JPH07150256A - Device for adjusting temperature of steel strip in continuous annealing furnace and method for flattening steel strip - Google Patents

Abstract

PURPOSE:To obtain a flat steel strip even if uneven temp. in the width direction of the steel strip is developed at the heating step by providing a comparatively simple and cheap steel strip temp. adjusting device in few meter length in a continuous annealing furnace. CONSTITUTION:A temp. adjusting device for steel strip in the continuous annealing furnace arranges plural heating devices 26 and cooling devices 24 in the width direction of the steel strip from the edge parts of the steel strip in parallel to the longitudinal direction of the steel strip faced to the steel strip surface in a soaking zone 16 and a cooling zone, and the distance between the heating device 26 or the cooling device 24 and the steel strip 22 in a cooling zone is adjustable one by one.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature adjusting device for a steel strip in a continuous annealing furnace, and a method for flattening the steel strip by adjusting the temperature of the steel strip to prevent the occurrence of defective shapes.

[0002]

2. Description of the Related Art Many techniques have been proposed in the past for a method or apparatus for preventing the occurrence of defective shape of a steel strip in a continuous annealing furnace, and basically, by adjusting the temperature in the width direction of the steel strip. It is known that it is effective to prevent temperature unevenness.

For example, as a technique for preventing temperature unevenness in the width direction of the steel strip in the heating and soaking stages, in JP-A-58-133326, shortening the contact time with the roll and performing uniform heating, In Japanese Patent Laid-Open No. 62-086126, it is possible to control the heat input amount of a steel strip in the width direction of the steel strip.
62-281291, JP-A-2-175823, JP-A-56
-19563, JP 60-2634, JP 60-24
4418, JP 62-99421, JP 2-1530
26, JP-A-1-157148, JP-A-1-157149
Japanese Patent Publications and the like respectively propose changing the heat input amount in the width direction of the steel strip by various methods.

Further, as a technique for preventing temperature unevenness in the width direction of the steel strip in the cooling stage, for example, JP-A-59-162230, JP-A-57-79156, JP-A-55-158228, and Japanese Patent Laid-Open No. 58-133326, Japanese Patent No. 1374325, Japanese Patent No. 1565883, Japanese Patent No. 12578312, and Japanese Patent Laid-Open No.
In JP-A 62-188731, JP-A-2-66125 and the like, a technique for uniformly cooling the steel strip in the width direction or controlling a temperature difference in the steel strip width direction is proposed. Japanese Patent Sho 61-
Japanese Patent No. 45691 discloses a method in which a plurality of U-shaped cooling tubes are arranged in a cooling zone and the cooling air amount is controlled to uniformly cool the steel strip in the width direction.

[0005]

However, in the prior art, since it is premised that the steel strip is uniformly heated, that is, the temperature difference in the width direction of the steel strip is suppressed for a long time, the continuous annealing furnace is used. Requires complicated equipment for realizing uniform heating in the width direction of the steel strip over the furnace length of several tens of meters constituting the heating zone, and there are problems in equipment cost and operability.

In the method of Japanese Patent Publication No. 61-45691, the cooling rate is controlled by controlling the cooling air flow rate, but since the cooling tube has a heat capacity,
There is a problem that the responsiveness of the temperature in the width direction of the steel strip is poor only by such control of the cooling air flow rate, and sufficient control capability cannot be obtained when changing the width of the steel strip.

The object of the present invention is not to rely on a comparatively simple and inexpensive steel strip temperature control device of several meters and the conventional uniform heating technique using the steel strip temperature control device. It is an object of the present invention to provide a method capable of obtaining a flat steel strip even if the temperature unevenness in the direction occurs.

[0008]

As a result of various investigations by the present inventors in order to solve such problems, the following recognition was first made regarding the current state of the art. The base material of the steel strip to be continuously annealed is flat, and it is heated and cooled uniformly in the width direction of the steel strip in the continuous annealing furnace, and the tension in the steel strip longitudinal direction is uniform in the steel strip width direction. In some cases, it is obvious that the product shape will be flat.

When the flatness of the base material is relatively good, uniform heating in the width direction of the steel strip corrects the shape of the base material due to the elongation generated in the heating stage, and uniform cooling in the width direction of the steel strip. By applying, a product with a good shape can be obtained.

However, it is difficult to obtain a completely flat base material shape by the current rolling technique. When the flatness of the base material is relatively poor, annealing is performed while applying appropriate tension in the longitudinal direction of the steel strip to the steel strip to cause elongation in the longitudinal direction of the strip and improve the flatness of the final product. The method of securing is adopted.

In such a case, the shape of the base material may not be corrected simply by uniformly heating and cooling the steel strip in the width direction. To solve this problem, the above-mentioned conventional technique proposes to correct the shape by changing the amount of cooling air in the width direction of the steel strip in the cooling stage.

On the other hand, the uniform cooling technique is premised on cooling the steel strip whose base material shape is corrected in the heating and soaking stages. Therefore, the uniform cooling technique alone cannot prevent the defective shape of the steel strip. That is, conventionally, uniform heating for a long time or forced correction has been performed.

Therefore, on the premise of such a conventional technique, the significance of the soaking that has not received much attention so far has been examined. As a result, unlike the conventional findings, the temperature difference in the width direction of the steel strip in the soaking and It was found that the soaking time has a critical significance for ensuring the flatness of the steel strip, and that it has a great effect even in a short time. In addition, in the soaking zone, it was unexpectedly found that the temperature difference in the width direction can be easily adjusted by a temperature adjusting device provided with a plurality of heating devices and cooling devices in parallel with the longitudinal direction of the steel strip. More preferably, the inventors have found that a uniform cooling device in the cooling zone is effective in deteriorating the shape of the steel strip once flattened in the soaking zone, and completed the present invention.

Here, in the present invention, in soaking in a continuous annealing furnace, a plurality of steel strips are provided facing the surface of the steel strip, parallel to the longitudinal direction of the steel strip, and sequentially from the end of the steel strip in the width direction of the steel strip. Is a steel strip temperature adjusting device including at least one unit including a heating device and a cooling device.

In a preferred embodiment of the present invention, further, in the continuous annealing furnace equipped with the above-mentioned apparatus, the steel strip is provided from the steel strip end portion in parallel with the steel strip longitudinal direction so as to face the steel strip surface in the cooling zone. A continuous annealing furnace, wherein a plurality of heating devices and / or cooling devices are sequentially provided in the band width direction, and the heating device and / or cooling device and the steel strip are attached so that the distance between them can be adjusted one by one. Is a temperature adjusting device for the steel strip in.

From another aspect, the present invention is characterized in that in the soaking zone of a continuous annealing furnace, the temperature difference in the width direction of the steel strip is kept within 6 ° C. for 10 seconds or more in a temperature range of 700 ° C. or more. It is a method for flattening a steel strip in a continuous annealing furnace.

[0017]

Next, the operation of the present invention will be described in detail with reference to the drawings. Regarding the continuous annealing furnace incorporating the apparatus of the present invention, FIG. 1 is a schematic explanatory view showing the configuration of a generally used horizontal continuous annealing furnace 10, in which the temperature adjusting apparatus of the present invention is soaked and optionally cooled in a cooling zone. Built in.

The continuous annealing furnace comprises a pre-heat zone 12, a heating zone 14,
It is composed of a soaking zone 16 and a cooling zone 18. The pre-zone 12 and the heating zone 14 are heated by an open flame burner or a radiant tube (not shown). In the heating stage of the steel strip, a temperature non-uniformity of up to about 50 ° C. occurs in the width direction of the steel strip at a heating rate of 5 to 40 ° C./sec. For this reason, the elongation becomes uneven in the width direction of the steel strip, and if it is cooled as it is, a defective shape occurs.

The apparatus of the present invention is a small-sized equipment having a length of several meters (for example, 6 meters) and is suitable for a horizontal continuous annealing furnace. A horizontal continuous annealing furnace will be described below. May be applied to. The steel strip processed according to the present invention is not particularly limited, but for example, the thickness is 0.2 to 0.6 mm and the width is 600 to 120.
It is a 0 mm steel strip.

In the temperature control device of the present invention incorporated in the soaking zone
2 with is a cross-sectional view of a temperature adjusting device 20 of the present invention a schematic plan view showing a structure incorporated into a soaking zone 16, FIG. 3 is a line A-A of FIG. In FIG. 2, the steel strip 22 runs from left to right as viewed in the drawing.

The temperature adjusting device 20 of FIG. 2 is composed of units 28a and 28b in the illustrated example, and the unit is composed of an air cooling tube 24 which is a cooling device and an electric heater 26 which is a heating device. The electric heater and the air-cooling tube are provided parallel to the longitudinal direction of the steel strip, and are arranged in this order in the width direction of the steel strip from the end of the steel strip. In the example shown,
An electric heater is further provided at the center. These heating and cooling devices perform temperature control in the strip width direction by appropriately adjusting the output, cooling air flow rate, etc. according to the temperature distribution measurement values in the strip width direction obtained by the strip thermometers 32a to 32c. .
In FIG. 2, an electric heater 26 divided into three in the width direction of the steel strip and an air cooling tube 24 divided into two are used for the sake of simplification of description, but the larger the number of divisions, the easier the temperature control becomes, which is preferable.

The electric heater 26 corrects the temperature difference in the width direction of the steel strip that occurs in the preceding heating zone, and at the same time prevents temperature unevenness such as cooling of the edge portion of the steel strip in the soaking zone. On the other hand, the air-cooling tube 24 provided in parallel with the electric heater 26 along the longitudinal direction of the steel strip cools a high temperature portion near the central portion of the steel strip to reduce the temperature difference in the width direction of the steel strip. A radiation thermometer having a scanning mechanism (not shown) is preferable as the steel strip thermometer for measuring the temperature variation in the width direction of the steel strip.

The heating and cooling capacities of the electric heater and the air-cooling tube differ depending on the size of the steel strip to be processed. For example, two 200 KW electric heaters and four air-cooling tubes with a flow rate of 100 Nm ³ / h may be provided. . Other examples of the heating device of the present invention include induction heating devices, and examples of the cooling device include gas jet cooling.

The furnace body 30 which constitutes the main body of the temperature control apparatus according to the present invention has a heating temperature 70 of the steel strip 22 which is subjected to continuous annealing.
Use a material and structure that can withstand the furnace temperature required to secure 0 ° C or higher.

Regarding the method for flattening a steel strip In the method for flattening a steel strip according to the present invention by controlling the temperature in the preheat zone and the soaking zone after the heating of the heating zone is finished,
When the temperature difference in the width direction of the steel strip exceeds 6 ° C, sufficient flatness cannot be secured. Further, if the temperature of the steel strip is less than 700 ° C, the elongation of the steel strip in the soaking zone cannot be secured, and the flattening effect is weakened. Furthermore, if the soaking time (the time to maintain the temperature difference in the predetermined width direction of the steel strip) is less than 10 seconds, the creep deformation time of the steel strip cannot be secured, and also sufficient elongation cannot be obtained and flatness is achieved. The aging effect diminishes. Therefore, the preferable conditions are a steel strip temperature of 700 to 1100 ° C. and a soaking time of 10 to 25 seconds. It is preferably 850 to 1100 ° C and 12 to 25 seconds. The temperature difference in the width direction of the steel strip is 6 ° C or less, preferably 4 ° C or less, preferably as small as possible. This will be described in more detail in the examples.

Thus, according to the present invention, in the soaking zone,
After correcting the temperature unevenness in the width direction of the steel strip and the defective shape, cooling is performed while ensuring the uniformity in the width direction of the steel strip in the cooling zone.
Although the cooling device in the cooling zone will be exemplified later, the cooling device is not limited thereto, and, for example, as in many conventional techniques, for example, gas jet cooling can be performed to control the air volume in the width direction. Good.

Thus, according to the method of the present invention, the pretropical zone,
Even a steel strip having a maximum temperature difference in the width direction of the heating zone of 50 ° C can be easily flattened, and a substantially flat steel strip can be obtained even if it has undergone a normal cooling history.

In a preferred embodiment of the temperature adjusting device in the cooling zone
4 with the cooling zone of a continuous annealing furnace, schematic plan view showing a structure incorporating a temperature regulating device 20 of the steel strip of the present invention using a cooling device, FIG 5 is a schematic side view of the device of FIG. 4 is there. In the figure,
The steel strip 22 runs from right to left as viewed in the drawing.

Since the steel strip temperature control method conforms to the above description, only the differences will be described. The feature of the apparatus shown in FIGS. 4 and 5 is that it adjusts the distance d between the steel strip 22 and the cooling tube 24.
This is the point where 40 is provided. In the figure, six cooling tubes 24 are provided in total, and six cooling distance adjusting devices 40 for moving the cooling tubes 24 are provided. However, the larger the number, the more advantageous the controllability. The moving speed is within the range allowed by the equipment cost, and it is preferable that the moving speed is high in order to improve the responsiveness. As a specific means, for example, an electric jack is used. By adjusting the cooling distance and the cooling gas, it becomes easy to quickly cool a part of the steel strip and make the temperature of the steel strip uniform.

FIG. 6 is a schematic plan view showing a structure in which a temperature adjusting device 20 for a steel strip of the present invention using a heating device is incorporated in a cooling zone of a continuous annealing furnace, and FIG. 7 is a schematic side view of the apparatus of FIG. It is a figure. In the figure, the steel strip 22 runs from right to left as viewed in the drawing. The feature of the apparatus shown in FIGS. 6 and 7 is that the apparatus 42 for adjusting the distance d between the steel strip 22 and the electric heater 26 is provided as in the above apparatus. The larger the number of electric heaters, the more advantageous in terms of controllability. In the figure, twelve electric heaters 26 and twelve heating distance adjusting devices 42 for moving the heaters are provided. The moving speed is within the range allowed by the equipment cost, and it is preferable that the moving speed is high in order to improve the responsiveness. As a specific means, for example, an electric jack may be used. By adjusting the heating distance and the heating output, it becomes easy to quickly heat a part of the steel strip and make the temperature of the steel strip uniform.

By providing these temperature adjusting devices in the cooling zone for uniform cooling, it is possible to prevent the steel strip once flattened in the soaking zone from being deteriorated in shape in the cooling zone, and to obtain a flatter steel strip. it can. Next, the present invention will be described more specifically by referring to examples.

[0032]

【Example】

(Example 1) Preliminary test First, as a preliminary test, it was examined how the temperature difference in the width direction of the steel strip and the soaking time condition in the soaking zone affect the flatness. FIG. 8 shows a graph comparing the temperature difference in the width direction of the steel strip with the flatness. The soaking temperature (steel strip temperature in the soaking zone)
When the temperature was 700 to 850 ° C and the soaking time was 12 seconds, the temperature difference was 6 ° C or less and good flatness was obtained.

FIG. 9 shows a graph of soaking time and flatness. Soaking temperature is 700 to 850 ℃, temperature difference in the width direction of steel strip is 4 ℃
In the case of, the soaking time was 10 seconds or more and good flatness was obtained. It was also found that if the temperature of the steel strip is less than 700 ° C, the elongation of the steel strip in this soaking zone cannot be secured, and the effect will diminish. Therefore, the preferred conditions of the above embodiment are a steel strip temperature of 700 to 1100 ° C. and a soaking time of 10 to 25 seconds. The temperature difference in the width direction of the steel strip is 6 ° C. or less, preferably as small as possible.

Main Test In this example, the steel strip was continuously annealed using the continuous annealing furnace and the temperature adjusting device shown in FIGS. 1, 2 and 3, and the presence or absence of shape defects was investigated. The steel strip was received from the heating zone and the temperature was adjusted in the soaking zone. At that time, the temperature distribution in the width direction of the strip was 50 ° C at maximum. It was confirmed with a thermometer 32a that the steel strip width temperature was uniform in No. 1 zone, and in No. 2 zone, while maintaining the temperature uniformity in the steel strip width direction, at 700 ° C for 10 seconds or more. The line speed and the like were adjusted so as to carry out soaking. This flattens the strip and then sends it to the cooling zone.

In the cooling zone, the amount of gas jet cooling air flow in the direction of the steel strip was appropriately adjusted, uniform cooling was performed, and after cooling to 150 ° C., it was sent further downstream in the line. Table 1 collectively shows the processing conditions and the results of flatness in this example.

[0036]

[Table 1]

Even if the temperature difference in the width direction and the soaking time are appropriate as shown in Example A, the soaking temperature of 650 ° C does not have a sufficient effect, but as shown in Examples B and C, 700 ° C and 850 ° C. It became flat at the soaking temperature of ℃. When the soaking temperature is appropriate at 850 ° C. and the soaking time is also appropriate at 12 seconds, it becomes flat when the temperature difference in the width direction is 4 ° C. as shown in Example C, while as shown in Examples D and E. As described above, when the temperature difference in the width direction was 8 ° C. and 15 ° C., the surface did not become flat.

Further, as shown in Examples C and F, when the soaking temperature and the temperature difference in the width direction are appropriate, the soaking time is 12 seconds and
At 10 seconds, flatness is obtained, while as shown in Example G,
When the soaking time was insufficient at 8 seconds, it did not become flat.
The steel composition, mechanical properties, and shape of the steel strip used in this example are shown.

[0039]

[Table 2]

(Embodiment 2) Next, as a preferred embodiment of the present invention, a case where the device shown in FIGS. 4 and 5 is incorporated in a cooling zone will be described. This test was conducted without operating the apparatus of the present invention in the soaking zone.

Table 3 shows the device of the present invention, but assuming the prior art, the cooling distance adjusting device 40 is fixed, and the distance d between the steel tubes of the cooling tubes arranged in the width direction is constant. The flatness is shown. In addition, Fig. 10 shows the distribution of the steel strip temperature at that time.

Table 4 shows the flatness of the apparatus of the present invention when the distance d between each cooling tube arranged in the width direction and the steel strip surface is controlled. The flatness is indicated by the height of the peak / wavelength, and the left and right are viewed from the traveling direction of the steel strip. Further, Fig. 11 shows the distribution of the steel strip temperature at that time.

[0043]

[Table 3]

Comparing the above, it is understood that when the distance d from the steel strip surface is controlled, the temperature difference in the width direction at the outlet of the apparatus of the present invention is small and the flatness is high, which is preferable.
The reason for this is that, as shown in Fig. 12, the speed of temperature adjustment is, so to speak, a large difference in response time. It is better to control the distance d from the steel strip surface in a shorter time (if the line speed is the same, It can be seen that there is no temperature difference (with short equipment) and the surface becomes flat.

(Embodiment 3) Next, as a preferred embodiment of the present invention, a case where the device shown in FIGS. 6 and 7 is incorporated in a cooling zone will be described. This test was also conducted without operating the apparatus of the present invention in the soaking zone.

Table 5 shows the apparatus of the present invention, but assuming the prior art, the heating distance adjusting device 42 is fixed, all the outputs of the electric heaters are made constant, and the steels of the electric heaters arranged in the width direction are shown. The flatness is shown when the distance d from the strip surface is constant. Further, Fig. 13 shows the distribution of the steel strip temperature at that time.

Table 6 shows the flatness when the distance d between the electric heaters arranged in the width direction and the steel strip surface is controlled using the apparatus of the present invention. In addition, Fig. 14 shows the distribution of the steel strip temperature at that time.

[0048]

[Table 5]

Comparing the above, it can be seen that when the distance d from the steel strip surface is controlled, the temperature difference in the width direction at the exit of the apparatus of the present invention is small and the flatness is high, which is preferable.
The reason for this is that, as shown in Fig. 15, the speed of temperature adjustment is, so to speak, a large difference in response time. It is better to control the distance d to the steel strip surface in a shorter time (if the line speed is the same, It can be seen that there is no temperature difference (with short equipment) and the surface becomes flat.

[0050]

As described in detail above, according to the present invention,
Temperature can be controlled in the soaking zone of the continuous annealing furnace, and almost perfect flatness can be achieved by controlling the temperature in the width direction of the steel strip. Moreover, the equipment for that is simple and costly. It is advantageous.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of the configuration of a general horizontal continuous annealing furnace to which the present invention is applied.

FIG. 2 is a schematic plan view of a temperature adjusting device for a steel strip provided with a heating device and a cooling device in a soaking zone, which is an example of the present invention.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is a schematic plan view of a temperature adjusting device for a steel strip, which is one example of a preferred embodiment of the present invention, in which a cooling device capable of adjusting a distance from the steel strip is provided in the cooling zone.

5 is a schematic side sectional view of FIG.

FIG. 6 is a schematic plan view of a temperature adjusting device for a steel strip provided with a heating device capable of adjusting a distance from the steel strip in a cooling zone, which is an example of a preferred embodiment of the present invention.

FIG. 7 is a schematic side sectional view of FIG.

FIG. 8 is a graph showing the relationship between the temperature difference in the width direction of the steel strip and the flatness for studying the usage conditions of the device of the present invention.

FIG. 9 is a graph showing the relationship between soaking time and flatness for examining the usage conditions of the device of the present invention.

10 is a graph showing a steel strip temperature distribution when the distance between the cooling device and the steel strip is made constant as shown in Table 3 in the apparatus of FIG.

11 is a graph showing a temperature distribution of steel strip when the distance between the cooling device and the steel strip is appropriately adjusted as shown in Table 4 in the apparatus of FIG.

12] In the apparatus of FIG. 4, the temperature difference between the central portion and the edge portion of the steel strip is reduced when the distance between the cooling device and the steel strip is appropriately adjusted as shown in Table 4 and when it is not adjusted. 3 is a graph showing the state of the above with respect to time (seconds).

13 is a graph showing a steel strip temperature distribution when the distance between the heating device and the steel strip is constant as shown in Table 5 in the apparatus of FIG.

14 is a graph showing a steel strip temperature distribution when the distance between the heating device and the steel strip is appropriately adjusted as shown in Table 6 in the apparatus of FIG.

FIG. 15 shows a reduction in the temperature difference between the central portion and the edge portion of the steel strip in the apparatus of FIG. 6 when the distance between the heating device and the steel strip is appropriately adjusted as shown in Table 6 and when it is not adjusted. 3 is a graph showing the state of the above with respect to time (seconds).

[Explanation of symbols]

 10: Horizontal continuous annealing furnace 12: Pre-tropical zone 14: Heating zone 16: Soaking zone 18: Cooling zone 20: Steel strip temperature adjusting device 22: Steel strip 24: Cooling device 26: Heating device 28a: 1st unit 28b: 2nd Unit 30: Furnace body 32a to 32c: Steel strip thermometer 40: Cooling distance adjusting device 42: Heating distance adjusting device

Claims (3)

[Claims] 1. In a soaking zone in a continuous annealing furnace, a plurality of heating devices facing the surface of the steel strip, parallel to the longitudinal direction of the steel strip, and sequentially provided in the width direction of the steel strip from the end of the steel strip. A temperature adjusting device for a steel strip, comprising at least one unit composed of a cooling device. 2. A continuous annealing furnace equipped with the temperature adjusting device according to claim 1, wherein the cooling zone faces the surface of the strip and is parallel to the longitudinal direction of the strip and extends from the end of the strip to the width direction of the strip. A plurality of heating devices and / or cooling devices are sequentially provided, and the distance between the heating device and / or cooling device and the steel strip can be adjusted one by one. The temperature of the steel strip in the continuous annealing furnace. Adjustment device. 3. A steel strip in a continuous annealing furnace, characterized in that, in the soaking zone of the continuous annealing furnace, the temperature difference in the width direction of the steel strip is kept within 6 ° C. for 10 seconds or more in a temperature range of 700 ° C. or more. Planarization method.