JPS6261652B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an annealing furnace for annealing steel sheet coils, and particularly relates to an annealing furnace for finish annealing steel sheet coils such as grain-oriented electrical steel sheets coated with an annealing separator. .

For example, grain-oriented electrical steel sheets contain 0.085% or less of carbon, 4% or less of silicon, and 0.07% or less of elements such as sulfur and aluminum to promote secondary recrystallization.
A hot coil whose composition has been adjusted to contain less than It is manufactured by final annealing the coil. The final annealing is performed for the purpose of secondary recrystallization, formation of a surface film, and removal of impurities in the steel, and is usually performed in a high-purity reducing atmosphere gas at a high temperature for a long period of time (1100°C or higher).
This is done by soaking for 10 hours or more.

By the way, conventionally, the above-mentioned finish annealing is performed in the first
Since the annealing process was carried out using an annealing furnace with the configuration shown in the figure,
There were drawbacks as described below. That is, FIG. 1 is a schematic cross-sectional view showing a moving hearth type annealing furnace as an example of a conventional finish annealing furnace. A hearth 2 is arranged on the lower side of the heat insulating cover 1 so as to run along the heat insulating cover 1 by means of rollers 3, and a coil holder 5 on which a steel plate coil 4 is placed is attached to the hearth. The steel plate coil 4 is placed on the coil holder 5 so that its axis is perpendicular, and the steel plate coil 4 is covered with an inner cover 7. With the cover 7 filled with a reducing atmospheric gas such as hydrogen, the entire inside of the furnace is heated by a heating device, ie, a burner 8, provided at the lower part of the side wall of the heat-insulating cover 1. Note that reference numeral 9 in FIG. 1 is a sealing portion for sealing between the heat retaining cover 1 and the hearth 2.

However, in the above-mentioned conventional annealing furnace, the burner 8 is installed at a low position to raise the combustion gas or gas whose specific gravity has decreased due to heating, and heat the upper and middle parts of the furnace with these gases. However, this is designed to maintain a nearly uniform temperature throughout the furnace. However, because the burner 8 is installed at a low position, the hearth 2 is directly heated by the burner 8, and its temperature becomes as high as that of the ceiling of the furnace.
As a result, the temperature difference between the hearth 2 and the atmosphere becomes significantly large, so the amount of heat transferred from the hearth 2 to the atmosphere, that is, the amount of heat radiated from the hearth, increases, and the amount of heat stored in the hearth 2 increases. Conventional annealing furnaces have had problems such as poor thermal efficiency and high running costs.

This invention was made in view of the above circumstances, and aims to provide a finish annealing furnace that has good thermal efficiency and can save energy. The heating device is placed above the upper end of the steel plate coil, which is placed on a coil holder so that its axis is perpendicular and covered with an inner cover.

In other words, the inventors of the present invention have conducted extensive research on temperature changes and heat transfer over time in various parts of the furnace based on the installation position of the heating device, and have obtained the knowledge described below, leading to the creation of this invention. .

When a steel sheet such as a grain-oriented electrical steel sheet is annealed, it is usually done by applying an annealing separator such as slurry magnesia to the surface or both sides of the sheet and drying it.
Because the thermal conductivity of the annealing separator is extremely low,
The amount of heat transferred between the winding plates (ie, in the radial direction of the coil) is small, whereas the steel plate itself has high thermal conductivity, so the amount of heat transferred in the width direction of the plate (ie, in the axial direction of the coil) is large. In addition, the coil pedestal on which the annealed steel coil is placed is usually made of heat-resistant steel, but as shown in Figure 2, the thermal conductivity of heat-resistant steel is lower than that of ordinary steel in the range of 0 to 500℃. 1/3 to 1/2 of
Moreover, the thickness of the coil pedestal is set to 100 to 250 mm in order to obtain the necessary strength, so the coil pedestal becomes an obstacle to heat transfer from the lower end side of the steel plate coil, which causes the coil to be annealed. The amount of heat input from the lower end side of the steel plate coil becomes extremely small.

Considering the above two points, the heat input to the steel plate coil should occur mainly from the upper end side, regardless of the installation position of the heating device, and the inventors of the present invention, based on this recognition, As a result of experiments, it was discovered that the steel plate coil could be sufficiently heated even if the heating device was placed above the upper end of the steel plate coil, and this invention was achieved.

Embodiments of the present invention will be described below. FIG. 3 is a schematic cross-sectional view showing a moving hearth type finishing annealing furnace according to the present invention, in which a furnace body, that is, a heat insulating cover 10
is similar to the heat insulation cover in a conventional annealing furnace.
The heat insulating cover 10 has a predetermined length and is configured to be open at the lower end, and a hearth 12 is disposed at the lower end of the heat insulating cover 10 so as to be moved along the heat insulating cover 10 by a roller 11. A coil pedestal 14 is provided on the hearth 12 via a support portion 15 for placing the coil so that its axis is perpendicular. Further, an inner cover 16 is arranged on the hearth 12 to cover the steel plate coil 13 on the coil pedestal 14, and the heat insulation cover 1 is further disposed on the hearth 12.
0, a steel plate coil 1 placed on a coil holder 14 is shown.
A heating device 17 made of a gas burner, a heavy oil burner, or the like is provided toward the inside of the furnace so as to be located above the upper end of the heating device 3 . In addition, the code 1 in Figure 3
Reference numeral 8 denotes a sealing portion, which is formed by immersing the lower end of a sealing plate 19 projecting downward on the lower edge of the heat-insulating cover 10 and the lower side of the hearth 12 in a sealing liquid 20. It is designed to seal between it and the hearth 12.

To anneal the steel plate coil 13 using the above-mentioned annealing furnace, the steel plate coil 13 is placed on the coil pedestal 14 so that its axis is perpendicular, and the inner cover 16 is placed over the steel plate coil 13.
The inner cover 16 is filled with a reducing atmosphere gas such as hydrogen, and in this state the inside of the furnace is heated by the heating device 17. Then, the temperature gradually rises from the upper side (ceiling side) inside the heat insulating cover 10, but since the steel plate coil 13 has good heat conduction in its axial direction as described above, the temperature on the hearth 12 side increases. Even if the temperature does not become too high, the temperature of the entire steel plate coil 13 begins to rise.

4 and 5 are graphs showing the results of measuring temperature changes at various points after the start of heating for the conventional annealing furnace shown in FIG. 1 and the annealing furnace according to the present invention shown in FIG. 3. . In addition, in this experiment,
As a steel sheet coil to be annealed, a grain-oriented electrical steel sheet containing 4% or less silicon in order to impart magnetic properties is hot-rolled, then cold-rolled and annealed one or more times, and an annealing separator is applied. I used one wound around a coil. In addition, the polygonal lines A to D in FIG. 4 and polygonal lines A1 to D1 in FIG. Point C, C1
In addition, temperature changes in the ceiling portions D and D1 of the heat-retaining covers 1 and 10 are shown, respectively.

As shown in Fig. 4, in the conventional annealing furnace, the temperature of the upper surface B of the hearth 2 remains at a high temperature comparable to that of the ceiling D, and the temperature of the lower surface A of the hearth 2 also rises linearly. The temperature eventually rose to around 350°C (after 70 hours). On the other hand, in the annealing furnace according to the present invention, as shown in FIG. The temperature remained lower by about 50 to 400°C than in the conventional annealing furnace, and the temperature of the lower surface A1 of the hearth 12 also remained lower by 50 to 100°C. Furthermore, in the annealing furnace according to the present invention, the temperature at the coldest point C1 of the steel sheet coil 13 remains about 50°C lower than that in the conventional annealing furnace, but eventually (after 70 hours) The temperature could be raised to the same temperature (approximately 1200℃) as in the case of .

As is clear from the above results, in the annealing furnace according to the present invention, since the temperature of the hearth 12 remains low, the heat storage loss in the hearth 12 is small, and the lower surface A1 of the hearth 12 in contact with the atmosphere is reduced. Since the temperature remains low, it is recognized that the amount of heat transferred to the atmosphere, that is, the amount of heat released, decreases. Therefore, according to the annealing furnace of the present invention, in the heating process, out of the heat input by the heating device 17, the amount of heat used to heat parts other than the steel plate coil 13 and the amount of heat dissipated to the atmosphere are reduced, so that the thermal efficiency is improved. can be significantly improved compared to conventional annealing furnaces.

Although the above embodiment has been explained by taking a moving hearth type finish annealing furnace as an example, the present invention is not limited to the above embodiment, but can also be applied to a batch type finish annealing furnace. It can also be used when annealing steel sheets other than magnetic steel sheets.

As is clear from the above description, according to the finish annealing furnace of the present invention, the heating device for heating the inside of the furnace is mounted on a coil holder so that the axis is perpendicular, and the steel plate coil is covered with an inner cover. Since the structure is provided above the upper end, the heating of the steel plate coil is at least approximately as low as that of the conventional method, since the steel plate coil is heated and heated mainly by heat conduction in its axial direction. In contrast, in terms of heat loss, the amount of heat spent heating the hearth is smaller, and the amount of heat radiated to the atmosphere is accordingly smaller, so the overall heat loss is lower than before. Therefore, according to the annealing furnace of the present invention, not only can the steel plate coil be heated without any trouble, but also the thermal efficiency can be improved more than ever before.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view showing an example of a conventional annealing furnace, Fig. 2 is a graph showing the thermal conductivity of heat-resistant steel and ordinary steel forming the coil pedestal, and Fig. 3 is an embodiment of the present invention. 4 is a graph showing the temperature transition at each temperature measurement point in the conventional example shown in FIG. 1, and FIG. 5 is a graph showing the temperature at each temperature measurement point in the embodiment of the present invention shown in FIG. It is a graph showing the transition. 13... Steel plate coil, 14... Coil holder, 1
6... Inner cover, 17... Heating device.

Claims (1)

[Scope of Claims] 1. A steel plate coil to be annealed is placed on a coil holder so that its axis is perpendicular, and the steel plate coil is covered with an inner case, and the outside thereof is further covered with a protective cover. A finishing annealing furnace for a steel sheet coil, characterized in that a heating device for heating the inside of the furnace is provided above an upper end of the steel sheet coil. 2. The finishing annealing furnace for a steel plate coil according to claim 1, wherein the steel plate coil is a steel plate coil coated with an annealing separator. 3. The coil pedestal is provided on a hearth running on a circumference of a predetermined radius, and the protective cover covers the outside of the inner case within a certain range of the running range of the hearth. A finishing annealing furnace for steel sheet coils according to claim 1.