JPH0639633B2 - Electroslag remelting electrode - Google Patents

Description

The present invention relates to an electroslag remelting electrode, and more particularly to an electrode capable of reducing power loss in the case of a large alternating current.

[Conventional technology]

An outline of the electroslag remelting method (hereinafter referred to as ESR method) will be described with reference to FIG. The metal electrode 4 held by the stub 2 is moved up and down by an elevating device 6, immersed in the molten slag 10 in the water-cooled copper crucible 8, and melted by the juule heat of the molten slag 10 by the current from the AC power supply 12. Then, it becomes molten steel 14 and solidifies to become a steel ingot 16. If the steel ingot 16 to be manufactured is small relative to the capacity of the crucible 8, the electrode 4 descends as it melts, but at the end of melting, the electrode tip is deep inside the crucible 8 and the upper part of the electrode 4 melts. Can not. For this reason, the stub 2 is used to hold the electrode 4,
The stub 2 is generally smaller than the diameter of the melting electrode 4 so that it can be connected to the electrodes 4 having various other diameters.

On the other hand, the AC power supply 12 used in the ESR method efficiently generates heat from the molten slag 10, has a low voltage and a large current, and generally has a power supply equipment cost of 50 and 60 Hz because of the prevention of molten steel flow due to electromagnetic force. A commercial AC power source 12 is used.

In such a case, a problem is a heat generation phenomenon of the stub 2 due to the use of the AC large power supply. That is, it is known that an alternating current flows only near the surface of a conductor, and for example, the distribution of the current density in the case of a cylindrical conductor decreases exponentially with the distance from the surface, as shown in the following equation (1). To do. The depth at which the current density decreases to 37% of the surface is
It is called the current penetration depth δ and can be obtained by the following equation (2). As shown in Table 1, the value of δ at room temperature is significantly smaller than the stub diameter in steels commonly used as stub materials. It is a value.

However, i (r): current density at the position r (m) from the center (A
/ M ² ) a: Radius of cylindrical conductor (m) I: Total current in cross section (A) δ: Current penetration depth (m) σ: Conductivity of conductor (1 / Ω · m) μ: Permeability of conductor (Wd / AT · m) ω: Current angular frequency = 2πf (rad / s) f: Current frequency (Hz) Therefore, even with a conductor having a large cross-sectional area, the alternating current can flow only in a very narrow region represented by the product of the circumferential length and the current penetration depth δ. This phenomenon is generally called the skin effect. As a result, the actual conductor resistance is much higher than in the case of direct current, and in the case of stubs, a large current flows through this part, and the resistance heat near the surface heats the interior of the stub, and in extreme cases red heat. It becomes a state. This phenomenon is remarkable in a stub having a diameter smaller than that of the melting electrode.

The heat generation of the stub not only wastefully consumes the electric power that should originally be used for melting the electrode, but also causes a decrease in the strength of the welded portion between the stub and the electrode, and there is a risk of dropping the electrode. Further, the red-heated stub is not preferable in terms of life, because it is significantly oxidized and worn in the atmosphere. Further, due to the radiant heat, it becomes difficult for an operator to approach the periphery of the electrode for monitoring the inside of the mold or replenishing the slag, and the workability is also impaired.

As a measure against this, if the stub diameter is increased, the heat generation amount decreases in inverse proportion to the increase in the circumferential length, but on the other hand, the weight of the stub increases with the square of the radius, so the stub production cost increases and the stub weight increases and decreases. It is not economical because it requires enhancement of system specifications. Also, because it is necessary to secure the minimum distance to the inner wall of the crucible,
There is a limit to the increase in stub diameter. Therefore, as a result of inevitably lowering the operating current to deal with it, a decrease in productivity cannot be avoided, and it becomes difficult to keep the dissolution rate within an appropriate range.

On the other hand, in the case of dealing with water cooling of the stub, although the problem caused by the temperature rise can be solved, the wasteful consumption of electric power that is heat generation itself is not improved, and the equipment cost increases. It should be noted that the method of lowering the resistance and reducing the amount of heat generation by making a part or all of the stub from stainless steel or copper with a large current penetration depth is an essential measure, but it is generally expensive and practical. Poor sex.

[Problems to be solved by the invention]

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide an economical electrode for remelting electroslag, which prevents temperature rise and power loss in the stub.

[Means and Actions for Solving Problems]

The gist of the present invention is as follows. That is, in the electrode for electroslag remelting, which is composed of an electrode that is melted by the slag heat of molten slag and a non-melting steel stub that holds the electrode and is connected to the upper part of the electrode, the horizontal section of the stub The electroslag remelting electrode is characterized in that the surface of the stub is provided with irregularities so that the peripheral length l (m) satisfies the following formula.

Where I is the effective value of the AC component of the current flowing through the electrodes
(A) f: Frequency of alternating current component of current flowing through the electrode (Hz) In the present invention, the cross-sectional area of the alternating current is determined by the product of the current penetration depth and the circumferential length, as described above. Since the permeation depth of the is inherent to the material, it is generally difficult to increase it unless an expensive material is used, but on the other hand, the present invention focuses on the fact that the perimeter of the cross section can be easily increased without changing the cross sectional area. Was completed.

That is, in order to reduce the amount of heat generation and temperature without changing the material of the stub, the unevenness is provided on the outer circumference so that the cross section of the stub becomes non-circular to increase the circumferential length, and the cross-sectional area is not increased. By increasing the cross section through which the stub flows, the heat generated by the resistance in the stub is reduced, and at the same time, the temperature rise of the stub is prevented by increasing the heat radiation surface.

Incidentally, JP-A-52-68819 and JP-A-52-12
In 3904, it is disclosed that a slit is provided on the side surface of the melting electrode to control the passing current, but this is completely different from the present invention in its object, structure, action and effect.

The details of the present invention will be described with reference to the embodiment shown in FIG.
A plurality of (N) side plates 20 having a thickness t and a width b are welded to the outer periphery of the stub body 18 which is a cylindrical conductor having a radius a. Since the circumference of this stub 2 is 2πa + 2bN, the side plate 20
The perimeter can be easily increased by increasing the number of sheets. Conversely, cutting the groove of depth b in the cross section of the stub body 18 can also increase the circumferential length.

Further, if the cross-sectional shape is other than circular, it can be made longer than a circle having the same cross-sectional area. Therefore, the outer periphery may be formed into a non-circular shape with a corrugated shape or a triangular mountain shape, that is, an uneven shape. However, in order to carry out the present invention more advantageously in terms of processing and manufacturing costs, a pillar based on a circular shape, an oval shape, a triangular shape, or a polygonal shape is welded to the surface with a plate-like body as shown in FIG. 1 or a groove is formed on the surface. It is desirable to cut off, and the cooling and heat generation amount reduction effects are higher than in the case of only a non-circular simple strut, and the temperature rise and heat generation loss can be effectively suppressed.

Next, the peripheral length of the cross section required to reduce the heat generation amount and temperature of the stub will be described. The current distribution in the cylindrical conductor is
Since it is expressed by the equations (1) and (2), the distribution q (r) (Kcal / m ³ .h) of the calorific value per unit volume is expressed by the following equation (3).

However, q (r): calorific value per unit volume at r from the center (Kcal / m ³ .h) The calorific value in the cylinder per unit length Q is calculated by integrating this over the entire cross-sectional area. ₁ can be found in (4) below.

In equation (4), the denominator l (= 2πa) represents the perimeter of the cross section, and it can be seen that the heat generation amount is inversely proportional to the perimeter l.

On the other hand, the heat radiation amount Q ₂ per unit length is expressed by the following equation (5).

Q ₂ = 1 / α (θ _o −θ _a ) ... (5) where θ _o : Stub surface temperature (° C) θ _a : Ambient temperature (° C) α: Surface heat transfer coefficient (Kcal / Kcal / m ² · h · c) In the equilibrium state, Q ₁ = Q ₂ , so if the surface temperature of the stub at this time is θ _eq , then equation (6) below holds.

However, 2πa = 1 is set.

According to the research by the present inventor, in the case of general carbon steel, the right side of the equation (6) is approximately proportional to θeq in a wide range, and the equation (6) can be approximated as the equation (7).

That is, the temperature of the carbon steel stub can be approximately predicted by the following equation (8).

In general, carbon steel is markedly oxidatively depleted at temperatures above 600 ° C and cannot be specified. Further, at temperatures above this, workability is poor due to radiant heat, so in actual operation, θeq ≤ 6
A temperature of 00 ° C is appropriate. Therefore, the perimeter l of the stub is limited to satisfy the following expression (9).

It is more preferable that l is larger within the range that satisfies the above expression (9) because loss due to heat generation and stub temperature rise are reduced.

〔Example〕

380 mm diameter C: 0.18%, Si: 0.55%, Mn: 1.50%
As shown in Fig. 1, the width of the carbon steel cylinder is 75 mm,
Eight flat bars having a thickness of 12 mm were welded to extend the circumferential length to manufacture a stub satisfying the limitation of the circumferential length according to the present invention.

On the other hand, for comparison, a cylinder having a diameter of 380 mm and made of the same material as the above was used as a stub, and this was used as a conventional example.

2 using a 60Hz power supply with these stubs
The ESR method was operated at an operating current of 0.5 KA and the temperature of the stub was measured.

In this case, the temperature of the stub should be 600 ℃.
From formula (9), the circumference is required to be 1.27 m, whereas the circumference of the embodiment of the present invention is 2.39 m, whereas the circumference is 1.19 in the conventional example.
m, which does not satisfy the conditions of the present invention.

In the ESR operation, the temperature of the stub is 630 in the conventional example.
However, in the example of the present invention, the temperature rise was only 370 ° C., and the power loss of the stub was reduced to 40% of the conventional example.

〔The invention's effect〕

As is apparent from the above-mentioned embodiment, the present invention increases heat generation and temperature rise of the stub by providing unevenness on the surface of the stub so that the circumferential length of the horizontal cross section of the stub satisfies the limiting condition. The effects of suppressing and reducing power loss and improving workability and safety can be implemented simply and economically.

[Brief description of drawings]

FIG. 1 is a sectional view showing a stub according to an embodiment of the present invention, and FIG. 2 is a front view of an apparatus for explaining the ESR method. 2 ... Stub, 4 ... Electrode 10 ... Molten slag, 18 ... Stub body 20 ... Side plate

Claims (1)

[Claims] 1. An electrode for remelting electroslag, comprising an electrode which is melted by the gyrus heat of molten slag and a non-melting steel stub which holds the electrode and is connected to the upper part of the electrode, wherein An electrode for remelting electroslag, characterized in that the surface of the stub is provided with irregularities so that the perimeter l (m) of the horizontal section satisfies the following formula. Where I is the actual value of the AC component of the current flowing through the electrodes
(A) f: Frequency of alternating current component of current flowing through the electrode (Hz)