JPH0729123B2 - Joining method of billets in hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a steel strip such as a sheet bar that is previously conveyed and a subsequent steel strip that is subsequently conveyed to a hot rolling facility. The present invention relates to a method for joining steel pieces, which is particularly useful when butt-joining is performed on the inlet side of the steel sheet and the joined steel pieces are continuously supplied to the rolling line.

(Prior Art) Conventionally, in a hot rolling line, a steel strip to be rolled is heated to a target temperature, and then, one by one, a rough rolling process and a finish rolling process are performed to finish a hot rolled sheet having a desired thickness. Was,
In such a rolling method, especially in finish rolling, troubles such as line stop due to defective biting of the rolled material are likely to occur, and the yield is largely reduced due to defective shape of the leading end and the trailing end of the rolled material. , The early solution of such a problem was desired.

To eliminate the above problems in the hot rolling line,
As an attempt to further improve the productivity, JP
A rolling technique as disclosed in JP-A-60-244401 or JP-A-61-159285 is known.

(Problems to be Solved by the Invention) In each of the technologies disclosed in the above publications, the trailing end of the preceding rolling material and the leading end of the succeeding material following the joining are joined on the entry side of the finish rolling step, It is intended to continuously supply the rolling material of several to several tens of pieces to the finish rolling process,
According to such a rolling method, it was possible to remarkably improve the productivity without causing the biting failure and the like that occurred when the steel pieces were supplied to the rolling line one by one.

However, when continuous rolling is performed while joining steel pieces, the rear end of the preceding steel piece and the leading end of the following steel piece must be joined quickly and reliably and stably. The method of high-frequency heating of the joint portion of the steel slab as disclosed in Japanese Patent Publication No. 60-244401 has the advantage that it can be heated to the target joining temperature in a relatively short time, but is not related to the joining of the steel slab. It consumes a large amount of energy used for the heating because even unnecessary areas are heated.
In the case of applying current heating such as the technology disclosed in JP-A 60-159285, when a scale is attached to the surface of the steel slab, an arc is generated due to the contact electric resistance between the electrode roll and the steel slab, and There is a risk of damage, and any of these methods was insufficient to realize continuous hot rolling of the steel slab.

The present invention proposes a novel joining method that can simply and promptly join a steel slab without wasting energy, and can surely join the steel slab so that the joined portion of the steel slab does not break apart during rolling. The purpose is to

(Means for Solving the Problem) The present invention is configured such that, on the entry side of a hot rolling facility, the trailing end of a steel piece that is previously conveyed and the leading end of a succeeding steel piece that follows the steel piece are butted against each other. Upon joining, a process of contacting the front end portion and the rear end portion of each of the steel pieces described above to apply an alternating magnetic field that penetrates in the thickness direction of the steel pieces in that region to heat, and a process of pressing the steel pieces. It is a method of joining steel pieces in hot rolling (first invention), characterized in that the steel pieces are brought into close contact with each other by combining them.

In the present invention, the contact area between the preceding steel piece and the following steel piece should be at least both ends in the width direction of the steel piece (second invention), and when joining each steel piece, At least one of the alternating magnetic field generating coils has a C-shaped core that sandwiches the steel piece in the thickness direction, and the alternating magnetic field that heats the contact area of the steel piece is heated while pressing at least one side (third invention). (4th invention).

FIG. 1 shows an example of rolling equipment suitable for carrying out the present invention. In FIG. 1, reference numeral 1 is a hot finish rolling mill group, and 2 is an entry side of the hot finish rolling mill 1. Steel sheet (hereinafter referred to as a preceding sheet bar), 3 is a steel sheet subsequent to the steel sheet 2 (hereinafter referred to as a subsequent sheet bar), 4 is a sheet bar 2, 3 and the like. The pinch rolls 5 for applying pressure at the time of joining are the alternating magnetic field generating coils having the role of heating the contact area a between the rear end of the preceding sheet bar 2 and the leading end of the succeeding sheet bar 3. The alternating magnetic field generating coil 5 comprises a core 5a forming a magnetic pole, a coil 5b and a power source 5c. Here, this alternating magnetic field generating coil 5
When applied alone, it is placed in the center of the seat bar in the width direction. Further, 6 is a looper for absorbing the joining time of the sheet bar, and this looper 6 is omitted in the case where the alternating magnetic field generating coil 5 can move in synchronization with the conveyance of the sheet bar. .

(Operation) The alternating magnetic field generating coil 5 disposed in the contact region a in the widthwise central portion of the seat bar 5 in a contact state by abutting the rear end portion of the preceding sheet bar 2 and the front end portion of the succeeding sheet bar 3. When an alternating magnetic field d is applied by
An eddy current e as shown in FIG. 2 is induced along each of the widthwise ends of the. The end portions of the seat bars 2 and 3 are heated by the heat generated due to the circulation of the eddy current e. Since there is a contact electric resistance in the contact area a of the seat bar, this resistance causes Due to Joule heat generation, the temperature of the contact surface at each end is raised preferentially as shown in FIG. Therefore, by heating at least one of the sheet bars 2 and 3 toward the sheet bars to be joined while raising the temperature in this contact state, or by heating the temperature as described above in a state of being pressed in advance, it is possible to achieve an extremely high efficiency. The contact area can be brought into close contact in a short time, and since the coil 5 is of a non-contact type, there is no possibility of damaging the equipment due to generation of an arc.

In the second aspect of the invention, in order to perform the above heating more advantageously, that is, in order to shorten the heating time at the time of joining and to reduce the input power required for this, the contact area a of the preceding sheet bar 2 and the succeeding sheet bar 3 As shown in FIGS. 4 (a) to 4 (g), at least both end regions in the width direction of each seat bar,
It is decided to provide gaps in the other areas.

The above-mentioned joining of the steel pieces having the shape shown in FIG. 4 is more advantageously applicable to the joining of the steel pieces having a planar shape as shown in FIG. 5 (a). When the joint end of the steel slab is heated and pressed, the joint region of the steel slab expands from both ends to the central portion with a relatively small pressing force, as shown in FIG. This is because, under the joining margin, the joint portion of the steel slab does not break and separate even by the subsequent finish rolling.

FIG. 6 shows the results of an examination of the joining margin in the joining of the steel pieces as described above and the state of breakage during finish rolling. As is clear from the figure, the welding margin W in the contact area is 0.1 times or more the width B of the billet, respectively.
If it is 0.2 times or more, there is no possibility that the joined portion will break and separate during the subsequent finish rolling.

FIG. 4 (a) shown in FIG. 4 shows that when the rear end portion of the preceding sheet bar 2 and the leading end portion of the succeeding sheet bar 3 are cut into a concave shape with the same curvature, FIG. When the front and rear ends of the bars 2 and 3 are concave, but their curvatures are different, in the figure (c), when one has a flat planar shape and the other is concave, the figure (d) Is a case where one side is convex and the other side is concave, and the curvature of the concave shape is made slightly larger than the curvature of the convex shape.In all cases, only the widthwise ends of the seat bar are contacted. Although it is shown as an example in which a gap is provided in the central area, the cutting shape suitable for the present invention is not limited to this, and as shown in FIGS. You may make contact at three points and provide a gap between them,
Although not shown, the contact portions may be provided at four points or more, and a gap may be provided therebetween. Further, as shown in FIG. 9G, the center portion in the width direction may be cut out in a rectangular shape.

As a cutting method for forming the above shape, shearing, gas cutting, laser fusing, etc. can be applied,
A drum shear with two curved blades is particularly advantageous, especially when cutting concavely with a certain curvature.

Next, as a joining mode in the case of joining steel pieces, the joining mode is such that heating and raising the temperature of the planned joining portion to a target joining temperature and pressing after stopping the heating, heating and raising temperature are continued. There are various conceivable forms, such as a joining form that presses when the target joining temperature is reached as it is (however, the temperature does not exceed the melting temperature of the joining part), or a heating form in which the steel slab is heated in advance. However, the temperature of the steel pieces in the joining process is usually about 1000 to 1100 ° C., and the joining of the respective steel pieces proceeds to some extent even by simple pressing. For this reason, in the third aspect of the invention, in particular, the steel piece is heated while being pressed, so that the joining time is shortened and the input power required for heating / heating is reduced.

Next, a schematic diagram of an alternating magnetic field generating coil 5 suitable for carrying out the present invention is shown in FIG. 7, and by using such an alternating magnetic field generating coil 5, the alternating magnetic field generating coil 5 is arranged in the thickness direction of the steel piece. Hereinafter, a method of applying an alternating magnetic field that penetrates will be referred to as a transverse method. As the alternating magnetic field generating coil 5 that can be adapted to the above-mentioned transverse method, application of a split type or homopolar horseshoe type alternating magnetic field generating coil, etc., which are individually arranged above and below so as to sandwich the steel piece in the thickness direction, is also considered. However, as the fourth invention, an alternating magnetic field generating coil having a C-shaped core sandwiching the thickness direction of the steel slab is applied here. The alternating magnetic field generating coil of this type facilitates the operation when joining while synchronizing with the movement of the steel slabs, and can easily and accurately align the magnetic poles. In joining the steel pieces having a flat planar shape of the end portions, when the alternating magnetic field generating coil is used alone, the joint surface can be heated uniformly,
It is desirable to move along the width direction. Further, in the case where a plurality of alternating magnetic fields d are applied along the width direction of the steel slab, it can be dealt with by providing the alternating magnetic field generating coils by the corresponding amount.

FIGS. 8A and 8B show an example in which a plurality of alternating magnetic fields d are applied along the width direction of the steel slab.

In addition, the alternating magnetic field applied to the steel slab varies depending on the size of the steel slab to be joined, but the applied power is approximately 500 to 3000k.
W, it is desirable to apply under the condition of heating time 2-8 seconds,
Regarding the pressing force at the time of joining, a surface pressure of about 3 to 8 kgf / mm ² is sufficient, and a heating temperature is 1250 to 1450 ° C.
Is desirable.

By the way, FIG. 9 shows a schematic diagram of a case where high-frequency heating is performed using a solenoid coil S, which is different from the transverse method in the present invention. When joining a steel piece such as a sheet bar by induction heating using a solenoid coil, the energy loss becomes large because the region 1 (including the longitudinal direction of the steel piece) facing the coil is heated, When heating with a particularly high frequency to shorten the bonding time, there is a risk that only the surface layer will melt before the target bonding temperature is reached due to the local temperature rise of only the surface area of the sheet bar. There is.

(Example) A sheet bar having a flat shape as shown in FIG. 2 having a width of 1000 mm and a thickness of 30 mm is obtained by applying the equipment shown in FIG. 1 equipped with a 7-stand tandem rolling mill ( Low carbon steel) was continuously supplied to the rolling mill while being joined according to the following conditions, and a hot rolled sheet having a sheet thickness of 3 mm was finished.

Alternating magnetic field (C-type magnetic pole): Input power: 2000Kw, Heating time: 12 seconds, Frequency: 500Hz, b. Heating temperature: 1400 ℃, c. Pressing force: 3kgf / mm ² in contact pressure, d. Pressing time: 3 seconds, e. Joining form: Pressing after contacting and heating the steel pieces f. Moving the alternating magnetic field along the joining surface, and as a result, the joint part of the sheet bar may not be broken during rolling. It could be rolled stably. In addition, compared with the conventional high-frequency heating method, it is possible to reduce the power consumption by about 50% compared to the case of joining sheet bars with the same shape and shape. Also, the joining time is about 12 seconds and the conventional joining method under the same conditions. It was confirmed that the welding time could be shortened by about 20% compared to the welding time of 15 seconds.

In addition, a flat sheet bar (low carbon steel) as shown in Fig. 4 (a) with a width of 1000 mm, a thickness of 30 mm, and a radius of curvature of 20 m at both the front and rear ends is used. (C-type magnetic pole): Input power: 2000Kw, Frequency: 500Hz, b. Heating temperature: 1400 ℃, c. Pressing force: Face pressure is 3kgf / mm ² , d. Joining margin after heating and pressing 2W = 200mm ( One side 100 mm), e. Joining form: We also investigated the joining condition when pre-pressing and joining under the conditions of heating. Even in such joining, the joining part does not break due to rolling, and the sheet bar The heating time required for joining was further shortened to about 2.4 seconds, compared with the case where the front end and the rear end were flat.

Further, the case where only the joining mode of the sheet bar was changed in the example of the plane shape of FIG. 4 (a) described above and the case where the steel pieces were brought into contact with each other and heated and then pressed was also investigated.
In this case, since the temperature of the joint surface does not rise easily compared to when heating while pressing, the joining margin was halved compared to when heating by pressing, but by extending the heating time by about 1.6 seconds Predetermined joining is possible.

(Effect of the invention) Thus, according to the present invention, since the rear end portion of the steel piece conveyed in advance and the front end portion of the subsequent steel piece can be joined quickly and reliably, the heating equipment may be increased in size, The continuous rolling line is not extended, and continuous hot rolling with high productivity can be realized.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of rolling equipment suitable for carrying out the present invention, FIG. 2 is an explanatory view of a joining procedure of steel slabs according to the present invention, and FIG. 3 is a temperature of a joining region. The figure which showed distribution, FIG.4 (a)-(g) is the figure which showed the planar shape of the steel piece, FIG.5 (a) (b) is the figure which showed the joining condition of the steel piece, FIG. 6 is a graph showing the condition of the joint portion of the seat bar, and FIG. 7 is a schematic diagram of an alternating magnetic field generating coil having a C-shaped magnetic pole suitable for carrying out the present invention, FIG. FIGS. 9A and 9B are diagrams showing an arrangement example of the alternating magnetic field generating coils, and FIG. 9 is a diagram schematically showing a conventional type induction heating system. 1 ... Finishing rolling mill group, 2 ... Leading sheet bar, 3 ...
Subsequent sheet bar, 4 ... Pinch roll, 5 ... Alternating magnetic field generating coil, 5a ... Core, 5b ... Coil, 5c ... Power supply,
6 ... Looper, d ... Alternating magnetic field, e ... Eddy current

Front page continued (72) Inventor Fujio Aoki 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works (72) Inventor Naoki Hadano 1 Kawasaki-cho, Chiba Chiba Works Chiba Works (72) ) Inventor Hideo Takekawa 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works (56) Reference JP-A-63-90302 (JP, A)

Claims (4)

[Claims] 1. At the joining side of a hot rolling facility, the rear end of a steel piece that is conveyed first and the front end of a subsequent steel piece that is subsequently conveyed are butted and joined together. A step of bringing the front end and the rear end of each of the steel pieces into contact with each other and applying an alternating magnetic field penetrating in the thickness direction of the steel pieces in that region to heat, and a step of pressing at least one of the steel pieces. A method for joining steel slabs in hot rolling, characterized in that the steel slabs are brought into close contact with each other by combining. 2. The contact area between the preceding billet and the following billet is
The method according to claim 1, which is at least both end regions in the width direction of the steel slab. 3. The method according to claim 1, wherein the steel piece is heated while being pressed. 4. An alternating magnetic field for heating the contact area of the steel slab,
The method according to claim 1, 2 or 3, wherein the application is performed by at least one alternating magnetic field generating coil having a C-shaped core sandwiching the steel piece in the thickness direction.