JP5929581B2 - Metal strip coil annealing method and metal strip coil manufacturing method - Google Patents

Description

  The present invention relates to a method of annealing a metal strip coil and an annealing furnace, and in particular, can prevent the occurrence of defects in the metal strip by preventing the winding of the coil in the annealing of the metal strip coil, especially in the cooling process. The present invention relates to a method for annealing a metal strip coil and an annealing furnace.

  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 coil end and an abdominal stretch at the center in the width direction.

  Since this shape defect is caused by the non-uniformity of the temperature distribution in the coil, various methods for making the temperature distribution of the coil uniform during annealing 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

  By the way, in particular, as a shape defect that becomes a problem in the cooling process of annealing, there is winding tightening that occurs when the outer winding of the coil is thermally contracted before the inner winding or the inner winding. This occurs because the middle volume and the inner volume are hotter than the outer volume of the coil. When such tightening occurs, defects such as scratches occur on the surface of the metal band due to friction generated between the metal bands.

However, in Patent Documents 1 to 3 described above, there is no place to touch this tightening, and a way to eliminate the tightening has been desired.
Accordingly, an object of the present invention is to provide a metal band coil annealing method and an annealing furnace that can prevent winding tightening during the cooling process of annealing and suppress the occurrence of defects in the metal band. .

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 that a certain temperature difference occurs in the coil. It is actually difficult.
Therefore, the inventors diligently investigated a method for reducing the thermal stress of the coil that causes the tightening under the assumption that the temperature distribution of the coil is not uniform. As a result, in the annealing cooling process, it is effective to place a cooling body opposite to at least one of the end faces of the metal strip coil and to enhance the cooling capacity of this cooling body from the outside in the coil radial direction to perform cooling. As a result, the present invention has been completed.

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 band coil is heated and then cooled and annealed, at the time of cooling by disposing a cooling body opposite to at least one of the end faces of the metal band coil, the cooling body The metal band coil annealing method is characterized in that cooling is performed by enhancing the cooling ability of the coil from the outside in the coil radial direction to the inside.
(2) In an annealing furnace having an inner case in which a metal band coil wound with a metal band is accommodated, an annular cooling body for removing heat from the end surface of the metal band coil accommodated in the inner case An annealing furnace characterized in that the cooling body has an enhanced cooling ability from the radially outer side to the inner side.

  According to the present invention, in the annealing cooling process, the cooling body facing at least one end face of the metal strip coil is reinforced from the outside in the coil radial direction to the inside, so that the thermal stress of the coil is suppressed. Tightening can be prevented, and the occurrence of defects in the metal strip can be suppressed.

It is a figure which shows the temperature distribution of a metal strip coil in the cooling process of conventional batch type annealing. It is a figure which shows an example of a cooling body. It is a figure explaining the temperature change which arises in a metal strip coil by cooling by a cooling body. It is a figure which shows another example of a cooling body.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a temperature distribution inside a metal band coil in a cooling process of a conventional batch type annealing. As shown in this figure, in the conventional cooling process, the coil 1 is cooled from the outer peripheral side and the inner peripheral side as shown by the arrows in the figure, and the temperature of the outer winding and the inner winding of the coil is higher than that of the middle winding. Will also fall first. As a result, the coil 1 has a temperature distribution that is high inside and low outside. Under such a temperature distribution, the outer winding is thermally shrunk, while the middle winding is not lowered to a temperature at which heat shrinkage occurs. As a result, defects such as scratches occur on the surface of the metal band due to friction between the metal bands.

  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 virtually impossible 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 cooling is uneven, and eagerly studied how to prevent the tightening and prevent the occurrence of defects. did. As a result, in the annealing cooling process, it is effective to place a cooling body opposite to at least one of the end faces of the metal strip coil and to enhance the cooling capacity of the cooling body from the outside in the coil radial direction to perform the cooling. I found out. Hereinafter, the annealing method of the present invention will be described in detail.

  FIG. 2 is a diagram illustrating an example of a cooling body. In FIG. 2, the cooling body 3 includes three cooling bodies 3 a to 3 c having different cooling capacities, and is disposed so as to face both the 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 cooling body opposite to the end face of the coil.

  Here, the cooling capacity of the cooling bodies 3a to 3c is configured to be strengthened from the outer side in the coil radial direction to the inner side, in other words, 3a has the highest cooling capacity and 3c has the lowest cooling capacity. Has been. With such a cooling body 3, the inner winding of the coil 1 can be cooled earliest in the annealing cooling process.

  FIG. 3 is a diagram for explaining a temperature change that occurs in the metal band coil due to cooling by the cooling body described above. As shown in this figure, when cooling is performed by a cooling body having a changed cooling capacity, cooling starts from the vertical direction of the inner winding of the coil 1 and cools toward the radially outer side of the coil 1. . By cooling 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, it is possible to prevent tightening in the cooling process of the annealing and to suppress defects such as scratches. Hereinafter, a specific configuration of the cooling body will be described.

As the cooling bodies 3a to 3c, annular pipes, tubes, or the like capable of circulating a cooling medium such as a cooling gas or a fluid therein can be used.
Moreover, the number of cooling bodies shall be 1-10. This is because it is necessary to use at least one inner volume for which the temperature rise is to be suppressed, and the structure becomes complicated when the number is 10 or more. Preferably it is 3-6.

  Furthermore, it is preferable that the temperature difference between the cooling body disposed on the outermost side in the coil radial direction and the cooling body disposed on the innermost side in the coil radial direction is 10 ° C. or more. Thereby, generation | occurrence | production of the shape defect resulting from coil stress can be suppressed more effectively.

  FIG. 4 is a diagram illustrating another example of the cooling body. The annular cooling body 4 shown in this figure has an enhanced cooling ability from the radially outer side to the inner side. The length of the arrow in FIG. 4 indicates the amount of heat removed from the coil, and the cooling body 4 can reduce the amount of heat removed from the radially outer side to the inner side, so that the coil temperature is changed from the radially outer side to the inner side. The cooling through the temperature distribution shown in FIG. The cooling body 4 has a configuration in which, for example, a plurality of annular tubes having different diameters through which a cooling medium can flow can be used to gradually increase the arrangement density from the radially outer side to the inner side of the cooling body. realizable. Specifically, the cooling body 4 shown in FIG. 4 can be configured by arranging the cooling pipes so that the number of cooling pipes increases from the outer side in the radial direction toward the inner side without gaps. Control can be performed more precisely.

  The cooling bodies 3 and 4 illustrated in FIGS. 2 and 4 are opposed to each other in the vicinity of the upper and lower end faces of the coil 1, but may be arranged only on either the upper end face or the lower end face.

  In this way, during the cooling process of annealing, the thermal stress of the coil can be suppressed to prevent tightening, and the occurrence of defects such as scratches on the metal strip can be suppressed.

(Invention Examples 1 and 2)
Examples of the present invention will be described below.
The metal strip coil was annealed by the method of the present invention. That is, first, a thin plate made of steel (length: 3000 m, thickness: 0.5 mm, weight: about 10 t) was prepared as a coil material, and the thin plate was wound into a coil shape to obtain 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 raising the furnace temperature to 800 ° C., the entire coil was held until it reached 800 ° C., and then the coil was cooled to room temperature. At that time, the upper end face of the coil was cooled using the cooling body (Invention Example 1) shown in FIG. 2 and the cooling body (Invention Example 2) shown in FIG. Here, the cooling body in Invention Example 1 includes three cooling pipes having radii different from 0.6 m, 1.0 m, and 1.3 m, and air was flowed at a flow rate of 1000, 500, and 200 Nm ³ / hour, respectively. . The cooling body in Invention Example 2 is a disk-shaped cooling body having five cooling pipes inside, and the cooling body itself is configured to have a gentle temperature distribution in the radial direction. When the cooling of the coil was completed, the coil was removed from the annealing furnace.

(Comparative example)
Similarly to Invention Examples 1 and 2, when the metal strip coil was annealed, the end face of the coil was not cooled by the cooling body during the cooling process. Other conditions are the same as those of Invention Examples 1 and 2.

<Coil shape inspection>
Tightening of the coil processed by the inventive examples 1 and 2 and the comparative example and defects caused thereby were inspected. Here, the defects were evaluated based on the overall length of defects in shape and surface condition, such as the length of the wavy deformation generated in the coil and the scratches. The obtained results are shown in Table 1. In the comparative example, the length of the scratch was 500 m. In contrast, in Invention Examples 1 and 2, the scratch length was 50 m, which was greatly reduced compared to the comparative example.

  Table 1 shows the results obtained by examining the time spent cooling the coil to room temperature in the cooling process of annealing. As a result, while it was 80 hours in the comparative example, it was 50 hours in the invention examples 1 and 2, and the cooling time could be shortened. Thus, by the method of the present invention, it was possible to prevent the tightening in the annealing cooling process, to suppress the occurrence of defects in the metal strip, and to achieve a reduction in the cooling time.

DESCRIPTION OF SYMBOLS 1 Metal strip coil 2 Hearth 3, 3a, 3b, 3c, 4 Cooling body O Center axis

Claims (2)

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,
When cooling is performed by disposing a cooling body opposite to at least one of the end faces of the metal band coil, the cooling capacity of the cooling body is strengthened from the outer side in the coil radial direction to the inner side in the arbitrary radial direction of the metal band coil. A method for annealing a metal band coil , wherein, in a cross section, cooling is performed by lowering a temperature inside the metal band coil in a radial direction lower than a temperature outside the radial direction . A thin metal plate is wound into a coil shape to form a metal band coil, and the metal band coil is annealed by the method for annealing a metal band coil according to claim 1. Method.

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