JP6024260B2 - Metal strip coil annealing method and heat insulating material used therefor - Google Patents

Description

  The present invention relates to a method for annealing a metal band coil and a heat insulating material used therefor, and in particular, a method for annealing a metal band coil capable of suppressing the occurrence of shape defects in the heating process, particularly a heating process, and a heat insulation used therefor. It relates to materials.

  Conventionally, in a material manufacturer, when a heat treatment for a metal band such as a steel strip is performed for a relatively long time, the heat treatment is generally performed by winding the metal strip into a coil state. Since this method anneals in a coil state in which the overall thickness is larger than continuous annealing in which the metal strip is heat-treated as it is, it takes a relatively long time for heat to penetrate into the coil. Therefore, the temperature inside the coil is inevitably nonuniform, and as a result, thermal stress is generated in the coil.

  This thermal stress causes various shape defects such as a shape defect at the end of the metal strip and a belly stretch at the center in the width direction. Further, the metal strip may be rubbed and a scratch may be generated due to the compressive load in the coil radial direction. In particular, the above-described problems are likely to occur in a heat treatment at a high temperature.

Examples of locations where the above problems are likely to occur in the metal band coil include the hearth side end surface and the inner peripheral surface of the coil.
First, the coil hearth side end surface has a shape in which its own weight acts and the end portion is wavy. The mechanism is as follows.
(1) During the heat treatment, the outer winding of the coil that is most susceptible to radiant heat from the inner cover has the fastest temperature rise, and therefore the earliest timing for thermal expansion.
(2) Since the coil is wound tightly under tension, the frictional force between the front and back surfaces of the metal band acts, and both the middle and inner windings are lifted by the thermally expanded outer winding. That is, as shown in FIG. 1, the coil 1 changes from the state shown in FIG. 1A to the state in which the middle and inner windings as shown in FIG.
(3) At that time, the outer winding part lifts the entire coil, and the weight of the coil concentrates on the hearth side part of the outer winding, resulting in a defective shape here.

On the other hand, on the inner circumferential surface of the coil, very strong stress is generated in the circumferential direction of the coil, and in some cases, buckling occurs toward the center of the coil. The mechanism is as follows.
(I) Examining the temperature distribution in the radial direction of the coil, the inner peripheral surface of the coil receives radiant heat from the upper surface of the inner cover, and therefore the temperature rise of the inner coil is not as high as that of the outer coil. On the other hand, since the middle winding of the coil does not receive radiant heat, the temperature rise is the slowest.
(Ii) Therefore, the timing of the thermal expansion of the middle coil of the coil is the latest.
(Iii) For this reason, even if the inner winding of the coil is to be thermally expanded, the inner winding of the coil has not yet been thermally expanded, which hinders the expansion of the inner winding of the coil.
(Iv) Thus, a very strong stress is generated in the coil circumferential direction in the coil inner volume that cannot expand in the coil radial direction, and in some cases, the coil is buckled toward the center of the coil.
As described above, when the metal strip is annealed in a coil shape, the temperature distribution in the coil becomes non-uniform, which causes a problem of shape failure.

  Against this background, various methods for suppressing the occurrence of the above-described shape defects have been proposed. For example, Patent Document 1 discloses a method in which a heat insulating material is installed on the upper surface of a coil so as to block radiant heat to the inner winding of the coil and suppress the occurrence of ear elongation due to rapid heating and rapid cooling of the coil during annealing. Have been described.

  Further, Patent Document 2 discloses a heating process in which the temperature of the upper and lower portions (radiant heat) in the annealing furnace is made uniform by controlling the output of a plurality of burners installed in the height direction of the coil, and the heat generated in the coil. A technique for reducing stress is described.

  Furthermore, in Patent Document 3, by arranging a heat transfer control means including a plurality of heating bodies and cooling bodies around the coil, and controlling the heat transfer control means so that the temperature difference in the coil is within a predetermined range. A technique for reducing thermal stress generated in a coil is described.

JP-A-6-17150 JP-A-6-88138 JP 2005-226104 A

However, the techniques described in Patent Documents 1 to 3 have a problem in that the temperature distribution in the coil is not uniform enough to prevent the occurrence of shape defects in the annealing heating process.
Therefore, an object of the present invention is to provide a metal strip coil annealing method and a heat insulating material used therefor, which can suppress the occurrence of shape defects in the annealing heating process.

The inventors diligently studied how to solve the above problems. The techniques described in Patent Documents 1 to 3 are intended to reduce the generation of thermal stress by achieving uniformity of the temperature distribution in response to the non-uniformity of the temperature distribution in the coil during annealing. Yes. However, since it takes a certain amount of time for the radiant heat from the inner case to be transmitted to the inside of the coil, it is not possible to avoid a certain temperature difference in the coil, and thus it is not possible to make the temperature distribution of the coil uniform. It is actually difficult.
Therefore, the inventors diligently investigated a method for reducing the thermal stress of the coil that causes a shape defect or the like under the premise that the temperature distribution of the coil is not uniform. As a result, it has been found that it is effective to heat the metal strip coil under a temperature distribution in which the temperature of the metal strip coil decreases from the outside in the coil radial direction to the inside, and the present invention has been completed. It was.

That is, the gist of the present invention is as follows.
(1) A metal band coil wound with a metal band is placed in an annealing furnace with the center axis of the metal band coil aligned in the vertical direction, the metal band coil is covered with an inner case, and radiant heat from the inner case When the metal strip coil is heated and then cooled and annealed, the heating of the metal strip coil is a temperature at which the temperature of the metal strip coil decreases from the outside in the coil radial direction to the inside. An annealing method for a metal strip coil, which is performed under distribution.

(2) An annular heating body is disposed opposite to at least one of the end faces of the metal band coil, and the heating band is provided with a heating ability that decreases from the radially outer side to the inner side. The method according to (1) above, wherein the temperature distribution is given to.

(3) An annular heat insulating material is disposed on at least one of the end faces of the metal band coil, and the heat insulating body is provided with a heat insulating ability that increases from the radially outer side to the inner side, The method according to (1), wherein the coil is provided with the temperature distribution.

(4) An annular heat insulating material disposed on an end face of the metal band coil when the metal band coil wound with the metal band is annealed in an annealing furnace, and the heat insulating material is arranged from the radially outer side to the inner side. A heat insulating material characterized by having a heat insulating capability that increases toward the surface.

(5) The said heat insulating material is a heat insulating material as described in said (4) with which thickness increases toward inner side from the radial direction outer side.

(6) The said heat insulating material is a heat insulating material as described in said (4) which consists of a some cyclic | annular heat insulating body from which a diameter and heat insulation ability differ.

  According to the present invention, the metal band coil is heated under a temperature distribution in which the temperature of the metal band coil decreases from the outside in the coil radial direction to the inside. Occurrence can be suppressed.

It is a figure explaining the mechanism in which a shape defect generate | occur | produces on the coil hearth side. It is a figure which shows the temperature distribution of the metal strip coil in the heating process of batch type annealing. It is a figure which shows an example of the heating body used for the 1st Embodiment of this invention. It is a figure explaining the temperature change which arises in a metal strip coil by the heating by a heating body. It is a figure which shows another example of the heating body used for the 1st Embodiment of this invention. It is a figure which shows an example of the heat insulating material used for the 2nd Embodiment of this invention. It is a figure which shows another example of the heat insulating material used for the 2nd Embodiment of this invention. It is a figure which shows another example of the heat insulating material used for the 2nd Embodiment of this invention. It is a figure which shows the temperature distribution in the metal strip coil in the comparative example 2 and the invention example 3. FIG.

  The present invention will be specifically described below with reference to the drawings. Now, FIG. 2 is a figure which shows the temperature distribution inside a metal strip coil in the heating process of conventional batch type annealing. As shown in this figure, in the conventional heating process, the coil 1 is heated from the outer peripheral side and the inner peripheral side as indicated by the arrows in the figure, and the temperature of the outer and inner windings of the coil is higher than that of the middle winding. Also rises first. As a result, the coil 1 has a temperature distribution in which the outside is high and the inside is low. Under such a temperature distribution, the outer winding expands thermally, while the intermediate winding does not rise to a temperature that causes thermal expansion. Shape defects such as undulations at the side end faces and buckling at the inner winding of the coil will occur.

  Conventionally, as described above, efforts have been made to improve the uneven temperature distribution in the coil 1. However, since heat conduction to the inside of the coil requires a certain amount of time, it is extremely difficult to make the temperature distribution in the coil 1 uniform.

Under such a technical background, the inventors based on the premise that the temperature distribution of the coil at the time of heating is non-uniform, and intensively studied how to suppress the occurrence of shape defects. As a result, it was found that in the annealing heating process, it is effective to heat the metal strip coil under a temperature distribution in which the temperature of the metal strip coil decreases from the outside in the coil radial direction to the inside. is there. That is, by giving such a temperature distribution to the coil, the thermal stress generated in the coil is reduced, and the occurrence of shape defects such as undulations at the end surface on the hearth side of the coil outer winding and buckling at the inner winding of the coil. It can be suppressed.
Hereinafter, the annealing method of the present invention will be described in detail.

  FIG. 3 is a diagram illustrating an example of a heating body used in the first embodiment of the present invention. In FIG. 3, the heating body 3 includes three annular heating bodies 3 a to 3 c having different heating capabilities, and is disposed opposite to both upper and lower end faces of the coil. The coil 1 is obtained by winding a metal band around the central axis O, and there is a slight gap between the metal bands. Therefore, in the coil 1, heat is more easily transmitted in the coil axial direction than in the coil radial direction. Therefore, the temperature distribution of the coil can be easily controlled by disposing the heating body opposite to the end face of the coil.

  Here, the heating power of the heating bodies 3a to 3c is configured so that the heating power decreases from the outer side in the coil radial direction to the inner side, in other words, 3c has the highest heating power and 3a has the lowest heating power. Has been. The size of the heating bodies 3a to 3c in FIG. 3 reflects the high heating ability. With such a heating body 3, the outer winding of the coil 1 can be heated the fastest in the annealing heating process.

  FIG. 4 is a diagram for explaining a temperature change that occurs in the metal band coil due to the heating by the heating body. As shown in this figure, when heating is performed with a heating body having a different heating capability, heating starts from the vertical direction of the outer winding of the coil 1 toward the center of the middle winding, and directly toward the inner side in the radial direction of the coil 1. It will be heated. By heating in this way, the temperature on the radially inner side is lower than the temperature on the radially outer side in any radial cross section of the coil 1. As a result, the thermal stress generated in the coil is reduced, and the occurrence of shape defects can be suppressed. Hereinafter, a specific configuration of the heating body will be described.

As the heating bodies 3a to 3c, a heater, an induction heating device, or the like can be used.
Moreover, the number of heating bodies shall be 1-10. This is because when the number exceeds 10, the configuration of the apparatus becomes complicated. Preferably it is 3-7.

  Furthermore, it is preferable that the temperature difference between the heating element disposed on the outermost side in the coil radial direction and the heating element disposed on the innermost side in the coil radial direction is 10 ° C. or more. With this temperature difference, the temperature in the coil is changed in the radial direction. It decreases from the outside to the inside, preferably gradually. Thereby, since the temperature outside a coil can be raised more, the thermal stress in a coil can be reduced.

  FIG. 5 is a diagram showing another example of the heating element used in the first embodiment of the present invention. The annular heating body 4 shown in this figure has a heating ability that decreases from the radially outer side toward the inner side. The length of the arrow in FIG. 5 indicates the amount of heating from the heating body, and the heating body 4 can reduce the amount of heating from the radially outer side to the inner side, and the coil temperature can be reduced from the radially outer side. Heating is achieved through the temperature distribution shown in FIG. 4, decreasing towards the inside. The said heating body 4 is realizable by making it the structure which reduces those arrangement | positioning densities from the radial direction outer side of a heating body to an inner side, for example using several cyclic | annular heaters from which a diameter differs. In the heating body 3 of FIG. 3, since a plurality of independent heaters are used, the temperature cannot be controlled at the break between the heaters. On the other hand, by connecting the heaters to form the heating body 4, the heating body itself can have a continuous temperature distribution, and the temperature difference in the coil can also be continuous. Thus, the heating body 4 can perform temperature control in the radial direction more precisely.

  3 and 5 are opposed to each other in the vicinity of both upper and lower end faces of the coil 1, but may be arranged to face only one of the upper end face and the lower end face.

  Thus, according to the first embodiment of the present invention, the heating element having a heating ability that decreases from the radially outer side to the inner side is arranged oppositely on at least one of the end surfaces of the metal band coil to heat the metal band coil. Therefore, in the annealing heating process, the metal band coil can be heated under a temperature distribution in which the temperature of the metal band coil decreases from the outside in the coil radial direction to the inside, thereby reducing the thermal stress of the coil. Occurrence of shape defects can be suppressed.

  Next, a second embodiment of the present invention will be described. In the above-described first embodiment of the present invention, the heating of the metal strip coil in the annealing heating process is performed under a temperature distribution in which the temperature of the metal strip coil decreases from the outside in the coil radial direction to the inside. In addition, this temperature distribution was realized by heating a heating element disposed opposite to at least one of the end faces of the metal strip coil. Here, another method for realizing the temperature distribution will be described. That is, the above temperature distribution is realized by a heat insulating material disposed on at least one end face of the metal band coil and having a heat insulating ability that increases from the outside in the coil radial direction toward the inside.

  FIG. 6 shows an example of a heat insulating material used in the second embodiment of the present invention. This heat insulating material is an annular heat insulating material that covers the end face of the metal band coil when the metal band coil is annealed in an annealing furnace, and has a predetermined diameter for allowing atmospheric gas to pass through the center. Is provided, and has a heat insulating ability that increases from the radially outer side toward the inner side. In the heat insulating material 5 illustrated in FIG. 6A, this heat insulating ability is realized by gradually increasing (inclining) the thickness of the heat insulating material 5 from the radially outer side to the inner side. Thereby, heat insulation ability becomes high as it goes inside from the radial direction outer side. Therefore, when this heat insulating material 5 is disposed on both upper and lower end faces of the metal strip coil 1 as shown in FIG. 6 (b), the coil is subjected to heating by the radiant heat from the inner cover in the annealing heating process. While the temperature increase of the inner winding is largely suppressed, the temperature increase of the outer winding of the coil is not suppressed as much as the inner winding, so that the temperature of the coil decreases from the radially outer side to the inner side. Heating through the distribution is realized. Hereinafter, a specific configuration of the heat insulating material 5 will be described.

  As a material of the heat insulating material 5, iso wool (ceramic fiber) or heat insulating brick can be used. Among these, it is preferable to use isowool because it is easy to control heat insulation by changing the thickness.

  Moreover, the thickness of the heat insulating material 5 shall be 1 mm or more and 100 mm or less. This is because a thickness of 1 mm or more has a sufficient heat insulating effect. Moreover, it is because heat insulation will become excessive when it exceeds 100 mm, and the heating of a coil will become slow. Preferably, it is 1 mm or more and 30 mm or less.

Furthermore, the outer diameter of the heat insulating material 5 does not need to be greater than or equal to the outer diameter of the coil 1 and may be smaller than the outer diameter of the coil 1 to increase the amount of heat input to the coil outer winding. Specifically, the outer diameter is set to D / 2 or more and D or less with respect to the outer diameter D of the coil. Preferably, it is D / 2 or more and 3D / 4 or less.
Further, the inner diameter of the heat insulating material 5 defined by the vent hole in the central portion is set to 0 or more and d or less as the inner diameter d of the coil 1. Here, in order to more effectively suppress the heat input to the coil inner winding, as shown in FIG. 6 (b), it is preferable to make it smaller than d, d / 3 or more and d / 2 or less. It is more preferable.

  In the heat insulating material 5 shown in FIG. 6, the thickness of the heat insulating material 5 is gradually increased from the radially outer side to the inner side. However, like the heat insulating material 6 shown in FIG. It can also be made to increase discontinuously stepwise from the outside to the inside. The heat insulating material 6 is composed of three heat insulating materials 6a to 6c having the same inner diameter and different outer diameters, and is composed of one heat insulating material to increase the thickness stepwise from the radially outer side to the inner side. You can also.

  Moreover, although the heat insulating materials 5 and 6 shown in FIG. 6 and 7 are changing the thickness, the heat insulating capability of the radial direction of a heat insulating material is changed, but as shown in FIG. A plurality of annular heat insulators made of materials having different outer diameters (inner diameters) and different heat insulation capabilities may be combined. In this figure, the heat insulating material 7 is configured by combining three heat insulating bodies 7a to 7c having different diameters and heat insulating capabilities in the radial direction, and the heat insulating body 7a has the highest heat insulating performance. It has the lowest heat insulation capacity. By comprising in this way, the heat insulating material 7 can have the heat insulation ability which becomes high toward inner side from the radial direction outer side, having the same thickness in a radial direction.

  Thus, according to the second embodiment of the present invention, on the end face of the metal strip coil, the heat insulating material having a heat insulating capability that increases from the radially outer side to the inner side is disposed. The band coil can be heated under a temperature distribution in which the temperature of the metal band coil decreases from the outer side to the inner side in the radial direction of the coil, thereby reducing the thermal stress of the coil and suppressing the occurrence of shape defects. it can.

(Invention Examples 1 and 2)
Examples of the present invention will be described below.
The metal strip coil was annealed according to the first embodiment of the present invention described above. That is, first, a thin plate made of steel (length: 3000 m, thickness: 0.5 mm, coil outer diameter: 1300 mm, coil inner diameter: 500 mm, weight: about 10 t) is prepared as a coil material, and this thin plate is coiled. Was wound up into a metal strip coil. Next, this metal band coil was placed in an annealing furnace with the center axis of the metal band coil aligned in the vertical direction, and the metal band coil was covered with an inner case. Subsequently, after the furnace temperature was raised to 800 ° C. and the coil was heated, the entire coil was held until it reached 800 ° C., and then the coil was cooled to room temperature. During the heating process, the upper end face of the coil was heated using the heating element (Invention Example 1) shown in FIG. 3 and the heating element (Invention Example 2) shown in FIG. Here, the heating element of Invention Example 1 was composed of three hollow annular heaters having radii different from 0.3 m, 0.45 m, and 0.6 m, and the heating values were 23, 15 and 5 kW, respectively. In addition, the heating element of Invention Example 2 was configured by connecting five heaters having different heating capacities, and the heating value was 43 kW so that the total heating value was the same as that of Invention Example 1. After the cooling of the coil was completed, the coil was taken out from the annealing furnace.

(Comparative Example 1)
As in Invention Examples 1 and 2, when the metal strip coil was annealed, the end face of the coil was not heated by the heating element during the heating process. Other conditions are the same as those of Invention Examples 1 and 2.

<Coil shape inspection>
The shape defects of the coils processed according to Invention Examples 1 and 2 and Comparative Example 1 were inspected. The obtained results are shown in Table 1. In Comparative Example 1, shape defects such as waving and buckling at the end of the outer winding hearth were observed at 50 locations. On the other hand, in Invention Examples 1 and 2, the number of places where shape defects were observed was 25 and 15, respectively.

  The annealing time was also examined. The obtained results are shown in Table 1. As a result, while it was 80 hours in Comparative Example 1, it was 50 hours in Invention Examples 1 and 2, and the annealing time could be shortened. Thus, according to the method of the present invention, it was possible to suppress the occurrence of shape defects in the annealing heating process, and it was also possible to shorten the annealing time.

(Invention Examples 3 to 6)
The metal strip coil was annealed according to the second embodiment of the present invention described above. Here, instead of the heating body in the first embodiment, three types of heat insulating materials shown in FIGS. 6 to 8 are arranged on the end face of the metal band coil 1. All of these heat insulating materials were formed using Isowool (registered trademark) boards and blankets manufactured by Isolite Industry, and had an outer diameter of 1200 mm and an inner diameter of 500 mm. Specifically, the thickness shown in FIG. 6 is gradually increased (inclined) from 0 to 40 mm from the outer circumference to the inner circumference (Invention Examples 3 and 4), and the inner diameter shown in FIG. 7 is the same. It is composed of three heat insulators with different outer diameters stacked (Invention Example 5) and three annular heat insulators with different diameters and heat insulation capabilities shown in FIG. 8, and the heat conductivity of the heat insulator is Samples (Invention Example 6) having 1, 0.2 and 0.1 W / m · K from the outside in the radial direction were prepared. Here, in Invention Examples 3, 5 and 6, the heat insulating material was disposed only on the upper end surface of the coil, whereas in Invention Example 4, it was disposed on both upper and lower end surfaces of the coil. For Invention Example 5, the heat insulator having the largest diameter has an outer diameter of 1200 mm and an inner diameter of 500 mm as described above, but the remaining two have an outer diameter of 900 mm and an outer diameter of 600 mm. . Other conditions are the same as those of Invention Examples 1 and 2.

(Comparative Example 2)
As in Invention Examples 3 to 6, when performing annealing of the metal band coil, during the heating process, the outer diameter is 800 mm, the inner diameter is 500 mm, the thickness is 20 mm, and the heat insulation capacity is in the radial direction. The same insulation was placed on the end face of the coil. Other conditions are the same as those of Invention Examples 3 to 6.

<Coil shape inspection>
The shape defect of the coil processed by the invention examples 3-6 and the comparative example 2 was test | inspected. The obtained results are shown in Table 2. In Comparative Example 2, shape defects such as waving and buckling at the end of the outer winding hearth were observed at 30 locations. On the other hand, in the invention examples 3-6, the location where the shape defect was observed is 20, 15, 18 and 19 locations, respectively, and it can be seen that the locations are greatly reduced.

<Temperature distribution in the coil>
FIG. 9 shows the temperature distribution in the coil in Comparative Example 2 and Inventive Example 3. Here, FIG. 9A shows Comparative Example 2 and FIG. 9B shows Invention Example 3. As is clear from this figure, in Comparative Example 2, the temperature of the middle volume is low, whereas in Invention Example 3, the temperature of the inner volume is low, and the temperature increases toward the outside in the radial direction. I understand that. This was the same in Example 1.

DESCRIPTION OF SYMBOLS 1 Metal strip coil 2 Hearth 3, 3a, 3b, 3c, 4 Heating body 5, 6, 7 Heat insulating material 6a, 6b, 6c, 7a, 7b, 7c Heat insulating body O Center axis

Claims (6)

A metal band coil wound with a metal band is placed in an annealing furnace with the center axis of the metal band coil aligned in the vertical direction, the metal band coil is covered with an inner case, and the radiant heat from the inner case After heating the metal band coil, in cooling and annealing the metal band coil,
The heating of the metal band coil is a temperature distribution in which the temperature of the metal band coil decreases from the outer side in the coil radial direction toward the inner side by controlling the temperature of the end surface of the metal band coil from the outer periphery to the inner periphery. An annealing method for a metal strip coil, characterized by being performed under   An annular heating body is disposed opposite to at least one of the end faces of the metal band coil, the heating body is provided with a heating capability that decreases from the radially outer side to the inner side, and the temperature is applied to the metal band coil. The method of claim 1, wherein a distribution is provided. Said annular heat-insulating material so as to cover the entire or at least one end face of the end face of the metal strip coil disposed, the heat insulating material, to impart becomes higher insulation ability inward from the radially outer side, the metal The method of claim 1, wherein the temperature distribution is applied to a strip coil. When the metal band coil wound with the metal band is annealed in an annealing furnace, an annular heat insulating material disposed on the end surface of the metal band coil,
The heat insulating material has a size that covers the entire end face of the metal band coil, and has a heat insulating performance that increases from the radially outer side to the inner side.   The said heat insulating material is a heat insulating material of Claim 4 which thickness increases toward the inner side from a radial direction outer side.   The said heat insulating material is a heat insulating material of Claim 4 which consists of a some cyclic | annular heat insulating body from which a diameter and heat insulation ability differ.