JP2000271607A - Method for heating sheet bar in hot rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the target temperature on the outlet side of a finishing mill without increasing sheet passing speed at the finishing mill. SOLUTION: In a method for heating a sheet bar 3 with a high-frequency induction heating device 4 arranged on the inlet side of a hot finishing mill 5, based on the relationship between the Q function and the thickness of the sheet bar 3, the thickness of the sheet bar 3 is set so that the sheet temperature on the outlet side of the finishing mill 5 reaches the target temperature and heating is executed with the high-frequency induction heating device 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for heating a sheet bar in hot rolling.

[0002]

2. Description of the Related Art In the finishing rolling process of hot rolling, the quality of a product caused by a temperature drop in a rolling mill due to low-speed rolling of the sheet bar tip and a temperature drop due to heat radiation at the tail end of the sheet bar before the finishing rolling mill. In order to prevent defects, a high-frequency induction heating device is provided on the entrance side of the finishing mill to heat the sheet bar.

When a sheet bar is heated by a high-frequency induction heating device, the frequency of the alternating magnetic flux applied to the sheet bar is set near the point where the Q function shown by the following equation (1) is maximized. The absorbed electric power (calorific value of the plate) is maximized, and heating can be performed efficiently. Q = {1 / (D / δ)} × [{sinh (D / δ) −sin (D / δ)} / {cosh (D / δ) + cos (D / δ)}] (1) , Δ = 0.0503 (ρ _s / fμ _s ) ^1/2 δ: electroosmotic depth (m) ρ _s : electrical resistivity (μΩcm) f: frequency (Hz) μ _s : relative magnetic permeability (−) D : Sheet bar thickness (m)

[0004]

However, when the rolling load in the finish rolling is increased, the surface of the rolling roll of the finishing rolling mill may be easily roughened. In a hot rolling line that rolls various steel plates with a finished plate thickness of 1 to 10 mm, the sheet bar thickness varies in a range of 20 to 50 mm.

[0005] As described above, the optimum frequency of the high-frequency induction heating device for the thickness of the sheet bar which varies in the range of 20 to 50 mm varies from 1000 to 2000 Hz. In order to change the frequency of the high-frequency induction heating device, it is necessary to change the capacity of the condenser provided in the electric circuit of the high-frequency induction heating device. It is not realistic because it will increase.

Therefore, in an actual operation, the frequency of the high-frequency induction heating device is merely set so that the Q function is maximized with respect to the average thickness of the sheet bar to be rolled. It is not operating at
For this reason, in particular, the heating amount at the entrance side of the finishing mill is insufficient at the leading end and the tail end of the sheet bar, so that the exit temperature of the finishing mill cannot be set to the target temperature, which causes a reduction in product quality. Has become.

[0007] It is conceivable that the leading edge of the sheet bar for which the temperature is to be increased the most is to avoid the problem caused by the temperature drop by increasing the sheet passing speed. In order to prevent troubles related to threading, the threading speed in the finishing mill is set to 700
８００800 mpm (equivalent to the exit side of a finishing mill) cannot be increased, and therefore, it is difficult to prevent the temperature of the sheet from dropping due to high-speed sheet passing.

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a problem. In the hot rolling, it is possible to secure a target temperature on the exit side of a finishing rolling mill without increasing the passing speed of a finishing rolling mill. An object of the present invention is to provide a method for heating a sheet bar.

[0009]

In order to achieve the above object, a method for heating a sheet bar in hot rolling according to claim 1 is provided by a high frequency induction heating apparatus disposed on an inlet side of a hot finishing mill. In the method of heating the sheet bar according to the following, the thickness of the sheet bar is set based on the relationship between the Q function expressed by the following equation (1) and the sheet thickness of the sheet bar, and the sheet is heated by the high frequency induction heating device Is performed.

Q = {1 / (D / δ)} × [{sinh (D / δ) −sin (D / δ)} / {cosh (D / δ) + cos (D / δ)}] (1) ) _{here, δ = 0.0503 (ρ S /} fμ S) 1/2 δ: electrical penetration depth (m) [rho _S: electric resistivity (.mu..OMEGA.cm) f: frequency (Hz) mu _S: relative magnetic permeability ( -) D: Sheet bar thickness (m) In the method for heating a sheet bar in hot rolling according to claim 2, in claim 1, the thickness of the sheet bar is set at the front end and the tail end of the sheet bar. It is characterized by performing.

According to a third aspect of the present invention, in the method for heating a sheet bar in hot rolling, the thickness of the sheet bar is set in the vicinity of a joint portion of the sheet bar in endless rolling. I do.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory schematic diagram for explaining a sheet bar heating method in hot rolling, which is an example of an embodiment of the present invention, and FIG. 2 is a graph showing a relationship between a Q function and a sheet bar thickness. FIG. 3 is a graph showing the relationship between the sheet bar thickness, the rolling speed, and the temperature rise of the sheet bar. FIG. 4 is a sheet bar heating method in endless hot rolling according to another embodiment of the present invention. It is explanatory schematic drawing for demonstrating.

In FIG. 1, reference numeral 1 denotes a final stand of a row of rough rolling mills, 2 denotes a crop shear for cutting a crop of a sheet bar 3, and 4 denotes a solenoid for heating the front end and / or rear end or the entire length of the sheet bar 3. A mold high-frequency induction heating device, 5 is a finishing mill train, and 6 is a coiler. The final stand 1 of the rough rolling mill row has a running thickness changing function that can change the thickness in the bar 3 in batch rolling in which the sheet bar 3 is rolled one by one.

Here, when the sheet bar 3 is heated by the solenoid type high frequency induction heating device 4, the absorbed power per unit time (heat generation amount of the sheet bar) W and the temperature increase ΔT in the sheet bar 3 are as follows. It is represented by the following equation. ^{W = πfμ · H 2 · Q} · D · w · l ΔT = W / (C · γ · D · w · v) = {(πfμ · H 2
・ Q) / Cγ｝ ・ (l / v) where f: frequency (Hz) μ: magnetic permeability (H / m) H: magnetic field strength (A / m) Q: function D: sheet bar thickness (m ) W: sheet bar width (m) l: heating coil length (m) C: specific heat (kJ / kg · K) γ: specific weight (kg / m ³ ) v: transport speed (m / s) Magnetic susceptibility μ, magnetic field strength H, heating coil length l,
The transport speed v is determined by the specifications of the equipment, and the frequency f
Is usually set for the average sheet thickness of the sheet bar.

Therefore, the only way to increase the amount of temperature increase ΔT is to increase the Q function or reduce the transport speed v. In this case, since a descaling device for spraying high-pressure water onto the sheet bar surface and de-scaling the sheet bar surface by the impact force of the high-pressure water is installed on the finishing mill entry side, the conveying speed v is reduced. Then, the cooling time of the sheet bar by the high-pressure water becomes long, and as a result, the sheet bar temperature at the entrance to the finishing mill cannot be efficiently increased. On the other hand, increasing the Q function can increase the temperature increase ΔT without considering the increase in the cooling amount of the sheet bar by the descaling device.

FIG. 2 shows Q at a heating frequency of 1200 Hz.
The relation between the function and the sheet bar thickness is shown. In FIG. 2, the point at which the absorbed power is maximum is that the plate thickness is 35 mm and the value of the Q function at that time is 0.42. This sheet thickness of 35 mm is exactly the average sheet bar thickness in the hot rolling mill, and corresponds to the sheet bar thickness of a low carbon steel having a finished sheet thickness of 2 to 2.6 mm class.

However, the thinnest sheet bar having a finished plate thickness of 1 to 1.8 mm has a plate thickness of 27 to 30 mm.
About. This is because by reducing the thickness of the sheet bar, it is possible to prevent an increase in the load of the finish rolling and make it difficult for the surface of the roll to be roughened. In this case, the Q function also decreases from 0.37 to 0.40 from FIG. Therefore, 0.3
7 / 0.42 = 0.88, 0.40 / 0.42 = 0.9
This means that the operation is performed without raising the temperature by 5 and 12 to 5%. As a result, in particular, it is not possible to compensate for a temperature drop in the finishing mill due to the low-speed rolling of the sheet bar tip and a temperature drop due to heat radiation at the tail end of the sheet bar in front of the finishing mill, so that the finishing temperature reaches the target temperature. Disappears.

Therefore, in this embodiment, as shown in FIG. 3, the thickness of the sheet bar 3 at the front end and the tail end when rolling a thin material of 1.8 mm or less is set to Q with reference to FIG. Thickness is rolled beforehand in the final stand 1 of the row of rough rolling mills so that the function becomes the maximum (when the frequency is 1200 Hz: 35 mm), and the end of the sheet bar 3 is turned into a strip 9 by the finishing mill 5. The tip of the coiler 6
The sheet thickness of the sheet bar 3 is set to the original thickness (27 to 30 mm) at a position where the conveying speed v is increased by winding the sheet bar 3 to thereby maximize the temperature of the front end and the tail end of the sheet bar 3. As a result, the finishing temperature on the entire length of the sheet bar 3 reaches the target temperature. And
Regarding the steady portion other than the leading end and the trailing end, the rolling load is the same as before, and the roll surface is not likely to be roughened.

In the above-described embodiment, at least one or more rolling mills having a function of changing the running thickness is required in the row of rough rolling mills.
It is also possible to make the sheet thickness optimal for heating over the entire length of the sheet bar. In this case, since the sheet bar thickness also increases in the steady portion, it is necessary to determine the rolling schedule (the rolling reduction of each stand of the finishing mill) so as not to cause roll surface roughness.

In the above embodiment, the case where the present invention is applied to batch rolling is taken as an example.
The present invention may be applied to endless rolling. In the endless rolling, as shown in FIG.
The leading sheet bar and the trailing sheet bar are joined by the joining device 7 so that the leading sheet bar and the trailing sheet bar are continuously hot-rolled. The succeeding sheet bar is turned into a sheet bar coil by a winding / rewinding machine 8 installed between the joining device 7 and the rough rolling mill 1 and temporarily stands by. This is because the leading end 3b of the succeeding sheet bar is located at the position of the joining device 7 and the trailing end 3b of the preceding sheet bar.
This is to adjust the conveyance of the succeeding sheet bar so as to catch up with b.

Here, since the outer winding end and the inner winding end of the sheet bar coil come into contact with the atmosphere, the temperature drop becomes large and the temperature near the joint becomes low. In the vicinity of the joining portion of the sheet bar, that is, the sheet of the outermost winding and the innermost winding of the sheet bar coil so that the exit side sheet temperature of the finishing mill reaches the target temperature. It is preferable to set the thickness and perform heating by the high-frequency induction heating device 4.

In the above embodiment, the thickness of the sheet bar is set to 35 mm so that the Q function is maximized. However, it is not possible to perform constant rolling at 35 mm from the viewpoint of the rolling accuracy of the rough rolling mill. Since it is difficult, the approximate target rolling thickness may be set to 35 mm. However, if the thickness of the sheet bar deviates too much from the thickness at which the Q function becomes maximum, heating cannot be performed efficiently. Therefore, the thickness of the sheet bar is at least 96%, more preferably at least 98% of the maximum value of the Q function. It is good to make thickness which becomes the value of.

[0023]

As is apparent from the above description, according to the present invention, it is possible to obtain the effect that the target temperature on the finishing exit side can be secured without increasing the threading speed of the finishing mill. .

[Brief description of the drawings]

FIG. 1 is an explanatory schematic diagram for explaining a sheet bar heating method in hot rolling which is an example of an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a Q function and a sheet bar thickness.

FIG. 3 is a graph showing a relationship between a sheet thickness of a sheet bar, a rolling speed, and an amount of temperature rise of the sheet bar.

FIG. 4 is an explanatory schematic diagram for explaining a sheet bar heating method in endless hot rolling according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Final stand of rough rolling mill line 2 ... Finish crop shear 3 ... Sheet bar 4 ... High frequency induction heating device 5 ... Finish rolling mill line 6 ... Coiler

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshiaki Amagasa 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba F-term in the Chiba Works of Kawasaki Steel Corporation (Reference) 3K059 AB19 AB26 AC54 AD15 BD02 CD02 CD72 4E002 AD04 BD08 CB01 CB03

Claims (3)

[Claims] 1. A method for heating a sheet bar by a high-frequency induction heating device disposed on an entrance side of a hot finishing mill, comprising: a step of calculating a Q function represented by the following equation (1) and a sheet thickness of the sheet bar. A sheet bar heating method in hot rolling, wherein a sheet thickness of the sheet bar is set based on the relationship and heating is performed by the high-frequency induction heating device. Q = {1 / (D / δ)} × [{sinh (D / δ) −sin (D / δ)} / {cosh (D / δ) + cos (D / δ)}] (1) , Δ = 0.0503 (ρ _s / fμ _s ) ^1/2 δ: electroosmotic depth (m) ρ _s : electrical resistivity (μΩcm) f: frequency (Hz) μ _s : relative magnetic permeability (−) D : Sheet bar thickness (m) 2. The sheet thickness of the sheet bar is set at a front end and a tail end of the sheet bar.
A method for heating a sheet bar in the hot rolling as described above. 3. The method for heating a sheet bar in hot rolling according to claim 1, wherein the setting of the sheet thickness of the sheet bar is performed near a joint portion of the sheet bar in endless rolling.