JPH07164017A - Method for joining slab - Google Patents

Abstract

PURPOSE:To enable uniform heating over the width direction of a slab by making the distance by which the end parts in the width direction of a induction heating coil is protruded from the width direction of the slab and the distance between the magnetic pole faces of the induction heating coil and the surfaces of the slabs which are opposed to the magnetic pole faces proper. CONSTITUTION:To efficiently heat the end parts in the width direction of joint surfaces of slabs 9, 10 as well as the vicinity of the middle part, first, the end parts of the slabs evade the outer peripheral end of coil and ends of penetrating flux flows and the magnetic poles of the induction heating coils 11, 12 are outward protruded from the end parts in the width direction of the slabs. And, to reduce a dissipated flux and deflection of magnetic flux, the distance between the coil and the slab is reduced. Then, the amount B of protrusion satisfies 2.0Xdelta<=B in the relation of the depth delta of penetration. When the value of B is smaller than the value which is calculated by 2.0Xdelta, the temp. rising rate in the end parts in the width direction of the joint surfaces are dropped as compared to that in the middle part. And, the distance D between the magnetic pole of the induction heating coil and the slab is taken as a value by which D<=1.5XB is satisfied in the relation to the amount B of protrusion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining steel slabs, particularly in a rolling line. This method, for example, in the entrance side conveying line of finish rolling of hot rolling, the rear end of the steel piece to be conveyed in advance (hereinafter referred to as the preceding steel piece), and the steel piece to be conveyed subsequently to this (hereinafter, referred to as (Trailing billet)
It is useful for continuously hot rolling the steel slab by joining the tip end of the steel sheet and the tip portion of the steel sheet and then subjecting the steel sheet to finish rolling.

[0002]

2. Description of the Related Art As a method for joining a trailing end portion of a preceding steel piece and a leading end portion of a following steel piece in a rolling line while heating each of the steel pieces by resistance heating using an induced current, there is disclosed in Japanese Patent Application Laid-Open No. There is a technique disclosed in Japanese Patent Publication No. 62-234679. In this technology, the abutting surfaces of two steel pieces are made to face each other in a substantially parallel manner with a small gap therebetween, and a medium-frequency or high-frequency power is supplied to a pair of induction heating coils arranged so as to sandwich the upper and lower surfaces of the plate material. An alternating current that vertically penetrates the steel slab produces an induced current in the steel slab to heat the steel slab and press the butt surfaces together.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
When the method disclosed in Japanese Patent No. 4679 is applied to actual steel slab joining, the joining surface of the steel slab may not be uniformly heated in the width direction in some cases, and good joining may not be obtained. Specifically, the degree of temperature rise at the widthwise ends of the steel slab is significantly inferior to that at the widthwise central part, resulting in insufficient joining of the widthwise ends. In order to avoid this, it is possible to increase the pressing force between the abutting surfaces, but such a method of increasing the pressing force has a problem of causing an unnecessarily large equipment such as a clamp that is a pressing unit.

The present invention advantageously solves the above problems, and an object of the present invention is to propose a method for joining steel slabs capable of stably performing uniform heating in the width direction of the steel slabs.

[0005]

Means for Solving the Problems The inventors conducted research on the cause of the above-mentioned different temperature rising rates in the width direction of the billet. It was found that the positional relationship with the heating coil is one of the factors. That is, the position of the pair of induction heating coils arranged so as to sandwich the steel slab was moved variously in the width direction of the slab and the heating rate was examined over the width direction of the slab. There is a situation in which the speed is significantly inferior to that in the width direction, and the region in which the rate of temperature rise is inferior is limited to the width direction end. It was also found that the tendency largely depends on whether or not the steel piece width direction end is located between the magnetic poles of the coil.

From this, the essential constitution of the present invention in which the positional relationship between the steel billet and the induction heating coil is optimized is as follows. In the rolling line on the rolling mill entrance side, the trailing end of the steel piece that precedes the line and the leading end of the steel piece that follows and follows this steel piece are opposed to each other, and the opposed steel pieces are opposed to each other. By disposing one or more pairs of induction heating coils with their magnetic poles facing each other with the rear end portion and the front end portion sandwiched therebetween, and applying an alternating magnetic field penetrating from the magnetic poles of the coils in the thickness direction of the steel strip, In a method of joining steel pieces by a combination of a step of heating the steel pieces with an induction current generated in, and a step of pressing the steel pieces against each other, the magnetic poles of the induction heating coil are arranged in a width direction end portion of the steel piece more than the end portions. The length B (m) of the magnetic pole protruding outward from the steel piece in the width direction is expressed by the following equation in relation to the penetration depth δ of the induced current.

[Equation 2] A method for joining steel slabs, characterized in that

In the rolling line on the entrance side of the rolling mill, the rear end of the steel piece to be conveyed in advance and the front end of the steel piece to be conveyed following the steel piece are made to face each other. The magnetic poles were made to face each other with the rear end and the front end of the steel piece sandwiched between them.
A step of arranging more than one pair of induction heating coils and applying an alternating magnetic field penetrating in the thickness direction of the steel pieces from the magnetic poles of the coils to heat the steel pieces by an induction current generated in the steel pieces; In the method of joining steel pieces in combination with the step of pressing the pieces against each other, the magnetic poles of the induction heating coil are protruded outward from the widthwise end of the steel piece, and the magnetic poles are protruded in the width direction from the steel pieces. A method for joining steel pieces, characterized in that the height B (m) is satisfied by D≤1.5 × B in relation to the distance D (m) between the steel piece and the magnetic pole.

[0008]

1 to 3 are views showing a joining region between a preceding steel piece and a following steel piece for explaining the present invention. Figure 1
Is an example using what is called a C-type coil as an induction heating coil. This C-type coil 1 is formed by winding a current-carrying coil 2 in the vicinity of a gap of an iron core 3 having a substantially C-shape. By connecting the energizing coil to the AC power source 4, the facing surfaces of the gap of the iron core 3 form a pair of magnetic poles, and a magnetic flux is formed in this gap. Then, by passing the steel piece 5.6 through this gap, the magnetic flux penetrates in the thickness direction of the steel piece.

Further, FIG. 2 shows an example in which two pairs of the C-shaped induction heating coils 1 shown in FIG. 1 are arranged in the width direction of the steel pieces when joining the wide steel pieces 7 and 8. Furthermore, FIG. 3 is an example using an induction heating coil that is not a C type, and
The coils 11 and 12 are arranged so as to sandwich the joint ends of the above and below, and the AC power source 4 is connected to the coils 11 and 12.

The induction magnetic flux generated between the magnetic poles of the induction heating coil shown in FIGS. 1 to 3 is roughly divided into those which penetrate the steel piece in the thickness direction of the steel piece (I), and the steel piece in a space outside the steel piece. One is formed in parallel with the thickness direction (II), and one that dissipates the steel slab without penetrating the space (III). Among these induced magnetic fluxes, it is the magnetic flux (I) that penetrates the steel sheet in the thickness direction of the steel sheet that contributes to the current induced in the steel sheet, and the magnitude of the change rate of the vertical component of (I) is the induced current. It can be said that the greatest point of the present invention is that the device is devised so as to secure a large amount of magnetic flux as described in (1) because it is proportional to the strength of.

That is, since the widthwise end portion of the joining end portion (the rear end portion of the preceding steel piece or the leading end portion of the trailing steel piece) is surrounded by a space, the steel piece near the widthwise end portion is surrounded. The magnetic flux formed between the magnetic poles arranged so as to sandwich is bent so as to approach the steel piece. Because the magnetic permeability of the steel piece is larger than the magnetic permeability of the space, the magnetic flux penetrating the space bends toward the steel piece. Therefore, the magnetic flux that vertically penetrates the billet is also affected, and the billet penetrates the billet in a curved path. As a result, the strength of the vertical component of the magnetic flux penetrating the steel slab is likely to decrease as compared to the widthwise center of the joint end.

On the other hand, looking at the induction heating coil, since the magnetic flux induced by the coil penetrates, an induction current is also generated in the iron core as in the case of the steel piece. Here, it is known that the induced current concentrates on the surface and edges of the steel slab or iron core (skin effect), and the region where this induced current flows is inward from the surface of the steel slab or iron core. Is generally defined as the penetration depth δ as the distance (depth). This penetration depth δ
(m) is

[Equation 3] It is represented by.

Therefore, the current induced in the iron core mainly flows near the outer circumference of the coil cross section due to the skin effect. Since the induced current flowing in such an iron core generates a magnetic flux in the direction of canceling the alternating magnetic field generated in the coil, in the vicinity of the outer circumference of the coil iron core, the magnetic flux used for heating the steel piece is higher than that in the central portion of the iron core. Less. In addition, in the vicinity of the outer circumference of the coil core, the dissipation flux as described above
Since a large amount of (III) also occurs, the magnetic flux penetrating the steel piece facing the vicinity of the outer periphery of the iron core is reduced.

From the above, in order to efficiently heat the widthwise end portion of the joining end portion of the steel slab in the same manner as in the vicinity of the widthwise central portion, firstly, the end portion of the steel piece should be connected to the coil outer peripheral end and the through magnetic flux. It is very important to avoid it from the end of the flow and to arrange it inside the magnetic flux flow, that is, to make the magnetic pole of the induction heating coil protrude outside the end in the width direction of the billet. It can be said that it is important to reduce the passage of the penetrating magnetic flux, that is, to reduce the distance between the coil and the steel slab in order to reduce the bending of the coil. By appropriately selecting the above requirements, it becomes possible to uniformly and efficiently heat the steel slab to the end in the width direction.

Therefore, in the present invention, the amount of protrusion B (m)
Satisfies 2.0 × δ ≦ B in relation to the penetration depth δ. When the value of B is smaller than the value calculated by 2.0 × δ, the rate of temperature rise at the widthwise end portion of the joint surface is significantly lower than that in the widthwise central portion, as will be apparent from the examples described later. As a result, good joining over the joining surface cannot be obtained.

Further, the distance D (m) between the magnetic pole of the induction heating coil and the steel piece is set to satisfy D ≦ 1.5 × B in relation to the protrusion amount B. When the value of D is larger than the value calculated by 1.5 × B, the rate of temperature rise at the widthwise end of the joint surface is significantly lower than that at the widthwise center, as will be apparent from the examples described later. As a result, good joining over the joining surface cannot be obtained.

The amount of protrusion B specified in the present invention
Is defined as the smaller protrusion amount of the protrusion amount of the magnetic pole from each of the both ends in the width direction of the billet.
Similarly, the distance D between the steel piece and the coil (magnetic pole) is defined by the larger of the distances from the steel piece to the pair of magnetic poles.

Further, the satisfaction of 2.0 × δ ≦ B and the satisfaction of D ≦ 1.5 × B described above are satisfied if either one of them is satisfied in the width direction of the slab, which is the object of the present invention. Heating can be achieved, but if both are satisfied, a better effect can be obtained.

Further, as an example of the combination of the step of heating the billet by the induced current in the present invention and the step of pressing the billets against each other, 1) the rear end of the preceding billet and the tip of the trailing billet. Regardless of whether the part (bonding region) is in contact or not, when the temperature of this region reaches the target temperature, heating is stopped and then pressed. Regardless of whether it is in contact or not, if the temperature in this area reaches the target temperature, pressing is started with heating continued. 3) Press the steel pieces from the beginning. However, any method of heating the joint area at the same time, 4) pressing the steel pieces from the beginning and then starting heating the joint area may be used.

[0020]

EXAMPLE As an induction heating coil having a C-shaped iron core as shown in FIG. 1, a plurality of induction heating coils having different widths of magnetic poles (dimensions in the direction parallel to the width of the steel piece) facing the steel piece were prepared. By varying the protrusion amount B variously, the cold strip sheet bar (SUS 304, thickness 30 mm, width 1000 mm) after hot rough rolling is 10 mm.
Were heated by induction heating. During this heating, the gap D between the steel plate and the induction heating coil was kept constant at 0.05 m, and the frequency condition of the alternating current applied to the coil was changed to
The test was performed at 100 Hz, 500 Hz, 1 kHz, 10 kHz and 100 kHz (the same input power was applied) to investigate how the heating rate at the widthwise end of the slab changes. To measure the heating rate, a K-sheath thermometer was embedded at a position 2 mm from each end of the width and length of the sheet bar, and current was applied to the induction heating coil for 3 seconds to record the heating curve. The temperature rising rate (° C / s) was determined.

FIG. 4 shows the result of an examination of the relationship between the amount B of protrusion of the magnetic pole and the temperature rising rate at the end in the width direction of the billet from the data thus obtained. In FIG. 4, the amount of protrusion B is considered in relation to the magnetic field influence distance δ, and B / δ is expressed as B
By making it dimensionless, it is shown as a variable that can handle any magnetic pole shape, power supply frequency, and type of steel slab (relative permeability, resistivity). Incidentally, the penetration depth δ is 49 mm, 50 at 100 Hz.
22 mm at 0 Hz, 15 mm at 1 kHz, 5 mm at 10 kHz, 1.5 at 100 kHz
mm, and FIG. 4 shows the average value at each frequency. In addition, the heating rate is based on the case where the protrusion amount B is 4.0 × δ, and the heating rates for other protrusion amounts are
It is arranged in the form of a ratio from this standard heating rate.

It can be seen from FIG. 4 that the heating efficiency is remarkably reduced when a protrusion amount B smaller than 2.0 times the penetration depth δ is used as a boundary. This means that the effect of the width of δ from the outer circumference, which is the magnetic flux influence range in the coil core, is as the actual magnetic flux that vertically penetrates the steel slab.
It can be said that it appears as the influence range of 2δ including the dissipation and bending of the magnetic flux. Also, the protrusion amount B is more than 2.0 times δ.
It was found that the same heating rate can be obtained in the region where is large because the magnitude of the vertical component of the magnetic field is the same. Therefore, it was found that satisfying 2.0 × δ ≦ B is a condition for achieving efficient heating up to the widthwise end portion.

Next, the distance D between the coil and the steel piece is closely related to the bending of the magnetic flux and the dissipation of the magnetic flux. Therefore, when the protrusion amount B is small, it is desirable that the distance D between the coil and the steel piece is also small.

Therefore, the relationship between the ratio of the distance D between the coil and the steel slab to the protrusion amount B and the rate of temperature rise was investigated. As in the above experiment, the width of the magnetic pole facing the steel piece (dimension in the direction parallel to the steel piece width) as an induction heating coil having a C-shaped iron core as shown in FIG. A plurality of induction heating coils with different spacings from the steel slab were prepared, and the cold strip sheet bar (SUS 304, thickness 30
mm, width 1000 mm), facing each other with a gap of 10 mm, and induction heated. The frequency condition of the alternating current applied to the coil during this heating is 100 Hz, 500 Hz, 1 kHz, 10 kHz and 10 kHz.
The test was performed at 0 kHz (the same input power was applied) to investigate how the temperature rising rate at the widthwise end of the slab changes. To measure the heating rate, a K-sheath thermometer was embedded at a position 2 mm from each end of the width and length of the sheet bar, and current was applied to the induction heating coil for 3 seconds to record the heating curve. The temperature rising rate (° C / s) was determined.

From the data thus obtained, the relationship between the distance D between the coil and the steel slab and the rate of temperature rise was examined and the results are shown in FIG. In FIG. 5, the distance D between the coil and the steel slab
Was considered in relation to the protrusion amount B, and D was made dimensionless as D / B. Further, FIG. 5 shows the average value at each frequency. As is clear from FIG. 5, when D / B exceeds 1.5, a rapid decrease in the temperature rising rate was observed. This is D /
When B is within 1.5, it shows that the perpendicularity of the magnetic flux is the path of the magnetic flux that can be sufficiently guaranteed.

[0026]

According to the present invention, the distance B at which the end of the induction heating coil in the width direction protrudes from the width direction of the steel piece is made proper, and the distance D between the magnetic pole surface of the induction heating coil and the surface of the steel piece opposite thereto. By appropriately adjusting, it became possible to perform uniform heating in the width direction of the billet. As a result, there is no edge crack at the widthwise end of the joint during continuous rolling after joining, and at the time of joining, 1-2 kgf / mm
Bonding is possible with a small pressing force of about ² and the pressing equipment can be made very compact. Furthermore, it was possible to improve the rolling pitch by eliminating the need for extra time for heating the end portions in the width direction.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a state of arrangement of induction heating coils in a joining region between a preceding steel piece and a following steel piece according to the present invention.

FIG. 2 is an explanatory view showing another example of the arrangement of induction heating coils in the joining region between the preceding steel piece and the following steel piece in the present invention.

FIG. 3 is an explanatory view showing another example of the arrangement of induction heating coils in the joining region between the preceding steel piece and the following steel piece in the present invention.

FIG. 4 is a graph showing the effect of the ratio of the protrusion amount B and the penetration depth δ on the temperature rising rate at the widthwise end of the joining end.

FIG. 5 is a graph showing the effect of the ratio of the distance D between the magnetic pole and the steel slab and the amount of protrusion B on the temperature rising rate at the widthwise end of the joining end.

[Explanation of symbols]

 1 induction heating coil 2 energizing coil 3 iron core 4 AC power supply 5, 6, 7, 8, 9, 10 steel piece 11, 12 induction heating coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nozomu Tamura No. 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Inside the Chiba Steel Works, Kawasaki Steel Co., Ltd. (72) Toshiaki Amagasa, No. 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Works Co., Ltd. Chiba Steel Works (72) Inventor Hideyuki Nikaido 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Works Chiba Works (72) Inventor Hiroo Yamada 1 Kawasaki-cho, Chuo-ku, Chiba City Kawasaki Steel Co., Ltd. in Chiba Steel Works (72) Inventor Shigeru Isoyama 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. in Chiba Steel Works (72) Takeshi Hirabayashi 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Chiba Works (72) Inventor Kazuo Morimoto 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Sanryo Heavy Industries Co., Ltd. Inside the Hiroshima Laboratory (72) Inventor Gakuo Hashimoto 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Inside the Itami Works, Mitsubishi Electric Corporation (72) Hideo Sakamoto 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Machine Itami Manufacturing Co., Ltd.

Claims (2)

[Claims] 1. In a rolling line on the entrance side of a rolling mill, a rear end portion of a steel piece to be conveyed in advance and a front end portion of a steel piece to be conveyed following the steel piece are opposed to each other, and The magnetic poles were made to face each other with the rear end and the front end of the steel pieces facing each other 1
A step of arranging more than one pair of induction heating coils and applying an alternating magnetic field penetrating in the thickness direction of the steel pieces from the magnetic poles of the coils to heat the steel pieces by an induction current generated in the steel pieces; In the method of joining steel pieces in combination with the step of pressing the pieces against each other, the magnetic pole of the induction heating coil is projected outward from the width direction end of the steel piece, and the magnetic pole is extended from the steel piece in the width direction. B
The relation between (m) and the penetration depth δ of the induced current is given by A method for joining steel slabs, characterized in that 2. A rolling line on the rolling mill entrance side is arranged such that the trailing end of the steel piece to be conveyed in advance and the leading end of the steel piece to be conveyed following this steel piece are opposed to each other. The magnetic poles were made to face each other with the rear end and the front end of the steel pieces facing each other 1
A step of arranging more than one pair of induction heating coils and applying an alternating magnetic field penetrating in the thickness direction of the steel pieces from the magnetic poles of the coils to heat the steel pieces by an induction current generated in the steel pieces; In the method of joining steel pieces in combination with the step of pressing the pieces against each other, the magnetic poles of the induction heating coil are protruded outward from the widthwise end of the steel piece, and the magnetic poles are protruded in the width direction from the steel pieces. A method for joining steel pieces, characterized in that the relationship between the length B (m) and the distance D (m) between the steel piece and the magnetic pole satisfies D ≦ 1.5 × B.