JPS6217120A - Electrical heating method - Google Patents

Abstract

PURPOSE:To prevent the local heating of the end faces of a material to be heated and to uniformly heat said material by changing the contact pressing force of electrodes to the material to be heated according to temp. CONSTITUTION:A cylinder 3 is first actuated by the command from a pressing force control device 6 to press the electrodes 2, 2 with the strong pressing force to the end faces of the material 1 to be heated in the stage of heating said material 1. Electricity is conducted to the electrodes and the strong pressing is continued until the temp. detected by temp. detectors 5, 5-1 attains the prescribed temp. between 900-1,200 deg.C. Both end faces of the material 1 are thereby plastically deformed and flattened so that the electrodes 2, 2 and both end faces of the material 1 contact tightly with each other. The pressing force of the electrodes 2, 2 is weakend via the cylinder 3 by the control signal from the control device 6. The contact resistance is thereby decreased and is made irreversible, by which the uniform heating is executed. The generation of deformation such as bend and injury of the electrodes 2, 2 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heating method for heating a material by controlling the pressing force of an electrode on a material to be heated in direct current heating.

(Prior Art) - For example, steel materials such as slabs, blooms, and billets are heated to a predetermined temperature in a heating furnace and subjected to hot working such as hot rolling. As this heating means, /fiLNG, coke oven gas,
A heating furnace using fuel such as kerosene as a heating source is used. Furthermore, in recent years, electrical heating, which can achieve more uniform heating than the heating furnace described above, is being considered.

In current heating, electrodes are brought into contact with both ends of the material to be heated, such as a slab, and electricity is applied to heat it using Joule heat. 0 In current heating, the contact state between the material to be heated and the electrodes has a large effect on the uniformity of heating. Therefore, it is important to control the pressing force when the electrode contacts the material to be heated.

By the way, in direct current heating of steel materials, etc. The energization method takes into account the pressure force of the electrode on the material to be heated.
For example, it has been proposed in Japanese Patent Laid-Open No. 50-70946. One of the conventional methods is to increase the electrode pressing force at the initial stage of heating, and then weaken the pressing force after heating for the required time and carry out electrical heating. This is an electrical heating method in which the pressure is weakened, the pressing force is increased after heating for a required time, and the pressing force is further weakened after heating for a required time.

(Problems to be solved by the invention) When heating steel materials such as slabs with electricity,
For example, the slab is melt-cut to a predetermined slab length by a gas cutter on one side of the continuous casting machine, so many irregularities of approximately +3"'-3M are formed on the cut end surface. However, Even if an integral electrode is pressed against such an end surface and the pressing force is qualitatively changed as in the conventional method described above, the contact condition will not be good, and the contact state will not be good until about 200 feet from the contact end surface of the slab in contact with the electrode. Affected by heat conduction due to localized heating at the end surface, yield could be reduced due to quality abnormalities and cracks occurring during the rolling process.Also, the pressing force of the electrode to the slab was inappropriate. This may cause deformation such as bending in the electrode or deformation in the slab.

The present invention prevents local heat generation on the end face of the heated material and achieves uniform heating by changing the contact pressure of the W pole to the heated material in accordance with the temperature during current heating, and also prevents bending of the electrode. An object of the present invention is to provide an electrical heating method that can prevent deformation or damage to the material.

(Ninth Means for Solving the Problems) The gist of the present invention is that when an electrode is pressed and brought into contact with the end face of a heated material and heated with electricity, the temperature of the heated material is 900 to 900°C.
The pressing force of the electrode is increased <t until it is heated to 1200°C.
, 900 to 1200 t: This is an electrical heating method characterized by conducting electrical heating at a temperature of 900 to 1200 t or higher while weakening the pressing force of the electrode.

(Function) Next, the function in electrical heating by the method of the present invention will be explained.

In the method of the present invention, the pressing force of the pole is 900 to 1200
The reason why it is strengthened until it is heated to a temperature of 1°C is that at temperatures below 900°C, due to the material of the material to be heated, etc., the above-mentioned pressing force will deform the uneven portions of the end face and it will not become flat.
If the pressing force is increased to a fairly high temperature of 2000°C or higher, the deformation will be excessive and dents will occur, or the electrodes will be deformed such as bending.

This is because damage will occur. That is, by applying a strong pressing force until the material is heated to a temperature between 900 and 1200C determined by the material of the material, etc., the unevenness of the end surface of the material to be heated that is in contact with the electrode is plastically deformed, and the end surface is is flattened and this causes.

Even if the pressing force is weakened after the above temperature is reached, the current can be applied uniformly. Further, the contact resistance of the contact portion between the electrode and the end surface of the heated material is irreversible, the contact resistance of the contact portion is small, and there is no local heat generation at the end surface of the heated material.

Furthermore, when the temperature rises, the pressing force is weakened, so that the electrode and the heated material are not bent or damaged.

(Example) An example of the present invention will be described below in detail with reference to the drawings.

In the drawings, l represents a material to be heated, for example a slab. 2
．． Reference numerals 2 denote electrodes that are pressed against both ends of the heated material 1, and are connected to a pressing force adjusting device, for example, a cylinder 3, via a piston rod 4, and are brought into contact with the end surface of the heated material 1! It is flexible. By operating this cylinder 3, the pressing force of the stain electrode 2 against the surface of the heated material 114 is adjusted and controlled. 5° 5-1 are temperature detectors, each directed toward the end faces on both sides of the heated material l or the vicinity thereof;
Detects the temperature at or near the end face. Reference numeral 6 denotes a pressing force control device, into which the temperature signal from the temperature detector 5.5-1 is input, and the temperature signal is compared with a predetermined temperature and the pressing force of the electrode 2 against the end surface of the heated material l is controlled depending on the magnitude of the temperature. Outputs a signal to control pressure. This signal causes the cylinder 3 to operate and the pressing force of the electrode 2 to be controlled.

To heat the material to be heated l using the above device.

First, the cylinder 3 is activated by a command from the pressing force control device 6.
The electrodes 2 and 2 are connected to both ends of the material to be heated.
Press with strong pressure. The strong suppression described above is then continued until the temperature detected by the temperature detector 5.5-1 reaches a predetermined temperature between 900 and 1200°C. By applying strong pressure until the temperature reaches the above-mentioned predetermined temperature, both end surfaces of the heated material l are plastically deformed and become flat.
! The pole and both end faces are in close contact. When the electrode 2.2 is heated to the predetermined temperature or higher, the pressing force of the electrode 2.2 is weakened by 1 via the cylinder 3 in response to a control signal from the pressing force control device 6. Even if the pressing force is weakened, the end surface of the material to be heated that is in contact with the electrode 2 is plastically deformed and becomes flat as described above, so that the electrode 2 and the end surface of the material to be heated are in a dense layer. Therefore, the contact resistance is also small.

Furthermore, it is irreversible and allows for uniform heating. 22nd. In the figure, the electrode pressing force is strengthened at the initial stage of energization heating of the steel material using the above-described embodiment apparatus, and when the steel material temperature exceeds 1000°C, the electrode pressing force is weakened. As can be seen from Figure 2, which shows the relationship between the temperature at the center and end surfaces of the steel material, the contact resistance value of the electrode-steel material, and the electrode pressing force, when the temperature at the end surface of the steel material is 1000°C or higher, even if the pressing force of the electrode is weakened. The unevenness on the end face of the steel material is plastically deformed due to creep, and the adhesion between the end face of the steel material and the electrode is good, and the contact resistance is irreversible and does not increase.

Therefore, there is no local heat generation at the end face of the steel material, and uniform heating is possible by applying electricity until a predetermined temperature is reached, with almost no temperature deviation from the center part of the steel material.

In order to clarify the effects of the above method of the present invention.

The data obtained using the conventional method is shown below.

Figure 3 shows the current heating time of the steel material when using the conventional heating method, in which the electrode pressing force is increased at the initial stage of energizing the steel material, and then the electrode pressing force is weakened and heated at a steel material temperature of 850°C. As can be seen from Figure 3, which shows the relationship between the temperature distribution at the center and end surfaces of the steel, the electrode-steel contact resistance, the electrode, and the pressing force, when the pressing force of the electrode is weakened when the steel temperature is below 900°C, the end surface of the steel The plastic deformation due to creep is not complete, the contact resistance between the electrode and the end surface of the steel material is reversible, and the end surface temperature of the steel material becomes locally heated. In addition, the temperature at the edge of the steel material becomes high due to local heating, and even if the electrode pressing force is subsequently increased, the contact resistance between the electrode and the steel material will improve, but it will be difficult to eliminate the temperature difference between the edge surface and the center of the steel material. .

(Effect of the invention) According to the method of the present invention, the pressing force of the electrode can be increased from 900 to 1200.
Since the pressure is applied strongly until it is heated to a temperature of ℃, the pressed surface of the material to be heated becomes flat.

After that, the electrode pressing force is weakened when the steel material temperature exceeds about 900 to 1200°C, so the electrode is not exposed to strong pressing force in the high temperature range, there is no bending due to electrode creep, and the material to be heated is This has the effect that local heating does not occur.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the arrangement of an apparatus according to an embodiment of the present invention, and FIG.
The figure illustrates the operation of an embodiment of the present invention. Agent Patent Attorney Masa Akizawa Two Mitsugai 71'3 Diagram Kabura school energization hU Heat time constant 2 Diagrams Cone general energization 〃0 Heat poetry dark

Claims (1)

[Claims] (1) When bringing the electrode into contact with the end surface of the material to be heated and heating it with electricity, the pressing force of the contact of the electrode to the material to be heated should be 900 to 1
Intensify until heated to a temperature of 200℃, 900-120℃
An energization heating method characterized by energization heating at a temperature of 0° C. or higher while weakening the pressing force.