JP3126745B2 - 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 butt joint of a previously conveyed steel slab such as a sheet bar and a subsequent slab conveyed subsequently thereto at the hot rolling entry side. The present invention relates to a method of joining steel slabs which is particularly useful for continuously supplying the joined slabs to a rolling line.

[0002]

2. Description of the Related Art Conventionally, in a hot rolling line, a billet to be rolled is heated to a target temperature and then a rough rolling process is performed one by one.
It was then subjected to a finish rolling process to finish it into a hot-rolled sheet with the desired thickness.However, in such a rolling method, particularly in finish rolling, troubles such as line stoppage due to poor biting of the rolled material easily occur. In addition, the yield is greatly reduced due to the defective shape of the leading and trailing ends of the rolled material. This is the reason why such a problem should be solved early.

[0003] In order to solve the above-mentioned troubles in the hot rolling line and to further improve the productivity, the rear end of the preceding billet and the rear end of the preceding billet in the incoming conveying line of the hot finishing rolling mill. A rolling technique has been proposed in which the leading end of the subsequent steel slab conveyed subsequently is sequentially joined and subjected to finish rolling, and various methods of joining the steel slabs have been developed accordingly. For example, in Japanese Patent Application Laid-Open No. 60-244401,
An induction heating pressure welding method using a so-called solenoid type coil is disclosed, and an electric heating pressure welding method using an electrode roll is disclosed in JP-A-61-159285. According to the technique of joining and rolling slabs in this way, it is possible to improve productivity without causing poor biting or the like that occurred when slabs were supplied one by one to a rolling line. become.

[0004]

In order to perform continuous rolling while joining steel pieces, the rear end of the preceding steel piece and the front end of the subsequent steel piece are quickly, reliably and stably joined. There is a need. However, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 60-244401, the method of high-frequency induction heating of the joints of the steel slabs has the advantage that it can be heated to the target joining temperature in a relatively short time. However, there is a problem that a large amount of energy is consumed for heating to an unnecessary area not related to the joining of the billet.
In the case of heating by energization as in the technology disclosed in Japanese Patent Publication No. 285, an arc is generated due to contact electric resistance between the electrode roll and the steel slab when scale is attached to the surface of the steel slab, and the electrode roll is damaged. In any case, any of these methods is insufficient for realizing continuous hot rolling of the billet.

[0005] A new joining method is proposed that can simply and quickly join the billets without wasteful energy, and can surely join the billets so that the joining portions of the billets do not separate or break during rolling. It is the purpose of this invention to do so.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a rear end portion of a previously conveyed slab and a succeeding steel slab conveyed subsequently to the rear end portion of the slab which is conveyed at the entrance of the hot rolling equipment for the slab. A method in which the tips of the pieces are brought into contact with each other in a contact state, and then heated and joined, wherein the leading end of the precedingly transported steel piece and the leading end of the subsequent steel piece subsequently transported are When butting is performed, the leading and trailing ends of each billet are shaped so that at least a contact region including both ends in the billet width direction and a non-contact region other than the contact region are formed. The leading end and the rear end of the slab are brought into abutting contact with each other to form a contact area including at least both ends in the width direction of the slab and a non-contact area excluding the contact area. A process in which both ends in the width direction are heated by induced current generated by application from the magnetic pole; At least one of the steel slabs is pressed against the other steel slab, and the magnetic pole has a magnetic pole width along the steel slab width direction which is smaller than the magnetic pole length along the longitudinal direction of the steel slab. The present invention is a method for joining steel slabs in hot rolling, characterized in that by forming a slender shape that is large and does not exceed the width of the steel slab, a short-circuit induced current generated in the steel slab immediately below the magnetic pole is suppressed.

According to the present invention, the following equation is obtained based on the relationship between the width / length ratio of the magnetic pole and the magnetic pole cross-sectional area: W / L ≧ 0.33 + 0.38 (1 / S) −0.05 (1 / S) ² +0.0024 (1 / S) ³ where W: width of the magnetic pole (m) L: length of the magnetic pole (m) S: cross-sectional area of the magnetic pole (m ² ) (second invention).

FIG. 1 shows an example of a magnetic pole according to the present invention in a cross section facing a steel slab. FIG. 2A shows an example of a rectangular shape, FIG. 2B shows an example of an elliptical shape, and FIG. The shape of the magnetic pole is
(b), the magnetic pole width in a case other than a rectangle as shown in (c), when a line parallel to the width direction of the steel slab is drawn on the pole face,
The length when the line segment is the longest.On the other hand, the pole length is the length when the line segment is the longest when a line parallel to the longitudinal direction of the steel slab is drawn on the pole face. Say. For example,
When the shape of the magnetic pole is elliptical as shown in FIG. 3B, the magnetic pole width is the major axis of the ellipse, and the magnetic pole length is the minor axis of the ellipse. In the present invention, the number of magnetic poles is not limited to one, and it is possible to arrange a plurality of magnetic poles along the width direction of the steel slab. In this case, the cross-sectional area of the magnetic poles and the width and length of the magnetic poles are the same for each magnetic pole. And the sum of

[0009]

First, the circumstances that led to the development of the method for joining billets of the present invention will be described. The inventors have conducted research and development on a joining method that can easily, quickly, and surely join without wasteful energy when joining the billets, and as a result, the leading end and the trailing end of each billet were joined. Contacting, in the region to apply the alternating magnetic field penetrating in the thickness direction of the slab and heating, and obtained a finding that it is particularly effective to combine the treatment of pressing at least one of the slab, A patent application was filed earlier (see Japanese Patent Application No. 2-203991). According to this method, the eddy current is induced by the alternating magnetic field in the joining region, and the heat generated by the circulation of the eddy current causes the temperature to rise particularly at both ends in the width direction of the steel slab. The contact area can be brought into close contact, and the magnetic pole for applying the alternating magnetic field is not in contact with the steel slab. Became possible.

In such a joining method, it is particularly important that an induced current circulating through both ends of the steel slab in the width direction is strong, but depending on the shape of the magnetic pole for applying a magnetic field to the steel slab. In addition to this circulating induction current, the short-circuit induction current generated immediately below the magnetic pole becomes strong, and the steel slab immediately below this magnetic pole melts down, causing not only the problem of damaging the joining equipment, but also the circulating induction current. In some cases, there is a problem that extra time is required for joining the end portions. Such a round induction current and a short-circuit induction current are indicated by symbols e and s in FIG. 2, respectively, and the situation of burn-out is shown in FIG. Therefore, from this fact, further research and development were conducted to suppress the short-circuit induced current generated immediately below the magnetic pole, and as a result, it was found that it is particularly effective to form the magnetic pole into a slender shape having a width larger than the length. It has been developed.

[0011] By making the magnetic poles slender, the short-circuit induced current is suppressed, so that the joining of the steel slabs can be performed more reliably and safely. The cross-sectional shape of the magnetic pole is not limited to the rectangle, ellipse, and ellipse shown in FIG. 1, and the pole width measured along the width direction of the slab is smaller than the pole length measured along the length direction of the slab. Any shape may be used as long as it satisfies a large shape.

When the number of the magnetic poles is one, the position of the magnetic pole is set at the center in the width direction of the steel slab. preferable.

According to the second aspect of the invention, the magnetic pole is expressed by the following equation based on the relationship between the width / length ratio and the magnetic pole cross-sectional area: W / L ≧ 0.33 + 0.38 (1 / S) −0.05 (1 / S) ² +0.0024 ( 1 / S) ³ where W: width of the magnetic pole (m) L: length of the magnetic pole (m) S: cross-sectional area of the magnetic pole (m ² ) FIG. 4 shows the results of examining the effect of the magnetic pole cross-sectional area and the width / length ratio of the magnetic pole to various values, and the effect on the meltdown of the steel slab immediately below the magnetic pole. Although the cross-sectional shape of the magnetic pole at this time was rectangular, similar results were obtained even when the shape was different. As is clear from the figure,
To prevent the slab immediately below the magnetic pole from melting, the magnetic pole must be of width W
(M) / pole length L (m) ratio and pole cross section S
It is necessary to satisfy W / L ≧ 0.33 + 0.38 (1 / S) −0.05 (1 / S) ² +0.0024 (1 / S) ³ in the relational expression with (m ² ). Therefore, in the second aspect of the present invention, the magnetic pole is expressed by the following formula based on the relationship between the width / length ratio and the magnetic pole: W / L ≧ 0.33 + 0.38 (1 / S) −0.05 (1 / S) ² +0.0024 (1 / S) ³ Here, W: width of the magnetic pole (m) L: length of the magnetic pole (m) S: cross-sectional area of the magnetic pole (m ² )

Regarding the upper limit of the size of the magnetic pole, it is preferable that the width of the magnetic pole does not exceed the width of the steel slab to be joined from the viewpoint of avoiding excessive heating of the width direction end of the steel slab. The length of the magnetic pole and the cross-sectional area of the magnetic pole are naturally calculated from the upper limit.

FIG. 5 shows an example of rolling equipment applied to the joining of steel slabs using the magnetic poles described above. In the figure, reference numeral 4 denotes a hot finishing rolling mill group, and reference numeral 5 denotes a hot finishing rolling mill 4.
(Hereinafter, referred to as a preceding sheet bar), 6 is a succeeding steel sheet (hereinafter, referred to as a succeeding sheet bar) following this steel piece 5, and 7 is a sheet bar 5, A pinch roll 8 for conveying 6 and pressurizing them during joining;
Is an alternating magnetic field generator serving to heat a contact area a between the rear end of the preceding sheet bar 5 and the front end of the succeeding sheet bar 6, and the alternating magnetic field generator 8 has a core 8a forming a magnetic pole, It comprises a coil 8b and a power supply 8c. here,
When this alternating magnetic field generator 8 is applied alone, it is arranged at the center in the width direction of the sheet bar. Reference numeral 9 denotes a looper for absorbing the joining time of the sheet bar. This looper 9 is omitted in a case where the alternating magnetic field generator 8 can be moved in synchronization with the conveyance of the sheet bar. .

As described above, in a contact state where the rear end of the preceding sheet bar 5 and the front end of the succeeding sheet bar 3 are in contact with each other, the alternating magnetic field disposed in the contact area a at the center of the sheet bar in the width direction. When an alternating magnetic field d is applied by the generator 8, an eddy current e as shown in FIG. 6 is induced in each end of the sheet bars 5, 6 along the width direction. Each end of the sheet bars 5 and 6 is heated by the heat generated due to the circulation of the eddy current e. In particular, since there is a contact electric resistance in the contact area a of the sheet bar, the end portions of the sheet bars 5 and 6 are heated. Due to Joule heat, the temperature of the contact surface at each end rises preferentially as shown in FIG. Therefore, at least one of the sheet bars 5, 6 is pressed toward the sheet bar to be joined while the temperature is raised in this contact state, or
Alternatively, the contact area can be efficiently brought into close contact in a very short time by heating and raising the temperature in the state of being pressed in advance, and since the alternating magnetic field generator 5 is a non-contact type, arcing causes damage to the equipment. There is no fear of giving.

In the present invention, in order to perform the above-mentioned heating more advantageously, that is, to shorten the heating time at the time of joining and to reduce the input power required for this, the preceding sheet bar 2 is used.
8 (a) to 8 (g), at least both end regions in the width direction of each sheet bar, and gaps are provided in the other regions.
Here, the joining of the slabs having the shape shown in FIG. 7 above is more advantageously adapted, for example, in joining the slabs having the planar shape shown in FIG. 9 (a). 9 is heated and pressed, the joint area of the billet is
As shown in (b), it expands from both ends to the center with a relatively small pressing force, and under a specific joining allowance, the joint of the slab breaks and separates even after finish rolling. Because there is nothing.

FIG. 10 shows the results of an examination of the joining margin in the joining of the slabs described above and the state of breakage during finish rolling. As is clear from the figure, if the joint allowance W in the contact area is 0.1 times or more each of the billet width B and 0.2 times or more in total, there is a possibility that the joints will break and separate during the subsequent finish rolling. Not at all.

FIG. 8A shown in FIG. 8 shows that when the rear end of the preceding sheet bar 5 and the front end of the succeeding sheet bar 6 are cut into a concave shape at the same curvature, FIG. In the case where the front and rear ends of each of the sheet bars 5 and 6 are concave, but their curvatures are different, FIG. 3C shows a case where one of the sheet bars 5 and 6 has a flat planar shape and only the other has a concave shape. d) is a case where one is convex and the other is concave, and the concave curvature is slightly larger than the convex curvature.In each case, only the width direction both ends of the sheet bar are used. Although it is shown as an example in which a contact is made and a gap is provided in the center area, a cut shape suitable for the present invention is not limited to this, and as shown in FIGS. Middle 3
Contact may be made at points, and a gap may be provided between them.Although not shown, the number of contact portions is four or more,
A gap may be provided between them.
Further, as shown in FIG. 11 (g), the widthwise central portion may be cut out in a rectangular shape.

As a cutting method for obtaining the above-mentioned shape, shearing, gas cutting, laser fusing, and the like can be applied. In particular, when cutting into a concave shape with a specific curvature, two cutting blades are used. Drum shears are particularly advantageously adapted.

Next, when joining the steel slabs, a joining mode is such that the scheduled joining portion is heated and heated to a target joining temperature, and the heating is stopped and then pressed.
Joining method such as pressing when the target joining temperature is reached while heating / heating is continued (however, the temperature does not exceed the temperature at which the joint melts), or heating with the steel slab pressed in advance There are various possible forms such as
Normally, the temperature of the steel slab in the joining process is about 1000 to 1100 ° C., and the joining of the steel slabs proceeds to some extent only by simple pressing. For this reason, it is preferable to shorten the joining time and reduce the input power required for heating / heating by heating while pressing the steel slab.

Next, FIG. 11 shows a schematic diagram of an alternating magnetic field generator 8 suitable for use in carrying out the present invention.
Hereinafter, a method of applying an alternating magnetic field that penetrates this will be referred to as a transverse method. As the alternating magnetic field generator 8 that can be adapted to the above-mentioned transverse method, a split type or a homopolar horseshoe type alternating magnetic field generator, which is individually arranged vertically so as to sandwich a steel slab in its thickness direction, is also considered. However, an alternating magnetic field generator having a C-shaped core sandwiching the thickness direction of the steel slab is preferable. Such a type of alternating magnetic field generator facilitates the operation when joining while synchronizing with the movement of the steel slab, and allows simple and accurate alignment of the magnetic poles. In joining steel slabs in which the flat shape of the end is flat, when using the alternating magnetic field generator alone, along the width direction so that the joint surface can be uniformly heated. It is desirable to move. 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 corresponding alternating magnetic field generators.

FIGS. 12 (a) and 12 (b) show examples in which a plurality of alternating magnetic fields d are applied along the width direction of the billet.

The alternating magnetic field applied to the steel slab varies depending on the size of the steel slab to be welded, but it is desirable to apply it under the conditions of approximately 500 to 3000 kW of applied power and heating time of 2 to 8 seconds. The pressing force at the time of
Approximately 8 kgf / mm ² is sufficient, and the heating temperature is desirably 1250-1450 ° C.

[0025]

[Embodiment] The equipment shown in FIG. 5 provided with a tandem rolling mill of 7 stands is applied, and the width is 1000 mm and the thickness is 30 m.
m, the radius of curvature at the front and rear ends is 20 m.
Sheet bar with a flat shape as shown in (a) (low carbon steel)
Was continuously supplied to a rolling mill while being joined under the following conditions to finish a hot-rolled sheet having a thickness of 3 mm. a. Alternating magnetic field (C-type magnetic pole): Input power: 2000 kW Heating time: 2.4 seconds, Frequency: 500 Hz, Number of magnetic poles: 1 Magnetic pole shape: Rectangular Magnetic pole width: 0.48 m Magnetic pole length: 0.3 m b. Heating temperature: 1400 ° C, c. Pressing force: 3 kgf / mm ² in terms of surface pressure, d. Joining form: Heating while contacting and pressing a steel slab As a result, there is no meltdown at the center of the sheet bar joint in the width direction during rolling The rolling was performed stably without breaking the joint.

Next, an experiment was carried out under the same conditions as described above, except that the shape of the magnetic pole was made elliptical, the steel pieces were brought into contact with each other, heated, and then pressed. There was no melt-down at the center in the width direction, and the joint could be stably rolled without breaking.

Further, an experiment was conducted on a case where two magnetic poles were arranged along the width direction of the steel slab. The magnetic pole shape at this time is an oval, and the width and length of each magnetic pole are each 0.
24 × 2 m, 0.3 m. Otherwise, the billet width is 1.
Same as above except for 2 m. As a result, it was also possible to perform rolling stably without causing meltdown at the center in the width direction of the joint portion of the sheet bar during rolling, and without breaking the joint portion.

[0028]

According to the method for joining billets of the present invention, the leading end and the trailing end of the billet are brought into contact at least at both ends in the billet width direction, and penetrate the contact area in the billet thickness direction. The preceding process consists of a combination of a process of heating both ends in the width direction by an induced current generated by applying an alternating magnetic field from a magnetic pole and a process of pressing at least one steel slab toward the other steel slab. Can quickly and reliably join the rear end of the slab to be conveyed and the leading end of the succeeding slab without increasing the size of the heating equipment or extending the continuous rolling line. High continuous hot rolling can be realized, and the magnetic pole has a slender shape whose magnetic pole width along the slab width direction is larger than the magnetic pole length along the longitudinal direction of the slab,
It is possible to stably join the steel slab directly under the magnetic pole without burning off the slab without damaging the equipment.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a magnetic pole according to the present invention.

FIG. 2 is an explanatory diagram of a short-circuit induced current generated in a steel slab.

FIG. 3 is an explanatory diagram of a situation of melting-down at a joint portion of a steel slab.

FIG. 4 is a graph showing the effect of changing the magnetic pole cross-sectional area and the width / length ratio of the magnetic pole to various values on the meltdown of the steel slab immediately below the magnetic pole.

FIG. 5 is an explanatory diagram of a configuration of a rolling facility suitable for use in carrying out the present invention.

FIG. 6 is an explanatory diagram of a joining procedure of a steel slab according to the present invention.

FIG. 7 is a diagram showing a temperature distribution in a bonding region.

FIG. 8 is a diagram showing a plan shape of a billet.

FIG. 9 is a view showing a joining state of a billet.

FIG. 10 is a graph showing a state of a joint portion of a sheet bar.

FIG. 11 is a schematic diagram of an alternating magnetic field generator having a C-shaped magnetic pole suitable for use in carrying out the present invention.

FIG. 12 is a diagram showing an arrangement example of an alternating magnetic field generator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Slab conveyed before 2 Succeeding slab following a precedent slab 3 Magnetic pole 4 Hot finishing rolling mill group 5 Preceding sheet bar 6 Subsequent sheet bar 7 Pinch roll 8 Alternating magnetic field generator 9 Looper

Continuation of the front page (72) Inventor Fujio Aoki 1 Kawasaki-cho, Chiba City, Chiba Prefecture Kawasaki Steel Corporation Chiba Works (56) References JP-A-4-158905 (JP, A) JP-A-62-234679 ( JP, A) JP-A-4-89120 (JP, A) JP-A-4-89178 (JP, A) JP-A-4-288908 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 15/00 B21B 1/26 B23K 20/04

Claims (2)

(57) [Claims] At the entry side of a hot rolling equipment for a billet, a rear end of a preceding billet conveyed is brought into contact with a front end of a succeeding billet subsequently conveyed. And then heating and joining, when the rear end of the previously conveyed steel slab and the front end of the subsequent steel slab conveyed subsequently thereto are butted, at least the steel slab After shaping the leading and trailing ends of each billet into a shape in which a contact region including both ends in the width direction and a non-contact region other than the contact region are formed, the leading and trailing ends of each billet are formed. Are brought into contact with each other to form a contact area including at least both ends in the width direction of the slab and a non-contact area excluding the contact area, and an induced current generated by applying an alternating magnetic field penetrating in the thickness direction of the slab from the magnetic pole. By heating both ends in the width direction, and The magnetic pole has a magnetic pole width along the steel slab width direction larger than the magnetic pole length along the steel slab length direction and exceeds the width of the steel slab. A method of joining steel slabs in hot rolling, characterized in that short-form induction currents occurring in the steel slab immediately below the magnetic poles are suppressed by having a slender shape. 2. The magnetic pole has the following formula: W / L ≧ 0.33 + 0.38 (1 / S) −0.05 (1 / S) ² +0.0024 in relation to the width / length ratio of the magnetic pole and the magnetic pole cross-sectional area. (1 / S) ³ where W: width of the magnetic pole (m) L: length of the magnetic pole (m) S: cross-sectional area of the magnetic pole (m ² ) Joining method.