JPH08246067A - Apparatus and method for continuous annealing of steel sheet - Google Patents

Abstract

(57) [Summary] [Purpose] When a continuous annealing of a steel sheet is carried out by using an electric heating together, the steel sheet is prevented from being defective in shape. [Structure] An electric heating device is provided after the heating zone 2 to heat the steel sheet 1 by directly applying an electric current thereto. A soaking area 4 is provided in front of the low-temperature side energizing roll 6 of the energizing heating device, and a sealing device 8 is provided between the low-temperature side energizing roll 6 and the high-temperature side energizing roll 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for continuously annealing a steel sheet using electric heating.

[0002]

2. Description of the Related Art Cold rolled steel sheets have a fibrous structure and are poor in workability. Therefore, recovery by annealing,
It is necessary to recrystallize and grow grains to improve workability. Compared with coil annealing, continuous annealing, in particular, enables uniform processing of continuous strips and obtains a homogeneous material, shortens processing time, and can significantly reduce the number of process days. Is excellent in terms of.

For continuous annealing, it is necessary to continuously heat a strip-shaped steel sheet to a temperature equal to or higher than the recrystallization temperature, soak it if necessary, and then continuously cool it. Further, as a heating method, there are direct fire type non-oxidizing heating, radiant tube heating, indirect electric heating, etc., and in many actual equipment, radiant tube heating is adopted.

By the way, the principle of these heating methods such as direct-fired non-oxidizing heating, radiant tube heating, and indirect electric heating is heat transfer based on a temperature difference between a high-temperature heating source and a low-temperature object to be heated. The heating source, for example, the radiation tube, cannot heat the steel sheet that is the object to be heated unless the temperature of the radiation tube is higher. Then, as the temperature of the steel sheet becomes higher, the temperature difference from the heating source becomes smaller, and the heating rate must be slowed. Therefore, in order to sufficiently heat the steel sheet without further increasing the temperature of the heating furnace, lengthening the heating furnace, or slowing down the stripping speed, a current is directly applied to the steel sheet through the energizing roll, It is conceivable to use electric heating to heat the steel sheet by Joule heat of the steel sheet itself.

For example, Japanese Unexamined Patent Publication No. 5-230524 discloses a continuous steel sheet heating apparatus that uses both atmospheric heating and electric heating in which the steel sheet being heated in the atmosphere is further electrically heated by using a roll as an electrode. It is said that this apparatus can heat only the steel sheet at a high temperature at a normal furnace temperature without major modification of existing equipment.

Further, Japanese Patent Application No. 5-250896 describes that electric conduction heating is adopted in a high temperature region of 600 ° C. or higher when continuously annealing a steel sheet. It is said that this not only greatly improves the heating rate and heating efficiency in the high temperature region but also improves the responsiveness of temperature control.

[0007]

As described above, the combined use of electric heating with heating in continuous annealing has various advantages, but on the other hand, there is a problem that a defective steel sheet shape occurs during electric heating. That is, wavy wrinkles and the like are generated on the low-temperature side energizing roll on the steel sheet that enters the energizing heating device through the heating zone. This is because the steel plate temperature is 400-60
The number of wrinkles is particularly large at 0 ° C., and these wrinkles cause sparks on the high-temperature side energizing rolls, and further cause shape defects on the high-temperature side energizing rolls. Further, when the heating temperature rise amount between the low temperature side energizing roll and the high temperature side energizing roll is large, the shape defect may occur in the high temperature side energizing roll even if the shape defect does not occur in the low temperature side energizing roll. There is. And, in the above-mentioned conventional technique, no measures are taken for the occurrence of such a defective shape of the steel sheet.

[0008] Therefore, an object of the present invention is to provide a continuous annealing apparatus and method for a steel sheet in which a defective shape of the steel sheet does not occur even when electric heating is used together.

[0009]

The continuous annealing apparatus of the present invention is as follows.

An energization heating device that heats the steel sheet by directly passing an electric current is provided after the heating zone, and a soaking region is provided in front of the low temperature side energization roll of the energization heating device, and a low temperature side energization roll and a high temperature side energization roll are provided. A continuous annealing device for steel plates, characterized in that a sealing device is provided between the two.

A continuous annealing device for a steel sheet, characterized in that an electric heating device for directly supplying an electric current to the steel plate to heat the steel plate is provided after the heating zone, and a soaking region is provided in front of the low-temperature side current applying roll of the electric heating device.

A steel sheet characterized in that an electric heating device for heating the steel sheet by directly passing an electric current is provided after the heating zone, and a sealing device is provided between the low-temperature side energizing roll and the high-temperature side energizing roll of the energizing heating device. Continuous annealing equipment.

A continuous annealing device for a steel sheet, characterized in that an electric heating device for directly applying an electric current to the steel plate to heat the steel plate is provided after the heating zone, and a holding roll capable of moving up and down is provided on the high temperature side current applying roll.

In the continuous annealing method of the present invention, the continuous annealing apparatus is used, and the distance L (m) between the low temperature side current-carrying rolls and the high temperature side current-carrying rolls between the current-carrying rolls and the heating by the current-carrying between the two current-carrying rolls. When the relationship with the temperature amount ΔT (° C.) is ΔT / L> 100, the above-mentioned pressing roll is lowered by the high-temperature side energizing roll and the steel sheet is energized and heated while being rolled down. Is.

[0015]

According to the present invention, in order to solve the problem that the low temperature side energizing roll has a defective shape of the steel sheet, a soaking region is provided before the low temperature side energizing roll, and the low temperature side energizing roll and the high temperature side energizing roll are provided. We decided to deal with this by installing a seal device between the and.

The cause of the defective shape of the steel sheet on the low-temperature side energizing roll is that the steel sheet heated in the heating zone and entering the energizing heating device has a temperature deviation in the sheet width direction and a temperature gradient in the longitudinal direction. It can be mentioned that thermal stress is generated.
If such a steel sheet directly contacts the low-temperature side current-carrying roll, the thermal stress causes a defective shape of the steel sheet. On the other hand, the temperature distribution of the steel sheet is made uniform by providing a soaking region in front of the low temperature side energizing roll. The soaking region is not limited to a specific structure as long as the temperature deviation and temperature gradient of the steel sheet can be eliminated and the temperature distribution can be made uniform, and a soaking zone structure that has been conventionally used can also be adopted. .

Further, if the temperature of the low-temperature side energizing roll that comes into contact with the steel sheet is low, the steel sheet is contact-cooled, which also causes a defective shape. Therefore, for this, by providing a sealing device between the low-temperature side energizing roll and the high-temperature side energizing roll, and keeping the low-temperature side energizing roll in an atmosphere whose temperature is equal to that of the steel plate, Cooling was prevented to prevent contact cooling of the steel sheet. Further, the sealing device also has an effect of preventing the high-temperature side energizing roll from being cooled by disconnecting the high-temperature side energizing roll from the low-temperature side energizing roll. In order to prevent cooling of the low-temperature side energizing roll, it is preferable to cover the rear side of the low-temperature side energizing roll with a sealing device, leaving a portion required for passage of the steel sheet.

As described above, the functions of the soaking area and the sealing device are independent of each other. Therefore, even if either one of them is provided, there is some effect, but it is possible to reliably prevent the occurrence of defective shapes. Therefore, both are preferably provided.

Next, when the shape defect which independently occurs in the high temperature side energizing roll is examined, as shown by the mark X in FIG. 6, the distance L (m) between the low temperature side energizing roll and the high temperature side energizing roll And the relationship between the temperature rise amount ΔT (° C.) due to energization heating between both energizing rolls is ΔT / L> 100.
It was revealed that compressive stress acts on the high-temperature side energizing roll when the amount of temperature rise is large, causing shape defects such as streaky wrinkles. Therefore, a pressing roll that can move up and down is provided on the high-temperature side energizing roll, and when ΔT / L> 100, the energizing heating is performed while lowering the pressing roll and pressing the steel sheet. Since the steel plate of the high temperature side energizing roll is also at a high temperature, it is possible to prevent the occurrence of defective shape by rolling it down.

When the occurrence of the defective shape of the high temperature side energizing roll does not pose a problem, it is preferable not to use the pressing roll in order to avoid troubles when passing through the welded portion of the steel sheet.

The electric heating means to form a closed circuit including a steel plate and an electric roll, and to heat the steel plate by Joule heat of the steel plate itself by passing an electric current through the closed circuit. JP-B-60-26818 As described in the publication,
A case where a steel sheet is directly energized from an external power source through an energizing roll, and a method disclosed in JP-A-1-142032 or JP-A-1-18
As described in Japanese Patent No. 7789, an energizing roll is provided before and after a steel plate passage that penetrates an annular transformer, and both energizing rolls are connected by a conductive member to form a closed circuit by the steel plate, the energizing roll, and the conductive member. However, there is a case where an induction current is generated by using the closed circuit as a secondary coil by supplying an alternating current from an external power source to the annular transformer.
The present invention can be adopted in any case.

[0022]

Embodiment 1 FIG. 1 shows an embodiment of the continuous annealing apparatus of the present invention. After the steel plate 1 is heated by the radiation tube 3 in the heating zone 2,
It is further heated by an electric heating device composed of the low-temperature side energizing roll 6, the high-temperature side energizing roll 11, the annular transformer 10 and the like, and then subjected to soaking treatment in the soaking zone 14 and continuously annealed.
In the continuous annealing apparatus of the present invention, the soaking area 4 is provided near the end of the heating zone 2 and in front of the low temperature side energizing roll 6, and between the low temperature side energizing roll 6 and the high temperature side energizing roll 11. A sealing device 8 is provided.

FIG. 2 also shows the continuous annealing apparatus of the present invention. In this example, the pressing rolls 7 and 12 of the energizing roll shown in FIG.
Is not provided, and the steel plate 1 is wound around the energizing rolls 6 and 11 a little and brought into contact with the energizing rolls 6 and 11 for energizing and heating.

Table 1 shows the results of continuous annealing of a steel plate having a thickness of 0.24 mm and a plate width of 850 mm using the continuous annealing device shown in FIG.

[0025]

[Table 1]

No. No. 1 is a conventional example in which electric heating is not used together. 2 and No. No. 4 is a comparative example in which a continuous annealing apparatus provided with neither a soaking region nor a sealing device is used together with electric heating, No. 3 and No. 5 is an example of using the embodiment of the continuous annealing apparatus of the present invention shown in FIG. Comparative Example No. 2 and No. Since No. 4 employs electric heating, it is possible to lower the temperature of the heating zone and perform high-temperature annealing, but a problem of defective shape of the steel sheet occurs. On the other hand, in Example No. 3 and No. In No. 5, it was possible to carry out continuous annealing utilizing the advantages of electric heating without causing shape defects in the steel sheet.

Further, in Comparative Example No. 2 and Example No. The temperature history of the steel sheet of No. 3 is schematically shown in FIGS. 3 and 4. Comparative Example N
o. In Example 2, as shown in FIG. 3, the material was rapidly cooled at the energization heating start position, and the variation in temperature was large. In 3, the rapid cooling is avoided as shown in FIG.
The variation in temperature was also reduced.

[0028]

[Embodiment 2] FIG. 5 shows an embodiment of a continuous annealing apparatus of the present invention in which a high-temperature side energizing roll 11 is provided with a press roll 15 which can be raised and lowered. Further, in FIG. 6, when the continuous annealing apparatus was used to electrically heat the steel sheet 1 while pressing down the steel plate 1 with the pressing roll 15 when ΔT / L> 100, wrinkles could be prevented from being generated on the high temperature side current applying roll. Here is an example.

[0029]

According to the present invention, it is possible to solve the problem that a defective shape of a steel sheet occurs at a contact point between the current-carrying roll and the steel sheet during electric heating. As a result, it becomes easy to use the electric heating having excellent heating ability and heating efficiency and good responsiveness of temperature control for continuous annealing of the steel sheet.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a continuous annealing apparatus of the present invention.

FIG. 2 is a diagram showing an embodiment of a continuous annealing device of the present invention.

FIG. 3 is a diagram showing a temperature history of a steel sheet during continuous annealing.

FIG. 4 is a diagram showing a temperature history of a steel sheet during continuous annealing.

FIG. 5 is a diagram showing an example of a continuous annealing apparatus of the present invention.

FIG. 6 is a distance L (m) between energizing rolls and an energization heating temperature rise amount Δ.
It is a figure which shows about the relationship between T (degreeC) and wrinkle generation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Heating zone 3 Radiant tube 4 Soaking area 5 Thermometer 6 Low temperature side energizing roll 7 Holding roll 8 Sealing device 9 Conductive member 10 Annular transformer 11 High temperature side energizing roll 12 Holding roll 13 Thermometer 14 Soaking zone 15 Holding roll

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location C21D 9/56 101 C21D 9/56 101J

Claims (5)

[Claims] 1. An electric heating device for heating a steel sheet by directly passing an electric current after the heating zone is provided, a soaking area is provided in front of the low-temperature side energizing roll of the energizing heating device, and a low-temperature side energizing roll and a high-temperature side energizing are provided. A continuous annealing device for steel plates, characterized in that a sealing device is provided between the roll and the roll. 2. A continuous annealing of a steel sheet, characterized in that an energization heating device for directly applying an electric current to the steel plate to heat the steel plate is provided after the heating zone, and a soaking region is provided in front of the energizing roll on the low temperature side of the energization heating device. apparatus. 3. A heating device is provided with an energization heating device for directly applying an electric current to the steel plate to heat the steel plate, and a sealing device is provided between a low temperature side energizing roll and a high temperature side energizing roll of the energization heating device. Continuous annealing equipment for steel sheets. 4. A continuous annealing apparatus for a steel sheet, comprising an energization heating device for directly applying an electric current to the steel sheet to heat the steel sheet after the heating zone, and a press roll capable of moving up and down on the high temperature side energizing roll. 5. The continuous annealing apparatus according to claim 4, wherein the distance L (m) between the current-carrying rolls between the low-temperature side current-carrying roll and the high-temperature side current-carrying roll, and the amount of temperature rise ΔT (° C. due to current-carrying between the current-carrying rolls). ) Is ΔT / L> 100, the method for continuous annealing of a steel sheet is characterized in that the pressing roll is lowered by a high-temperature side energizing roll and the steel sheet is energized and heated while being rolled down.