, measures must be taken to prevent unintended carburization. Furthermore, these gases are explosive, necessitating explosion-proof measures.

[0004] In response to this, Patent Document 1 describes a technology in which an electric heating device is provided in the heater of an annealing furnace to maintain a non-oxidizing atmosphere or a high-concentration hydrogen atmosphere inside the furnace. Electrical heating does not reduce the heating rate even in high-temperature regions, so it is possible to prevent the equipment from becoming too long. Furthermore, because annealing can be performed under a controlled atmosphere, no scale is generated on the steel sheet surface, and the pickling process for removing the scale can be simplified or omitted. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-278679 Summary of the Invention [Problem to be solved by the invention]

[0006] When resistance heating is used as in Patent Document 1, it is possible to increase the heating rate and heat in a controlled atmosphere, but because current is passed through the steel sheet by contacting it with a current-carrying roll, spark marks are likely to occur on the steel sheet surface. Induction heating is considered to be a method that does not cause spark marks and that allows heating in a controlled atmosphere, but Patent Document 1 states that induction heating cannot be used to heat austenitic stainless steel sheets, and that it is difficult to use for ferritic stainless steel sheets because an extremely high frequency is required.

[0007] As described in Patent Document 1, LF-type induction heating (Longitudinal Flux Induction Heating), which generates a magnetic flux that penetrates the steel sheet in the longitudinal direction and generates an induced current that circulates within the steel sheet's widthwise cross section, is unable to heat non-magnetic steel sheets such as austenitic stainless steel sheets or thin steel sheets that have lost their magnetism due to their temperature exceeding the Curie point. However, due to the penetration depth of the high-frequency current, the currents flowing through the steel sheet cross section tend to flow in opposite directions on the front and back of the steel sheet, canceling each other out and preventing current flow, making it impossible to heat. However, according to extensive research by the present inventors, TF-type induction heating (Transverse Flux Induction Heating), which generates a magnetic flux that penetrates the steel sheet in the thickness direction and generates an induced current that circulates along the steel sheet surface, is capable of induction heating non-magnetic steel sheets or steel sheets whose temperature exceeds the Curie point.

[0008] Therefore, the present invention aims to provide continuous processing equipment for metal strips that can achieve efficient high-temperature heating by appropriately utilizing induction heating to heat metal strips under a controlled atmosphere, while suppressing, controlling, or preventing the formation of scale on the surface of the metal strips, and that is capable of performing a variety of heat treatments. [Means for solving the problem]

[0009] [1] A continuous processing equipment for metal strips that processes continuously transported metal strips, comprising: an atmosphere control means for controlling the atmosphere in a space through which the metal strips pass; a heating means for heating the metal strips in the space by induction heating using both the LF method and the TF method; and a cooling means for cooling the metal strips that have been heated in the space. [2] The continuous processing equipment for metal strips described in [1], further comprising a heat insulation means for keeping the metal strips heated in the space warm, and the cooling means for cooling the metal strips that have been heated in the space and then kept warm. [3] The continuous processing equipment for metal strips described in [2], wherein the heat retention means includes a plurality of heating devices and a plurality of cooling devices arranged alternately along the conveying direction of the metal strips, and the plurality of heating devices and the plurality of cooling devices can each be individually switched on and off. [4] The continuous processing equipment for metal strips according to [3], further comprising a partition wall that separates the alternatingly arranged heating devices and cooling devices in the conveying direction of the metal strips. [5] A continuous processing facility for metal strips according to any one of [1] to [4], further comprising a descaling means for descaling the metal strips and a switching means for switching whether or not the metal strips use the descaling means. [6] The continuous processing equipment for metal strips described in [5], wherein the descaling means includes a pickling tank, and the switching means includes a roll that supports the metal strip transported above the pickling tank and is movable along the transport direction of the metal strip. [7] A continuous processing facility for metal strips according to any one of [1] to [6], wherein the atmosphere control means creates a non-oxidizing atmosphere in the space and controls the hydrogen concentration in the space to 4% by volume or less. [Effects of the Invention]

[0010] According to the above configuration, by appropriately utilizing induction heating to heat a metal strip under a controlled atmosphere, efficient high-temperature heating can be achieved, and the generation of scale on the surface of the metal strip can be suppressed, controlled, or prevented, thereby enabling a variety of heat treatments to be performed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing a schematic configuration of a continuous processing facility for a metal strip according to an embodiment of the present invention. [Figure 2A] FIG. 2 is a diagram showing an example of a combination of an LF type and a TF type induction heating device in the example shown in FIG. 1. [Figure 2B] FIG. 2 is a diagram showing an example of a combination of an LF type and a TF type induction heating device in the example shown in FIG. 1. [Figure 2C] FIG. 2 is a diagram showing an example of a combination of an LF type and a TF type induction heating device in the example shown in FIG. 1. [Figure 2D] FIG. 2 is a diagram showing an example of a combination of an LF type and a TF type induction heating device in the example shown in FIG. 1. [Figure 3] FIG. 2 is a diagram showing a specific example of the arrangement of temperature control means in the example shown in FIG. [Figure 4] FIG. 4 is a diagram showing a modification of the arrangement example shown in FIG. 3. [Figure 5] FIG. 2 is a diagram showing a specific example of the arrangement of pickling means in the example shown in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0013] FIG. 1 is a diagram showing a schematic configuration of a continuous processing equipment for metal strips according to one embodiment of the present invention. The continuous processing equipment 10 processes a continuously transported metal strip S. The continuous processing equipment 10 has a heat treatment space 120 sealed with sealing devices 111 and 112 and with a controllable internal atmosphere. In the illustrated example, the heat treatment space 120 includes a heating chamber 121, a cooling chamber 122, a soaking chamber 123, and a cooling chamber 124. Each chamber is connected by a hood 125. The heat treatment space 120 functions as an atmosphere control means for controlling the gas atmosphere, dew point, and other aspects of the heat treatment space 120 through which the metal strip S passes, for example, by connecting a gas supply device or moisture supply device (not shown). The atmosphere in the heat treatment space 120 is controlled to, for example, a non-oxidizing atmosphere. The atmosphere in the heat treatment space 120 may also be controlled so that the hydrogen concentration is 4% by volume or less.

[0014] The heating chamber 121 is provided with a heating means 130 that heats the metal band S by induction heating using a combination of an LF-type induction heating device 131 and a TF-type induction heating device 132. The LF-type induction heating device 131 generates a magnetic flux that penetrates the metal band S in the longitudinal direction by, for example, passing a high-frequency current through a solenoid coil surrounding the outer periphery of the metal band S, and generates an induction current that circulates within the widthwise cross section of the metal band S to heat the metal band S. On the other hand, the TF-type induction heating device 132, for example, has a magnetic core disposed opposite an induction coil disposed opposite the plate surface of the metal band S, and passes a high-frequency current through it to generate a magnetic flux that penetrates the metal band S in the thickness direction, and generates an induction current that circulates in the area along the plate surface of the metal band S to heat the steel plate.

[0015] When induction heating is performed using a TF type induction heating device such as the one described above, the temperature of the edge portions of the metal strip S tends to become high, so the induction heating device may include a shielding member that shields the edge portions from excess magnetic flux, or a device that controls the strength and direction of the magnetic flux generated by the induction coil so that the magnetic flux is concentrated in areas other than the edge portions where there is a shortage of magnetic flux.

[0016] Among the induction heating devices constituting the heating means 130, the LF-type induction heating device (hereinafter also referred to as LF-IH) 131 can heat the metal band S with a uniform temperature distribution and has high power efficiency. However, if the metal band S is made of a non-magnetic or magnetic material and the temperature exceeds the Curie point (generally 730°C to 750°C), the high-frequency current penetrates deep, causing the induced currents on both sides of the metal band S to cancel each other out, making heating difficult. On the other hand, the TF-type induction heating device (hereinafter also referred to as TF-IH) 132 can heat the metal band S even if the metal band S is made of a non-magnetic or magnetic material and the temperature exceeds the Curie point, but compared to the LF-IH, it has a larger temperature deviation within the metal band S and lower power efficiency. Therefore, in this embodiment, the metal band S is effectively heated by combining the LF-IH and TF-IH, as shown in the examples of FIGS. 2A to 2D .

[0017] Figure 2A shows an example of using a TF-IH132 alone. As mentioned above, the TF-IH132 can heat all materials, including non-magnetic materials and magnetic materials above the Curie point. Therefore, using a single TF-IH132 is a highly versatile basic configuration when the required heating capacity is low. Figure 2B shows an example of using two TF-IH132A and 132B units in combination. When higher heating temperatures or faster heating rates are required, the number of TF-IH units can be increased. Figure 2C shows an example of using an LF-IH131 and a TF-IH132 in combination. As mentioned above, for heating magnetic materials and temperatures below the Curie point, the LF-IH131 has the advantage of uniform temperature distribution and high power efficiency. Therefore, when the metal strip S is magnetic, it is efficient to use the LF-IH131 to heat the material up to near the Curie point and then use the TF-IH132 for heating above that temperature range. Figure 2D shows an example of using two LF-IH131A and 131B units in combination with a TF-IH132. In this case, the temperature pattern required for quality control by annealing a magnetic metal strip S is generated by the LF-IH131A and 131B, and the TF-IH132 heats the metal strip S to the final required temperature.

[0018] For example, by configuring the heating means 130 shown in Figure 1 with two LF-IH 131s placed in the front stage and two TF-IH 132s placed in the rear stage, it is possible to realize induction heating in each pattern as shown in Figures 2A to 2D above.

[0019] In this embodiment, by installing the heating means 130, i.e., the main body of the induction heating device, inside the heat treatment space 120 with the atmosphere controlled as described above, there is no need to provide a muffle (partition) structure that not only prevents radiant heat from the induction-heated metal strip and thermally protects the main body of the induction heating device, but also functions as an atmosphere control, and a relatively simple structure is sufficient for the thermal protection measures alone. Furthermore, since only the metal strip S, which is the material to be heated, becomes hot during induction heating and the ambient temperature is relatively low, there is no need to provide an expensive fireproof or heat-insulating structure for the induction heating device.

[0020] Furthermore, TF-IH requires a magnetic flux control device to improve temperature distribution, which makes the equipment structure more complex and expensive than LF-IH. Therefore, if the equipment is configured so that magnetic materials with temperatures below the Curie point are heated with LF-IH, and non-magnetic materials that cannot be heated with LF-IH and magnetic materials with temperatures above the Curie point are heated with TF-IH, the equipment costs are lower than if all temperature ranges were heated with TF-IH alone, and there are advantages in that the temperature deviation is smaller and it is possible to heat to higher temperatures than with regular gas heating.

[0021] In the example shown in FIG. 1 , the cooling chamber 122, the soaking chamber 123, and the cooling chamber 124 are each provided with a temperature control means 140, specifically, cooling means 141 and 143 and a heat retention means 142, for maintaining a predetermined temperature of the metal strip S in each chamber. In this case, the metal strip S is cooled to a predetermined temperature by the cooling means 141 from the temperature achieved by heating by the heating means 130, then maintained at that temperature by the heat retention means 142, and finally cooled to a temperature at which post-processing is possible by the cooling means 143. The temperature change pattern of the metal strip S achieved by the temperature control means 140 is appropriately set, for example, from the perspective of quality control by annealing. For example, the cooling means 141 may be omitted or the heat retention means 142 may be used to maintain the temperature achieved by heating by the heating means 130, or a reheating means (not shown) may be provided to reheat the metal strip S after cooling by the cooling means 141.

[0022] FIG. 3 is a diagram showing a specific example of the arrangement of the temperature control means 140 in the example shown in FIG. 1. In the illustrated example, the cooling means 141 and the heat retention means 142 are integrated. Specifically, a plurality of panel heaters 144, which are heating devices using carbon, SiC, or the like, and a plurality of slit nozzles 145, which are cooling devices, are alternately arranged along the conveyance direction of the metal strip S. The functions of the cooling means 141 or the heat retention means 142 are realized by individually switching on and off the use of each panel heater 144 and slit nozzle 145. For example, the section corresponding to the cooling means 141 may use the slit nozzles 145 but not the panel heaters 144, and the section corresponding to the heat retention means 142 may use the panel heaters 144 but not the slit nozzles 145, or both the panel heaters 144 and the slit nozzles 145 may be used.

[0023] The heat-retaining means 142 keeps the metal strip S warm, for example, to mitigate temperature deviations that occur in a previous induction heating device or to ensure the required heat-retaining time for heat treatment to control the metallographic structure. The cooling means 141 cools the metal strip S to achieve the required cooling rate and cooling temperature for heat treatment to control the metallographic structure. As described above, in this embodiment, the heat-retaining means 142 and the cooling means 141 can be set to any desired zone by individually switching the panel heater 144 and the slit nozzle 145. To prevent the atmospheres from mixing between the zones set in this manner and preventing the intended temperature control of the metal strip S, a partition wall 146 may be provided between the alternatingly arranged panel heaters 144 and the slit nozzle 145 in the conveying direction of the metal strip S, as shown in FIG. 4. In this case, each zone separated by the partition wall 146 is set to either the zone constituting the heat-retaining means 142, the zone constituting the cooling means 141, or neither zone (a zone in which neither the panel heater 144 nor the slit nozzle 145 is used). In this case, the set temperature of the panel heater 144 and the airflow rate of the slit nozzle 145 may be set for each section divided by the partition wall 146 .

[0024] By using the cooling means and heat retention means as described above, for example, temperature deviations within the metal band S caused by heating using the TF-IH 132 in the heating means 130 can be alleviated by the heat retention achieved by the heat retention means 142. Furthermore, the temperature of the metal band S can be maintained for the time required for quality control by annealing, or the metal band S can be cooled at a predetermined cooling rate. In this embodiment, by heating the metal band S by the heating means 130 and controlling the temperature and application time of the metal band S by the temperature control means 140 in the atmosphere-controlled heat treatment space 120, it is possible to suppress the generation of scale on the surface of the metal band S and control the properties of the scale that does occur.

[0025] In the example shown in FIG. 1 , the continuous treatment equipment 10 includes a pickling means 150 constituting a descaling means. The pickling means 150 is located downstream of the heating means 130 and the temperature control means 140 and pickles the metal strip S that is cooled and then transported from the heat treatment space 120 through the sealing device 112. Depending on the scale characteristics, a mechanical descaling device or a salt bath may be installed between the temperature control means 140 and the pickling means 150. However, as described above, this embodiment can suppress the formation of scale on the surface of the metal strip S and control the characteristics of the scale that does form. Therefore, the pickling performed by the pickling means 150 is a simple pickling using a relatively weak acid, which can reduce the burden of wastewater treatment, as occurs when, for example, annealing in air removes stubborn scale. Alternatively, if substantially no scale is formed during annealing in the heat treatment space 120, the pickling means 150 can be omitted. For example, if scale may or may not be generated depending on the material of the metal strip S or the annealing conditions, a pickling means 150 with a switching means as described below may be provided.

[0026] 5 is a diagram showing a specific example of the arrangement of the pickling means 150 in the example shown in FIG. In the example shown, a fixed roll 151 and movable rolls 152A and 152B are provided in addition to the pickling means 150. The fixed roll 151 and the movable rolls 152A and 152B support the metal strip S being transported above the pickling tank 153 that constitutes the pickling means 150, and the movable rolls 152A and 152B are movable along the transport direction of the metal strip S. As shown in the figure, when the distance between the movable rolls 152A and 152B is increased and each is moved closer to the front and rear fixed rolls 151, the transported metal strip S hangs down between the movable rolls 152A and 152B and is immersed in the pickling tank 153. On the other hand, when the distance between the movable rolls 152A, 152B is narrowed and they are moved so that they are positioned at approximately equal intervals between the front and rear fixed rolls 151, the metal strip S is transported horizontally over the fixed rolls 151 and the movable rolls 152A, 152B and is not immersed in the pickling tank 153. In this way, the movable rolls 152A, 152B constitute a switching means for switching whether or not the metal strip S passes through the pickling means 150, i.e., whether or not the descaling means is used in the continuous treatment equipment 10.

[0027] Furthermore, in the example shown in FIG. 5 , a movable roll 154 and a salt bath 155 are disposed upstream of the pickling tank 153, and the movable roll 154 moves perpendicularly to the conveying direction of the metal strip S to switch whether the metal strip S passes through the salt bath 155. When the above-described operation of the movable rolls 152A and 152B prevents the metal strip S from passing through the pickling tank 153, the movable roll 154 is in the upper position and does not press down on the metal strip S, so that the metal strip S does not pass through the salt bath 155. On the other hand, when the metal strip S passes through the pickling tank 153, whether or not to use the salt bath 155 as a pre-treatment for pickling can be selected by switching the movable roll 154 between the upper position and the lower position and pressing down on the metal strip S. In this embodiment, the salt bath 155 constitutes a descaling means separate from the pickling tank 153, and the movable roll 154 switches whether or not to use the descaling means of the salt bath 155.

[0028] The means for removing scale is not limited to the pickling means 150 and / or the salt bath 155 illustrated in Fig. 5, and mechanical descaling means using, for example, shot blasting or roll bending may be provided in addition to or instead of these means. In this case, too, the present embodiment can suppress the generation of scale on the surface of the metal band plate S and control the properties of the scale that does occur, so that the mechanical descaling means can be simplified and it can be made possible to switch between using and not using the descaling means.

[0029] According to one embodiment of the present invention as described above, by performing the annealing treatment of the metal strip S in the atmosphere-controlled heat treatment space 120, it is possible to suppress the formation of scale on the upper surface of the metal strip S in the annealing flow and control the properties of the scale that does form. Furthermore, since the metal strip S is heated by induction heating using both the LF-IH131 and TF-IH132, it is possible to efficiently heat metal strips S of various materials and temperatures, including non-magnetic materials and magnetic materials whose temperatures exceed the Curie point. Therefore, even when the metal strip S is a stainless steel sheet, for example, scaling is suppressed by not annealing in air, allowing for simple pickling or elimination of the pickling treatment. This significantly reduces the cost of the pickling treatment and the burden of wastewater treatment. Scaling can be suppressed or controlled even for materials other than stainless steel sheets. Furthermore, because induction heating does not reduce the heating rate even at high temperatures, it is possible to prevent the need for large-scale annealing equipment even when high-temperature heating is required.

[0030] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications or alterations within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0031] 10...Continuous processing equipment, 111, 112...Sealing device, 120...Heat treatment space, 121...Heating chamber, 122, 124...Cooling chamber, 123...Heat equalization chamber, 125...Hood, 130...Heating means, 131, 131A, 131B...LF type induction heating device (LF-IH), 132, 132A, 132B...TF type induction heating device (TF-IH), 140...Temperature control means, 141, 143...Cooling means, 142...Insulation means, 144...Panel heater, 145...Slit nozzle, 146...Partition wall, 150...Pickling means, 151...Fixed roll, 152A, 152B...Moving roll, 153...Pickling tank, 154...Moving roll, 155...Salt bath, S...Metal strip plate.

Claims

1. A continuous processing facility for metal strips that processes continuously transported metal strips, an atmosphere control means for controlling the atmosphere of a space through which the metal strip passes; a heating means for heating the metal band plate by induction heating using both an LF method and a TF method in the space; a cooling means for cooling the metal band plate heated in the space; Equipped with The heating means heats the metal strip to a temperature finally required for annealing by induction heating of the TF type.

2. Further provided is a heat insulation means for keeping the metal band plate heated in the space warm, 2. The equipment for continuously treating metal strips according to claim 1, wherein the cooling means cools the metal strips that have been heated and then kept warm in the space.

3. 3. The continuous processing equipment for metal strips according to claim 2, wherein the heat retention means includes a plurality of heating devices and a plurality of cooling devices arranged alternately along the conveying direction of the metal strips, and the plurality of heating devices and the plurality of cooling devices can be individually switched between use and non-use.

4. 4. The equipment for continuously treating metal strips according to claim 3, further comprising a partition wall that separates the alternatingly arranged heating and cooling devices in the conveying direction of the metal strips.

5. descaling means for descaling the metal strip; a switching means for switching whether the metal strip uses the descaling means; The continuous processing equipment for metal strips according to any one of claims 1 to 4, further comprising:

6. the descaling means includes a pickling tank; 6. The equipment for continuously treating a metal strip according to claim 5, wherein the switching means includes a roll that supports the metal strip being transported above the pickling tank and is movable along the transport direction of the metal strip.

7. 7. The equipment for continuously treating a metal strip according to claim 1, wherein the atmosphere control means creates a non-oxidizing atmosphere in the space and controls the hydrogen concentration in the space to 4% by volume or less.

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