JP2905377B2 - Method of joining billets in hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of joining steel slabs in hot rolling, and more particularly to a joining method capable of obtaining a good joining state in the sheet width direction even when wide steel slabs are to be joined. It is about the method.

[0002]

2. Description of the Related Art Conventionally, in the hot rolling of steel slabs, since the steel slabs extracted from a heating furnace have been rolled one by one, various troubles described below have occurred particularly in a finish rolling process. . a) Poor biting of the billet tip. b) Narrowing down the rear end of the billet. c) Trouble running on the runout table at the end of the billet. d) Dimensional defects at the front and rear ends of the billet.

[0003] As a solution to the above problem, a leading steel slab (hereinafter, referred to as a "heading") is provided on an inlet side conveyance line of a hot finishing mill.
The leading end of a preceding slab) and the leading end of a slab to be conveyed subsequently (hereinafter referred to as a succeeding slab) are sequentially joined and then subjected to finish rolling, whereby the slab is continuously heated. A method of hot rolling has been proposed, and accordingly, various methods of joining billets have been developed.

[0004] Among them, as a method for completing the bonding in a relatively short time, there is an induction heating pressure welding method disclosed in Japanese Patent Application Laid-Open No. 60-244401. In this method, a rear end of a preceding steel slab and a front end of a succeeding steel slab are induction-heated using a solenoid type coil as a heating means, and then joined by pressing both ends.

[0005]

However, since the above-mentioned method is a method in which a steel piece to be joined is inserted into an electromagnetic induction coil and heated, a steel piece wider than the inner diameter of the coil is used. There was a problem that heating and joining could not be performed. In order to avoid the problem, if a coil having an inner diameter larger than the maximum width steel slab to be joined is prepared, the magnetic flux generated in the coil when joining the narrow width slab is reduced. Since the portion does not contribute to the heating of the billet, there is a problem that the heating efficiency is lower than the input power.

The present invention advantageously solves the above-mentioned problem, and proposes a method of joining steel slabs in hot rolling that can efficiently and quickly join even wide-width slabs. The purpose is to:

[0007]

SUMMARY OF THE INVENTION The present invention relates to a rear end portion of a preceding billet conveyed in advance at the entrance side of a hot rolling facility, and a succeeding billet conveyed subsequently to the preceding billet. The leading end of the preceding slab and the leading end of the succeeding slab were applied with an alternating magnetic field penetrating in the thickness direction of the slab to induce heating at both ends. Thereafter, in a method of butt joining by pressing at least from one side to the other, a plurality of magnetic pole pairs of the induction heating coil for applying an alternating magnetic field across the end of the steel piece to be joined are arranged in the width direction of the steel piece. Te, and the gap between each pole pair, a method of joining the steel pieces in hot rolling, characterized by the following five times the penetration depth d ₀ represented by the following formula. Where d ₀ = {ρ × 10 ⁷ / (μ ₀ × f)} ^1/2 / 2π where d ₀ : penetration depth (m) f: alternating magnetic field frequency (Hz) ρ: electric resistivity of steel slab ( Ω · m) μ ₀ : relative magnetic permeability of steel slab (-)

[0008]

The following is a description of how the method for joining billets of the present invention was developed. The present inventors have conducted research and development on a joining method that can easily, quickly, and reliably join the steel slab without wasting energy when joining the slab, and as a result, FIG. 1 shows a slab joint used in the present invention. As shown in the schematic view of the point, the rear end of the preceding steel slab 1a to be joined and the front end of the following steel slab 1b are several to
An alternating magnetic field penetrating in the thickness direction of the steel slab is applied to each end from an induction heating coil 2 having a pair of magnetic poles arranged with a gap of several tens of mm and sandwiching the steel slab in this area. After heating, it was found that joining by pressing at least one of the steel slabs 1a and 1b to the other was particularly effective. In FIG. 1, the induction heating coil 2 includes an iron core 3 sandwiching a steel slab, a conductor 4 wound around the iron core, and a power source 5 for applying electric power to the conductor 4.

According to such a so-called transverse type induction heating method, as shown in a plan view of the joining region in FIG. 2, the rear end of the preceding steel slab 1a and the front end of the following steel slab 1b are formed. In each case, an eddy current e is induced by an alternating magnetic field applied from a magnetic pole 6 of the induction heating coil (corresponding to the end facing the steel slab of the iron core shown in FIG. 1), and resistance heat generated by the eddy current e causes Since the surface to be joined of the slab is preferentially heated, the slab can be heated efficiently and in a very short time, and the slab can be joined reliably by the subsequent pressing.

[0010] In such a joining method, it is particularly necessary to uniformly flow the induced current flowing on the joining surface (joining surface) of the steel slab over the entire joining surface, in order to obtain good joining. It is important. Here, FIG.
When the magnetic pole width is sufficiently large with respect to the width of the steel slab as shown in (1), the induced current e flows uniformly over the entire joint surface. However, when heating and joining a wide range of slabs, the magnetic pole width is relatively smaller than the slab width. Therefore, since the penetration amount of magnetic flux is reduced at the end of the billet width direction, the induced current is reduced at the width direction end of the joining surface,
It is difficult to perform uniform joining. On the other hand, when the magnetic pole width is increased, it is necessary to increase the current flowing through the induction heating coil in order to obtain a satisfactory amount of magnetic flux penetrating per unit area of the billet. The current flowing through the coil must be controlled so that the coil does not melt down due to Joule heat and the iron core does not melt down.
The power that can be applied to the alternating magnetic field generating coil is limited. Therefore, the amount of magnetic flux per unit area decreases, and as a result, there is a disadvantage that the heating time of the steel slab must be increased.

Therefore, in order to heat and join even a wide steel slab in a short time, the induction heating coil may be divided and a plurality of pairs of magnetic poles may be provided in the width direction. I arrived. However, simply arranging a plurality of magnetic pole pairs along the slab width direction at the joint end of the slab in this way, when the interval between the magnetic poles is large, the temperature of the slab rises in the gap. Because the speed decreases relatively,
When the other region reaches the temperature at which bonding can be performed, a problem occurs in which the temperature at which bonding is not possible has not been reached. On the other hand, if heating is continued until the region where the temperature rise rate corresponding to the magnetic pole gap is reduced to a temperature at which welding can be performed, the other parts will melt down, and the problem of damaging the welding machine will be newly introduced. I found out.

Therefore, in order to solve the above-mentioned inconvenience,
As a result of further research and development by the inventors, the gap between a plurality of magnetic poles arranged along the width direction of the billet is set within a predetermined range according to the frequency of the alternating magnetic field to be applied.
The inventors have found that a decrease in the rate of temperature rise between the magnetic poles can be suppressed within a range in which there is no problem, and have completed the present invention.

This will be described with reference to the drawings. FIG. 3 shows a plan view in which two magnetic poles 7a and 7b are arranged along the width direction of the joint area of the steel slabs 1c and 1d. If the magnetic poles are arranged in such a manner and the gap is set within a predetermined range, the induced currents generated by the magnetic poles are combined to flow a large current. As a result, a decrease in the rate of temperature rise in the magnetic pole gap can be suppressed.

Regarding the range of the magnetic pole gap, d ₀ = {ρ × 10 ⁷ / (μ × f)} ^1/2 / 2π where d _{0 is the} penetration depth (m F: Alternating magnetic field frequency (Hz) ρ: Electric resistivity of slab (Ω · m) μ: Less than 5 times the penetration depth d ₀ (m) calculated by relative permeability (-) of slab It is important to do it. 4, the magnetic poles of the two pairs are arranged on the steel strip width direction, in the case of changing only the pole gap variously, the impact value of the ratio of the pole gap for penetration depth d ₀ is on the pole in the joint surface The ratio of the rate of temperature rise of the portion corresponding to the magnetic pole gap when the corresponding portion is 100%, and the rate of temperature rise of less than 90% for the portion corresponding to the magnetic pole in the width direction of the joint surface. The results obtained by examining the length of the region are shown in a graph. Other conditions at this time are as follows: billet width: 1500m
m, magnetic pole width: 1000 mm × 2 units, applied power: 1000 KW, and alternating magnetic field frequency: 1 KHz.

As is apparent from FIG.
₀ In the case of larger than 5 times, the portion corresponding to the magnetic pole gap
90% of the heating rate of the part corresponding to the magnetic pole
And there are concerns that problems may occur in actual operations.
Was. In addition, the region where the temperature rise rate is less than 90% gradually increases from 0.
Become larger. Therefore, in the present invention, the penetration depth d
₀ Is limited to 5 times or less.

[0016]

The present invention will be described more specifically with reference to the following examples. FIG. 5 schematically shows the entrance-side transfer line of a finishing mill incorporating a suitable joining device used in the embodiment of the present invention. In the figure, reference numeral 8 denotes a coil box for rewinding a coiled steel piece, 9 denotes a pinch roll, and 10 denotes a leveler. Reference numeral 11 denotes a cutting device for adjusting the shape of the steel piece end portion, and reference numeral 12 denotes a joining device including an induction heating coil, a power supply, a carriage, and the like. On the upstream side of the joining device 12, a width gauge 13 is provided to measure the width of the slab, and when the slab width is larger than the magnetic pole width of the induction heating coil, a plurality of induction heating coils are moved in the slab width direction. To be placed in Although FIG. 1 shows an example in which the heating and joining processes are performed during the so-called running while synchronizing with the traveling of the steel slabs 1a and 1b as the joining device 12, the present invention is not limited to the running joining device. Heating and joining processing may be performed with the joining device 12 stopped, in which case, a looper 14 indicated by a broken line is used. Reference numeral 15 denotes a descaler, and reference numeral 16 denotes a first stand of the finishing mill.

In the present invention, first, the cutting device 11 cuts the rear end of the preceding steel slab 1a and the front end of the following steel slab 1b. The shape of the end portion by this cutting is not particularly limited, and may be any shape as long as the entire surface can be compensated for by deformation due to subsequent pressing. Next, the rear end of the preceding slab 1a and the front end of the following slab 1b
They face each other with a gap. This gap is preferably about several to several tens mm.

Next, the induction heating coil is arranged so as to vertically sandwich the rear end of the preceding slab 1a and the front end of the succeeding slab 1b. As an example of this induction heating coil, in addition to the coil shown in FIG. 2, there is an induction heating coil 17 in which magnetic poles sandwiching a billet shown in FIG. 6 are connected by a C-shaped iron core,
The induction heating coil 17 of FIG. 6 is more preferable because the generated magnetic flux can be effectively applied to the steel slab. Two such C-shaped core induction heating coils are arranged symmetrically from the center in the width direction of the slab in the joining region.

At the time of joining, the slab temperature before finish rolling is about 900 to 1000 ° C., and in this temperature range, the electrical resistivity ρ of the slab is about 120 × 10 ⁸ Ω · m regardless of the steel type. Therefore, when induction heating is performed with the frequency of the alternating magnetic field being 500 Hz, the penetration depth d ₀ can be calculated to be about 25 mm. Here, when the above-described induction heating coil having the C-shaped iron core is arranged, the insulation limit of the two adjacent coils is reduced as shown in FIG.
As shown in FIG. 8, the limit of the pole gap is 150 mm (d ₀ × 6). Therefore, as shown in FIG. 8, the heating calorie distribution in the width direction of the steel slab shows that the heating calorie in the joining region corresponding to the pole gap is As a result, the bonding area corresponding to the magnetic pole gap cannot be sufficiently bonded as a result of not reaching 90% or more of the bonding area corresponding to the magnetic pole.

Therefore, the C-shaped iron core is devised so that a magnetic pole gap that satisfies the present invention is formed. As shown in FIG. 9, protrusions toward the magnetic poles are formed on the iron core, and the magnetic pole gap is reduced to 75 mm. As a result, as shown in FIG. 10, the heating heat can be maintained at 90% even in the magnetic pole gap.
The specific means for satisfying the magnetic pole gap according to the present invention is not limited to the above example of the magnetic pole gap of 75 mm, and the gap may be 0 mm.

When a sheet bar (low carbon steel) having a width of 1800 mm and a thickness of 30 mm as a leading billet and a trailing billet, respectively, is supplied to the hot rolling line shown in FIG. After facing the leading end of the succeeding sheet bar with a gap of 10 mm, the induction heating coil having a C-shaped core shown in FIG. 9 (magnetic pole width 800 mm, magnetic pole length 250 mm) ) Are arranged in the billet width direction with two gaps of 75mm.
Induction heating was performed by applying an alternating magnetic field to the steel slab. The heating conditions at this time are as follows: the input power is 1500 kW and the frequency is 500
Heated at 1400 ° C. over the entire sheet bar by heating at Hz for 10 seconds. Subsequently, the steel slab was pressed with a pressing force of 3 kgf / mm ² to complete the joining. After joining, rolling was performed to a plate thickness of 3 mm by a 7-stand hot finishing mill. At that time, good continuous rolling could be continued without breaking the joining region.

[0022]

According to the present invention, in a method of joining slabs for induction heating by a magnetic flux penetrating in the thickness direction of the slab, a plurality of induction heating coils are arranged in the width direction of the slab.
By setting the gap within a predetermined range, good heating can be performed over the entire surface even with a wide billet, and as a result, a good joint surface can be obtained and stable continuous hot finish rolling can be performed. .

[Brief description of the drawings]

FIG. 1 is a schematic view of a billet joining apparatus used in the present invention.

FIG. 2 is a plan view of a joint area of a billet.

FIG. 3 is a plan view arranged along a width direction of a joining region of two magnetic pole pieces.

FIG. 4 is a graph showing the effect of the value of the ratio of the magnetic pole gap to the penetration depth d ₀ .

FIG. 5 is a schematic diagram of an entrance-side transfer line of a finish rolling mill incorporating a joining device suitable for use in the embodiment of the present invention.

FIG. 6 is a diagram showing another example of the induction heating coil used in the present invention.

FIG. 7 is a cross-sectional view illustrating a conventional joining procedure.

FIG. 8 is a graph showing a heating calorie distribution in a billet width direction in a conventional joining procedure.

FIG. 9 is a cross-sectional view illustrating a joining point of the present invention.

FIG. 10 is a graph showing a heating calorie distribution in a slab width direction in the joining procedure of the present invention.

[Explanation of symbols]

 1a, 1c Leading slab 1b, 1d Trailing slab 2 Induction heating coil 3 Iron core 4 Conductor wire 5 Power supply 6 Magnetic pole 7a, 7b Magnetic pole 8 Coil box 9 Pinch roll 10 Leveler 11 Cutting device 12 Joining device 13 Width meter 14 Looper 15 Descaler 16 First stand of finishing mill 17 Induction heating coil

──────────────────────────────────────────────────の Continuing on the front page (72) Nozomi Tamura 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works (72) Hiromi Yamada 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Inside Steel Works, Chiba Works (72) Inventor Hideyuki Nikaido 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Works Inside Chiba Works, Chiba (72) Inventor Shigeru Isoyama 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Corporation Company Chiba Works (72) Inventor Takeshi Hirabayashi 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd.Chiba Works (72) Inventor Kanji Hayashi 4-622 Kannon Shinmachi, Nishi-ku, Hiroshima Hiroshima Prefecture Mitsubishi Heavy Industries Hiroshima Manufacturing Co., Ltd. (72) Inventor Hiroo Hashimoto 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Corporation (72) Inventor Hideo Sakamoto 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Corporation Itami Works (56) References JP 4-89109 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) B21B 1/26 B21B 15/00 B23K 13/02

Claims (1)

(57) [Claims] At the entry side of a hot rolling facility, a gap is formed between a rear end of a preceding billet conveyed in advance and a front end of a succeeding billet conveyed subsequently to the preceding billet. After applying an alternating magnetic field that penetrates in the thickness direction of the slab to the rear end of the preceding slab and the front end of the succeeding slab to induce heating of both ends, at least one of the slabs is directed toward the other. In the method of butt joining by pressing and pressing, a plurality of magnetic pole pairs of an induction heating coil for applying an alternating magnetic field across the end of the steel slab to be joined are arranged in the width direction of the steel slab, and a gap between each magnetic pole pair is provided. a penetration depth d ₀ represented by the following formula
A method for joining billets in hot rolling, wherein the method is not more than 5 times the diameter of the steel. Where d ₀ = {ρ × 10 ⁷ / (μ ₀ × f)} ^1/2 / 2π where d ₀ : penetration depth (m) f: alternating magnetic field frequency (Hz) ρ: electric resistivity of steel slab ( Ω · m) μ ₀ : relative magnetic permeability of steel slab (-)