JPH0489109A - Method for joining billets in hot rolling - Google Patents

Abstract

PURPOSE:To simply and quickly join billets without consuming useless energy by joining the billets tightly to each other through combination of a treatment of heating the billets and a treatment of pressurizing the billets as the front and rear parts of each billet are brought into contact and an alternating field passing through the direction of thickness of the billet is applied in this area. CONSTITUTION:When the rear end part of a preceding sheet bar 2 and the front end part of a succeeding sheet bar 3 are abutted and made into contact, and an alternating field is applied by an alternating field generating coil 5 arranged in the central part in the width direction of the sheet bar in this contacted part (a), an eddy current (e) is induced in each end part of the sheet bars 2, 3 along the width direction. Each end part of the sheet bars 2, 3 is heated by heat caused by circulation of this eddy current (e). By pressing at least one of each sheet bar 2, 3 to a sheet bar to be joined as temperature is elevated in a contact state or heating it and elevating its temperature in a previously pressed state, a contact area can be joined tightly efficiently and in an extremely short time.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention provides a method for transferring a steel billet, such as a sheet bar, which is conveyed in advance, and a subsequent steel billet, which is conveyed subsequently, to a hot rolling facility. This invention relates to a method of joining steel billets that is particularly useful when butt joining is performed on the entry side of a steel billet and the joined steel billet is continuously supplied to a rolling line.

(Prior art) Conventionally, in a hot rolling line, after heating the steel billet to be rolled to a target temperature, the billet is passed one by one through a rough rolling process and a finishing rolling process to finish it into a hot rolled plate with a desired thickness. was, but
Such rolling methods tend to cause troubles such as line stoppages due to poor biting of the rolled material during finish rolling, and decreases in yield due to defects in the shape of the leading and trailing ends of the rolled material. Due to the large scale of the project, it was hoped that this problem would be resolved as soon as possible.

Eliminate the above troubles in hot rolling lines,
Attempts to further improve productivity include JP-A-60-244401 and JP-A-61-159.
A rolling technique as disclosed in Japanese Patent No. 285 is known.

(Problems to be Solved by the Invention) The techniques disclosed in the above-mentioned publications all join the rear end of the preceding rolled material and the leading end of the subsequent material at the entry side of the finish rolling process, and The purpose is to continuously supply one to several dozen pieces of rolled material to the finish rolling process,
If such a rolling method is followed, it is possible to significantly improve productivity without causing defects such as biting that occurs when steel billets are fed one by one to a rolling line.

However, when continuous rolling is performed 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. The method disclosed in Japanese Patent No. 60-244401 that uses high-frequency heating to join steel billets has the advantage of being able to heat the joint to the target joining temperature in a relatively short period of time, but it is difficult to join steel billets. Since unnecessary areas are heated, the amount of energy used for this is large.On the other hand, in the case of electrical heating such as the technique disclosed in JP-A No. 61-159285, scale adheres to the surface of the steel piece. When rolling the steel billet, an arc is generated due to the electrical contact resistance between the electrode roll and the steel billet, which may damage the electrode roll, and either method is not suitable for continuous hot rolling of the billet. It was sufficient.

This invention proposes a new joining method that can easily and quickly join steel billets without wasting energy, and moreover, can reliably join steel billets so that the joint portions will not separate and break during rolling. The purpose is to

(Means for Solving the Problems) The present invention abuts the rear end of a previously conveyed steel bill with the leading end of a succeeding steel bill at the entry side of a hot rolling facility. In joining, the tip and rear ends of each of the steel pieces are brought into contact and heated by applying an alternating magnetic field that penetrates the steel pieces in the thickness direction in that area, and the process of pressing the steel pieces is performed. This is a method for joining steel pieces in hot rolling (first invention), characterized in that copper pieces are brought into close contact with each other by combining them.

In this invention, the contact area between the preceding steel billet and the following steel billet is at least at both ends of the steel billet in the width direction (second invention), and when joining each steel billet, the contact area of the steel billet is At least one side is heated while being pressed (third invention), and the alternating magnetic field responsible for heating the contact area of the steel slab is generated by at least one alternating magnetic field generating coil having a C-shaped core that sandwiches the steel slab in the thickness direction. (fourth invention).

FIG. 1 shows an example of rolling equipment suitable for carrying out the present invention. In the figure, number 1 is a group of hot finishing mills, and number 2 is a preceding mill on the entry side of hot finishing mill 1. 3 is the subsequent steel piece following this steel piece 2 (hereinafter referred to as the succeeding sheet bar), and 4 is the conveyance of the sheet bars 2 and 3 and these. 5 is an alternating magnetic field generating coil that has the role of heating the contact area a between the rear end of the leading sheet bar 2 and the tip of the trailing sheet bar 3; The alternating magnetic field generating coil 5 includes a core 5a forming a magnetic pole, a coil 5b, and a power source 5c.

Here, when this alternating magnetic field generating coil 5 is used alone, it is arranged at the center in the width direction of the seat bar. Further, 6 is a looper for absorbing the joining time of the sheet bars, and this looper 6 is omitted when the alternating magnetic field generating coil 5 is of a type that can move in synchronization with the conveyance of the sheet bars. .

(Function) When the rear end of the preceding seat bar 2 and the leading end of the following seat bar 3 are in contact with each other, the alternating magnetic field generating coil 5 disposed in the center of the width direction of the seat bar is placed in the contact area a. When an alternating magnetic field d is applied by the sheet bar 2.
An eddy current e as shown in FIG. 2 is induced along the width direction at each end of 3. Each end of the seat bars 2 and 3 will be heated by the heat generated from the circulation of this eddy current e, but since there is contact electrical resistance particularly in the contact area a of the seat bar, the Due to Joule heat generation, the temperature of the contact surfaces at each end increases preferentially as shown in FIG. Therefore, by pressing at least one of the sheet bars 2.3 toward the sheet bar to be joined while raising the temperature in this contact state, or by heating and raising the temperature in the previously pressed state as described above, The contact areas can be brought into close contact in a short time, and since the coil 5 is of a non-contact type, there is no risk of damaging the equipment due to arc generation.

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

Here, joining of steel pieces having a shape as shown in FIG. 4 above is more advantageous when joining steel pieces having a planar shape as shown in FIG. 5(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 5(b), and a specific This is because, under the joint allowance, the joints of the steel billets will not break and separate even during the subsequent finish rolling.

FIG. 6 shows the results of an investigation into the welding allowance in joining the steel slabs as described above and the state of fracture during finish rolling. As is clear from the figure, if the welding allowance W in the contact area is at least 0.1 times or more than the billet width B, and at least 0.2 times in total, the joint will break and separate during the subsequent finish rolling. There is no fear that this will happen.

The diagram (a) shown in FIG. 4 above shows the case where the rear end of the leading sheet bar 2 and the tip of the trailing seat bar 3 are cut into a concave shape with the same curvature, and the diagram (b) shows the shape of each sheet. bar 2.3
If both the tip and rear end are concave but have different curvatures, Figure (C) shows that one side is flat and only the other is concave, and Figure (D) shows that one side is convex. The other side is concave, and the curvature of the concave is somewhat larger than the curvature of the convex.In both cases, only the widthwise ends of the sheet bars are in contact, and the center area is Although the cutting shape is shown as an example in which a gap is provided at both ends, the cutting shape suitable for the present invention is not limited to this, and as shown in FIG.
It is also possible to make contact at a point with a gap between them, or, although not shown, the contact portion may be made at four or more points,
A gap may be provided in between.

Furthermore, as shown in FIG. 3(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 cutting methods to obtain the above shape.
A drum shear with two curved blades is particularly advantageous when making concave cuts with a particular curvature.

Next, when joining steel pieces, the joining method is to heat and raise the temperature of the part to be joined to the target joining temperature, and then press after stopping the heating, and continue heating and raising the temperature. Various joining methods are possible, such as one in which the steel pieces are left as they are (but not exceeding the temperature at which the joint part melts) and then pressed when the target joining temperature is reached, or one in which the steel pieces are pressed in advance and then heated. However, the temperature of the steel piece during the joining process is usually about 1000 to 1100°C,
The joining of the steel pieces progresses to some extent even with mere pressing. Therefore, in the third aspect of the invention, the joining time and the power required for heating and temperature raising are reduced by particularly heating the steel pieces while pressing them.

Next, a schematic diagram of an alternating magnetic field generating coil 5 suitable for carrying out the present invention is shown in FIG. Hereinafter, the method of applying a penetrating alternating magnetic field will be referred to as the transverse method. As the alternating magnetic field generating coil 5 that is compatible with the transverse method described above, it is also possible to consider the application of a split type or a homopolar horseshoe type alternating magnetic field generating coil that is individually arranged at the top and bottom so that the steel piece is sandwiched in the thickness direction. However, here, as the fourth invention, an alternating magnetic field generating coil having a C-shaped core sandwiching the thickness direction of the steel piece is applied. This type of alternating magnetic field generating coil 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 with flat ends and using a single alternating magnetic field generating coil, it is necessary to heat the joint surfaces uniformly.
It is desirable to move along the width direction. Furthermore, 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 generating coils corresponding to the number of alternating magnetic fields d.

FIGS. 8(a) and 8(b) show an example in which a plurality of alternating magnetic fields d are applied along the width direction of a steel piece.

In addition, the alternating magnetic field applied to the steel pieces varies depending on the size of the steel pieces to be welded, but the applied power ranges from 500 to 3
It is desirable to apply under the conditions of 000 kW and heating time of 2 to 8 seconds, and the pressing force during bonding is 3 to 8 in terms of surface pressure.
kgf/mm" is sufficient, and the heating temperature is preferably 1250 to 1450"C.

Incidentally, FIG. 9 shows a schematic diagram of high-frequency heating using a solenoid coil S, which is different from the transverse method according to the present invention. When joining steel pieces such as sheet bars by induction heating using a solenoid-type coil, especially the area ffi (Iiii1
(including the longitudinal direction of the sheet bar), resulting in large energy loss, and when heating at a high frequency to shorten the bonding time, the local temperature of only the surface area of the sheet bar may be reduced. Due to this increase, there is a risk that only the surface layer portion will melt before the target bonding temperature is reached.

(Example) By applying the equipment shown in Fig. 1 above, which is equipped with a tandem rolling mill with 7 stands, a width of 1000 mm and a thickness of 30 m is applied.
Sheet bars (low carbon copper) having a planar shape as shown in FIG.

a. Alternating magnetic field (C-type magnetic pole): Throw-in type crab 2000Kw
, Heating time: 12 seconds, Frequency: 5007, b, Heating temperature: 1400°C1 C0 Pressing force: 3 kgf/mm2d as surface pressure, Pressing time: 3 seconds, e, Joining form: Heating with steel pieces in contact After pressing f,
The alternating magnetic field was moved along the joint surface, and as a result, the sheet bar joints did not break during rolling, and stable rolling was possible. In addition, compared to joining sheet bars of the same shape and under the same conditions using the conventional high-frequency heating method,
It was confirmed that the power consumption can be reduced by about 50%, and the bonding time is about 12 seconds, which is about 20% shorter than the bonding time of 15 seconds in the conventional bonding method under the same conditions.

In addition, a sheet bar (low carbon w/I) with a planar shape as shown in FIG.
Alternating magnetic field (C-type magnetic pole) 2-piece energized crab 2000Kw, frequency: 500 Hz.

b. Heating temperature: 1400°C1 C1 pressing force 2 Surface pressure 3 kgf/mm2d, joining width after heating and pressing 2 W = 200 mm (100 mm on one side
(Body), e. Bonding form: We also investigated the bonding conditions when the sheets were pressed in advance and bonded according to the heating conditions, but even in such bonding, the joint did not break due to rolling, and the sheet bar The heating time required for joining was further reduced to approximately 2.4 seconds, compared to the case where the front and rear ends were joined together.

In addition, we also investigated a case in which only the joining form of the sheet bar was changed in the example of the planar shape shown in FIG.
In this case, the temperature of the joint surface is less likely to rise compared to heating while pressing, so the joining cost was halved compared to heating while pressing, but the heating time was extended by about 1.6 seconds. This made it possible to perform the desired bonding.

(Effects of the Invention) Thus, according to the present invention, the rear end of a previously conveyed steel piece and the leading end of a subsequent steel piece can be quickly and reliably joined. There is no need to extend the continuous rolling line, and continuous hot rolling with high productivity can be achieved.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the configuration of rolling equipment suitable for carrying out the present invention, Fig. 2 is an explanatory diagram of the procedure for joining steel pieces according to the invention, and Fig. 3 is a temperature diagram of the welding area. A diagram showing the distribution, Figure 4 (a
) to (g) are diagrams showing the planar shape of the steel piece, and Figure 5 (a)
)(b) is a diagram showing the state of joining of steel pieces, FIG. 6 is a graph showing the state of joints of sheet bars, and FIG. 7 is a diagram showing a state of joints of sheet bars. A schematic diagram of an alternating magnetic field generating coil with C-shaped magnetic poles. Figure 8 (a) and (b) are diagrams showing an example of the arrangement of an alternating magnetic field generating coil. Figure 9 is a diagram of a conventional induction heating method. It is a diagram showing an outline. 1... Finish rolling mill group 2... Leading sheet bar 3
...Following seat 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 Fig. 4 Fig. 6 WEB (lunar eclipse 1) Fig. 5 (a) Fig. 7 Fig. 9

Claims (1)

[Claims] 1. At the entry side of the hot rolling equipment, the rear end of the previously transported steel billet is brought into contact with the tip end of the subsequent steel billet that is subsequently transported. In joining, the front end and the rear end of each of the steel slabs are brought into contact, and an alternating magnetic field that penetrates through the thickness of the steel slab is applied in that region to heat the steel slab, and at least one of the steel slabs is pressed. A method for joining steel billets in hot rolling, characterized in that the steel billets are brought into close contact with each other by a combination of treatment. 2. The method according to claim 1, wherein the contact area between the preceding steel piece and the following steel piece is at least at both ends of the steel piece in the width direction. 3. The method according to claim 1 or 2, wherein the steel piece is heated while being pressed. 4. The method according to claim 1, 2 or 3, wherein the alternating magnetic field responsible for heating the contact area of the steel piece is applied by at least one alternating magnetic field generating coil having a C-shaped core sandwiching the steel piece in the thickness direction.