JP3901436B2 - Hot rolling method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot rolling facility for performing continuous hot rolling by joining the front and rear ends of two or more coarse bars, and a hot rolling method using the hot rolling facility.
[0002]
[Prior art]
In hot rolling in which a slab is rolled to form a hot-rolled steel strip, conventionally, batch rolling in which the slabs are rolled one by one has been performed. However, in this batch rolling, there has been a problem that the line stop occurs due to the biting failure when the material to be rolled bites into the rolling mill. In addition, there is a problem in that defects in shape and material occur due to the fact that the front and rear ends of the material to be rolled are unconstrained, resulting in a decrease in yield.
[0003]
Therefore, in recent years, a continuous hot rolling method has been developed in which the front and rear ends of a plurality of rough bars are sequentially joined to form a continuous rough bar and continuous finish rolling is performed.
Various proposals have been made regarding a method for joining rough bars, which is an essential and key technology for such a continuous hot rolling method. As a representative example, in JP-A-4-89109, the front end and the rear end of each coarse bar are brought into contact, an alternating magnetic field penetrating the coarse bar in the thickness direction is applied and heated, A technique for joining coarse bars by pressing the coarse bars is disclosed.
[0004]
This technique is shown in FIG. In FIG. 5, 6 is a transverse flux type induction heating device, 7 is a clamp, 8a is a preceding coarse bar, and 8b is a subsequent coarse bar. The transverse flux type induction heating device 6 heats the rear end of the preceding coarse bar 8a and the front end of the subsequent coarse bar 8b. The heated part is pressed and joined. The coarse bars 8a and 8b are supported by the clamp 7 during heating and pressure welding.
[0005]
As a technique similar to the present invention, Japanese Patent Application Laid-Open No. 10-244301 discloses a hot rolling facility in which a rough rolling mill, a joining device, an induction heating device, and a finish rolling mill are installed in this order, and a rolling using the same. A method is disclosed.
[0006]
[Problems to be solved by the invention]
However, the technique disclosed in Japanese Patent Laid-Open No. 4-89109 has the following problems. That is, since the joining of the coarse bars is performed by heating and pressure welding, the coarse bars are stopped during this time, and the temperature of the coarse bars is lowered. Therefore, problems such as an increase in the finish rolling load and difficulty in securing the rolling finish temperature occur. Therefore, a technique for shortening the bonding time is required.
[0007]
In the technique disclosed in Japanese Patent Application Laid-Open No. 10-244301, an induction heating device is installed behind the joining device, which is not useful for shortening the joining time. This prior art is aimed at temperature compensation of the low temperature portions before and after the joint. The low temperature portion is caused by the clamp at the time of joining or the temperature of the rough bar tip and the rear end being originally lower than the other portions.
[0008]
These low temperature portions exist immediately before and after the bonding portion, and it is extremely difficult to heat only the low temperature portion so as not to affect the bonding portion. If the joining portion is heated, there is a high possibility that it will break during finish rolling. Conversely, if the low temperature part is not heated before finish rolling, the material will deteriorate there.
[0009]
This invention is made | formed in view of such a situation, and makes it a subject to provide the method of shortening the time which joining of a rough bar, and preventing the fall of the temperature of a rough bar.
[0010]
The subject includes a roughing mill that rolls a slab into a rough bar, and a finishing mill that rolls the rough bar into a hot-rolled steel strip, and the rough bar is between the roughing mill and the finishing mill. In this order, an induction heating device that heats only the front and rear ends of the front and rear ends, and a joining device that heats the rear end of the preceding coarse bar and the front end of the subsequent coarse bar and press-contacts both of them are arranged in this order. A hot rolling method using a hot rolling facility, wherein only the rear end of the preceding coarse bar and the front end of the subsequent coarse bar are heated by the induction heating device, and then the rear end and rear of the preceding coarse bar are heated. This is solved by a hot rolling method characterized in that the ends of the rough bars to be joined are joined by the joining device.
[0011]
In this means, as a means for joining the coarse bars, as described in JP-A-4-89109, the leading end of the preceding coarse bar and the leading end of the following coarse bar are heated and then both are pressed. A joining device is provided. And in order to shorten the joining time in this joining device, an induction heating device that heats only the rough bar tip rear end and the coarse bar over the entire width direction is provided before this joining device. The part to be joined of the coarse bar is heated in advance. Thereby, since the heating time in a joining apparatus is shortened, the time which joining requires is also shortened and the fall of the temperature of a rough bar can be prevented.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of the arrangement of hot rolling equipment as an example of an embodiment of the present invention. In FIG. 1, 1 is a roughing mill, 2 is a conveyance roller, 3 is a solenoid type induction heating apparatus, 4 is a joining machine, and 5 is a finish rolling mill. In the present embodiment, as shown in FIG. 1, the rough rolling mill 1, the solenoid induction heating device 3, the joining machine 4, and the finishing mill 5 are arranged in this order.
[0021]
The joining device 4 employs a method including heating of a coarse bar, such as heating and pressure welding. For example, as described in Japanese Patent Laid-Open No. 4-89109 shown in FIG. 5, a transverse flux type induction heating apparatus 6 is used to connect the rear end of the preceding coarse bar 8a and the front end of the subsequent coarse bar 8b. A system in which the rough bars 8a and 8b are gripped and pressed by the clamp 7 can be used while being heated.
[0022]
In such a joining method, the rear end of the rough bar 8a and the front end of the rough bar 8b must be kept in the joining device 4 during heating and pressure welding, and heat loss during the joining time is a problem. It is. Therefore, in the hot rolling facility of the present embodiment, the solenoid induction heating device 3 is installed before the joining device 4. The front and rear ends of the coarse bar are heated to the necessary temperature by the solenoid induction heating device 3 while being conveyed from the rough rolling mill 1 to the finishing mill 5. Thus, by shortening the heating time in the bonding apparatus 4, the heat loss of the coarse bars 8a and 8b can be reduced.
[0023]
In the hot rolling method of the present invention, since the rough bars 8a and 8b are heated during conveyance, the heating device installed on the entry side of the joining device 4 preferably has a high heating rate and high heating efficiency. An induction heating apparatus is employed as a heating method with the largest temperature increase rate. There are two known types of induction heating methods for heating a plate-like object such as a coarse bar, a solenoid type and a transverse flux type. Among these, when compared with the performance of heating a rough bar having a thickness of 30 to 50 mm, the solenoid type has high heating efficiency. Further, due to the simplicity of the inductor, the solenoid type induction heating device 3 is generally less expensive. From the above, the solenoid induction heating device 3 is employed in the hot rolling equipment of the present embodiment.
[0024]
In order to ensure the necessary temperature rise before entering the joining device 4, the inductor of the solenoid induction heating device 3 must be made sufficiently long to increase the heating time. However, the heating device cannot be lengthened unnecessarily. As shown in FIG. 2, when the heating device is lengthened unnecessarily, the leading end or the rear end of the coarse bar 8 is bent between the conveying rollers 2 and comes into contact with the solenoid induction heating device 3, and the inductor is turned on. This is because there is a risk of damage. Therefore, in the hot rolling facility of the present invention, the solenoid induction heating device 3 is divided into a plurality of parts, and the conveying roller 2 is always sandwiched between them.
[0025]
Care must be taken when using a solenoid type induction heating device to heat the coarse bar. In the solenoid type induction heating apparatus, the vicinity of the surface of the coarse bar is intensively heated by the skin effect. Since the heat is rapidly dissipated from the hot surface, the rough bar should be joined immediately after induction heating is completed. It is desirable that the time from the completion of the heating of the rough bar by the solenoid induction heating device to the start of bonding is 10 seconds or less. By doing so, the Joule heat concentrated on the surface of the rough bar, which is peculiar to the solenoid type induction heating apparatus, can be used for shortening the joining time.
[0026]
In the hot rolling facility of the present invention, the order of the solenoid induction heating device and the joining device is reversed from the facility described in Japanese Patent Laid-Open No. 10-244301. If a portion that becomes a low temperature portion after joining is heated before joining by the solenoid type induction heating device, temperature compensation of the low temperature portion can be performed without further heating the joining portion by the solenoid type induction heating device. Therefore, the present invention is superior.
[0027]
In the hot rolling method of the present invention, a hot-rolled steel strip is manufactured using the hot rolling equipment described above. The slab is rolled with a roughing mill 1 to form a rough bar, which is conveyed to the joining device 4 while the leading end of the preceding rough bar 8a and the leading end of the following rough bar 8b are connected to the solenoid induction heating device 3. After being used and heated, bonding is performed by the bonding apparatus 4. Since the coarse bar is heated in advance by the solenoid type induction heating device 3, the heating time of the coarse bar by the joining device 6 can be shortened, and thus the joining time itself is shortened. The rough bar after joining is rolled by a finishing mill 5 to form a hot-rolled steel strip in the same manner as normal continuous hot rolling.
[0028]
【Example】
The effect of this invention is demonstrated in an Example.
Example 1
In the hot rolling facility of the present embodiment, eight solenoid induction heating apparatuses 3 having a capacity of 6000 kW and a length of 500 mm in the transport direction are installed between the transport rollers 2. The joining device 4 is provided with a transverse flux induction heating device 6 having a capacity of 3000 kW in the form shown in FIG.
[0029]
Using such equipment, two rough bars having a thickness of 40 mm and a width of 1250 mm were joined. Before carrying out the method of the present invention, that is, when the solenoid type induction heating device 3 is not used, the time required for joining was about 20 seconds, and the temperature of the coarse bar was lowered by about 30 ° C. during that time. When the method of the present invention is carried out and the trailing end of the preceding coarse bar 8a and the leading end of the following coarse bar 8b are heated while being conveyed by the solenoid type induction heating device 3, the joining time is reduced to about 7 seconds. During this time, the temperature drop of the coarse bar was about 10 ° C., and the heat loss was reduced to about one third.
[0030]
(Example 2)
Using the same hot rolling equipment as in Example 1, the relationship between the elapsed time after the heating of the coarse bar by the solenoid induction heating device and the coarse bar surface temperature was examined.
The coarse bars used in the test are 30 mm thick, 1000 mm wide, 40 mm thick, and 1000 mm wide. After the tip of the coarse bar was heated with a solenoid induction heating device, the tip was taken out of the solenoid induction heating device and allowed to stand as it was to measure the surface temperature. The time change of the surface temperature is shown in FIG. At any plate thickness, the surface temperature decreases rapidly because the surface temperature is high immediately after heating. Thereafter, the temperature distribution in the plate thickness direction is in a steady state, and the cooling rate is constant.
[0031]
FIG. 4 schematically shows the temperature distribution in the plate thickness direction of the coarse bar immediately after induction heating and in a steady state. The time for switching from the unsteady state where the surface temperature after induction heating is high to the steady state is about 10 seconds after the end of heating. In order to use the amount of heat concentrated on the surface of the coarse bar, which is unique to the solenoid type induction heating device, the coarse bar is heated within 10 seconds after the heating of the coarse bar by the solenoid type induction heating device is completed. It is desirable to join.
[0032]
【The invention's effect】
As described above, according to the present invention, the time required for joining the coarse bars is shortened, and the effects of improving productivity and reducing heat loss can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of the arrangement of hot rolling equipment as an example of an embodiment of the present invention.
FIG. 2 is a diagram showing problems when the solenoid induction heating apparatus is long.
FIG. 3 is a diagram showing a change in elapsed time and temperature of a coarse bar after heating by a solenoid type induction heating device.
FIG. 4 is a diagram schematically showing a plate thickness direction temperature distribution of a coarse bar immediately after induction heating and in a steady state.
FIG. 5 is a schematic view showing a conventional joining apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Rough rolling mill, 2 ... Conveying roller, 3 ... Solenoid type induction heating apparatus, 4 ... Joining apparatus, 5 ... Finishing rolling mill, 6 ... Transverse flux type induction heating apparatus, 7 ... Clamp, 8 ... Rough bar, 8a ... preceding coarse bar, 8b ... following coarse bar

Claims (1)

It has a roughing mill that rolls slabs into rough bars, and a finishing mill that rolls rough bars into hot-rolled steel strips, and only the leading and trailing ends of the rough bars are between the roughing mill and the finishing mill. , An induction heating device that heats the entire width direction, and a hot rolling facility in which a joining device that heats the trailing end of the preceding rough bar and the leading end of the following rough bar and presses them together in this order is arranged In which only the trailing end of the preceding rough bar and the leading end of the following rough bar are heated by the induction heating device, and then the trailing end of the preceding rough bar and the following rough bar A hot rolling method, wherein the tips of the steel plates are joined by the joining device.

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