JPS63168258A - Channel refractory for intermediate channel type induction heating tundish - Google Patents

Abstract

PURPOSE:To improve the durability of hollow refractory and to reutilize it by cooling to the room temp. after casting by using aluminacarbon quality brick having the specific carbon content as the hollow refractory quality forming a channel. CONSTITUTION:The hollow refractory 7, which uses the alumina-carbon quality refractory having 5-35% carbon content, is arranged at the middle between the receiving molten steel room 1 supplying the molten steel from a ladle 3 and the discharging molten steel room 2 pouring the molten steel through a submerged nozzle 8. In this way, the development of crack is eliminated and the restriction on casting timing caused by exchanging the hollow refractory is reduced and the operational cast is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a refractory material for a tundish portion in an intermediate groove type induction heating tundish.

(Prior Art) The superheating temperature (hereinafter abbreviated as SH) of molten metal in a continuous casting tundish (hereinafter abbreviated as tundish) has a great influence on the quality of slabs. When S)I is high, the equiaxed product rate decreases and center segregation tends to increase. On the other hand, if it is low, defects due to non-metallic inclusions tend to increase due to factors such as a decrease in the viscosity of the molten metal and the tendency to generate cracks in the mold.

Therefore, it is preferable to always control SH to the target SH, but in reality, the temperature of the molten metal in the ladle gradually decreases due to heat dissipation, so if you want to secure the Sll at the final stage of casting, , overall it will be cast at a higher price than the target.

Therefore, attempts are currently being made to provide a heating function to the tandish to keep the SH constant. As a heating source, an induction heating method using electric power is known because it is excellent in controllability and economical efficiency.

Induction heating methods include a crucible type that uses high-frequency current,
There is a groove type that uses a low frequency current and has an iron core.
The groove type is preferable because it has greater heat generation efficiency and can be used without converting the commercial frequency, resulting in lower equipment costs.

The principle of heating is that by winding a coil around the iron core and applying alternating current, the molten metal in the groove becomes a secondary coil.
An induced current i is generated according to Faraday's law of electromagnetic induction, and the molten metal is heated by Joule heat 12R.

Among the groove-type induction heating methods, the intermediate groove-type induction heating method has a structure in which a penetrating space is provided in the middle of the molten metal container, and the induction coil and iron core are passed through that space. This is called a medium rtrI groove type induction heating tundish. (Unexamined Japanese Patent Publication No. 6
1-38754) This is shown in Figure 5 (a) and (b).
As shown in (c), the tanditsu is divided into a receiving chamber 1 where molten metal is supplied from a ladle 3 and a tapping chamber 2 where molten metal is poured into a mold 11 through an immersion nozzle 8, and the tundish is divided into a plurality of hollow refractory holes. By joining with material 7, a channel through which molten metal can flow is formed.

Then, by passing the iron core 5 around which the coil 4 is wound to m through the space 6 created by providing these plurality of hollow refractories 7, an energizing loop corresponding to a secondary coil is formed through the molten steel in the hot water channel. be done.

Here, the material properties of the hollow refractory 7 are that, in addition to being low-priced and having excellent spalling resistance and corrosion resistance, the hollow refractory 7 has the following characteristics: It is also necessary that the specific resistance of 7 is high.

Therefore, for the hollow refractory 7, there is a method of using a precast product obtained by off-line molding of a high alumina castable having an almost infinitely large specific resistance, with the highest priority placed on preventing the generation of induced current.

(Problems to be Solved by the Invention) However, this material has poor spalling resistance, and cracks may occur in the hollow refractory 7 during preheating or during flow of molten metal.

Furthermore, even if the casting is successfully completed and it is confirmed that no cracks have occurred in the hollow refractory 7, it is impossible to use it again due to concerns that cracks may occur during preheating, and It was necessary to dismantle the side wall of the tundish and replace the hollow refractory 7 every time the process was completed.

For this reason, there was a problem that the operating rate of the tundish was lowered, and the high cost of refractories more than offset the benefits of introducing the induction heating method.

(Means for Solving the Problems) The present invention solves the problem that the hollow refractory 7 easily cracks during preheating of the tundish or during the flow of molten metal, and that it must be replaced every time one casting is completed. This aims to solve the problem that the tundish refractories must be used, improve the operating rate of the tundish, and reduce the cost of the tundish refractories.

That is, the present invention provides a material for the hollow refractory 7 that can be reused even after cooling to room temperature after actual casting by improving the durability, especially the spalling resistance, of the hollow refractory 7. . Namely, (1) a refractory groove for an intermediate groove type induction heating tundish characterized in that an alumina-carbonaceous brick having a carbon content of 5 to 35% is used as the hollow refractory material forming the groove;

(2) A large intermediate groove type induction heating tundish characterized by using high alumina castable with a silicon carbide content of 5 to 20% as the hollow refractory material forming the groove.

It is.

As a means to solve these problems, it is a good idea to incorporate carbon such as scaly graphite into the refractory.

Figure 1 shows the specific resistance of an alumina-carbonaceous brick, and when the hollow refractory 7 is manufactured using this material and tundish induction heating is performed, the temperature of the molten steel is kept constant at 1,500°C, and the induction coil has a power of 1,000 kw. The relationship between the temperature rise inside the hollow refractory 7 and the electrical efficiency determined from the ratio of molten steel temperature rise heat amount/input power converted heat amount is shown.

From this figure, the specific resistance of the hollow refractory 7 is o, ootΩ-
In the case of C■, the temperature increase inside the hollow refractory 7 is 1,
1,650 150°C higher than the temperature of molten metal at 500°C
℃, the current density flowing through the molten metal in the gutter decreases, and the electrical efficiency decreases to about 80%. on the other hand.

When the specific resistance is ≧0.01 Ω-cm, the temperature increase relative to the temperature of the molten metal inside the hollow refractory 7 is ≦35° C., and the decrease in electrical efficiency is so small that it can be ignored.

Figure 2 shows the relationship between the carbon content of an alumina-carbonaceous fired brick and the thermal wRN fracture resistance coefficient, which is an index of resistivity and durable poling property. The carbon content is ≦35
%. The thermal shock rupture resistance coefficient is.

When the carbon content increases rapidly from ≧5%, for example, when 5% is added, the carbon content becomes about three times that of a product without additives, and it is possible to prevent the occurrence of cracks during preheating of the tundish or during the flow of molten metal. However, if ≧35% is added, the carbon bond will become weaker! The impact fracture resistance coefficient tends to decrease.

On the other hand, the maximum operating temperature of the alumina-carbonaceous brick and the monolithic refractory used around the hollow refractory 7 is 1.65
Since the temperature is 0°C, the heat generation temperature due to the generation of induced current in the hollow refractory itself needs to be 5150°C.

Therefore, the upper limit of the carbon content of the hollow refractory 7 is set to 35%.

That is, when the carbon content of the hollow refractory 7 is 5%, the spalling resistance is poor and it is insufficient to prevent cracking during preheating or during the flow of molten metal. Due to the heat generated by the induced current in the refractory 7 itself,
The temperature of the hollow refractory 7 and the surrounding monolithic refractories exceeds the permissible temperature.

There is a concern that melting damage will progress abnormally and that water will get wet.

Therefore, the carbon content of the hollow refractory 7 made of alumina-carbonaceous bricks is in the range of 5 to 35%. Note that the carbon content in this case is the sum of the carbon components of the scaly graphite added as a buffer material and the resin pitch added as a binder.

By the way, in order to form an alumina-carbonaceous brick into a hollow shape like the hollow refractory 7, it is necessary to form it by special press working, which increases the manufacturing cost.

Therefore, in order to reduce costs, we decided to use 1 weight! 1. Value is about 1
It is a good idea to use a precast product molded from castable material, which is cheap at /10.

High alumina is commonly used as a castable material, but as mentioned above, this material is prone to cracking and is difficult to use discontinuously many times.

Therefore, in order to improve the spalling resistance of high alumina castables, it is effective to improve the thermal conductivity, and silicon carbide is generally added.

Figures 3 and 4 show the silicon carbide content in high alumina castable and 1-8i killed steel at 1,600'C.
The relationship between the erosion loss ratio and thermal shock fracture resistance coefficient in a rotational erosion test with IHr retention is shown.

The amount of erosion due to rotational erosion decreases when the amount of silicon carbide added is up to 20%, but tends to increase when it exceeds 20%.

On the other hand, the thermal shock fracture resistance coefficient is 15% for silicon carbide content.
The thermal shock rupture resistance coefficient also tends to increase as the content increases. For example, by adding 5%, the thermal shock rupture resistance coefficient becomes R=90, which is about three times that when no additive is added, and it can be used many times even in intermittent operations. However, if the silicon carbide content is ≧23%, then R<90, making it impossible to use it multiple times.

Note that the specific resistance of silicon carbide itself is high, for example, 3,100 Ω-am at 500°C and 430 Ω-cm at 1,000°C, so even if castable to which silicon carbide is added is used for hollow refractories, induced current will not be generated. Due to this, heat generation in the hollow refractory 7 rarely occurs.

Therefore, when using high alumina castable for hollow refractories, the appropriate amount of silicon carbide to be added is in the range of 5 to 20%. That is, when R is 5% and ≧20, the thermal shock fracture resistance is low (R) is 90, making it difficult to use it many times in intermittent operation.

<Example-1> Example of using alumina carbonaceous bricks for hollow refractories.

In a large tundish capable of receiving 46 tons of molten steel, the ladle 3 shown in Fig. 5 also has a receiving chamber 1 to which molten steel is supplied.
and a tapping chamber 2 into which molten steel is injected through an immersion nozzle 8.
Inner diameter Loomsφ, outer diameter 1501■φ, length 1 in the middle
, 200 mm, isostatically press-molded with a carbon content of 10%, and alumina-carbonaceous hollow refractory 7 using resol-based resin as a binder is 40
The hollow refractories 7 were installed in parallel at intervals of 0.01 to allow molten steel to pass through the hollow refractories 7.

Between the two parallel hollow refractories 7, an iron core 5 around which an induction coil 4 was wound was passed through in a perpendicular direction.

The amount of molten steel flowing through the hollow refractory 7 is approximately 1 to
n/min, and the exit side molten steel temperature is MAX2 compared to the input side.
Apply voltage 400 to 1 for induction coil 4 so that the temperature rises by 5℃.
, 200V, current 620~1.85OA, frequency 50
An alternating current of c/s was applied.

The operation pattern was an intermittent one in which the castings were cooled down to room temperature after each heat casting, but no cracks other than hair cracks were observed and up to 6 heats could be used. The reason for discontinuing the use was that the carbon added during heating and cooling for each heat use was oxidized, a decarburized layer was generated, and the remaining thickness of the healthy layer became small.

Table 1 shows changes in the composition and physical properties of the sound layer before and after use of the hollow refractory 7, and these changes are slight.

Table 1 <Example 2> An example in which a high alumina precast product containing silicon carbide is applied to a hollow refractory.

Using the same manufacturing method as in Example (1) described above, A et al.
= 62%, 5LO2 = 36%, Ca0 = 1.5% in low cement castable with SiC298%, particle size ≦
1. Hollow refractory 7 was applied, which was made by precasting high alumina castable to which 65 m of silicon carbide was added and its content was 10%.

Although the operation pattern was an intermittent one in which the castings were cooled down to room temperature after each heat casting, no cracks other than hair cracks were observed, and up to 6 heats could be used as in Example (1).

The reason for discontinuing the use was that the inner surface of the hollow refractory 7 lost about 3IIIW4 for each heat, so the remaining thickness became small.

The composition and physical properties of this hollow refractory 7 before and after use are shown in Table 2.
As shown in the figure, the compressive strength after use has approximately doubled, indicating that densification has progressed due to sintering.

Table 2 (Effects of the invention) As explained above, by applying the alumina-carbonaceous brick according to the present invention to the hollow refractory 7, the occurrence of cracks is largely eliminated, and even in intermittent operation, multiple uses of 6 heats are possible. It's now possible. This results in 1
Replacement of the hollow refractory 7 for each heat was avoided, the casting timing was less restricted by the replacement of the hollow refractory 7, and great benefits were obtained in terms of reduced work costs.

On the other hand, if a precast product made by adding silicon carbide to high alumina castable is applied to the hollow refractory 7, it can be used 6 times intermittently, and furthermore, the unit price of the hollow refractory 7 can be reduced by about 1/2. Since it is inexpensive at 10, it is also highly effective in reducing refractory costs.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the specific resistance, temperature rise, and electrical resistance of hollow refractories. ftfl! Figure 3 shows the relationship between the silicon content in high alumina castable and the amount of corrosion loss, and Figure 4 shows the relationship between the silicon content in high alumina castable and the thermal shock coefficient. It is a diagram. FIG. 5 is an overall view of an intermediate groove type induction heating tundish to which the present invention is applied. 1: Hot water receiving room, 2: Hot water supply room, 3: Ladle,
4: Coil, 5: Iron core, 6: Space, 7: Hollow refractory, 8: Immersion nozzle. Fig. 2 Amount of cross-wire content (%) of alumina - secondary IF brick Fig. 3 Fig. 4 Amount of normal content (%) of 7 high alumina chikasuta (%) Procedure correction Yoshi Showa 62 year month 23rd

Claims (2)

[Claims] (1) A gutter refractory for an intermediate gutter type induction heating tundish, characterized in that an alumina-carbonaceous brick having a carbon content of 5 to 35% is used as the hollow refractory material forming the gutter. (2) A gutter refractory for an intermediate groove type induction heating tundish, characterized in that high alumina castable having a silicon carbide content of 5 to 20% is used as the hollow refractory material forming the gutter.