JP3151651B2 - Electric heating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric heating method for heating a running metal strip such as iron, aluminum or copper by passing an electric current thereto. The present invention relates to a current-carrying heating method capable of preventing drawing or breakage of a metal strip.

[0002]

2. Description of the Related Art Conventionally, when a metal strip is continuously annealed, the heating and keeping of the temperature are mostly performed by radiation by gas heating or indirect heating by an electric heater. However, since these heating methods indirectly heat the material to be heated, there is a problem that rapid heating cannot be performed, and when the sheet thickness or the sheet width changes, the productivity is greatly restricted.

In order to solve this problem, it has been proposed to employ energization heating. For example, JP-A-61-82
No. 954 discloses that a steel sheet is directly energized through a current-carrying roll to raise the temperature of the steel sheet itself as a heating element.
JP-A-1-142032 and JP-A-1-18778
No. 9 discloses a method in which energizing rolls are provided before and after a metal strip passage passing through an annular transformer, and the metal strip is heated by energization.

When a current is directly applied to a metal strip and heated by Joule heat as described above, the heating capacity per unit time is higher than that of indirect heating of gas or electricity, and the production accompanying a change in the sheet thickness or the sheet width is performed. It is excellent in that it can eliminate the problem of reduced properties and can make the equipment compact.

[0005]

However, there is a serious problem in operation when the running metal strip is sandwiched between the current-carrying roll and the holding roll and heated by current-carrying. In order to process a large number of metal strips continuously, welding of the dispensed coil is continuous, but this weld has a bad shape and
To pass through the place where the energizing roll and the holding roll are pressed down and pinched, for example, in the case of lap welding, when the stepped portion of the welded part passes, an excessively large rolling force is applied to the energizing roll temporarily, and the roll Damage.
In addition, for example, in the case of lap welding, since the cross-sectional area of the welded portion increases and is different from the cross-sectional area of the metal strip before and after welding, a large temperature difference occurs between the metal strips before and after the welded portion, The metal strip deforms due to thermal stress, and tends to be drawn. There is a risk that the roll may be damaged by the generated squeezing, and there is also a problem that the metal strip itself breaks and the operation is stopped.

[0006] Therefore, as a method of passing through the welded portion, Japanese Patent Laid-Open No. 6-279841 discloses a method in which a plurality of energized roll sets are prepared and the rolls are opened and closed in accordance with the passage of the welded portion. . This method is desirable because it can surely energize the welded portion without damaging the energizing roll, but requires an extra device,
In addition, there is a problem that the installation cost is increased because the installation space is wide.

Therefore, the present invention provides a method for passing a welded portion without increasing the space and requiring a low equipment cost.

[0008]

According to the present invention, a metal strip running between an energizing roll and a pair of pressing rolls having a pressing device provided opposite thereto is sandwiched, and the metal strip is continuously fed from the energizing roll. In the electric heating method of heating the metal strip by energizing the plate, when the welded portion of the traveling metal strip passes through the energized roll, one of the energized roll and the press roll before the welded portion passes. Or move both,
An electric heating method characterized in that an electric current is applied by bringing the metal strip into contact with the electric roll so as to be wound thereon. In addition, it is preferable to make the energizing current after passing the welding portion smaller than the energizing current before passing.

[0009]

The operation of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining the electric heating method according to the present invention. Leading metal strip 1 and trailing metal strip 3
Are joined by welding, have a welded portion 2, and are energized while being pinched by press rolls 5 and 7 by energizing rolls 4 and 6 connected by a power source 8 and a conductive member 9, respectively, and heated.

FIG. 1A shows a state in which the welded portion 2 is located between the energizing roll 4 and the energizing roll 6. FIG. 1 (b)
An example of the movement of the holding roll 7 when the welding portion 2 approaches the energizing roll 6 will be described. As the weld 2 approaches the energizing roll 6, the holding roll 7 moves below the right pass line in this case and winds the preceding metal strip 1 around the energizing roll 6. Since the metal strips 1 and 3 are pressed against the energizing roll 6 by tension, the metal strips 1 and 3 can be energized without sparking to a certain amount of current. If the energizing current is large enough to cause sparking, it is desirable to reduce the current in advance and energize. If there is no risk of sparking, it is desirable that the current to be supplied be equal to or less than the set current of the thinner plate so as not to blow.

The position of the welded portion 2 can be determined by a computer based on tracking information of the welded portion 2 or by a method of detecting the welded portion 2 using a thickness sensor or the like before contacting the energizing roll 6. Then, the moving speed of the holding roll 7 is included in the calculation, and the holding roll 7
Should be moved. In addition, the movement of the holding roll 7 is as follows.
The roll chock is moved by an electric cylinder or a hydraulic cylinder.

FIG. 1C shows a state in which the welding portion 2 is in contact with the energizing roll 6. In this case, since the welded portion 2 is not pressed down by the pressing roll 7 and the energizing roll 6, no local load is applied to the energizing roll 6 and the pressing roll 7, so that damage to the roll can be prevented. . Further, since the front and rear portions of the welded portion 2 are not pinched, it is possible to prevent the occurrence of drawing, and to prevent a shape defect and a plate breakage.

FIG. 1D shows a state in which the welded portion 2 has passed through the energizing roll 6. The pressing roll 7 returns to the energizing roll 6 again, and pinches the metal strip 3 to energize.
When the welding current is reduced when the welding portion 2 passes through the energizing roll 6, it is necessary to return the current to a predetermined current.

As described above, the problem of the welded portion can be solved by energizing the pressing roll and the energizing roll in a shifted manner, and it seems good to energize in such a configuration from the beginning.
If the running metal strip is energized without being pinched, the contact between the metal strip and the current-carrying roll becomes unstable, and a spark is easily generated, which is not preferable. Since the welded portion is an unsteady portion and is cut off, even if a spark occurs and damages the metal strip, there is not much harm. If it is absolutely necessary to avoid sparking, a method such as setting the energizing current to a current equal to or less than the spark generation limit when the welded portion passes, or temporarily cutting off the current may be employed.

In the above description, an example has been described in which the holding roll moves in the set of the current-carrying roll and the holding roll on the delivery side, but the case where the holding roll moves or the case where both the holding roll and the holding roll move The same is true for Also, 1
Although an example of a pair of energizing rolls and holding rolls has been described, even when there are multiple rolls, by moving one or both of the holding rolls and energizing rolls as necessary,
It is possible to stably supply current to the welded portion.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 2 shows an example of an apparatus for implementing the present invention. A ring transformer 10 is provided between the energizing roll 4 and the energizing roll 6.
To form a circuit including the metal strip 1, the energizing roll 4, the conductive member 9, the outgoing energizing roll 6, and the metal strip 1, and apply a primary current from the power supply 8 to the ring transformer 10 to form a ring. A secondary current is directly induced in the metal strip 1 passing through the transformer 10, and the induced current causes the metal strip 1 to be subjected to Joule heating between the energizing rolls 4 and 6.

The energizing roll 4 on the entry side has a diameter of 300
mm, a roll made of S45C steel having a body length of 1300 mm is used as a holding roll 5 to have a diameter of 300 mm and a body length of 1300 mm.
Using a rubber roll, a predetermined pressure was applied by a hydraulic pressure reduction device.

The metal strip 1 has a thickness of 0.18 mm,
A cold-rolled steel sheet with a width of 800 mm (0.023% C steel) and a cold-rolled steel sheet with a thickness of 0.24 mm and a width of 800 mm (0.023%
C steel) was lap welded, wound and used as one coil.

The energizing roll 6 and the holding roll 7 which come into contact with the metal strip 1 heated to a high temperature have diameters of 300 mm so that the profile does not easily change even when it comes into contact with a high-temperature material and spark does not occur. , Body length 1300m
m of graphite roll was used. The energizing roll 6 is fixed, and the pressing roll 7 can be moved horizontally in the line direction by the electric cylinder, and can also be moved vertically by the electric cylinder. The pinch is pressed down at the time of pinching and up to 15 mm below the pass line at the time of passing the welded portion. The roll can be pushed in.

The interval between the energizing rolls 4 and 6 is 30
00 mm.

Optical thickness sensors 11 and 11 'are provided 1 m in front of the energizing roll 4 so that a change in the thickness due to the passage of the welded portion can be detected. When a weld was detected, a control signal was sent to the electric cylinder in accordance with the line speed of the metal strip, and sequence control was performed so that the presser roll 7 first moved horizontally and then moved vertically.

The current-carrying roll 4 and the holding roll 5 were not provided with a moving mechanism in particular, since sufficient cold strength could be ensured even when the welding roll was passed in a pinched state and the rolls were less damaged.

The cold-rolled steel sheet was passed in the range of 10 to 50 mpm, and an electric current was applied in a state where an initial rolling force of 1600 kg was applied to the pressing roll 7, and the sheet was heated from room temperature to 750 ° C. The primary power supply used is a single-phase, 50 Hz, 600 V maximum voltage can be applied, and a coil wound around the ring transformer 10 can induce a secondary voltage of 1/7 to 1/28 on the metal strip 1. It is like that.

Table 1 shows the results of the current heating method according to the present invention and the case where current was applied while applying pressure to the current roll. In the electric heating methods 1 and 2 according to the present invention, when the welded portion passes, the holding roll on the high temperature side is moved to release the pinch state, and the steel sheet is wound around the energized roll. No shape change occurred. On the other hand, in Comparative Examples 3, 4, and 5 in which the steel sheet was passed through the welded portion while applying a linear reduction force of 1, 2, and 3 kg / mm, shaving occurred on the roll surface layer and a large drawing occurred on the steel sheet. In the present invention 1, since a very small spark was observed to cause almost no damage to the steel plate and the roll when the current was passed at 5 A / mm or more, the current was passed at 4 A / mm or less when the welded portion passed. Thus, stable heating with no spark was made possible.

[0027]

[Table 1]

[0028]

According to the present invention, in a current-carrying heating method in which a running metal strip is sandwiched between current-carrying rolls, roll damage due to local stress concentration on the current-carrying rolls generated when a coil-to-coil welding portion passes through the current-carrying rolls. And prevent the metal strip from squeezing due to the passage of the weld between the rolls to which the pressure is applied, and prevent the sheet from breaking due to the squeezing that has occurred. Roll life can also be extended.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an electric heating method of the present invention.

FIG. 2 is a diagram illustrating an electric heating method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal strip 2 Welded part 3 Metal strip 4 Power supply roll 5 Pressing roll 6 Power supply roll 7 Pressing roll 8 Power supply 9 Conductive member 10 Ring transformer 11, 11 'Plate thickness sensor

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) C21D 1/00, 1/40, 9/52 C21D 9/56, 9/62 H05B 3/00 B21B 39 / 00

Claims (2)

(57) [Claims] 1. A metal strip running between a current-carrying roll and a pair of pressing rolls having a pressing-down device provided opposite to the current-carrying roll. When the welding portion of the traveling metal strip passes through the current-carrying roll section, one or both of the current-carrying roll and the holding roll are moved before the welding section passes, and An energization heating method characterized in that an electric current is applied by bringing the plate into contact with the energization roll so as to be wound thereon. 2. The electric heating method according to claim 1, wherein
An energization heating method, characterized in that the energization current after passing through is less than that before passing through the weld.