JP2004225068A - Bell type annealing furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bell type annealing furnace in which in regard to the improvement of the bell type annealing furnace applied when coils of hot-rolled steel sheets and cold-rolled steel sheets, etc., are butch-annealed, the difference of the temperature rising speeds or the reaching temperatures at a lower piled coil and an upper piled coil, is eliminated and even in the case of having the difference of the coil piling position, the annealing condition becomes the same. <P>SOLUTION: In the bell type annealing furnace for coil annealing composed of an inner cover for covering a plurality of coils piled in the vertical direction and an outer cover further covering this inner cover and provided with burners at the lower part, a heat preventive plate is set on the outer periphery of the inner cover corresponding to the above burner position. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in a bell-type annealing furnace applied when batch annealing coils such as a hot-rolled steel strip and a cold-rolled steel strip.
[0002]
[Prior art]
FIG. 5 shows a cross section of a conventional bell type annealing furnace, that is, a moving furnace type single stack annealing furnace.
The bell-type annealing furnace includes an outer cover 2 provided with a burner 3 at a lower portion, and an inner cover 1 for preventing combustion gas from entering the annealing atmosphere gas. The coils 4 are stacked inside the inner cover 1 with the convector 5 interposed therebetween. By forcibly convection the atmosphere gas in the inner cover 1, heat transfer by convection is promoted and annealing is performed. Note that FIG. 5 illustrates a four-tiered furnace of coils A to D from below.
[0003]
In such a single-stack bell-type annealing furnace, as a method for eliminating unevenness in temperature in the height direction, a method for forced convection of an atmospheric gas already disclosed in Patent Document 1 and a method for controlling a burner disclosed in Patent Document 2 are disclosed. Etc. are well known.
[0004]
[Patent Document 1]
JP-A-6-116657 [Patent Document 2]
JP-A-6-88138 [0005]
[Problems to be solved by the invention]
In batch annealing using a bell-type annealing furnace, it is effective to increase the size of the coil to be loaded in order to improve the processing efficiency, and the gap between the outer winding portion of the coil and the inner cover is necessarily narrowed.
By the way, in order for the combustion heat of the burner attached to the outer cover to raise the temperature of the coil inside the inner cover, both the heat transfer of the atmospheric gas and the radiant heat of the inner cover contribute. As the gap becomes smaller, the effect of radiant heat becomes relatively large.
[0006]
Therefore, the conventional method of changing the forced convection direction of the atmosphere gas in the inner cover and controlling the burner combustion amount eliminates the vertical temperature difference of the coils stacked in the inner cover, and raises all the coils. It is difficult to make the heating rate uniform.
Here, the temperature difference in the vertical direction can be solved by taking a certain amount of time for soaking in annealing, but the temperature rise rate of each coil cannot be made uniform.
[0007]
In addition, the present inventors have found that in annealing in a so-called HN gas atmosphere, which is a mixed gas of hydrogen and nitrogen of about 3 to 10% in particular, there is a case where a difference occurs in the surface properties of the coil depending on a heating rate. It has been found that in a high Cr steel such as stainless steel, a nitride layer is formed on the surface of the coil due to a rapid rise in heat, and appears as unevenness during subsequent pickling.
[0008]
The present invention provides a bell-type annealing furnace that eliminates the difference between the heating rate and the ultimate temperature of the lower coil and the upper coil as described above, so that the annealing conditions are the same even if the coil stacking position is different. Is what you do.
[0009]
[Means for Solving the Problems]
The bell-type annealing furnace of the present invention improves the inner cover in batch annealing to improve the vertical temperature difference and the temperature rise rate difference in the furnace, thereby enabling uniform annealing.
That is, the present invention provides a coil comprising: an inner cover that covers a plurality of vertically stacked coils; and an outer cover that further covers the inner cover and that has a burner at a lower portion. This problem has been solved by a bell-type annealing furnace for annealing, wherein a heat-insulating plate is provided on the outer periphery of an inner cover corresponding to the burner position.
[0010]
Further, in the present invention, it is preferable that the heat insulating plate is provided so as to be bent so as to be uneven along the outer periphery of the inner cover.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
A preferred embodiment of the present invention will be described with reference to FIG. The same members as those of the conventional bell-type annealing furnace described in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted.
The present invention is characterized in that, as shown in FIG. 1, a heat insulating plate 10 is provided below the inner cover 1 which is directly heated by the flame of the burner 3.
[0012]
By installing the heat shield plate 10, it is possible to prevent overheating of the lower portion of the inner cover 1 and to prevent rapid heating of the outer winding portions of the lower stacked coils (particularly, the coils A and B) due to radiant heat. become.
In addition, as shown in FIG. 2, it is preferable that the heat shield plate 10 be bent and mounted along the outer periphery of the inner cover 1 so as to be uneven. That is, the heat insulating plate 11 shown in FIG. 2 as another embodiment of the present invention is configured such that an uneven iron plate 12 is wound along the outer periphery of the inner cover 1 and a belt 13 is wound around a required portion to be stopped. .
[0013]
By doing so, since only a part of the uneven iron plate 12 is in contact with the inner cover 1, it is possible to prevent fluctuation and deformation of the heat shield plate 11, while securing a sufficient gap between the heat shield plate 11 and the inner cover 1. As a result, the temperature of the lower portion of the inner cover 1 is not unevenly raised.
In FIG. 2, an example in which the uneven iron plate 12 is wound along the outer periphery of the inner cover 1 is shown, but the iron plate to be wound is not limited to a rectangular uneven shape as shown in the drawing. It may be a shape folded in a bellows shape.
[0014]
【Example】
Actual annealing was performed using the conventional bell-type annealing furnace shown in FIG. 5 and the annealing furnace of the present invention shown in FIG. 1, respectively, and the temperature rise inside the inner cover was compared. In addition, in the annealing furnace of the present invention, the heat insulating plate 10 was bent and mounted along the outer periphery of the inner cover 1 so as to be uneven, as shown in FIG.
[0015]
FIG. 3 is a graph showing the temperature rise of four coils A to D (A to D) in the conventional bell type annealing furnace shown in FIG. BLT is the bell temperature, which indicates the transition of the temperature at the top of the inner cover.
In FIG. 3, the temperature rise of the coils A and B, which are the lower coils, is steeper than the temperature rise of the coils C and D, which are the upper coils. It is uneven.
[0016]
On the other hand, in the bell type annealing furnace shown in FIG. 1 equipped with the heat insulating plate of the present invention, as shown in FIG. 4, the temperature rises of the four coils A to D (A to D stacks) are almost the same. Has achieved soaking.
That is, as shown, in both cases of FIGS. 3 and 4, the annealing temperature finally becomes uniform, but in the conventional example (FIG. 3), the heating rate varies considerably depending on the coil stacking position. The temperature of the outer winding of the lower two coils near the burner rises considerably faster than that of the upper coil. On the other hand, in the example of the present invention (FIG. 4), such non-uniformity of the temperature rise does not occur, and the temperature rise rate of the lower coil and the upper coil is almost equal to the final temperature. It has become possible to perform annealing under the same conditions without depending.
[0017]
【The invention's effect】
According to the present invention, it was possible to eliminate the difference in annealing conditions depending on the coil stacking position in the furnace, which was a problem in the related art. In addition, even in the annealing of a high Cr steel in an HN gas atmosphere, nitriding due to rapid heating can be effectively prevented, and the occurrence of unevenness during pickling can be effectively suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic view of a bell-type annealing furnace showing a preferred embodiment of the present invention.
FIG. 2 is a schematic view showing another preferred embodiment of a heat shield applied to the present invention.
FIG. 3 is a graph showing transition of a conventional temperature rise of each coil stacked in a bell-type annealing furnace.
FIG. 4 is a graph showing a transition of a temperature rise of each coil stacked in a bell-type annealing furnace by applying the present invention.
FIG. 5 is a schematic diagram illustrating a conventional bell-type annealing furnace.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Inner cover 2 Outer cover 3 Burner 4 Coil 5 Convector 10, 11 Heat insulation plate 12 Irregular iron plate 13 Belt

Claims (2)

An inner cover that covers a plurality of vertically stacked coils,
An outer cover which further covers the inner cover and has a burner at a lower part thereof,
A bell-type annealing furnace for coil annealing comprising:
A bell type annealing furnace, wherein a heat insulating plate is provided on an outer periphery of an inner cover corresponding to the burner position. The bell-shaped annealing furnace according to claim 1, wherein the heat insulating plate is provided so as to be bent so as to be uneven along the outer periphery of the inner cover.

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