JP2938689B2 - 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 joins a rear end of a slab to be conveyed in advance and a front end of a subsequent slab to be conveyed subsequently to the steel slab on the entry side of a hot finishing rolling plant. The present invention relates to a method for joining billets in hot rolling, which enables continuous hot finish rolling by performing the method.

[0002]

2. Description of the Related Art Conventionally, in hot rolling of billets, billets extracted from a heating furnace have been rolled one by one. However, in such a method, a) poor biting of a billet tip, b ) Narrowing of the rear end of the slab, c) Trouble running on the runout table at the front end of the slab, d) Dimensional defects at the front and rear ends of the slab, etc. In the entry-side transfer line, a continuous hot rolling method is being adopted in which a rear end of a preceding steel slab and a front end of a steel slab to be subsequently conveyed are sequentially joined and then subjected to finish rolling.

[0003] Here, as a joining method of the billets, a mechanical joining method in which the ends of the billets are overlapped and a wedge is driven into the overlapped portion, the ends of the billets are abutted, and a A joining method in which welding such as thermit is performed and joining is performed, or a joining method in which the ends of the slab are heated by a burner and when the slab reaches a predetermined temperature, the slabs are pressed together to perform joining. However, all of these methods require complicated operations, and it takes a long time to join the billets. Therefore, when joining the billets in a state where the billet is stopped, a long loop is required to absorb them. On the other hand, when the method is performed while the billet is being transported, there is a disadvantage that the equipment length becomes long.

[0004] In order to solve the above problems,
Japanese Patent Application Laid-Open No. 4-89109 discloses that the rear end of a preceding steel slab and the front end of a subsequent steel slab are joined so that at least both ends in the width direction of the slab are in contact with each other, and then penetrate in the thickness direction of the slab. A method is disclosed in which a steel slab is joined by pressing the steel slab while applying heat to the joint by applying Joule heat of an induced current generated by the alternating magnetic field.

[0005]

In the joining method disclosed in the above publication, at least one pair of magnetic poles for applying an alternating magnetic field to a steel slab is arranged with a butt area of the steel slab sandwiched in the thickness direction. doing. Here, if the longitudinal direction of the slab is displaced between the butting area of the slab and the magnetic pole, the slab at the position between the magnetic poles penetrates more magnetic flux than usual, so Since the eddy current generated in the step becomes strong, there is a problem that the temperature rises excessively to reach the melting point of the steel slab, and this part melts down. When such meltdown occurs, there is a remarkable concern that a good bonding interface cannot be obtained and the subsequent hot finish rolling will cause breakage, and that the melted molten steel will fall on the magnetic poles and damage the magnetic field application device. There was also.

The present invention advantageously solves the above-mentioned problem, and proposes a method of joining steel slabs in hot rolling that enables good joining by avoiding melting of a slab joint. With the goal.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a rear end portion of a billet to be conveyed in advance and a leading end of a succeeding billet to be conveyed subsequently to the billet on the entrance side of a hot finishing rolling plant. The part is machined into a shape in which at least both ends in the width direction of the slab contact at the time of butt contact of both, and then the rear end of the preceding slab and the front end of the subsequent slab are brought into contact with each other, Pressing at least one of the steel slabs toward the other steel slab while applying and heating an alternating magnetic field that penetrates the slab in the thickness direction of the slab, in the method of joining the slabs, for applying the alternating magnetic field The steel in hot rolling characterized in that the magnetic poles are arranged such that the deviation between the center of the magnetic pole length in the direction along the length of the slab and the butting area is suppressed to less than 40% of the magnetic pole length. This is a method of joining pieces.

[0008]

The present invention will be specifically described below. In FIG.
An example of an entrance-side transfer line of a finishing rolling mill incorporating a suitable joining device for use in carrying out the present invention is schematically shown. In the figure, reference numeral 1a denotes a billet to be transported in advance (hereinafter referred to as a preceding billet), 1b denotes a subsequent billet (hereinafter referred to as a succeeding billet) to be transported following the preceding billet 1a, 2 denotes a coil box, 3a, 3b and 3c are pinch rolls, 4 is a leveler, 5 is a cutting device, and 6 is a joining device. In the figure, as a joining device 6, heating and joining processes are performed on steel slabs 1a and 1b.
In the case of performing the heating and the joining process in a state where the joining device 6 is stopped, the looper 7 indicated by a broken line is used. become. 8 is the descaler, 9
Is the first stand of the finishing mill.

The joining procedure of the slabs on the entry side conveyance line of the finishing mill shown in FIG.
The rear end of a and the front end of the succeeding slab 1b are machined into a shape such that at least both ends in the width direction of the slab come into contact at the time of butt contact between the two. In the line shown in FIG.
This process has been applied. Then, the rear end of the preceding steel slab 1a and the front end of the following steel slab 1b are brought into contact with each other, and an alternating magnetic field penetrating in the thickness direction of the steel slab is applied to the butting area a by the joining device 6. By pressing at least one steel slab toward the other steel slab while heating, the rear end of the preceding steel slab 1a and the front end of the subsequent steel slab 1b are joined.

As shown in FIG. 2, an example of the main part of this joining apparatus uses a so-called transverse heating method. An alternating magnetic field generating coil for generating an alternating magnetic field.The alternating magnetic field generating coil 10 is composed of a pair of cores 10a, which are provided with steel slabs sandwiched vertically and form magnetic poles, and a coil 10b continuously wound around these cores. And a power supply 10c.

Such an alternating magnetic field generating coil 10 is arranged so that the magnetic pole is located at the butting portion a, and the leading steel slab 1 is formed.
When an alternating magnetic field is applied to the center region of the butting portion a of the subsequent billet 1a, an eddy current e as shown in FIG. 3 is induced in the butting portion a, and the butting contact region is preferentially heated. Will be in close contact. By pressing the slab while performing such heating, the joining area is expanded in the slab width direction, and a joining strength that does not break even in the subsequent finish rolling is obtained.

FIG. 4 in the joining method described above is a plan view of a butt joint of a slab, showing an example in which a gap is provided at the center in the width direction of the slab. (A) in FIG. 3 and (b) in FIG. As shown in FIG. 4 (a), when there is no displacement in the longitudinal direction of the slab between the butted area of the slab and the magnetic pole, the eddy currents e ₂ and e ₃ generated near the magnetic pole are small, and the eddy current e ₂ and e ₃ , the slab is not melted down. However, as shown in FIG. 4 (b), when the butt area of the slab and the magnetic pole are displaced in the longitudinal direction of the slab, the slab is caught by this magnetic pole. In the slab at the position shown in FIG.
_{Since the} strength of ₂ became stronger, there was a problem that the temperature was raised excessively compared with other regions to reach the melting point of the steel slab, and this portion was melted down.

Therefore, in the present invention, the deviation of the magnetic pole for applying the alternating magnetic field between the center of the magnetic pole length in the direction along the length of the steel slab and the abutting region is suppressed to 40% of the magnetic pole length. By arranging, the above-mentioned slab is prevented from being melted down.

In the present invention, the cross-sectional shape of the magnetic pole is not limited to the rectangle shown in FIG. 4, but may be a diamond, a circle, an ellipse, or the like. The central part of the magnetic pole length refers to the central part of these magnetic poles in the cross section, and the magnetic pole length refers to the length of these magnetic poles in the cross section in the longitudinal direction of the steel slab. Further, regarding the deviation between the magnetic pole and the butting area, when a gap as shown in FIG. 4 is formed in the butting area, the center of the gap in the longitudinal direction of the steel slab is used as a reference.

Next, according to the present invention, the above-mentioned deviation is calculated as
% Will be explained. FIG. 5 is a graph showing the results of examining the effect of the deviation on the magnetic pole length on the temperature of the steel sheet at the position sandwiched by the magnetic poles when the joining of the billet is completed. In the figure, the mark ○ indicates the temperature of the steel sheet on the side where the magnetic pole has approached due to the deviation, of the rear end of the preceding steel slab and the tip of the succeeding steel slab, and the mark □ indicates that the magnetic pole has separated due to the deviation. This shows the steel sheet temperature on the side of the steel sheet. The temperature of the steel sheet on the finishing mill side of the hot rolling mill is usually 900 to 1000 ° C., but as is apparent from FIG. 5, when the deviation with respect to the magnetic pole length is larger than 40%, the sheet is sandwiched between the magnetic poles. The temperature at the point where it reached reached 1550 ° C, the melting point of the billet, and the billet melted down.
Therefore, in the present invention, the deviation is limited to less than 40%.

As a specific means for suppressing the deviation to less than 40% as described above, for example, the position of the rear end of the preceding steel slab is calculated from the roll diameter and the number of rotations of the pinch roll 3a on the entry side of the joining apparatus. Then, when reaching the center position of the core, the moving speed of the traveling type joining apparatus and the conveying speed of the billet may be synchronized.

The traveling type joining apparatus has been described above. However, even when a fixed type joining apparatus is used, a displacement in the longitudinal direction with respect to the magnetic pole due to a defective abutment position between the preceding and following steel pieces. However, it is needless to say that the present invention can be applied.

[0018]

EXAMPLE A sheet bar (low carbon steel) having a width of 1000 mm and a thickness of 30 mm is applied to the line shown in FIG. 1 so that the rear end of the preceding sheet bar and the front end of the succeeding sheet bar are shown in FIG.
After cutting into a flat shape as shown in Fig. 2 and making butt contact, the traveling speed of the traveling type joining device and the conveying speed of the slab are synchronized, and 2000 kW of 2,000 kW penetrates the butt portion in the thickness direction of the slab. An alternating magnetic field was applied from a pair of magnetic poles to heat the joint of the slab to 1400 ° C., and pressed to join at a surface pressure of 3 kgf / mm ² . At this time, the magnetic pole has a rectangular cross-sectional shape, a length of 200 mm in the longitudinal direction of the slab, and a length in the width direction of the slab.
300 mm. The gap formed between the preceding sheet bar and the succeeding sheet bar at the center in the width direction of the billet was 40 mm at the start of butt contact and 20 mm at the end of joining. Further, the heating time was 12 seconds.

Here, the displacement in the longitudinal direction of the slab (the displacement toward the preceding slab) between the butt portion of the slab and the center of the magnetic pole is 20.
mm. Then, the temperature of the slab at the position between the magnetic poles was 1230 ° C for the preceding material and 1080 ° C for the succeeding material, and the slab did not melt down. Even if it is rolled to 3 mm, the joining surface does not separate,
Good continuous rolling operation could be continued.

[0020]

According to the present invention, the deviation of the magnetic pole for applying the alternating magnetic field between the center of the magnetic pole length in the direction along the length of the slab and the abutting region is less than 40% of the magnetic pole length. By arranging the steel pieces in such a manner, the steel slab does not melt down at the position sandwiched by the magnetic poles, and good joining was achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of an entrance-side transfer line of a finishing mill incorporating a suitable joining device used in the embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of a main part of a joining device.

FIG. 3 is an explanatory diagram of billet joining by a transverse heating method.

FIG. 4 is a plan view showing a butt joint of a steel slab.

FIG. 5 is a graph showing the effect of the deviation with respect to the magnetic pole length on the temperature of the steel sheet immediately below the magnetic pole when the joining of the billet is completed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1a Leading billet 1b Trailing billet 2 Coil box 3a Pinch roll 3b Pinch roll 3c Pinch roll 4 Leveler 5 Cutting device 6 Joining device 7 Looper 8 Descaler 9 First stand of finishing rolling mill 10 Alternating magnetic field generating coil a Butting portion e Eddy current

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshisada Takechi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works (72) Inventor Hideyuki Nikaido 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Inside the Chiba Works, Steel Works Co., Ltd. (72) Norio Takashima, inventor No. 1, Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Inside the Chiba Works, Chiba Works, Ltd. Mitsubishi Heavy Industries, Ltd. Hiroshima Works (72) Inventor Kazuo Morimoto 4-6-22 Kanon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Research Center (72) Inventor Ikuo Wakamoto 4 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture No. 6-22, Mitsubishi Heavy Industries, Ltd. Hiroshima Laboratory (56) References JP-A-4-89113 (JP, A JP-A-4-288913 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B23K 20/00 340 B21B 1/26 B21B 15/00 H05B 6/10 381

Claims (1)

(57) [Claims] At the entry side of a hot finishing rolling plant, a rear end of a slab to be transported in advance and a tip of a subsequent slab to be transported subsequently to the steel slab are brought into contact at the time of butt contact between the two. At least both ends in the width direction of the slab are processed so as to be in contact with each other. Then, the rear end of the preceding slab and the front end of the subsequent slab are brought into contact with each other. A method of joining at least one steel slab toward the other steel slab while applying and heating an alternating magnetic field penetrating the steel slab, wherein the magnetic pole for applying the alternating magnetic field extends along the length of the slab A method of joining steel slabs in hot rolling, wherein a deviation between a central portion of the magnetic pole length in the direction and the abutting region is suppressed to less than 40% of the magnetic pole length.