JPS6348927B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a continuous annealing furnace for metal strips, and the technology described in this specification applies to the use of hearth rolls to prevent meandering of the steel strip in the continuous annealing furnace. We propose a continuous annealing furnace with a structure that allows adjustment of the roll crown, especially the thermal crown.

(Prior Art) Conventionally, measures to prevent meandering of a steel strip in a continuous annealing furnace have mainly been taken by installing a steering device, improving roll roughness, and improving the roll profile. For example, the roll profile has a particularly close relationship with the occurrence of meandering, and meandering occurs unless the amount of crown of the roll has a sufficient centering effect on the steel strip. Of course, various roll profiles have been invented to prevent this.

However, it is important to note that with this technology, when the continuous annealing furnace is in operation, the profile will be different from that at room temperature due to the thermal effects from the furnace atmosphere and the steel strip placed on the hearth roll. (thermal crown). Moreover, this thermal crown varies depending on the operating conditions of the continuous annealing furnace (target steel strip temperature, steel strip speed, steel strip dimensions), and in some cases, the roll crown amount may deviate from the appropriate range, causing meandering. becomes. Of course, such a phenomenon cannot be dealt with by conventional methods based on roll crowns at room temperature.

Other techniques for controlling the amount of crown by heating or cooling the roll or by providing a roll bending device are available, for example, in Japanese Patent Laid-Open No.
It has been proposed as No. 177980 and Utility Model Application Publication No. 55-172859. However, in order to apply these methods to actual operations, a crown amount measuring device and a control device must be provided for each roll, which leaves many problems in addition to increased costs.

(Problems to be Solved by the Invention) In consideration of the above-mentioned points, the present invention provides an appropriate roll to advantageously correct the meandering of the strip during threading caused by the influence of thermal crown. The object of the present invention is to propose a continuous annealing furnace having a structure that can maintain the amount of crown.

(Means for Solving the Problems) According to the research conducted by the present inventors, when the temperature of each part of the hearth roll in a continuous annealing furnace was measured, it was found that in the heating zone and soaking zone, the center of the roll and both ends of the roll It was found that there was a temperature difference between 50°C and 250°C depending mainly on the radiant tube temperature. They also discovered that this was the cause of the thermal crown on the roll.

Therefore, the present invention provides a means for controlling the thermal crown between a hearth roll installed in the heating zone and soaking zone of a continuous annealing furnace as shown in the first illustrated example, and a radiant tube located near the hearth roll. It was decided to provide a heat isolation device comprising a heat exchange chamber into which combustion air is introduced and which is preheated by the heat of the radiant tube. Specifically, as shown in the second illustrated example, the above-mentioned problem can be solved by having a structure of a continuous annealing furnace in which the heat cutoff device is composed of a requiperator attached so as to surround a part of the radiant tube. do.

(Function) FIG. 3 shows the arrangement of hearth rolls and radiant tubes in the heating zone and soaking zone of a conventional continuous annealing furnace. In the diagram, 1 is hearth roll, 2
is a steel strip, and 3 is a radiant tube. FIG. 4 shows an example of the results of measuring the temperature distribution in the width direction of the roll in the case of such an arrangement. As can be seen from this figure, in the heating zone and soaking zone, the temperature of the part where the hearth roll 1 is in contact with the steel strip 2 is
In the case of T _RC , the temperature at both ends not in contact with the steel strip 2 is lower than T _RE , and the overall temperature distribution is concave (as shown in the figure). Furthermore, Fig. 5 shows that the furnace temperature, that is, the radiant tube temperature T _g , is kept constant.
The figure shows changes in roll center temperature T _RC and stream end temperature T _RE when the steel strip temperature T _S is changed by changing the steel strip feeding speed (line speed) LS. As can be seen from this figure, the roll center temperature T _RC fluctuates with changes in the temperature T _S of the steel strip 2, whereas the roll end temperature T _RE is hardly influenced by T _S. The value remains almost constant. From this fact, it can be seen that the roll center temperature T _RC is controlled by the steel strip temperature T _S and that T _RE is controlled by the radiant tube temperature T _g .

By the way, in the actual operation of a continuous annealing furnace,
When heating a steel strip to a specific annealing temperature, the radiant tube temperature T _g is determined by the thickness D and line speed.
Must be changed by LS.

Here, the thermal load L of the furnace can be expressed as the product of the line speed S and the thickness D (L = LS x D), but the greater the thermal load of the furnace, the more it is necessary to increase the radiant tube temperature T _g . There is. However, this increases the temperature T _RE at the end of the roll and reduces the roll crown. In order to prevent this phenomenon and maintain an appropriate roll crown for any furnace load L, from the above, it is necessary to reduce the thermal influence that the radiant tube 3 has on the hearth roll 1. .

Therefore, in the present invention, as shown in FIGS. 1 and 2, a heat isolation device having a heat exchange chamber is interposed between the radiant tube 3 and the hearth roll 1, and as the heat isolation device, the roll of the radiant tube is A large requioperator 4 was installed on the surface of the nearest part. Incidentally, FIG. 2 shows details of the structure of the recuperator 4 and the radiant tube 3. This recuperator 4 differs from a commonly seen structure built inside a radiant tube 3, in which combustion air 7 flows in from the outermost periphery and absorbs the heat of the radiant tube 3, thereby being preheated. At this time, the surface temperature of the recuperator 4 section is naturally lower than the surface of the other radiant tubes 3, and the thermal influence on the facing hearth roll 1 is reduced, achieving a heat shielding effect.

In addition, in this configuration, when the furnace load L increases and the radiant tube temperature T _g increases, the combustion air is increased together with the fuel, so that the increase in the surface temperature of the requiperator 4 is automatically alleviated. It will have a function. With this configuration, the temperature distribution in the roll width direction can always be maintained at a constant value regardless of the furnace load L, and as a result, it is possible to always maintain an appropriate roll crown.

The above has been explained using an example in which the requiperator 4 is provided in the radiant tube 3 closest to the hearth roll 1, but a hollow heat shield plate with a heat exchange chamber inside is provided between the hearth roll 1 and the radiant tube 3 closest to the hearth roll 1. Preheating may be performed by introducing air, and the same effect as the above-mentioned recuperator can be obtained.

(Example) Figure 6 shows the temperature distribution of the roll closest to the radiant tube when the radiant tube 3 with an external requiperator is installed in the furnace, and the temperature distribution of the hearth roll closest to the hearth roll when a normal radiant tube is installed. This is a comparison. As can be seen from this figure, in the case of the present invention, the temperature at the center of the roll
The difference between T _RC and the temperature T _RE at both ends ΔT = T _RE − T _RC is smaller than that of the conventional example, and as shown in Figure 7, the abnormal crown a at room temperature is different from the normal crown a at room temperature. Due to the centering effect caused by the occurrence of thermal crown b, the threading speed LS of the steel strip could be increased by an average of 10%.

(Effects of the Invention) As explained above, according to the present invention, the thermal crown can be effectively controlled, so the meandering of the steel strip is significantly reduced, and as a result, the line speed is increased, so productivity can be significantly improved. Since radiant tube heat is effectively used to preheat the combustion air, it also greatly contributes to energy savings.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a part of the continuous annealing furnace of the present invention, FIG. 2 is a partially cutaway front view showing details of the heat shielding means of the present invention, and FIG. 3 is a conventional continuous annealing furnace. FIG. 4 is a cross-sectional view showing the relationship between the arrangement of hearth rolls and radiant tubes in the furnace. FIG. 4 is a graph showing the temperature distribution in the width direction of the heating zone hearth roll during operation of a conventional continuous annealing furnace. FIG. A graph showing the relationship between radiant tube temperature, steel strip temperature, roll center temperature, and both end temperature in the tropics.
Figure 6 is a graph comparing the temperature distribution in the width direction of the roll in the heating zone and soaking zone of a conventional continuous furnace and a continuous annealing furnace to which the present invention is applied. FIG. 4 is a front view showing the appearance of the roll crown. 1... Hearth roll, 2... Steel strip, 3... Radiant tube, 4... Requioperator, 5...
...Main burner, 6...Pilot burner,
7... Combustion air.

Claims (1)

[Claims] 1 Combustion air is introduced between the hearth roll installed in the heating zone and soaking zone of a continuous annealing furnace and the radiant tube located near the hearth roll, and the combustion air is passed through the radiant tube. 1. A continuous annealing furnace for metal strip, characterized in that it is equipped with a heat cutoff device having a heat exchange chamber for preheating the metal strip with heat from the metal strip. 2. The continuous annealing furnace according to claim 1, wherein the heat cutoff device comprises a recuperator attached to surround a part of the radiant tube.