JPH05337610A - Heating mold for continuous casting - Google Patents

Abstract

PURPOSE:To provide a heating mold for continuous casting heating molten metal in a molten metal discharging passage in the different type to an induction heating type. CONSTITUTION:This mold is constituted with a mold body 1 arranged near a tundish, a cylindrical exothermic body 2 provided in the mold body 1 and forming the molten metal passage 20 passing through the molten metal with an inner wall surface 20a and an electrode part 3 arranged by contacting with the outer peripheral surface of the exothermic body 2.The electrode part 3 is composed of electrodes 31-35 arranged in a prescribed interval along the direction of the molten metal discharging passage 20. The exothermic body 2 is formed with a mixed ceramic containing 90wt.% magnesia, 5% zirconia and 5% alumina and the heat is generated by Joule heat.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a heating mold for continuous casting. This heating mold for continuous casting can be applied to both horizontal continuous casting and vertical continuous casting.

[0002]

2. Description of the Related Art Conventionally, a copper mold has been used as a heating mold for continuous casting. In this case, powder is used to prevent seizure between the copper mold and the slab. This powder flows between the copper mold and the slab, forms an oscillation mark on the surface of the slab, deteriorates the surface properties of the slab, and is trapped inside the slab to become inclusions.

Therefore, a heating mold for continuous casting has been developed which solves the above problems. This heating mold for continuous casting has a cylindrical upper heating part containing graphite, a cylindrical lower cooling part, and an induction coil coaxially arranged around the upper heating part, and energizes the induction coil. By
The upper heating part is heated by induction heating (JP-A-1-278944 and JP-A-2-37943).

Further, as a heating mold for continuous casting, it has a mold body and an induction coil coaxially arranged around the mold body, and the induction coil is energized to generate a magnetic field, thereby solidifying the slab. It is known to apply an electromagnetic force to the interface (Japanese Patent Laid-Open No. 2-205240). By the way, the above-mentioned JP-A-1-278944 and JP-A-2
In the continuous casting heating mold according to Japanese Patent Publication No. 37943, since a method of heating the upper heating portion by induction heating is adopted, a cooling device for the induction coil and a large power supply device are required.
Further, in continuous casting, it is important to control the solidification of the outer surface of the solidified shell, but in the induction heating method, the inside of the outer surface of the solidified shell is also easily affected by induction heating, and the control of the solidified shell is not easy.

Further, the heating mold for continuous casting according to the above-mentioned Japanese Patent Application Laid-Open No. 2-205240 is intended to separate the slab from the inner wall surface of the heating mold.

[0006]

SUMMARY OF THE INVENTION The present invention has been developed in view of the above-mentioned circumstances, and provides a heating mold for continuous casting for heating the molten metal in the tap passage by a method different from the induction heating method. With the goal.

[0007]

The heating mold for continuous casting according to the present invention has a mold body provided in the vicinity of the tap opening of the tundish, and a tap hole which is provided in the mold body and through which the metal melt passes, on the inner wall surface. It is characterized in that it is composed of a cylindrical heating element that generates heat with energization and at least two electrode portions that are provided on the outer peripheral surface side of the heating element and that conduct current to the heating element.

The mold body is a part for holding a heating element. The heating element is mounted on the mold body, and its inner wall surface forms a hot water outlet passage. The heating element can be formed mainly of conductive ceramics. The heating element can be generally composed of magnesia (MgO), zirconia (ZrO ₂ ), alumina (Al ₂ O ₃ ), a mixture of magnesia and zirconia, or a mixture of magnesia, zirconia and alumina. Although magnesia is an electrically insulating material in the normal temperature range, it has conductivity near 1500 ° C., which is near the melting point of steel, and a required specific resistance value can be obtained. Here, alumina is effective in controlling the resistance value of the heating element, and zirconia is effective in improving the heat resistance, impact resistance, and hot characteristics of the heating element, and is also effective in controlling the resistance value. is there. In this case, considering the thermal shock resistance, the thermal expansion property, the specific resistance value, etc., the mixing ratio thereof is, for example, by weight, magnesia is preferably 60 to 99%, and particularly preferably 85 to 95%.
Zirconia is 1-40%. 5 to 25% is particularly preferable,
Alumina is preferably 1 to 40%, particularly preferably 2.5 to 15%.

When the molten metal is molten steel or stainless type molten steel, the specific resistance value of the heating element is 1500 ° C.
20Ωcm or more is desirable in the vicinity, especially 2
It is desirable that it is at least 00 Ωcm. Note that the particle size of the ceramics forming the heating element may affect the resistance value and the uneven distribution of current, so the maximum particle size of the ceramic powder is preferably about 0.5 mm to 5 mm, and particularly about 0.7 mm to 3 mm. Is desirable.

The electrode portion is provided in contact with the heating element and is for supplying electricity to the heating element. The material of the electrode portion is selected in consideration of conductivity, heat transfer coefficient, etc., and, for example, carbon paper, solid alumina graphite-based material, or porous carbon-based refractory can be adopted. The arrangement, shape, and strength of the electrode parts are preferably such that the influence of thermal expansion of the heating element can be avoided.

[0011]

The metal in the hot water passage is heated by energizing the heating element from the electrode section to heat the heating element while the electrode section is connected to the power source. By adjusting the heat generation form of the heating element,
The solidification of the molten metal in the tap passage is adjusted.

[0012]

EXAMPLE An example of a heating mold for continuous casting according to the present invention will be described with reference to FIGS. The main part of the heating mold for continuous casting according to this example is shown in FIG. This heating mold includes a mold body 1, a cylindrical heating element 2, and a heating element 2
It is composed of a carbon-based electrode portion 3 that conducts electricity.

The mold main body 1 is composed of an iron skin 10 and a refractory layer 11 having a required thickness, which is lined on the inner wall surface of the iron skin 10. The refractory layer 11 contains porous magnesia as a main component. The heating element 2 is embedded in the refractory layer 11. The hot water outlet passage 20 is formed by the inner wall surface 20 a of the heating element 2. The heating element 2 is made of mixed ceramics containing 90% of magnesia, 5% of zirconia, 5% of alumina, and inevitable impurities in weight%. In this embodiment, the heating element 2 has an axial length L of about 200 mm, an outer diameter D1 of 80 mm, and an inner diameter D2 of 60 mm.

The heating element 2 was manufactured as follows. That is, the raw material is crushed by a crusher such as a roll crusher or an impeller breaker into coarse and medium particles, and further crushed by a ball mill, a vibration mill or the like to make fine particles, and each particle is blended so as to obtain an appropriate particle size constitution. And mixing, adjusting step of adding water to the powder to form a slurry, molding step of pouring the slurry into the cavity of the mold to mold, curing after molding the molded body from the mold, a drying step of drying, It was manufactured by sequentially performing a sintering step of sintering the dried compact.

The electrode portion 3 is provided in contact with the outer peripheral surface of the heating element 2. The electrode part 3 includes a first electrode part 31 and a second electrode part 3 which are sequentially arranged from one end side in the axial direction of the heating element 2.
2, third electrode portion 33, fourth electrode portion 34, fifth electrode portion 35
It is composed of. Here, the distance from one end of the heating element 2 to the first electrode portion 31 is L1, and the first electrode portion 31 and the second electrode portion 31 are
The distance between the electrode portion 32 and the second electrode portion 32 is L2, the distance between the second electrode portion 32 and the third electrode portion 33 is L3, the third electrode portion 3
The distance between the third electrode portion 34 and the fourth electrode portion 34 is L4, the distance between the fourth electrode portion 34 and the fifth electrode portion 35 is L5, and the distance from the other end of the heating element 2 to the fifth electrode portion 35 is When the distance is L6, L1 and L6 are about 15 mm, and L2 to L5 are 5 mm.
It is a degree. The width M of each electrode portion 31 to 35 is 30 mm.
It is a degree.

In the present embodiment, as shown in FIG. 2, the two first electrode portions 31 facing each other are connected to the power source 41 via the conducting wire 31a. Two second facing each other
The electrode portion 32 is connected to the power source 42 via the conducting wire 32a. The two third electrode portions 33 facing each other are connected to the power supply 43 via the conducting wire 33a. The two fourth electrode portions 34 facing each other are connected to the power supply 44 via the conducting wire 34a. The two fifth electrode portions 35 facing each other are connected to the power supply 45 via the conducting wire 35a. The conducting wires 31a to 35a are embedded in the refractory layer 11 to ensure electrical insulation. Current-carrying lines 31a-3
In order to improve the electric insulation of 5a, the conducting wires 31a to 35a
It is also possible to embed the ceramics pipe through which is inserted into the refractory layer 11.

Next, the case of use will be described. In this embodiment, the tundish holds molten metal of austenitic stainless steel (SUS304). During continuous casting, the molten metal in the tundish passes through the outlet passage 20 of the heating element 2 from the inlet 2a to the outlet 2b, is cooled on the cooling device 5 side and solidification proceeds, and the slab W is formed. W is pulled out by the pinch roller 6.

The operating condition of continuous casting is that the injection temperature is 151
At 0 ° C., the casting speed is 1.5 m / min, the casting time is 120 min / time, and in this embodiment, a certain amount of the cast slab W is drawn,
It was carried out by the "intermittent drawing method" in which the process of holding for a certain period of time and then returning a little was repeated. In the present embodiment, during continuous casting, the heating element 2 is energized from each of the power sources 41 to 45 through each of the electrode portions 31 to 35, and the heating element 2 generates Joule heat. As a result, the hot water outlet passage 20 of the heating element 2
The molten metal inside is heated. In this case, the heat generation form of the heating element 2 is made larger toward the inlet 2a side. That is, the input power amount is 4 KW for the first electrode portion 31 and the second electrode portion 32, 2 KW for the third electrode portion 32, and 1 KW for the fourth electrode portion 34.
The fifth electrode portion 35 has 0 kW.

It has been confirmed that the above-mentioned examples can withstand 20 or more operations. If the heating element 2 is energized and preheated before the operation of continuous casting, rapid heating of the heating element 2 due to contact with the molten metal can be prevented, and cracks in the heating element 2 due to rapid heating can be prevented. It is advantageous to prevent. Further, by the above-mentioned preheating, it is possible to secure the conductivity of the heating element 2 which has magnesia as a main component and has conductivity in a high temperature region.

As described above, in the present embodiment, the inside of the hot water passage 20 is generated by the heat generated when the heating element 2 is energized without adopting the induction heating method which requires the large power supply device and the cooling device for the induction coil. The metal melt can be heated. Further, in this embodiment, the electrode portion 3 is divided along the direction of the hot water discharge passage 20 of the heating element 2. In other words, the hot water outlet passage 2 of the heating element 2
The first electrode portion 31 to the fifth electrode portion 35 are arranged along the direction of 0, and the first electrode portion 31 to the fifth electrode portion 35 are individually and independently heated. The heat generation distribution and heat generation form in the direction can be adjusted. Therefore, it is easy to adjust the position of the solidification start point of the molten metal along the direction of the tap passage 20 of the heating element 2. By the adjustment, the solidification starting point can be separated from the molten metal surface, and as a result, a slab having good surface properties can be obtained. Since a slab having good surface properties can be obtained in this way, even if the slab is rolled in an unmaintained state, defects occurring in the rolled product can be reduced or avoided.

By the way, the inner wall surface 20a of the heating element 2 is easily worn at the solidification starting point. Even in this case, the solidification starting point is avoided by avoiding the worn portion by adjusting the heat distribution and the heating pattern of the heating element 2. Can be set, and in this sense, an increase in the number of times of service of the heating mold according to the present embodiment can be expected. On the other hand, in the conventional case where the induction heating system using the induction coil is adopted, even if the induction coil divided along the direction of the hot water passage 20 of the heating element 2 is provided and each induction coil is individually energized, the magnetic field of each coil is Since they affect each other, accurate adjustment of the position of the solidification start point cannot be expected.

In addition, in the present embodiment, the first electrode portion 31 to the fifth electrode portion 35 arranged along the hot water discharge passage 20 of the heating element 2 can individually and independently generate heat. The thickness of the solidified shell can be gradually increased from the inlet 2a to the outlet 2b, which is advantageous for producing an appropriate solidified shell. Further, in this embodiment, since the heating element 2 is a magnesia-zirconia-alumina system, the tapping passage 2
It is possible to avoid invasion of a carbon component into the molten metal passing through 0, which is advantageous for maintaining the material quality of the molten metal, and is also excellent in erosion resistance.

(Other Example) In the above-mentioned embodiment, the heating element 2 has a cylindrical shape, but like the other example whose cross section is shown in FIG. 7 may be used. In this case, the electrode portions 70, 70 provided on the opposite side surfaces of the heating element 7 are connected to the power source 71 by the electric wire 70a, and the electrode portions 73 provided on the opposite side surfaces of the heating element 7, 73 are connected to the power supply 74 by the electric wire 73a.

By the way, the heating mold for continuous casting made of ceramics as in this embodiment is inferior to the conventional copper mold in terms of heat removal. Therefore, in the case of a large cross section, even if the heating power is set to 0 at the lower part of the mold, solidification occurs. It is possible that the shell is not well formed. In that case, like the conventional heating mold, a cooling unit such as a copper mold can be provided below the heating mold according to the present embodiment.

[0025]

According to the heating mold for continuous casting of the present invention, the heat generated when the heating element is energized without adopting the induction heating method that requires the large power supply device and the cooling device for the induction coil, The molten metal in the tap passage can be heated. Further, according to the heating mold for continuous casting according to the present invention, if the electrode portion is divided along the direction of the hot water discharge passage of the heating element and each divided electrode portion is individually controlled, the heat generation distribution of the heating element, the heat generation form Can be adjusted. Therefore, the effect of adjusting the position of the solidification start point of the molten metal in the direction of the hot water discharge passage of the heating element is obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part of a heating mold for continuous casting.

FIG. 2 is a vertical sectional view of a heating element having an electrode portion.

FIG. 3 is a cross-sectional view of a heating element having an electrode portion.

FIG. 4 is a cross-sectional view of a heating element having an electrode portion according to another example.

[Explanation of symbols]

In the figure, 1 is a mold body, 2 is a heating element, 20 is a hot water outlet passage, 3
Is an electrode part, and 6 is a pinch roller.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eizo Kojima 4-11 Koya no Waki, Kagiya Town, Tokai City, Aichi Prefecture

Claims (1)

[Claims] 1. A mold body provided in the vicinity of a tap opening of a tundish, a tubular heating element that is provided in the mold body, forms a tap passage through which a molten metal passes through with an inner wall surface, and generates heat with energization, A heating mold for continuous casting, comprising: at least two electrode portions provided on the outer peripheral surface side of the heating element and energized to the heating element.