JP5906816B2 - Metal strip coil annealing method and annealing furnace - Google Patents

Description

  The present invention relates to a method for annealing a metal band coil and an annealing furnace, and in particular, various shape defects by appropriately blocking the radiant heat to the inner peripheral surface of the metal band coil and optimizing the temperature distribution in the metal band coil. It is intended to prevent the occurrence of scratches.

Conventionally, in a material manufacturer, when a heat treatment for a relatively long time is performed on a metal strip such as a steel plate, the heat treatment in a coil state is generally performed.
In this method, since annealing is performed in a coil state in which the overall thickness is larger than in the continuous annealing in which the metal strip is heat-treated as it is, it takes a relatively long time for the heat to penetrate inside. Therefore, the temperature of the entire coil inevitably becomes non-uniform, and thermal stress is generated.
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. 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-mentioned problems are likely to occur in the metal strip coil include the hearth side and the inner peripheral surface of the coil.
First, on the coil hearth side, its own weight acts to form a waved end. 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 friction between the bands works, and the intermediate winding and the inner winding 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) That is, when the outer winding lifts the entire coil, its own weight is concentrated on the hearth side outer winding portion, resulting in a defective shape.

Next, 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, the temperature rise is the slowest because the coil winding is not subjected to radiant heat.
(Ii) Therefore, the timing of the thermal expansion of the coil winding is the slowest.
(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.

In order to prevent the above defects, it is considered that a method for controlling the temperature distribution in the coil is effective.
As such a method, for example, in Patent Document 1, the temperature distribution in the height direction of the inner cover is adjusted by controlling the output of a plurality of burners installed in the height direction along the side wall of the annealing furnace. A technique for balancing the radiant heat from the inner cover and thereby controlling the temperature distribution in the height direction of the coil is disclosed.

Japanese Patent Laid-Open No. 06-88138

If the burner output control disclosed in Patent Document 1 described above is used, it is expected that the temperature rise of the coil inner winding is suppressed by reducing the burner output on the furnace top side. The reason is that only the upper surface of the inner cover geometrically exchanges radiant heat with the inner peripheral surface of the coil. Therefore, if the temperature of the upper surface of the inner cover can be lowered, the temperature increase of the inner winding of the coil can be suppressed. Because.
However, in the burner output control as described above, it is substantially impossible to reduce the temperature of the upper surface of the inner cover.
That is, the coil annealing furnace is often designed to have a narrow internal space from the viewpoint of heating efficiency. Therefore, the atmospheric gas diffuses and mixes quickly, so that a sufficient temperature gradient is not easily generated in the inner cover. In addition, when the design has a wide internal space, it takes time to raise the furnace temperature, resulting in a decrease in production efficiency.

In addition, as shown in FIG. 2, a method of placing the heat insulating material 3 on the upper surface of the coil 1 and blocking the radiant heat to the coil inner peripheral surface 4 is also conceivable. According to this method, the temperature increase of the inner volume during the heat treatment can be suppressed.
However, the heat insulating material 3 hinders the heat dissipation of the coil inner peripheral surface 4 during the cooling process that greatly affects the final metal strip shape. If the thermal contraction timing of the inner coil of the coil is delayed, the order of the thermal contraction is outer, middle, and inner. However, in this case, the inner coil undergoes thermal contraction of the outer coil as opposed to during heating. A winding tightening in which the inner winding hinders the heat shrinkage occurs, and various defects are caused.
That is, the heat insulating material 3 that can block radiant heat during the heat treatment hinders heat dissipation and adversely affects during the cooling treatment.

  The present invention has been developed in view of the above situation, and by appropriately controlling the temperature distribution in the metal band coil, the metal band coil can prevent various shape defects and scratches of the metal band. It aims at proposing the annealing method of this with the annealing furnace suitable for the annealing method.

That is, the gist configuration of the present invention is as follows.
1. A metal band coil in which a metal band is coiled is covered with an inner cover, and when the metal band coil is annealed by radiant heat from the inner cover, at least the first half of the annealing is the inner peripheral surface of the metal band coil A method for annealing a metal strip coil, wherein the radiant heat is blocked while the cooling process is released.

2. In an annealing furnace comprising an inner cover for covering the metal band coil in which the metal band is coiled and radiating radiant heat to heat the metal band coil,
An annealing furnace characterized in that a heat blocking material for blocking radiant heat from the inner cover toward the inner peripheral surface of the metal band coil is installed so as to be movable between a blocking position and a retracted position.

3. 3. An annealing furnace as described in 2 above, wherein the heat shielding material is a pipe-shaped heat insulating material capable of moving up and down to the coil central space.

4). 3. An annealing furnace as described in 2 above, wherein the heat shielding material is a plate-shaped heat insulating material that can move horizontally or vertically to the upper surface of the coil central space.

  According to the present invention, it is possible to appropriately block the radiant heat to the inner peripheral surface of the metal strip coil using the heat blocking material, so that the temperature distribution in the coil can be optimized, and various shape defects and scratches are generated. Can be prevented. In addition, the time required for the cooling process is not extended.

It is a figure for demonstrating the generation | occurrence | production mechanism of the shape defect by the side of a metal strip coil hearth. It is a figure for demonstrating the method of mounting a heat insulating material on the metal band coil upper surface, and interrupting | blocking the radiant heat to an inner peripheral surface of a metal band coil. It is a figure for demonstrating the 1st embodiment of the annealing method of the metal strip coil which concerns on this invention. (A) shows the state which has interrupted radiant heat. (B) shows the state which released the interruption | blocking of the radiant heat. It is a figure for demonstrating the 2nd embodiment of the annealing method of the metal strip coil which concerns on this invention. (A) shows the state which has interrupted radiant heat. (B) shows the state which released the interruption | blocking of the radiant heat. It is a figure for demonstrating the other example of the 2nd embodiment of the annealing method of the metal strip coil which concerns on this invention. The annealing point in the Example of this invention is shown.

Hereinafter, the present invention will be specifically described.
(First embodiment)
First, the 1st embodiment of the annealing method of the metal strip coil which concerns on this invention is demonstrated using FIG. FIG. 3A shows a state in which radiant heat is blocked according to the first embodiment of the method for annealing a metal strip coil according to the present invention. FIG.3 (b) shows the state which open | released interruption | blocking of the radiant heat according to 1st embodiment of the annealing method of the metal strip coil which concerns on this invention.
In the figure, 1 is a metal strip coil, 5 is a pipe-shaped heat insulating material, and 6 is a support member. The same components as those shown in FIG. 2 are denoted by the same reference numerals.

In the method of annealing a metal strip coil according to this embodiment, when the metal strip coil 1 in which the metal strip is wound in a coil shape is covered with an inner cover and the metal strip coil 1 is annealed by radiant heat from the inner cover, at least annealing is performed. In the first half of the heat treatment, the radiant heat to the inner circumferential surface 4 of the metal strip coil is cut off, while this cut off is released during the cooling treatment.
Specifically, the radiant heat is blocked by inserting the pipe-shaped heat insulating material 5 into the coil central space by the support member 6 as shown in FIG.
The release of the radiant heat block is performed by storing the pipe-shaped heat insulating material 5 under the floor as shown in FIG. On the contrary, it may be slid upward.
The timing for releasing the blocking of the radiant heat may be at the end of the annealing heat treatment, but is preferably the latter half of the heat treatment. Particularly preferred is the time when the temperature reaches 80 to 85% of the target temperature. The reason why the timing of releasing the radiant heat block is set to the second half of the heat treatment is that the temperature of the coil 1 gradually increases so as to approach the set furnace temperature in the second half of the heat treatment. This is because there is no possibility that the temperature difference in the coil 1 becomes large, and because the thermal stress is easily relaxed when the temperature rises.

(Second embodiment)
Next, a second embodiment of the method for annealing a metal strip coil according to the present invention will be described with reference to FIG. Fig.4 (a) shows the state which has interrupted | blocked the radiant heat according to 2nd embodiment of the annealing method of the metal strip coil which concerns on this invention. FIG.4 (b) shows the state which released | released interruption | blocking of a radiant heat according to 2nd embodiment of the annealing method of the metal strip coil which concerns on this invention.
In the figure, 7 is a plate-shaped heat insulating material, 8 is a support member, 9 is an inner cover, and 10 is a slit.

In this embodiment, the radiation heat described in the first embodiment is blocked by closing the opening on the upper surface of the coil 1 with the plate-like heat insulating material 7 as shown in FIG. Specifically, the support member 8 is attached to the plate-shaped heat insulating material 7, the inner cover 9 is provided with a slit 10, and the plate-shaped heat insulating material 7 is slid from the furnace wall by the support member 8 through the slit 10. It is preferable to do.
Further, in order to release the above-described blocking of the radiant heat, it is preferable to slide the plate-like heat insulating material 7 toward the furnace wall as shown in FIG. Alternatively, as shown in FIG. 5, the plate-like heat insulating material 7 may be slid up and down.

In addition, in the place shown in FIG. 3, it is preferable to make the clearance gap between the coil internal peripheral surface 4 and the pipe-shaped heat insulating material 5 uniform in the circumferential direction, and to minimize it from the standpoint of obtaining a radiation heat blocking effect. For this purpose, the cross-sectional shape of the pipe-shaped heat insulating material 5 is preferably circular as shown in the figure.
In addition, in the place shown in FIG. 4, the shape of the plate-shaped heat insulating material 7 is not particularly limited. However, from the viewpoint of generating a symmetrical temperature distribution in the coil 1, it is optimal to have a disk shape as illustrated. is there. The diameter of the disk shape is preferably {coil inner diameter + (0.1 to 0.6) t}, where the coil thickness is t (= coil outer diameter−coil inner diameter). More preferably {coil inner diameter + (0.2 to 0.4 t)}.
If the diameter of the disk is less than (coil inner diameter +0.1 t), the heat blocking effect is not sufficient, and if it exceeds one (coil inner diameter +0.6 t), the heat input from the upper surface of coil 1 to the inside of coil 1 is reduced. This is because the time required for the heat treatment is reduced.

Examples of the present invention will be described below.
An experiment using an actual machine was performed on a coil made of an iron plate having a length of 3000 m and a weight of 10 t.
Specifically, annealing heat treatment, soaking treatment and cooling treatment were sequentially performed as shown in FIG. In the heat treatment, the furnace temperature was raised to 620 ° C., and the heating was finished when the measured temperature of the thermocouple installed at the center of the coil cross section (position indicated by P in FIG. 3 (a)) reached 600 ° C. . Thereafter, the furnace temperature was maintained at 620 ° C. for 10 hours (soaking), and then cooling treatment was started. The cooling end time was the time when the measured temperature of the thermocouple was lowered to 100 ° C.
Specific conditions are shown in Table 1. 1-5.

No. Reference numeral 1 is a conventional example that does not block radiant heat to the inner peripheral surface of the coil. No. 2 is a comparative example in which radiant heat is cut off during both heat treatment and cooling treatment. No. 3 is the invention example 1 which uses the pipe-shaped heat insulating material 5, as shown in FIG. No. 4 is the invention example 2 which uses the plate-shaped heat insulating material 7, as shown in FIG. No. 5 is No.5. 4 is Invention Example 3 in which the blocking of radiant heat is released in the latter half of the heat treatment. The release of the radiant heat block was performed when the thermocouple temperature reached 500 ° C.
The heat treatment described above was performed with each of the above-described actual machines, and the length of occurrence of a coil defect (defective shape or scratch) and the time required for heat treatment and cooling treatment were investigated.
The results are shown in Table 2.

No. of the conventional example. In No. 1, the heat treatment time was the shortest, but the length of the iron plate on which the defect occurred was extremely long, and the productivity was poor. Comparative Example No. In No. 2, no. Although the number of defects was greatly reduced as compared to 1, the defect still occurred at a length of 300 m, and the annealing time for 20 hours was extended.
No. of Invention Example 1 In No. 3, the defect occurrence length was very short, and although the annealing time was increased by 10 hours compared with the conventional example, the productivity was greatly improved. No. of Invention Example 2 In No. 4, defects could be completely prevented. Furthermore, No. 3 of Invention Example 3 was obtained. In No. 5, not only the occurrence of defects could be prevented completely, but also the heat treatment time could be maintained at the same level as in the conventional example.
No. 3 and no. From the comparison of 4, it can be seen that the use of a plate-like heat insulating material that can completely block the radiant heat to the coil inner winding provides a more remarkable effect than the use of a pipe-like heat insulating material. No. 2 and No. From the comparison of 4, it can be seen that it is important to release the interruption of radiant heat during the cooling process in order to reduce defects.
From the above examples, it was confirmed that the metal strip coil annealing method and annealing furnace according to the present invention can optimize the temperature distribution in the metal strip coil and reliably prevent the occurrence of shape defects and scratches.

DESCRIPTION OF SYMBOLS 1 Metal strip coil 2 Hearth 3 Heat insulating material 4 Coil inner peripheral surface 5 Pipe-shaped heat insulating material (heat insulation material)
6 Supporting member 7 Plate-like heat insulating material (heat shielding material)
8 Support member 9 Inner cover 10 Slit

Claims (4)

A metal band coil in which a metal band is coiled is covered with an inner cover, and when the metal band coil is annealed by radiant heat from the inner cover, at least the first half of the annealing is the inner peripheral surface of the metal band coil A method for annealing a metal band coil , comprising: covering the entire inner surface of the metal band coil with a heat blocking material in order to block radiant heat, while releasing the block during the cooling process. In an annealing furnace comprising an inner cover for covering the metal band coil in which the metal band is coiled and radiating radiant heat to heat the metal band coil,
A heat blocking material for blocking radiant heat from the inner cover toward the inner peripheral surface of the metal band coil, a blocking position that covers the entire surface of the inner peripheral surface of the metal band coil during at least the first half of the annealing heat treatment, and a cooling process An annealing furnace characterized in that it is installed so as to be movable between a retreat position for releasing the shut-off.   The annealing furnace according to claim 2, wherein the heat shielding material is a pipe-shaped heat insulating material capable of moving up and down to a coil central space. The annealing furnace according to claim 2, wherein the heat shielding material is a plate-like heat insulating material that can move horizontally or move up and down to the upper surface of the coil central space.

Images