JP2905347B2 - 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, a pair of at least one magnetic pole for applying an alternating magnetic field to a steel slab is sandwiched in a thickness direction of a butt region of the steel slab. In addition, they are arranged symmetrically from the center in the billet width direction. In this case, when the magnetic pole is shifted to one end in the width direction when the magnetic pole is displaced in the width direction of the slab in the butt area of the slab due to poor setting of the magnetic pole or meandering of the slab, the magnetic pole is shifted. The rate of temperature rise at the end on the side becomes lower, and the rate of temperature rise at the end on the side farther from the end increases, so that a difference occurs in the rate of temperature rise at both ends in the width direction.

[0006] If the difference in the temperature rising temperature at both ends in the width direction of the billet is remarkable, when one of the ends in the width direction of the billet has reached a temperature range suitable for joining, the other of the ends becomes If this preferred temperature range is not reached, or far beyond this preferred temperature range, the billet will melt down and in each case insufficient bonding will be obtained and subsequent hot finish rolling In this case, the breakage was remarkable.

[0007] The present invention advantageously solves the above-mentioned problems, and suppresses the difference in the rate of temperature rise at both ends in the width direction of the steel slab within an acceptable range, thereby enabling a hot joining that enables good joining. An object of the present invention is to propose a method of joining billets in rolling.

[0008]

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 magnetic pole is characterized in that it is arranged to suppress the deviation between the central part of the magnetic pole length in the direction along the steel slab width direction and the central part of the slab width direction of the butting area within 15% of the magnetic pole length. This is a method for joining billets in hot rolling.

[0009]

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.

[0010] The joining procedure of the billet on the entrance 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 such 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 shows a plan view of a butt joint of billets in an example in which a gap is provided at the center in the billet width direction. As shown by arrows in FIG. 4, when the magnetic poles are shifted from the center of the slab in the slab butt area, the rate of temperature rise at the near end decreases, and the temperature at the distant end decreases. As already described, the rate of temperature rise is increased, and eventually, a difference occurs in the rate of temperature rise at both ends in the width direction.

Therefore, in the present invention, the magnetic pole for applying the alternating magnetic field is determined by calculating the deviation between the central part of the magnetic pole length in the direction of the width of the steel slab and the central part of the butting area in the width direction of the steel slab. The difference in the rate of temperature rise at both ends in the width direction of the billet is suppressed to a range where there is no problem by arranging it within 15% of the height.

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 pole length of
The term "pole length" refers to the central portion in the cross section, and the term "magnetic pole length" refers to the length of these poles in the width direction of the slab in the cross section.

Next, according to the present invention, the above deviation is calculated as
The reason for setting the percentage within% will be described. FIG. 5 is a graph showing the result of examining the effect of the above deviation on the magnetic pole length on the rate of temperature rise at the end of the slab in the case of using the magnetic pole shown in FIG. Here, both ends in the width direction of the slab are set to DS and WS, respectively, and FIG. 4 shows an example in which the magnetic pole is shifted to the WS side. In this case, as shown in FIG.
When the deviation with respect to the pole length is greater than 15%,
Either the WS side is insufficiently heated or the DS side melts down. Therefore, in the present invention, the deviation is limited to within 15%.

As a specific means for suppressing the deviation to within 15% as described above, for example, a billet width meter 11 as shown in FIG. The center of the billet in the width direction may be calculated according to 11, and the magnetic pole in the joining device may be moved so as to coincide with the center of the billet in the width direction.

[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 planar shape as shown in Figure 3 and making butt contact, while controlling to move the magnetic pole in the joining device to the center of the slab width direction, an alternating magnetic field of 1500 kW penetrating the butt portion in the thickness direction of the slab Was applied from a pair of magnetic poles to heat the joint of the steel slabs to 1400 ° C. and pressed at a surface pressure of 3 kgf / mm ² to join them. At this time, the magnetic pole has a rectangular cross-sectional shape,
The length in the billet longitudinal direction is 200 mm, and the length in the billet width direction is 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 shift in the width direction of the slab (the shift to the WS side) between the center in the width direction of the slab and the center of the magnetic pole was 10 mm. Then, when the billet temperature at the end of the billet width direction reached 1330 ° C. on the DS side, it was 1300 ° C. on the WS side. Moreover, even after rolling to a plate thickness of 3 mm by a 7-stand mill, the joined surfaces did not separate, and a 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 from the center of the magnetic pole length along the width direction of the slab to the butting area is 15% of the magnetic pole length.
By arranging them within the range, the heating rates at both ends in the width direction of the slab become almost the same, 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 rate of temperature rise at the end of the billet width direction.

[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 mill 10 Alternating magnetic field generating coil 11 Steel strip width Total a Butt section e Eddy current

Continued on the front page (72) Inventor Hideyuki Nikaido 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works (72) Inventor Norio Takashima 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corp. Inside the steelworks (72) Inventor Takeshi Hirabayashi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Kawasaki Steel Corporation Inside the Chiba Works (72) Inventor Kanji Hayashi 4-6--22 Kanon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries Hiroshima Works (72) Inventor Kazuo Morimoto 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd.Hiroshima Research Laboratory (72) Inventor Ikuo Wakamoto 4-622 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture No. Mitsubishi Heavy Industries, Ltd. Hiroshima Laboratory (56) References JP-A-4-89109 (JP, A) JP-A-4-89110 (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. The 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 is in the width direction of the slab. Wherein the deviation between the central portion of the magnetic pole length along the direction and the central portion of the slab width direction of the abutting region is suppressed to within 15% of the magnetic pole length. Joining method.