JPH04288912A - Method for joining slab on hot rolling - Google Patents

Abstract

PURPOSE:To quickly and surely join each top and without damaging to the equipment in order to roll continuously by joining the rear end part of the slab carried in preceding and the top end part of the slab carried in following this, at the inlet side of the hot rolling equipment for the slab. CONSTITUTION:The top end part and the rear end part of each slab are made in contact, at least, with both ends of the lateral direction of slab, the treatment to heat both end parts of this lateral direction with the induction current generated by impressing the alternating magnetic field which penetrates to the wall thickness direction of slab at the this contacting zone from the magnetic pole, and the treatment to press one hand of the slab at least, to the other slab are combinated and composed, and the above magnetic field which is lapped on the joining parts formed at both end parts of the lateral direction of steel billet is controlled unitl 0.3 times of each part to be joined respectively, and positioned near the central part of the lateral direction of slab.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is a method of butt-joining a steel billet, such as a sheet bar, which is conveyed in advance and a subsequent steel billet which is conveyed subsequently, at the entry side of hot rolling. This invention relates to a method of joining steel billets that is particularly useful for continuously supplying the billet to a rolling line.

0002

[Prior Art] Conventionally, in a hot rolling line, after heating the steel billets to be rolled to a target temperature, a rough rolling process is carried out one by one.
The hot-rolled sheet was then subjected to a finish rolling process to finish it into a hot-rolled sheet with the desired thickness, but this rolling method is prone to problems such as line stoppages due to poor biting of the rolled material, especially during finish rolling. In addition, the yield is greatly reduced due to poor shapes at the leading and trailing ends of the rolled material. This is why early resolution of such problems is desired.

In order to eliminate the above-mentioned troubles in the hot rolling line and further improve productivity, the trailing end of the preceding steel billet and this A rolling technique has been proposed in which the tips of subsequent steel billets that are subsequently transported are sequentially joined and subjected to finish rolling, and various methods for joining steel billets have been developed accordingly. For example, JP-A-60-244401
No. 61-159285 discloses an induction heating pressure welding method using a so-called solenoid coil.
The publication discloses an electrically heated pressure welding method using an electrode roll. By following the technology of joining and rolling steel billets in this way, it is possible to improve productivity by eliminating the problems such as jamming that occurs when steel billets are fed one by one to the rolling line. become.

0004

[Problem to be Solved by the Invention] In order to perform continuous rolling while joining steel billets, it is necessary to quickly, reliably, and stably join the rear end of the preceding steel billet and the tip of the following steel billet. There is a need. However, the above-mentioned Japanese Patent Application Publication No. 60-244401
As disclosed in the publication, although the method of high-frequency induction heating of the joints of steel billets has the advantage of being able to heat the joints to the target joining temperature in a relatively short time, there are unnecessary There is a problem in that a large amount of energy is consumed in order to heat the area, and on the other hand, in the technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-159285, which uses electrical heating, scale adheres to the surface of the steel piece. When rolling the steel billet, an arc may be generated due to the electrical contact resistance between the electrode roll and the steel billet, and the electrode roll may be damaged. was insufficient.

[0005] We propose a new joining method that can easily and quickly join steel billets without wasting energy when joining them, and moreover, can reliably join steel billets so that the joints will not separate or break during rolling. It is the purpose of this invention to do so.

[0006]

[Means for Solving the Problems] The present invention provides a method for controlling the rear end of a steel billet that is conveyed in advance and the following steel billet that is conveyed subsequently at the entry side of a hot rolling facility for steel billets. A method in which the tips of the pieces are brought into contact with each other, and then heated and joined. A process of heating both ends in the width direction by an induced current generated by applying an alternating magnetic field that penetrates through the thickness of the steel billet from the magnetic pole, and a process of pressing at least one of the steel billets toward the other steel billet. The above-mentioned magnetic poles are arranged near the center in the width direction of the steel billet so that the overlap with the joints formed at both ends of the steel billet in the width direction is suppressed to 0.3 times the respective joint allowances. This is a method for joining steel billets in hot rolling, which is characterized by suppressing short-circuit induced current occurring at the joint.

[0007]

[Operation] First, the circumstances that led to the development of the steel billet joining method of the present invention will be explained. The inventors have repeatedly researched and developed a joining method that can simply, quickly, and reliably join steel billets without wasting energy. It has been found that it is particularly effective to combine a process of bringing the steel pieces into contact with each other and applying an alternating magnetic field penetrating the steel piece in the thickness direction in that region to heat it, and a process of pressing at least one of the steel pieces, A patent application was filed earlier (Patent application No. 2-20399)
(See Specification No. 1). According to this method, eddy currents are induced in the welding area by an alternating magnetic field, and the heat generated by the circulation of these eddy currents raises the temperature particularly at both ends of the steel billet in the width direction. The contact area can be brought into close contact with the steel pieces, and since the magnetic poles for applying the alternating magnetic field are not in contact with the steel pieces, there is no risk of damaging the equipment due to arc generation, and the steel pieces can be reliably joined. became possible.

By the way, in such a joining method, as shown in FIG.
The induced current e that circulates through both ends of the steel piece in the width direction as shown in Fig. 1 is particularly important for joining these ends, but the arrangement position of the magnetic pole for applying a magnetic field to the steel piece and the joining are important. As the amount of overlap with the section increases, as shown in Fig. 2, a short-circuit induced current s, other than the circulating induced current e, will occur at the joint near the magnetic pole, causing the steel billet joint immediately below the magnetic pole to Both ends melt and fall off, which not only causes damage to the bonding equipment, but also causes the inconvenience that the bonding itself is not performed well.

In order to solve the above problem, we conducted further research and found that by arranging the magnetic poles closer to the center in the width direction of the steel billet, short-circuit induced currents occurring in the joints can be advantageously suppressed. This led to the completion of this invention.

[0010] By arranging the magnetic pole near the center in the width direction of the steel pieces in this way, short-circuit induced current is suppressed, so that the steel pieces can be joined more reliably and safely.

FIG. 3 shows the joining allowance W on one side of the widthwise end of the steel piece.
The results of investigating the effect on the heating efficiency of the joint by varying the overlapping amount of the magnetic poles are shown below. The width of the steel piece used in the test was 1000 mm, and the welding allowance on one side was 1.
00mm, number of magnetic poles is 2, magnetic pole size is 250m wide
m, and the length was 300 mm. As is clear from the figure, the closer the magnetic pole is to the joint, the better the heating efficiency becomes. However, the magnetic pole overlaps the joint, and the amount of overlap is 0.
If it exceeds 3 times, a short circuit current will occur at the junction near the magnetic poles, resulting in a significant decrease in heating efficiency. At this time, the short-circuit induced current is concentrated particularly at both ends of the joint, resulting in damage to the equipment. Therefore, the overlap between the magnetic poles and the joint was limited to 0.3 times the joining distance. Here, the joining allowance W is set to be 0.1 times or more the width B of the steel piece in order to ensure joint strength as described later. Note that it is usually about 0.1 to 0.3 times the width B of the steel piece, more preferably 0.1 to 0.2 times.

When arranging one magnetic pole, it is placed at the center of the steel piece in the width direction, and when two or more magnetic poles are arranged side by side in the width direction of the steel piece, they are arranged symmetrically with respect to the widthwise center of the steel piece. It is preferable to place the FIG. 4 shows an example in which two magnetic poles are arranged.

FIG. 5 shows an example of rolling equipment used for joining steel pieces using magnetic poles as described above. In the figure, number 4 is the hot finishing rolling mill group, and 5 is the hot finishing rolling mill 4.
6 is a subsequent steel piece following this steel piece 5 (hereinafter referred to as a succeeding sheet bar); 7 is a sheet bar 5; Pinch rolls for conveying 6 and applying pressure when joining them; 8
is an alternating magnetic field generating device that has the role of heating the contact area a between the rear end of the leading sheet bar 5 and the tip of the trailing sheet bar 6, and this alternating magnetic field generating device 8 includes a core 8a forming a magnetic pole; It consists of a coil 8b and a power source 8c. here,
When this alternating magnetic field generating device 8 is used alone, it is arranged at the center in the width direction of the seat bar. Reference numeral 9 denotes a looper for absorbing the joining time of the sheet bars, and this looper 9 is omitted when the alternating magnetic field generator 8 is of a type that can move in synchronization with the conveyance of the sheet bars. .

As mentioned above, when the rear end of the preceding seat bar 5 and the leading end of the following seat bar 3 are in contact with each other, an alternating magnetic field is applied to the contact area a, which is placed at the center in the width direction of the seat bar. When an alternating magnetic field d is applied by the generator 8, eddy currents e as shown in FIG. 6 are induced along the width direction at each end of the sheet bars 5, 6. Each end of the seat bars 5 and 6 will be heated by the heat generated by the circulation of this eddy current e, but since there is electrical contact resistance particularly in the contact area a of the seat bar, the Due to Joule heat generation, the temperature of the contact surface of each end increases preferentially as shown in FIG. Therefore, in this contact state, at least one of the sheet bars 5 and 6 is pressed toward the sheet bar to be joined while increasing the temperature, or
Alternatively, the contact area can be brought into close contact efficiently and in a very short time by heating and raising the temperature in the previously pressed state, and since the alternating magnetic field generator 5 is a non-contact type, there is no risk of damage to equipment due to arc generation. There is no fear of giving it away.

In the present invention, in order to perform the above-mentioned heating more advantageously, that is, to shorten the heating time during bonding and reduce the input power required for this, the preceding sheet bar 2
The contact area a of the following sheet bar 3 is shown in FIG. 8(a) to (
g) As shown in (g), at least both end regions in the width direction of each sheet bar are provided, and gaps are provided in the other regions. Here, the joining of steel pieces having the shape shown in Fig. 7 above is more advantageous when joining steel pieces having the planar shape shown in Fig. 9(a), for example. When the joint ends of the steel pieces are heated and pressed, the joint area of the steel pieces expands from both ends to the center with a relatively small pressing force, as shown in Figure 9(b), and a specific joint width is increased. This is because the joints of the steel pieces do not break apart even during the subsequent finish rolling.

FIG. 10 shows the results of an investigation into the welding allowance in joining the above-mentioned steel pieces and the state of fracture during finish rolling. As is clear from the figure, the welding allowance W in the contact area is 0.1 with respect to the width B of the steel strip.
If it is at least 0.2 times or more in total, there is no fear that the joint portion will break and separate during the subsequent finish rolling.

The diagram (a) shown in FIG. 8 above is
If the rear end of the leading seat bar 5 and the leading end of the trailing seat bar 6 are cut in a concave shape with the same curvature, Figure (b) shows that although both the tip and rear end of each seat bar 5 and 6 are concave, When the curvatures of the two sides are different, the same figure (c) is obtained when one side has a flat planar shape and the other side has a concave shape.
d) is a case in which one side is convex and the other is concave, and the curvature of the concave shape is somewhat larger than the curvature of the convex shape; in both cases, only both ends of the sheet bar in the width direction are Although shown as an example in which they are in contact with each other and have a gap in the central region, the cutting shape that is compatible with the present invention is not limited to this, and as shown in Figures (e) and (f), both ends and Contact may be made at three points in the center with a gap between them, or the contact portion may be made at four points (not shown).
It may be a dot or more, with a gap between them. Furthermore, as shown in FIG. 2(g), the center portion in the width direction may be cut out in a rectangular shape.

Shearing, gas cutting, laser cutting, etc. can be used as a cutting method to obtain the above-mentioned shape, but especially when cutting in a concave shape with a specific curvature, it is necessary to use a cutting method that has two curved blades. Drum shears are particularly advantageously suited.

[0019] Next, the joining form when joining the steel pieces is: (1) a joining form in which the part to be joined is heated and raised to the target joining temperature, and after the heating is stopped, pressing is performed; (2)
A joining method that presses the steel piece when it reaches the target joining temperature while continuing to heat and raise the temperature (but does not exceed the temperature at which the joint part melts), or ■Heating the steel billet after it has been pressed in advance. Although various joining forms such as
00° C., and the joining of the steel pieces progresses to some extent even with mere pressing. For this reason, it is particularly preferable to shorten the joining time and reduce the input power required for heating and temperature raising by heating the steel pieces while pressing them.

Next, a schematic diagram of an alternating magnetic field generating device 8 suitable for carrying out the present invention is shown in FIG. 11, and by using such an alternating magnetic field generating device 8, Hereinafter, the method of applying an alternating magnetic field that penetrates the magnetic field will be referred to as the transverse method. As the alternating magnetic field generating device 8 that is compatible with the transverse method described above, it is also possible to consider the application of a split-type or homopolar horseshoe-shaped alternating magnetic field generating device that is individually arranged above and below so as to sandwich the steel piece in the thickness direction. However, it is preferable to use an alternating magnetic field generator having a C-shaped core sandwiching the steel piece in the thickness direction. This type of alternating magnetic field generator facilitates operation when joining the steel pieces in synchronization with the movement of the steel pieces, and allows easy and accurate alignment of the magnetic poles. In addition, when joining steel pieces whose ends have a flat planar shape,
When the alternating magnetic field generator is used alone, it is desirable to move it along its width so that the joint surface can be heated uniformly. Further, in the case where a plurality of alternating magnetic fields d are applied along the width direction of the steel piece, this can be handled by providing alternating magnetic field generators corresponding to the number of alternating magnetic fields d.

FIGS. 12(a) and 12(b) show an example in which a plurality of alternating magnetic fields d are applied along the width direction of a steel piece.

[0022]Although the alternating magnetic field applied to the steel pieces varies depending on the size of the steel pieces to be welded, it is desirable to apply it under conditions of approximately 500 to 3000 kW of input power and 2 to 8 seconds of heating time. Regarding the pressing force during joining, a surface pressure of about 3 to 8 kgf/mm2 is sufficient;
Further, the heating temperature is preferably 1250 to 1450°C.

[0023]

[Example] Applying the equipment shown in Figure 5 above, equipped with a tandem rolling mill of 7 stands, the width of 1000 mm,
Thickness: 30mm, radius of curvature at both tip and rear ends: 20
Sheet bars (low carbon steel) with a planar shape as shown in Figure 8(a) are continuously fed to a rolling mill while being joined according to the following conditions to finish hot-rolled sheets with a thickness of 3 mm. Ta. a. Alternating magnetic field (C-type magnetic pole): Input power: 2000 k
W heating time: 2.4 seconds, frequency: 500 Hz, number of magnetic poles: 2 (rectangular) magnetic pole width: 0.25 m magnetic pole length: 0.3 m b. Joining distance: 0.1 m on one side c. Distance from the end of the steel piece in the width direction to the pole tip (L in Figure 4)
): 0.2 m d. Heating temperature: 1400°C, e. Pressure force: 3kgf/mm2 as surface pressure
, f. Joining form: The steel pieces are brought into contact and heated while being pressed. As a result, the joint part of the sheet bar does not melt down at the center in the width direction during rolling, and the joint part does not break and is stable. It was possible to roll it.

Next, an experiment was conducted under the same conditions as above except that the distance from the end of the steel strip in the width direction to the pole tip was 0.07 m. No melting occurred in the central portion in the direction, and the bonded portion did not break, allowing stable rolling.

[0025] Furthermore, regarding the case where the width of the steel slab is 1500 mm, the joining allowance is 0.2 m on one side, and the distance from the end of the steel slab in the width direction to the pole tip is 0.2 m, the steel slabs are brought into contact with each other, heated, and then pressed. We conducted an experiment. The results also showed that during rolling, no melting occurred at the center in the width direction of the joints of the sheet bars, and the joints did not break, allowing stable rolling.

[0026]

[Effects of the Invention] The steel billet joining method of the present invention brings the front end and rear end of the steel billet into contact at least at both ends in the width direction of the steel billet, and penetrates this contact area in the thickness direction of the steel billet. By combining a process of heating both ends in the width direction by an induced current generated by applying an alternating magnetic field from the magnetic poles, and a process of pressing at least one steel piece toward the other steel piece, The rear end of the steel billet being conveyed by the steel billet can be quickly and reliably joined to the leading end of the following steel billet, which eliminates the need to increase the size of heating equipment or extend the continuous rolling line. Continuous hot rolling with high properties can be achieved, and the overlap of the magnetic poles with the joints formed at both ends of the steel billet in the width direction is suppressed to 0.3 times the welding allowance in the width direction of the steel billet. By arranging it closer to the center, it is possible to stably join without causing any damage to the equipment without melting off the steel pieces at the joint near the magnetic poles.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a circulating induced current flowing in a steel billet joint.

FIG. 2 is an enlarged view of a widthwise end of a steel billet joint.

FIG. 3 is a graph showing the relationship between the overlapping amount of magnetic poles and the heating efficiency of the joint with respect to the joining margin W on one side of the widthwise end of the steel piece.

FIG. 4 is a plan view showing an example of the arrangement of magnetic poles facing a steel piece. .

FIG. 5 is a diagram illustrating the configuration of a rolling facility suitable for carrying out the present invention.

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

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

FIG. 8 is a diagram showing a planar shape of a steel piece.

FIG. 9 is a diagram showing a state of joining steel pieces.

FIG. 10 is a graph showing the state of the joint of the seat bar.

FIG. 11 is a schematic diagram of an alternating magnetic field generator with C-shaped magnetic poles 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]

1. Steel pieces transported in advance 2.Subsequent steel billet following the preceding billet 3 Magnetic pole 4 Hot finishing rolling mill group 5 Advance seat bar 6. Subsequent seat bar 7 Pinch roll 8 Alternating magnetic field generator 9 Looper

Claims (1)

[Claims] Claim 1: At the entry side of hot rolling equipment for steel billets, the rear end of the steel billet that is conveyed in advance and the tip end of the subsequent steel billet that is conveyed subsequently are brought into contact with each other. Match it with
Next, the method involves heating and joining, in which the tip and rear ends of each of the steel slabs are brought into contact at least at both ends in the width direction of the steel slab, and an alternating magnetic field is applied to this contact area in the thickness direction of the steel slab. It consists of a combination of a process of heating both ends in the width direction by an induced current generated by being applied from a magnetic pole, and a process of pressing at least one steel piece toward the other steel piece, and the magnetic pole is The short-circuit induced current generated at this joint is placed near the center in the width direction of the steel piece, with the overlap with the joints formed at both widthwise ends of the steel piece being suppressed to 0.3 times the joint width of each joint. A method for joining steel billets in hot rolling, which is characterized by suppressing.