JPH09279227A - Device for uniformly heating rolling material with induction heating and heating method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a uniform heating method of a rolling material which can uniformize the temp. in the cross section of the rolling blank without specially complicating an equipment constitution, and a device thereof. SOLUTION: In the uniform heating device of the rolling material by induction-heating while shift-carrying the solid rolling material of a metallic material to supply this heated material to a rolling-mill in the downstream side, a heat restorating zone 3 for restorating the heat in the material to be heated while stopping or shifting, is arranged between an induction heating device 2 and the rolling-mill 5 in the downstream side. Further, in the induction heating device 2, a discriminating means for the material to be heated and an input electric power control device 8 to the induction heating device, and the induction heating device and a carrying speed control device 8 in the heat restorating zone, are combined to measure the surface temps. of the material to be heated before and after induction-heating. The heat restorating time related to the temp. distribution in the cross section of the material suitable to the rolling process in the downstream side is calculated to control the passing time of the heat restorating zone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating apparatus and a heating method for induction-heating a solid steel material such as carbon steel or stainless steel while moving and feeding the steel material to a rolling process.

[0002]

2. Description of the Related Art Induction heating is one of the means for heating metal materials such as steel, and is also used as a method for heating rolled materials. The usage form is not only the method of using induction heating alone, but also the method of using induction heating in combination with other heating means, for example, JP-A-56-6291.
No. 9, a skid mark erasing method in a radiant heating furnace, or a radiant heating furnace as disclosed in Japanese Patent Laid-Open No. 5-302114 is heated to the grain boundary oxidation critical temperature of the material and then required. How to raise the temperature,
Various.

Further, as a method of transporting and supplying the rolled material after induction heating to the hot rolling step, a method of directly connecting the induction heating step 2 with the rolling step 5 as shown in FIG. 2 or not shown. However, a method is used in which a rolling material is conveyed by a conveying table or transfer and supplied to the rolling process. If there is a distance between the induction heating device and the rolling mill, and radiative cooling from the rolling material during that time poses a problem, a heat retaining means may be provided for the purpose of suppressing it.

[0004]

However, the above-mentioned conventional method has the following problems. First, as a problem peculiar to induction heating, there is a problem of a so-called skin effect in which the distribution of the induced current generated in the material to be heated is largest on the surface and becomes smaller toward the central portion. FIG. 3 schematically shows this phenomenon with the distribution of the induced current density in the longitudinal direction and the depth direction of the material to be heated.

For this reason, the material to be heated is more likely to be heated toward the surface layer. For example, when a plurality of induction heating coils are used for multi-stage heating, the surface layer is heated by repeating heating and cooling as shown in FIG. On the other hand, since the temperature of the central portion gradually rises, the temperature in the cross section of the material to be heated gradually becomes nonuniform.

On the other hand, by hot rolling, the rolled material is stretched in the advancing direction by the amount that the cross-sectional area is reduced. However, if the stretching is not uniform, the material is cracked. The idea is to make it as uniform as possible. However, the hot deformation resistance of metals such as steel generally has a strong temperature dependency, so if the temperature in the cross section is non-uniform, there will be a difference in the material stretching during rolling, causing the problem of inducing cracks in the material. is there.

One of the measures to make the temperature in the cross section uniform during induction heating is to set the oscillation frequency to the low frequency side. In that case, if the oscillation frequency is lowered as shown in FIG. Go down. Therefore, it is necessary to take facility measures such as increasing the amount of input electric power and lengthening the total length of the heating coil, which causes a problem of increasing facility cost.

In addition, it is conceivable that the amount of input electric power per unit length is reduced to gently heat the material to be heated while keeping the temperature difference inside the material to be heated small. The extension must be lengthened and the equipment cost will increase.

Further, even if there is a transfer table or transfer between the induction heating device and the rolling mill and there is time between the induction heating and the rolling, the heat is recovered by utilizing the internal heat conduction of the material itself. It is not explicitly intended to make the temperature in the cross section uniform, and therefore, the fact is that the temperature in the cross section is not made uniform with high accuracy.

Therefore, an object of the present invention is to provide a method for uniformly heating a rolled material and an apparatus therefor which can make the temperature in the cross section of the rolled material uniform without making the equipment structure of the induction heating equipment particularly complicated. To do.

[0011]

The gist of the present invention is as follows. (1) In a uniform heating device for a rolled material that induction-heats while moving and transporting a solid rolled material of a metal material and supplies it to a downstream rolling mill, a heated material is provided between the induction heating device and the downstream rolling mill. A uniform heating device for rolled material by induction heating, which is provided with a retropic zone for recuperating heat while stationary or moving.

(2) In combination with the induction heating device, a means for determining the material to be heated and a control device for the amount of electric power input to the induction heating device, and an induction heating device and a transportation speed control device for the reheating zone,
Rolling by induction heating characterized by measuring the surface temperature of the material to be heated before and after induction heating, calculating the recuperation time that is the temperature distribution in the material cross section suitable for the downstream rolling process, and controlling the recuperation temperature transit time. Uniform heating method for wood.

Hereinafter, the present invention will be described in detail. FIG.
It is a top view which illustrates this invention. In the present invention, as shown in FIG. 1, the tropical zone 3 is arranged between the induction heating device 2 and the rolling mill 5, but in addition to this, the tropical zone 3 may be arranged between the induction heating devices. The retropical zone 3 is provided with a heat insulating means for suppressing cooling of the steel material 4 due to radiation and heat conduction to the outside, and a heat retaining means such as a heater if necessary.

The length of the retropic zone 3 is set to be equal to or longer than the length of the steel material when the steel material conveying speed is changed between the time of induction heating and the time of reheating. However, it is not limited to this when the value is constant. When the steel material condition, the heating condition, and the reheat condition change, the transfer device 1 can change the transfer speed.

Further, the induction heating may be partial heating which is continuous in the longitudinal direction such as heating both sides of the slab, or may be secondary heating after primary heating is performed in a radiant heating furnace.

Next, after the completion of induction heating, the time until the temperature in the cross section of the material is equilibrated by heat conduction and the temperature distribution suitable for rolling is grasped. As a grasping method, there is a method of embedding a thermocouple in the steel material 4 and measuring induction heating and reheating processes to obtain a required time.

In addition, there is also a method in which the physical property values of steel materials are used to obtain them by computer simulation. Further, if the representative steel types are actually measured with a thermocouple or the like and the approximate steel types are subjected to computer simulation, the required time of each steel type can be relatively easily and accurately grasped.

After performing the above, while the steel material 4 is being conveyed by the conveying device 1, the induction heating device 2 is supplied with electric power from the electric power supply device 7 to perform induction heating, and subsequently, a recuperation time previously grasped is given. As a result, the temperature in the cross section of the steel material is made uniform. In providing the recuperation time, the recuperative speed is changed if necessary, and the steel material is made to stand still inside the retropical zone as the case may be.

Here, the induction heating device, the reheating speed of the tropical zone, and the amount of electric power supplied to the induction heating device may be set manually. Further, as in the invention of claim 2, by combining means such as tracking for discriminating each steel material with a control device for the conveying speed and input electric energy, reheat conditions corresponding to steel material conditions and heating conditions are provided for each steel material. If it is calculated and given to, the human load is reduced and the accuracy of the temperature supplied to the rolling mill is increased.

As a method of calculating the reheat condition, there is a method of having a computer simulation program. However, since it takes time to calculate, for example, a method of holding a lookup table for reference, or limiting the condition, There is a method to calculate by a simple formula, etc.

Further, when the temperature of the steel material on the inlet side of the induction heating device varies at room temperature or above, such as the process of induction heating the steel material that is primarily heated in the radiant heating furnace, a thermometer 6 is provided on the inlet side of the induction heating device. By measuring the initial temperature of the steel material one by one and reflecting it in the reheat condition calculation, it is possible to further improve the accuracy of the temperature supplied to the rolling mill. Further, by providing thermometers 6 between the induction heating device and on the outlet side, the temperature of the steel material during the induction heating and after the induction heating is measured one by one and reflected in the reheat condition calculation, thereby further improving the accuracy. You can

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION A steel material 4 is sent to an induction heating device 2 by a carrying device 1 and heated by an induction heating device 2 which receives electric power input from a power input device 7. Depending on the case, it passes through the tropical zone 3 during the induction heating. Sufficient heat insulation measures are taken inside the retropic zone 3 to suppress the temperature drop due to the radiation of the steel material 4 and the heat conduction to the outside. Here, the steel material 4 equilibrates the temperature in the cross section by its own internal heat conduction. Variability is small.

When passing through the tropical zone 3 during induction heating, the next induction heating is subsequently performed. By repeating this, the temperature is raised so that the variation in the temperature in the cross section from the surface layer to the central portion does not become large.

Upon completion of induction heating, the recuperation time for sufficiently homogenizing the temperature in the steel material cross section so as to be suitable for downstream hot rolling is calculated according to the steel material conditions and induction heating conditions, and the recuperation time When the steel material 4 passes through the retropical zone 3 at a transportation speed that makes it possible to achieve a uniform temperature in the cross section of the steel material 4.

Further, according to the invention of claim 2, even if the steel material conditions and the induction heating device inlet side temperature of the steel material 4 are different for each one, each is discriminated for each one, and the induction heating device inlet side temperature is determined. Is reflected in the calculation of the reheat condition and the input electric energy and the conveying speed are appropriately controlled, so that there is almost no human load required for the condition setting, and the temperature supplied to the rolling mill can be maintained with high accuracy. Further, when the temperature during the induction heating or after the induction heating is measured one by one and reflected in the reheat condition calculation, the temperature supplied to the rolling mill is maintained more accurately.

[0026]

FIG. 6 shows an embodiment of the present invention. Secondary heating is performed 6 after the radiant heating furnace 9 that performs primary heating of the steel material 6
The induction heating device 2 of the pedestal, the retroping zone 3 having the steel material conveying means, and the rolling mill 5 are arranged. The transfer device 1 is arranged between the six induction heating devices 2. In addition, the induction heating device 2
A thermometer 6 is provided on the inlet side and the outlet side of.

Further, a power supply device (not shown) for supplying power to each of the transfer devices 1 and the induction heating device 2, and a thermometer 6.
Is controlled by a control device (not shown) having a steel material discriminating function. The retropical zone 3 is box-shaped and has a ceramic fiber lining inside to enhance heat insulation. Further, a roller is provided inside as a transporting means.

The steel material 4 that has been primarily heated to a predetermined temperature in the radiant heating furnace 9 is conveyed to the induction heating device 2 by the conveying device 1 after extraction, and the secondary heating by induction heating is started. At this time, the temperature before induction heating of the steel material is measured by the thermometer 6 installed on the inlet side of the induction heating device 2, and control is performed to adjust the amount of input electric power as a reference according to the difference from the reference temperature, Induction heating is performed.

After induction heating, a look-up table predetermined by the temperature at the end of induction heating of the steel material, the rolling start temperature, and the type of steel is searched, and the temperature in the tropical zone is returned to the predetermined recuperation time. Set the transport speed of. At this time, the temperature after induction heating is measured by the thermometer 6 installed on the output side of the induction heating device 2, and control is performed to adjust the staying time in the tropical zone.

For example, if the temperature before induction heating is low and the temperature after induction heating is as standard when the input electric energy is increased from the standard, the temperature increased by induction heating is higher than the standard, and therefore the temperature in the cross section is also standard. Decide that there is more variation and increase the time spent in the tropical zone.

If the temperature before induction heating is high and the temperature after induction heating is as standard when the amount of input electric power is reduced from the standard, the temperature increased by induction heating is lower than the standard, and therefore the temperature in the cross section is also standard. Decrease the variation and reduce the time spent in the tropical climate. The correction of the input power amount and the staying time in the tropical zone is performed by adding and subtracting each reference value searched in the look-up table by a simple formula using temperature as a variable term.

Further, since continuous rolling is carried out, control is also performed to keep the distance between the material concerned and the front and rear materials proper. For example, when the reference speed is set for the preceding material in a state where the return tropical transport speed is lower than the reference in order to increase the staying time of the preceding material in the tropical tropical zone, the material speed is also adjusted to the preceding material. The reason is that when the staying time in the tropical zone increases, the temperature in the cross section becomes more uniform, which is a safer direction for rolling.

Further, in order to shorten the return-to-tropical stay time of the preceding material, when the reference speed is set for the material in a state where the return-tropical transportation speed is higher than the reference, the material speed is set to the reference speed. This is because it is a safer direction from the viewpoint of material permeability that there is a gap with the preceding material. However, in these cases, the production efficiency will decrease. Therefore, in order to carry out stable production efficiently, if the recuperation time deviates from the standard value by a certain value or more, an alarm will be output to alert the operator.

FIG. 7 shows an example of the temperature history of the steel material during such induction heating and recuperation. The steel material heated to about 1050 ° C. by the primary heating is heated by 6 induction heating devices. Between each induction heating device, since only the transfer device is provided and no retroping zone is provided, the temperature of the steel material is significantly lowered by cooling.

After the induction heating is completed, the reheating is started. The target of the rolling start temperature at this time is 1200 ° C., and the target value is reached in the reheating time of about 50 seconds. Since the heat insulation measures are taken inside the retropical zone, the temperature drop of the steel material in the retropical zone is suppressed. In addition, the results of simulations in which the thermocouple was embedded in the steel material and the measured results are in good agreement.

By the above method, even when the steel material is induction-heated and supplied to the rolling process, the steel material having a uniform cross-section temperature can be obtained.
It is possible to obtain stable production efficiency without increasing the workload of the operator.

[0037]

[Effects of the Invention] According to the present invention, (1) improvement and stabilization of product quality by uniformizing the temperature in the cross section of steel material, (2) simplification of induction heating equipment and accompanying reduction of equipment cost, (3) operator work It can be expected to reduce the load.

[Brief description of drawings]

FIG. 1 is a plan view illustrating the present invention.

FIG. 2 is a plan view illustrating an example of a combination of an induction heating device and a rolling mill that do not have a retropical zone of the related art.

FIG. 3 is a chart illustrating the skin effect in induction heating.

FIG. 4 is a diagram illustrating a situation in which a temperature in a cross section is nonuniform due to a skin effect in induction heating.

FIG. 5 is a chart illustrating a relationship between an oscillation frequency and a coil efficiency.

FIG. 6 is a plan view showing an embodiment of the present invention.

FIG. 7 is a table illustrating a temperature history when heating a steel material according to an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conveyor device 2 Induction heating device 3 Restoring zone 4 Steel 5 Rolling machine 6 Thermometer 7 Electric power input device 8 Control device 9 Radiant heating furnace

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C21D 9/00 101 9352-4K C21D 9/00 101K (72) Inventor Akira Teramae 20-Shintomi, Futtsu-shi 1 Nippon Steel Co., Ltd. Technology Development Division

Claims (2)

[Claims] 1. A uniform heating device for a rolled material, which is induction-heated while moving and transporting a solid rolled material of a metal material and is supplied to a downstream rolling mill, wherein:
A uniform heating device for rolled material by induction heating, which is provided with a retropic zone for recovering heat while the material to be heated is stationary or moving. 2. A surface of a material to be heated before and after induction heating, wherein an induction heating device is combined with a means for determining a material to be heated and a control device for the amount of electric power input to the induction heating device, and an induction heating device and a transportation speed control device for retroping. A uniform heating method for a rolled material by induction heating, which comprises measuring a temperature, calculating a recuperation time that results in a temperature distribution in a material cross section suitable for a downstream rolling process, and controlling a recuperation temperature transit time.