JP2875054B2 - 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 for joining steel slabs suitable for continuous hot rolling of several to several tens of steel slabs such as sheet bars, slabs, billets and blooms. .

[0002]

2. Description of the Related Art Conventionally, in a hot rolling line, a slab to be rolled is heated one by one, roughly rolled, and then finish rolled to finish a hot rolled sheet having a desired thickness. In the final rolling method, it is easy to cause line stoppage due to poor rolling material biting in the finish rolling, and the yield is greatly reduced due to poor shape at the leading and trailing ends of the rolling material. In order to do so, prior to the finish rolling, a rolling method has been adopted in which the rear end and the front end of the steel slabs are joined together and continuously supplied to a hot rolling line. Japanese Patent Application Laid-Open No. 61-144203 is referred to as a reference concerning such continuous rolling of billets.

[0003]

SUMMARY OF THE INVENTION The above-mentioned JP-A-61-144203 is disclosed.
In the technology disclosed in the above publication, the rear end of a slab conveyed in advance (hereinafter referred to as a precedence slab) and a slab conveyed subsequently (hereinafter referred to as , The subsequent billet)
Are butted over the entire surface thereof, and both ends in the width direction thereof are pre-joined, and rolling is to be performed in this state. However, in such a technique, in order to provide a sufficient joining strength to the pre-joined portion, the joining time has to be lengthened, and it is necessary to take measures to extend the line.

[0004] In this regard, the present inventors have previously described in Japanese Patent Application No. Hei.
In the specification of Japanese Patent Application No. 03991 or the specification of Japanese Patent Application No. 2-203992, a method of joining the billets easily and quickly on the entry side of hot rolling was proposed. However, also in the above joining method, under special conditions, that is, the rear end of the preceding slab and a part of the tip of the succeeding slab (including at least both ends in the width direction) are used as joining surfaces, and pressed simultaneously with heating. Under the bonding conditions in which the treatment is performed to gradually increase the bonding area, a uniform temperature distribution is not necessarily obtained over the entire bonding region, and therefore, a sufficiently satisfactory bonding state may not be obtained in some cases.

That is, in such a joining method,
The induced current induced by the alternating magnetic field is set in advance to a constant value (the input power of the induction coil is fixed),
Although it is pressed with a predetermined pressing force, the current density on the bonding surface decreases as the bonding area increases, so that the rate of temperature rise decreases, and there is a limit to shortening the time required for heating. As a countermeasure to avoid such a problem, it is conceivable to set the input power to a high value in advance, but in this case, both ends in the width direction of the steel slab where the heating time is relatively long are required to have a necessary bonding margin. Therefore, it may not be an effective means because it may be melted before obtaining.

According to the present invention, when the above-described joining method is adopted, the temperature distribution in the joining region is made as uniform as possible, and the joining of steel slabs which can obtain a good joining state in a short time. The aim is to propose a method.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a hot rolling apparatus, comprising a rear end portion of a billet conveyed in advance, and a front end portion of a billet conveyed subsequently. And contacting at least at both ends in the width direction of each billet, applying an alternating magnetic field penetrating in the thickness direction of the billet, and pressing while heating by an induced current induced by the alternating magnetic field. A method of joining steel slabs in hot rolling, characterized by increasing the input power of an induction coil that generates an alternating magnetic field in accordance with the enlargement of the joint area when joining while gradually increasing the joint area. In the present invention, the heating method of each steel slab may be an electric heating method.

FIG. 1 shows an arrangement of equipment suitable for carrying out the present invention. In the figure, reference numeral 1 denotes a preceding steel slab which has undergone rough rolling, and reference numeral 2 denotes a succeeding steel slab which is conveyed following the preceding steel slab 1. The billet 3 is a hot finishing rolling equipment in which tandem arrangement of rolling mills F ₁ , F ₂ ,. Reference numeral 5 denotes an alternating magnetic field generator, which comprises a core 5a forming a magnetic pole, a coil 5b, and a power supply 5c. Also, 6
Is a detector for detecting the amount of indentation of the billet, 7 is a calculator for calculating the contact area when the preceding billet 1 and the succeeding billet 2 are joined, 8 is a supplied power calculator, and 9 is a supplied power setter.

[0009]

After cutting the rear end portion of the preceding slab 1 and the front end portion of the succeeding slab 2 so as to form a plane shape as shown in FIG. 2, a region including both ends in the width direction of each slab is joined. In the case where the pressing process is performed simultaneously with heating (constant input power of the induction coil) and the joining area is gradually increased as shown in FIG. 3, the current density on the joining surface is increased with the enlargement of the joining area. As a result, the temperature rise rate was inevitably reduced, and as a result, it was difficult to reduce the time required for heating. However, in the present invention, the induction coil 5b which generates an alternating magnetic field in accordance with an increase in the joint area by applying the device having the configuration shown in FIG.
Since the heating capacity is gradually increased by increasing the input power, it is possible to heat up to a predetermined temperature range in a state where the temperature distribution becomes substantially uniform over the entire joining region,
Therefore, the time required for joining the billets can be reduced as much as possible.
The specific control for increasing the input power in accordance with the increase in the contact area is as follows. First, the pushing amount detector 6 detects the pushing amount of the steel slab from the rotation angle of the pinch roll 4 after the start of pushing. Next, a contact area calculator 7
Calculates the contact area at the joint. And then
The input power is calculated by the input power calculator 8 based on the calculated contact area, and the power supply 5c is adjusted via the input power setting device 9 as appropriate so that the input power becomes the calculated input power.

[0010] In the present invention, the shape of the cut end of the steel slab is
In addition to those shown in FIG. 2 in which the ends of the preceding billet 1 and the succeeding billet 2 are concavely cut at the same curvature,
The rear end portion is concave, but their curvatures are different as shown in FIG. 4, or one of the plan shapes is flat and the other is concave as shown in FIG. 5, one is convex. It is also possible to apply one having various shapes, such as the one shown in FIG. 6 where the other is concave and the concave curvature is slightly larger than the convex curvature. In each of the examples of the above-described cut shapes, only the width direction both end regions of the slab were brought into contact with each other, and a gap was provided in the center region. However, the cut shape in the present invention is not limited to this. As shown in FIGS. 7 and 8, the steel slab is brought into contact at both ends in the width direction and at three points at the center, and a gap may be provided between them. Although not shown, the number of contact parts is four or more, A shape in which a gap is provided between them may be used.

As a cutting method for obtaining the above-mentioned shape, shearing, gas cutting, laser fusing, or the like can be applied. Drum shears having a curved edge are advantageously adapted.

The billet 1 on the entry side of the finishing mill 3
As a heating means in the local butt joining of No. 2, heating by a so-called transverse method in which an alternating magnetic field generating coil is used and an alternating magnetic field penetrating the steel slab in the thickness direction thereof is applied (Japanese Patent Application No. Hei. In addition to this, an electric heating method using an electrode roll 11 as shown in FIG. 9 can be applied.

[0013] As for the joining form of the billet,
With the heating and temperature rising continued (however, the temperature does not exceed the melting temperature of the part to be welded), the steel slab was pressed in advance by pressing the slabs when the target welding temperature was reached. Various joining forms such as joining in which heating is performed in a state (including pressing until a predetermined joining margin is obtained) can be adopted, but especially in the stage before hot finish rolling, the billet is 1000 to 1100 Since it is in a high temperature state of about ℃, the joining of the steel slabs proceeds only by simple pressing. By heating while performing the pressing treatment, the joining is effectively promoted, shortening the joining time and inputting required for heating We can expect reduction of electric power.

The temperature at which the joining of the slabs proceeds is 1250 ° C. or higher. However, if the heating temperature is too high, the ends of the slabs may be melted. Is preferred. In order to avoid breakage in the initial stage of the finish rolling, the joining margin 1 of the billet is preferably at least 0.1 W (W: full width of the billet) on one side and at least 0.2 W on both sides (FIG. 3).

The temperature of the slab at this stage is about 1000 to 1100 ° C. as described above, and it takes about 20 seconds or more from cutting to finish rolling at the end of the slab. Since the thickness of the scale generated on the cut surface of the slab may increase and it may not be possible to reliably join the central region in the width direction of the slab at the time of finish rolling, work in such an area should be within 20 seconds Is preferred.

[0016]

[Embodiment] A rolling equipment as shown in FIG. 1 having a tandem rolling mill of 7 stands is applied, and has a width of 1000 mm and a thickness of 1000 mm.
In the continuous hot rolling of a sheet bar (steel type: low carbon steel) having a thickness of 30 mm, first, at the entry side of the hot rolling equipment 5, the rear end and the front end of the sheet bar are respectively subjected to a radius of curvature by a drum shear. Was cut into a 20 m arc. Then, after joining both end regions of the rear end of the preceding sheet bar and the front end of the succeeding sheet bar in a contact state, a joining process was performed under the following conditions. a. Alternating magnetic field (C-type magnetic pole) Input power: Control in the range of 0 to 3500 kw (see Fig. 11) Frequency: 500 Hz b. Target heating temperature: 1400 ° C (Seat bar initial temperature 1000
C) Pressing force: 3 kgf / mm ² (contact pressure) d. Joining margin (contact length): 100 mm on one side e. Joining form: Heating starts at the same time as pressing, and one side in one second as shown in Fig. 10 Control was performed so that the per-joining margin was 100 mm. FIG. 7 is a diagram comparing a control pattern when the joining process according to the present invention is performed and a control pattern when the sheet bar having the same planar shape is subjected to the joining process by applying a constant power.
FIG. 11 and FIG. 12 show a comparison of the temperature distribution of the bonding surface in each pattern.

As is apparent from FIG. 1, under the condition 1 (comparative example) in which the heating and pressing treatment is performed with the applied power constant, the heating power at the end of the sheet bar is reduced, so that the initially set input power is reduced. 2000kw (Maximum input power of condition 2 is 60
%), The temperature of the end region of the sheet bar has reached about 1450 ° C., but under the condition 2 according to the present invention, the tendency is effectively improved in both patterns A and B. I was assured. The time required for the bonding process was 2.4 seconds under the condition 1, but was approximately 2.0 seconds under the condition 2, and the time required for the bonding could be reduced by about 17%.

[0018]

As described above, according to the present invention, in joining the billets, the rear end of the preceding billet and a part of the leading end of the succeeding billet are used as joining surfaces, and a pressing treatment is performed simultaneously with heating to gradually increase the joining area. Even in the case of performing such bonding, since the heating can be performed under a temperature distribution that is substantially constant over the entire surface of the bonding region, the planned bonding portion can be bonded in a very short time without fear of melting at the width end. .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a configuration of equipment suitable for carrying out the present invention.

FIG. 2 is a diagram showing a planar shape of a joint portion of a steel slab.

FIG. 3 is an explanatory view of a joint part of a billet.

FIG. 4 is a view showing another example of a planar shape at a joint portion of a steel slab.

FIG. 5 is a diagram showing another example of the planar shape at the joint portion of the steel slab.

FIG. 6 is a diagram showing another example of the planar shape at the joint of the billets.

FIG. 7 is a diagram showing another example of the planar shape at the joint of the billets.

FIG. 8 is a view showing another example of the planar shape at the joint portion of the steel slab.

FIG. 9 is a diagram showing a configuration of an apparatus suitable for use in applying an electric heating method.

FIG. 10 is a diagram showing a change state of a bonding area ratio.

FIG. 11 is a graph showing the relationship between the joining time and the applied power.

FIG. 12 is a graph showing a relationship between a distance from a width end of a sheet bar and a temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Leading slab 2 Subsequent slab 3 Hot finishing rolling equipment 4 Pinch roll 5 Alternating magnetic field generator 6 Detector of pushing amount of slab 7 Calculator for calculating contact area 8 Input power calculator 9 Input power setting device 10 sheet Bar looper 11 electrode roll

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Fujio Aoki 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. Inside the Chiba Works (72) Inventor Takashi Kawase 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. Chiba Works

Claims (2)

(57) [Claims] At the entry side of a hot rolling facility, the rear end of a previously conveyed slab and the front end of a subsequently conveyed slab are separated by at least the width of each slab. When contact is made at both ends in the direction, an alternating magnetic field penetrating in the thickness direction of the steel slab is applied, and while being heated and pressed by an induction current induced by the alternating magnetic field, the joining area is gradually expanded. In joining, a method of joining steel slabs in hot rolling, comprising increasing an input power of an induction coil for generating an alternating magnetic field in accordance with an increase in a joining area. 2. The joining method according to claim 1, wherein the heating method of each steel slab is an electric heating method.