JPH07268492A - Electric heating method of metallic strip - Google Patents

Abstract

PURPOSE:To provide an electric heating method of metallic strips in which the variation in tension generated at the time of heating in the vicinity of the weld zones of metallic strips with different sizes is absorbed in electric heating for the same. CONSTITUTION:This is an electric heating method of metallic strips in which, in the case the weld zones of metallic strips 1a and 1b with different cross-sectional areas are subjected to electric heating by a continuous running electric heating device for metallic strips, the variation in the passing tension of the metallic strips caused by the difference in temps. unavoidable before and after the weld places is measured or the variation is predicted, and, according to the measured quantity or predicted value, the axial center of a running developing device 5 arranged at electric heating electrodes 2 and 3 or in the vicinity of the same is moved to allow the variation in tension to absorb. Thus, the variation in tension generated at the time of heating in the vicinity of the weld zones is absorbed, the meandering of metallic strips caused by tension variation is prevented and a stable and suitable heating is made possible to improve the efficiency of the operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric heating method for continuously heat treating a metal strip.

[0002]

2. Description of the Related Art Conventionally, as a heating method in a continuous annealing furnace for metal strips, a direct fire type non-oxidizing heating method, a radiation tube heating method and the like have been used. Since this is a heating method by means of, the heating time per unit time must be long, and the heating time is inevitably long.

In response to such a heating method using heat transfer, a method of directly energizing a metal strip to heat it has been proposed in recent years. For example, Japanese Patent Publication No. 60-26818 proposes a method in which a metal strip is directly energized and heated through an energizing roll.

Further, in Japanese Patent Laid-Open No. 01-142032, a current-carrying roll is provided in front of and behind a metal band passage penetrating an annular transformer, and the two current-carrying rolls are connected by a conductive member to form a metal band, a current-carrying roll and a conductive member. Discloses a method in which an induction current is generated by using a closed circuit as a secondary coil and heating is performed by Joule heat due to the induction current.

[0005]

By the way, in these electric heating methods, the temperature of the strip abruptly changes when a welding portion having a different cross-sectional area passes through the electric roll.
Due to this change, tension fluctuations occur due to the thermal expansion of the steel sheet that occurs instantaneously.

Since this fluctuation in tension leads to unstable operation, conventionally, when the welded portion passed through the energizing roll, the power was temporarily turned off or the strip running speed was extremely reduced.

However, in the method of temporarily turning off the power supply, the constant length of the different cross-section area is not annealed at all, and the non-annealed part must be cut off. Moreover, since the material of the non-annealed portion is significantly different from the other portions, meandering will occur in the subsequent threading section.

Further, in the method in which the plate passing speed is extremely lowered when the welded part passes, not only the efficiency is lowered but also the soaking time and the cooling time are different from those of the normal heating part, so that the material of the same part is changed. Will occur.

The present invention provides a method for electrically heating metal strips of different sizes, which absorbs fluctuations in tension generated when heating the vicinity of the welded portion.

[0010]

The gist of the first invention is as follows.
When the welding part of a metal strip with a different cross-sectional area is electrically heated by the continuous running electrification heating device of the metal strip, the variation of the tension of the strip passing through the metal strip due to the unavoidable temperature difference before and after the welding part is measured. Based on the above, a method for electrically heating a metal band is characterized in that the electrode is heated by moving or the axis of the traveling deployment device arranged in the vicinity of the electrode is moved and absorbed.

Further, the gist of the second invention is that, when a welding portion of a metal strip having a different cross-sectional area is electrically heated by a continuous running electrification heating device for a metal strip, the metal is caused by an unavoidable temperature difference before and after the welding portion. Predict the fluctuation of strip tension in advance,
Based on this predicted value, a method for electrically heating a metal band is characterized in that the electrode is heated by moving or the axis of the traveling deployment device arranged in the vicinity thereof is moved.

[0012]

The operation of the present invention will be described in detail below with reference to examples.

FIG. 1 shows a state of being heated in a conventional electric heating device. 1 is a metal band, 1a
Is a metal strip with a large cross-sectional area, 1b is a metal strip with a large cross-sectional area 1
It is a metal strip of small cross-section that is connected to a and subsequently processed. The size of the metal strip 1a is 1 m wide and 0.65 mm thick.
Is. The size of the metal strip 1b is 1 m wide and 0.40 m thick
m.

Ratio of cross-sectional areas of metal strip (cross-sectional area of 1a / 1b
Cross-sectional area) is 1.6, and the plate temperature of the stationary part is 750 ° C. The metal strip is heated by the electric power from the power source 4 via the current-carrying electrode 2 and the electrode 3 on the high temperature side. The distance between the energizing electrode 2 and the high temperature side electrode 3 is 15 m.

When the welded portion passed between the current-carrying electrode 2 and the high temperature side electrode 3, the metal strip meandered greatly. At this time, the steel plate meandered greatly. Various tests and investigations were conducted to investigate the cause.

As a result, when the temperature of the metal strip passes between the current-carrying electrode 2 and the electrode 3 on the high temperature side, the plate temperature in the vicinity of the welded portion of the large cross-section steel plate 1a is locally reduced, and the small cross-sectional area is reduced. It was found that the plate temperature in the vicinity of the welded part of the metal band 1b locally rose, and the tension fluctuated due to the local thermal contraction or expansion of the metal band due to the change in the plate temperature, and the metal band meandered. . The temperature distribution (measured value) of the steel sheet at this time is shown in FIG.

In the case of this embodiment, the large cross sectional area metal strip 1a locally dropped to 470 ° C. and the small cross sectional area metal strip 1b locally rose to 1200 ° C. Current-carrying electrode 2 at this time
The metal strip between the high temperature side electrode 3 and the high temperature side electrode 3 is a stationary part (plate temperature 75
It contracted 12 mm from the 0 ° C. portion) and expanded 19 mm thereafter.

In order to absorb the abrupt contraction and expansion margins, the tension fluctuation absorber 6 is installed in this embodiment. This is shown in FIG. 3 (winding type).

In this embodiment, both bearings of a winding type energizing electrode are supported by a hydraulically operated tension fluctuation absorbing device 6 and can be operated in the piston axial direction, and the tension fluctuation amount is measured. The hydraulic device is operated in a direction to absorb the fluctuation amount. The method of moving the shaft center is not particularly limited, but a hydraulic method is preferable from the viewpoint of control response.

The amount of change in tension can be detected by a tensiometer 7 placed in contact with the metal strip. Alternatively, it can be measured by detecting the variation amount of the hydraulic pressure of the hydraulic operating device. Reference numeral 5 is a traveling deployment device.

As a method of absorbing the tension fluctuation, besides the above method, the tension fluctuation amount of the metal belt is predicted based on the heating temperature of the metal belt estimated from the electric power supplied, the size of the metal belt, and the strip speed of the metal belt. Then, feedforward control may be performed to compensate for this.

As an example of the feedforward control, the following method shown in FIGS. 5 (a) and 5 (b) can be considered. FIG. 5 shows a temperature distribution model in the longitudinal direction of the metal strip during heating by energization under constant current control.

FIG. 5A is a temperature distribution model in the longitudinal direction of the metal strip in the stationary part. The temperature of the metal strip is 2
And the electrode 3 on the high temperature side are assumed to change linearly. Note that T _S is the temperature of the metal strip before heating, T _O is the temperature distribution of the metal strip after heating, E _S is the Young's modulus of the metal strip before heating,
E _O is the Young's modulus of the metal strip after heating.

In this case, the average Young's modulus E _av = (E _S + E _O ) / 2 between the current-carrying electrode 2 and the high temperature side electrode 3 is obtained.

FIG. 5B shows a case where the welding points of the metal strips having different cross-sectional areas are located between the current-carrying electrode 2 and the high temperature side electrode 3 after time t (minutes) after passing through the current-carrying electrode 2. 3 is a temperature distribution model in the longitudinal direction of the metal strip of FIG.

In this case, the temperature of the metal strip having a large cross-sectional area drops sharply at the welding point. This temperature drop margin changes with the movement of the welding point, but the temperature at the moment of the largest drop is T _O / a ² . (However, a = cross-sectional area of large-section metal strip / cross-sectional area of small section) Along with this, Young's modulus sharply increases.

The Young's modulus corresponding to the above T _O / a ² is E ₁
And It is considered that the change in the Young's modulus at this time causes tension fluctuation. When the change in Young's modulus is ΔE _av and the _{strip running} speed is v (m / min), it is expressed as in Equation 1.

[0028]

[ _Equation 1] ΔE _av = (ΔE (t) + ΔE (t) ′) × (L
-Vt) / 2L

[0029]

Where ΔE (t) = (E ₁ −E ₀ ) ÷ (L / v) × t ΔE (t) ′ = ΔE (t) × vt / L

Feedforward control may be performed based on this ΔE _av .

The energizing electrode may be of the pinch type instead of the winding type, but an example of this case is shown in FIG. In this method, a traveling / deploying device 5a is installed outside the energizing electrode 3 and in the vicinity of the energizing electrode 3, and the traveling / deploying device 5a is operated in the same manner as the winding type energizing roll. The same effect can be obtained also in this method.

[0031]

As described above, according to the heating method of the present invention, when the metal strips of different sizes are heated by the current-carrying electrodes, the variation of the tension of the metal strip threading due to the temperature difference is measured, or the variation is measured. By predicting in advance and moving the energization heating electrode or traveling deployer axis based on this measured amount or predicted value, it becomes possible to absorb the tension fluctuations that occur during heating in the vicinity of the weld, and this tension fluctuation It is possible to prevent the meandering of the metal strip associated with the above, and to perform stable and appropriate heating, which can improve the efficiency of operation.

[Brief description of drawings]

FIG. 1 is a schematic side view showing a state in which metal strips having different cross-sectional areas are heated in a conventional winding type electric heating device.

FIG. 2 is a drawing showing a plate temperature distribution in the vicinity of a connection portion during heating by energization.

FIG. 3 is a diagram illustrating an electric heating method of the present invention using a winding type electric heating device.

FIG. 4 is a diagram illustrating an electric heating method of the present invention using a pinch type electric heating device.

FIG. 5 (a) is a temperature distribution model in the longitudinal direction of the metal strip in the stationary part, and FIG. 5 (b) is a case where the welding points of the metal strips having different cross-sectional areas are located between the current-carrying electrode and the high temperature side electrode. 3 is a drawing showing a temperature distribution model in the longitudinal direction of FIG.

[Explanation of symbols]

 1a Large cross-section steel strip 1b Small cross-section steel strip 2 Low temperature side electrode 3 High temperature side electrode 4 Power supply 5 Travel deployment device 6 Fluctuation absorption device 7 Pressure sensor

Front page continuation (72) Inventor Hiroyuki Aiko 1-1 Tobata-cho, Tobata-ku, Kitakyushu City Nippon Steel Corporation Yawata Works Co., Ltd.

Claims (2)

[Claims] 1. A method for electrically heating a welded portion of a metal strip having a different cross-sectional area by means of a continuous running electrification heating device for a metal strip,
The change in the tension of the metal strip passing plate due to the unavoidable temperature difference before and after the welded part is measured, and based on this measured amount, it is absorbed by moving the energizing heating electrode or the axis of the traveling expansion device arranged in the vicinity of it. A method for electrically heating a metal strip, which comprises: 2. When electrically heating a welded portion of a metal strip having a different cross-sectional area by a continuous traveling electric heating device for a metal strip,
By predicting in advance the fluctuation of the tension of the metal strip passing plate due to the unavoidable temperature difference before and after the welded part, based on this predicted value, by moving the energizing heating electrode or the axis of the traveling expansion device arranged in the vicinity of it. A method for electrically heating a metal strip, which is characterized by absorption.